diff --git a/CHANGELOG.md b/CHANGELOG.md
index d3736834d9..160dc49ee0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,46 @@
 
 Gaps between patch versions are faulty/broken releases.
 
+## 2.0.0
+
+ * Make string literal generation only escapes unicode that it has to.
+ * Internal code generation format options have been exposed.
+ * Change playground method binding operator from `:` to `#` removing ambiguous syntax with terns.
+ * Fix rest parameters in async and generator functions.
+ * Export/import declarations replace by the modules transformer now inherit comments.
+ * Added playground flag to `6to5-node`.
+ * `6to5-node` now behaves the same as `node`.
+ * `6to5-node` now uses `kexec` to become the forked process to correctly propagate signals on unix.
+ * Constants are now block scoped.
+ * Exposed ast transformer.
+ * Merged `commonInterop` and `common` module formatters.
+ * Fix generator comprehensions not inheriting `arguments`, `this` etc.
+ * Object and class mutator shorthand are now enumerable.
+ * Remove regenerator `Generator has already finished` error which isn't spec-compliant.
+ * Expose internal `spec` transformers that nicen up code output.
+ * Add export variable declaration default initializers.
+ * Propagate export declaration reassignments.
+ * Add initializer default to block scoped variable declarations within a loop.
+ * Flow type support.
+ * Make async/await contextual keywords.
+ * Allow `yield`ing of non-objects.
+ * Class declarations now lack an IIFE.
+ * Support falsy and `null` super classes.
+ * Add support for experimental abstract references `private` declarations.
+ * Leave out IIFE for class declarations.
+ * Switched to [core-js](https://github.com/zloirock/core-js) from [es6-symbol](https://github.com/medikoo/es6-symbol) and [es6-shim](https://github.com/paulmillr/es6-shim/) for built-in polyfill.
+ * `amd` and `umd` module formatters now behave the same as `common` with `interopRequire`.
+ * Micro-optimizations to boost performance by 200%.
+ * Rename module formatter methods `import` to `importDeclaration` and `export` to `exportDeclaration`.
+ * Support multiple declarators in export variable declarations.
+ * Freeze tagged template literal object.
+ * Remove inlined `regenerator` fork.
+ * Remove `ParenthesizedExpression`.
+ * Rename `object-spread` helper to `object-without-properties`.
+ * Rename `class-props` helper to `prototype-properties`.
+ * Rename `extends` helper to `inherits`.
+ * Completely rewritten `system` module formatter.
+
 ## 1.15.0
 
  * Don't alias `GeneratorFunction` and check the name which causes minifiers to remove the name and throw an error later on when we check if it's set.
diff --git a/README.md b/README.md
index d1f2e07244..eb4bb860c0 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,10 @@
 </p>
 
 <p align="center">
+  <a href="https://gratipay.com/sebmck">
+    <img alt="Gratipay" src="https://img.shields.io/gratipay/sebmck.svg?style=flat">
+  </a>
+
   <a href="https://travis-ci.org/6to5/6to5">
     <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
   </a>
@@ -24,7 +28,11 @@
   </a>
 </p>
 
-**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
+<p align="center">
+  <strong>6to5</strong> turns ES6+ code into vanilla ES5, so you can use next generation features <strong>today.</strong>
+</p>
 
-For more information view the [documentation](https://6to5.github.io). For
-support visit the [gitter room](https://gitter.im/6to5/6to5).
+<p align="center">
+  For more information view the <a href="https://6to5.github.io">documentation</a>. For
+  support visit the <a href="https://gitter.im/6to5/6to5">gitter room</a>.
+</p>
diff --git a/benchmark/index.js b/benchmark/index.js
index c7d04b1b65..f0f820081d 100644
--- a/benchmark/index.js
+++ b/benchmark/index.js
@@ -2,9 +2,9 @@ Error.stackTraceLimit = Infinity;
 
 var jsTrans = require("jstransform");
 var traceur = require("traceur");
-var es6tr   = require("es6-transpiler");
+//var es6tr   = require("es6-transpiler");
 var es6now  = require("es6now");
-var esnext  = require("esnext");
+//var esnext  = require("esnext");
 var to5     = require("../lib/6to5");
 
 //var uglify  = require("uglify-js");
@@ -56,12 +56,12 @@ var compilers = {
     }
   },
 
-  esnext: {
+  /*esnext: {
     runtime: readResolve("esnext/node_modules/regenerator/runtime.js") || readResolve("regenerator/runtime.js"),
     compile: function (code) {
       return esnext.compile(code).code;
     }
-  },
+  },*/
 
   es6now: {
     runtime: readResolve("es6now/runtime/ES6.js"),
@@ -70,13 +70,13 @@ var compilers = {
     }
   },
 
-  "es6-transpiler": {
+  /*"es6-transpiler": {
     compile: function (code) {
       var result = es6tr.run({ src: code });
       if (result.errors.length) throw new Error(result.join("; "));
       return result.src;
     }
-  },
+  },*/
 
   jstransform: {
     compile: function (code) {
diff --git a/bin/6to5/file.js b/bin/6to5/file.js
index 73c0f19a7f..a06bf304ea 100644
--- a/bin/6to5/file.js
+++ b/bin/6to5/file.js
@@ -113,16 +113,14 @@ module.exports = function (commander, filenames) {
     walk();
 
     if (commander.watch) {
-      var watcher = chokidar.watch(filenames, {
+      chokidar.watch(filenames, {
         persistent: true,
         ignoreInitial: true
-      });
-
-      _.each(["add", "change", "unlink"], function (type) {
-        watcher.on(type, function (filename) {
+      }).on("all", function (type, filename) {
+        if (type === "add" || type === "change" || type === "unlink" ) {
           console.log(type, filename);
           walk();
-        });
+        }
       });
     }
   };
diff --git a/bin/_6to5-node b/bin/_6to5-node
index 2133bf156e..842ebd666b 100644
--- a/bin/_6to5-node
+++ b/bin/_6to5-node
@@ -1,12 +1,14 @@
 #!/usr/bin/env node
 
-var commander = require("commander");
-var path      = require("path");
-var repl      = require("repl");
-var to5       = require("../lib/6to5");
-var util      = require("../lib/6to5/util");
-var vm        = require("vm");
-var _         = require("lodash");
+var roadrunner = require("roadrunner");
+var commander  = require("commander");
+var Module     = require("module");
+var path       = require("path");
+var repl       = require("repl");
+var to5        = require("../lib/6to5");
+var util       = require("../lib/6to5/util");
+var vm         = require("vm");
+var _          = require("lodash");
 
 commander.option("-e, --eval [script]", "Evaluate script");
 commander.option("-p, --print", "Evaluate script and print result");
@@ -14,28 +16,33 @@ commander.option("-i, --ignore [regex]", "Ignore all files that match this regex
 commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
 commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
 commander.option("-g, --playground", "Enable playground support");
+commander.option("-c, --cache", "Cache compiled files and require paths");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
 commander.usage("[options] [ -e script | script.js ] [arguments]");
 commander.parse(process.argv);
 
+if (commander.cache) roadrunner.load();
+
 //
 
 to5.register({
   experimental: commander.experimental,
   extensions:   commander.extensions,
-  ignore:       commander.ignore
+  playground:   commander.playground,
+  ignore:       commander.ignore,
+  cache:        commander.cache && roadrunner.get("6to5")
 });
 
 //
 
 var _eval = function (code, filename) {
   code = to5.transform(code, {
-    modules: "commonInterop",
     filename: filename,
     blacklist: ["useStrict"],
-    experimental: commander.experimental
+    experimental: commander.experimental,
+    playground: commander.playground
   }).code;
   return vm.runInThisContext(code, filename);
 };
@@ -44,21 +51,34 @@ if (commander.eval) {
   var result = _eval(commander.eval, "eval");
   if (commander.print) console.log(result);
 } else {
-  var filenames = commander.args;
+  if (commander.args.length) {
+    // slice all arguments up to the first filename since they're 6to5 args that we handle
+    var args = process.argv.slice(2);
 
-  if (filenames.length) {
-    _.each(filenames, function (filename) {
-      if (!util.isAbsolute(filename)) {
-        filename = path.join(process.cwd(), filename);
+    var i = 0;
+    _.each(args, function (arg, i2) {
+      if (arg[0] !== "-") {
+        i = i2;
+        return false;
       }
-
-      require(require.resolve(filename));
     });
+    args = args.slice(i);
+
+    // make the filename absolute
+    var filename = args[0]
+    if (!util.isAbsolute(filename)) args[0] = path.join(process.cwd(), filename);
+
+    // add back on node and concat the sliced args
+    process.argv = ["node"].concat(args);
+
+    Module.runMain();
   } else {
     replStart();
   }
 }
 
+if (commander.cache) roadrunner.save();
+
 function replStart() {
   repl.start({
     prompt: "> ",
diff --git a/doc/caveats.md b/doc/caveats.md
index 269d114207..67fd0d0a7b 100644
--- a/doc/caveats.md
+++ b/doc/caveats.md
@@ -2,22 +2,31 @@
 
 In order for certain features to work they require certain polyfills. You can
 satisfy **all** 6to5 feature requirements by using the included
-[polyfill](polyfill.md). You may alternatively selectively include what you need:
+[polyfill](polyfill.md).
 
-| Feature                     | Requirements                                                                                                                 |
-| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
-| Abstract References         | [experimental](usage.md#experimental), `Symbol`                                                                              |
-| Array destructuring         | `Array.isArray`, `Array.from`                                                                                                |
-| Async functions, Generators | [experimental](usage.md#experimental), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
-| Comprehensions              | [experimental](usage.md#experimental), `Array.isArray`, `Array.from`                                                         |
-| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                       |
-| Object spread/rest          | [experimental](usage.md#experimental), `Object.assign`                                                                       |
-| Spread                      | `Array.isArray`, `Array.from`                                                                                                |
+You may alternatively selectively include what you need:
 
-## Classes
+| Feature                     | Requirements                                                                                                           |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | [experimental](experimental.md), `Symbol`                                                                              |
+| Array destructuring         | `Array.isArray`, `Array.from`                                                                                          |
+| Async functions, Generators | [experimental](experimental.md), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
+| Comprehensions              | [experimental](experimental.md), `Array.isArray`, `Array.from`                                                         |
+| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                 |
+| Object spread/rest          | [experimental](experimental.md), `Object.assign`                                                                       |
+| Spread                      | `Array.isArray`, `Array.from`                                                                                          |
 
-Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
-limitations in ES5 implementations.
+## ES5
+
+Since 6to5 assumes that your code will be ran in an ES5 environment it uses ES5
+functions. So if you're using an environment that has limited or no support for
+ES5 such as lower versions of IE then using the
+[es5-shim](https://github.com/es-shims/es5-shim) along with the
+[6to5 polyfill](polyfill.md) will add support for these methods.
+
+## Internet Explorer
+
+### Classes (9 and below)
 
 If you're inheriting from a class then static properties are inherited from it
 via [\_\_proto\_\_](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto),
@@ -40,9 +49,11 @@ class Bar extends Foo {
 }
 ```
 
-## 6to5-node
+## Getters/setters (8 and below)
 
-It is necessary to manually install `kexec` package on Unix-like OSes for
-`6to5-node` to correctly handle signals.
+In IE8 `Object.defineProperty` can only be used on DOM objects. This is
+unfortunate as it's required to set getters and setters. Due to this if
+you plan on supporting IE8 or below then the user of getters and setters
+isn't recommended.
 
-**It is not recommended to use `6to5-node` with a process manager (`supervisord`, `upstart`, `systemd`, ...) without first installing `kexec`!**
+Reference: [MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty#Internet_Explorer_8_specific_notes).
diff --git a/doc/differences.md b/doc/differences.md
index 73f5babd0c..f4ef9475ee 100644
--- a/doc/differences.md
+++ b/doc/differences.md
@@ -1,6 +1,8 @@
 # Differences
 
-## Philosophy
+There are three main points that separate 6to5 from all other transpilers.
+
+### Readable code
 
 The fundamental concept behind 6to5 is that the generated code must be close as
 possible to the original, retaining all the same formatting and readability.
@@ -51,7 +53,27 @@ As you can tell, it's not very pretty, unreadable even. Instead of mapping
 directly to a runtime, like other transpilers, 6to5 maps directly to the
 equivalent ES5.
 
-Sometimes there are little things that 6to5 needs
+Sometimes there are little inline functions that 6to5 needs. These are
+placed at the top of your file much like coffee-script does. If these
+are bother you then you can use the [optional runtime](optional-runtime.md).
+We promise that these inline functions will never be significant and will
+always be used as little as possible.
+
+### Static analysis
+
+6to5 uses a lot of static analysis to simplify code as much as possible.
+Not many other transpilers do this, and those that do don't do it nearly
+as much as 6to5. This process is pretty intensive but it leads to higher
+quality code.
+
+### Spec compliancy
+
+6to5 prides itself on
+[spec compliancy](https://kangax.github.io/compat-table/es6/). We have
+excellent support for edgecases, something that many other transpilers
+suffer from, including Traceur. When you use 6to5 you can be confident
+that when you turn it off and use your code in a full ES6 environment
+**it'll just work**.
 
 ## Comparison to other transpilers
 
@@ -62,40 +84,44 @@ Sometimes there are little things that 6to5 needs
 | Source maps                  | ✓    | ✓       | ✓              | ✓      |        | ✓           |
 | No compiler global pollution | ✓    |         | ✓              | ✓      |        | ✓           |
 | Optional runtime             | ✓    |         | ✓              |        |        | ✓           |
-| Browser support              | ✓    | ✓       |                | ✓      |        |             |
+| Browser compiler             | ✓    | ✓       |                | ✓      |        |             |
 
 ### Language Support
 
-|                              | 6to5  | Traceur | es6-transpiler | esnext | es6now | jstransform |
-| ---------------------------- | ----- | ------- | -------------- | ------ | ------ | ----------- |
-| Abstract references          | ✓     |         |                |        |        |             |
-| Array comprehension          | ✓     | ✓       | ✓              |        |        |             |
-| Arrow functions              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Async functions              | ✓     | ✓       |                | ✓      |        |             |
-| Classes                      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Computed property names      | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Constants                    | ✓     | ✓       | ✓              |        |        |             |
-| Default parameters           | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Destructuring                | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Exponentiation operator      | ✓     | ✓       |                |        |        |             |
-| For-of                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Generators                   | ✓     | ✓       |                | ✓      |        |             |
-| Generator comprehension      | ✓     | ✓       |                |        |        |             |
-| Let scoping                  | ✓     | ✓       | ✓              |        |        |             |
-| Modules                      | ✓     | ✓       |                |        | ✓      |             |
-| Object rest/spread           | ✓     |         |                |        |        | ✓           |
-| Property method assignment   | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Property name shorthand      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Rest parameters              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Spread                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Template literals            | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Unicode regex                | ✓     | ✓       | ✓              |        |        |             |
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓    |         |                |        |        |             |
+| Array comprehension          | ✓    | ✓       | ✓              |        |        |             |
+| Arrow functions              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Async functions              | ✓    | ✓       |                | ✓      |        |             |
+| Async generator functions    | ✓    | ✓       |                |        |        |             |
+| Classes                      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Computed property names      | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Constants                    | ✓    | ✓       | ✓              |        |        |             |
+| Default parameters           | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Destructuring                | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓    | ✓       |                |        |        |             |
+| Flow types                   | ✓    |         |                |        |        | ✓           |
+| For-of                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Generators                   | ✓    | ✓       |                | ✓      |        |             |
+| Generator comprehension      | ✓    | ✓       |                |        |        |             |
+| JSX                          | ✓    |         |                |        |        |             |
+| Let scoping                  | ✓    | ✓       | ✓              |        |        |             |
+| Modules                      | ✓    | ✓       |                |        | ✓      |             |
+| Object rest/spread           | ✓    |         |                |        |        | ✓           |
+| Property method assignment   | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Property name shorthand      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Rest parameters              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| React                        | ✓    |         |                |        |        |             |
+| Spread                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Template literals            | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Unicode regex                | ✓    | ✓       | ✓              |        |        |             |
 
 ### [Traceur](https://github.com/google/traceur-compiler)
 
 Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
 While this can be trimmed down by selectively building the runtime, it's an
-unneccesary step when a large runtime can be eliminated entirely.
+unnecessary step when a large runtime can be eliminated entirely.
 
 ### [es6now](https://github.com/zenparsing/es6now)
 
diff --git a/doc/experimental.md b/doc/experimental.md
new file mode 100644
index 0000000000..3546d0cb82
--- /dev/null
+++ b/doc/experimental.md
@@ -0,0 +1,8 @@
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
+
+**WARNING:** These proposals are subject to change so use with
+**extreme caution**.
diff --git a/doc/features.md b/doc/features.md
index d23e891620..a5c55fda81 100644
--- a/doc/features.md
+++ b/doc/features.md
@@ -1,6 +1,6 @@
 # Features
 
-## Abstract references ([experimental](usage.md#experimental)) ([spec](https://github.com/zenparsing/es-abstract-refs))
+## Abstract references ([experimental](experimental.md)) ([spec](https://github.com/zenparsing/es-abstract-refs))
 
 ```javascript
 foo::bar;
@@ -8,7 +8,7 @@ foo::bar = baz;
 delete foo::bar;
 ```
 
-## Array comprehensions ([experimental](usage.md#experimental))
+## Array comprehensions ([experimental](experimental.md))
 
 ```javascript
 var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
@@ -39,7 +39,7 @@ var bob = {
 };
 ```
 
-## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
+## Async functions ([experimental](experimental.md)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -49,6 +49,12 @@ async function chainAnimationsAsync(elem, animations) {
 }
 ```
 
+## Async generator functions ([experimental](experimental.md)) ([spec](https://github.com/jhusain/asyncgenerator))
+
+```javascript
+
+```
+
 ## Classes
 
 ```javascript
@@ -130,7 +136,7 @@ var [a] = [];
 a === undefined;
 ```
 
-## Exponentiation operator ([experimental](usage.md#experimental)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+## Exponentiation operator ([experimental](experimental.md)) ([spec](https://github.com/rwaldron/exponentiation-operator))
 
 ```javascript
 var a = 2;
@@ -167,7 +173,7 @@ for (var n of fibonacci()) {
 }
 ```
 
-## Generator comprehensions ([experimental](usage.md#experimental))
+## Generator comprehensions ([experimental](experimental.md))
 
 ```javascript
 var nums = [1, 2, 3, 4, 5, 6];
@@ -208,7 +214,7 @@ export default test;
 0o767 === 503; // true
 ```
 
-## Object spread/rest ([experimental](usage.md#experimental)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
+## Object spread/rest ([experimental](experimental.md)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
 
 ```javascript
 var n = { x, y, ...z };
diff --git a/doc/index.md b/doc/index.md
index 507cf6435d..c6205dd5af 100644
--- a/doc/index.md
+++ b/doc/index.md
@@ -35,23 +35,24 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
 
 ## [Features](features.md)
 
- - [Abstract references](features.md#abstract-references) ([experimental](usage.md#experimental))
- - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
- - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
+ - [Abstract references](features.md#abstract-references) ([experimental](experimental.md))
+ - [Array comprehension](features.md#array-comprehension) ([experimental](experimental.md))
+ - [Async functions](features.md#async-functions) ([experimental](experimental.md))
+ - [Async generator functions](features.md#async-generator-functions) ([experimental](experimental.md))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
  - [Constants](features.md#constants)
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
- - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](usage.md#experimental))
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](experimental.md))
  - [For-of](features.md#for-of)
  - [Generators](features.md#generators)
- - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](experimental.md))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)
- - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](usage.md#experimental))
+ - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](experimental.md))
  - [Property method assignment](features.md#property-method-assignment)
  - [Property name shorthand](features.md#property-name-shorthand)
  - [React/JSX](react.md)
diff --git a/doc/modules.md b/doc/modules.md
index 5fcba15868..f58c68416f 100644
--- a/doc/modules.md
+++ b/doc/modules.md
@@ -19,12 +19,11 @@ to5.transform('import "foo";', { modules: "common" });
 
  * [AMD](#amd)
  * [Common (Default)](#common-default)
- * [Common Interop](#common-interop)
  * [Ignore](#ignore)
  * [System](#system)
  * [UMD](#umd)
 
-### Common (Default)
+### Common
 
 ```sh
 $ 6to5 --modules common
@@ -33,6 +32,11 @@ $ 6to5 --modules common
 **In**
 
 ```javascript
+export default test;
+
+export {test};
+export var test = 5;
+
 import "foo";
 
 import foo from "foo";
@@ -40,95 +44,30 @@ import * as foo from "foo";
 
 import {bar} from "foo";
 import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
 ```
 
 **Out**
 
 ```javascript
-require("foo");
+"use strict";
 
-var foo = require("foo").default;
-var foo = require("foo");
-
-var bar = require("foo").bar;
-var bar = require("foo").foo;
-
-exports.test = test;
-var test = 5; exports.test = test;
-
-exports.default = test;
-```
-
-### Common interop
-
-```sh
-$ 6to5 --modules commonInterop
-```
-
-**In**
-
-```javascript
-import "foo";
-
-import foo from "foo";
-import * as foo from "foo";
-
-import {bar} from "foo";
-import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
-```
-
-**Out**
-
-```javascript
 var _interopRequire = function (obj) {
   return obj && (obj["default"] || obj);
 };
 
-require("foo");
-
-var foo = _interopRequire(require("foo"));
-var foo = require("foo");
-
-var bar = require("foo").bar;
-var bar = require("foo").foo;
+exports = module.exports = test;
 
 exports.test = test;
 var test = exports.test = 5;
 
-exports["default"] = test;
-```
+require("foo");
 
-#### module.exports behaviour
+var foo = _interopRequire(require("foo"));
 
-If there exist no other non-default `export`s then `default exports` are
-exported as `module.exports` instead of `exports.default`.
+var foo = require("foo");
 
-**In**
-
-```javascript
-export default function foo() {
-
-}
-```
-
-**Out**
-
-```javascript
-module.exports = foo;
-
-function foo() {
-
-}
+var bar = require("foo").bar;
+var bar = require("foo").foo;
 ```
 
 ### AMD
@@ -151,9 +90,14 @@ export function bar() {
 
 ```javascript
 define(["exports", "foo"], function (exports, _foo) {
-  exports.bar = bar;
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -192,10 +136,15 @@ export function bar() {
   } else if (typeof exports !== "undefined") {
     factory(exports, require("foo"));
   }
-})(function (exports) {
-  exports.bar = bar;
+})(function (exports, _foo) {
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -288,7 +237,7 @@ ModuleFormatter.prototype.transform = function (ast) {
   // feel free to modify this however
 };
 
-ModuleFormatter.prototype.import = function (node, nodes) {
+ModuleFormatter.prototype.importDeclaration = function (node, nodes) {
   // node is an ImportDeclaration
 };
 
@@ -297,7 +246,7 @@ ModuleFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   // node is an ImportDeclaration
 };
 
-ModuleFormatter.prototype.export = function (node, nodes) {
+ModuleFormatter.prototype.exportDeclaration = function (node, nodes) {
   // node is an ExportDeclaration
 };
 
diff --git a/doc/playground.md b/doc/playground.md
index c1f143f0ad..e02e89c163 100644
--- a/doc/playground.md
+++ b/doc/playground.md
@@ -12,7 +12,7 @@ Playground is a proving ground for **possible** ES7 proposals.
 to5.transform("code", { playground: true });
 ```
 
-**NOTE:** Enabling `playground` also enables [experimental support](usage.md#experimental).
+**NOTE:** Enabling `playground` also enables [experimental support](experimental.md).
 
 ## Features
 
@@ -52,11 +52,11 @@ if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
 ### Method binding
 
 ```javascript
-var fn = obj:method;
-var fn = obj:method("foob");
+var fn = obj#method;
+var fn = obj#method("foob");
 
-["foo", "bar"].map(:toUpperCase); // ["FOO", "BAR"]
-[1.1234, 23.53245, 3].map(:toFixed(2)); // ["1.12", "23.53", "3.00"]
+["foo", "bar"].map(#toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(#toFixed(2)); // ["1.12", "23.53", "3.00"]
 ```
 
 equivalent to:
diff --git a/doc/plugins.md b/doc/plugins.md
index 3c4fa70137..3785d31575 100644
--- a/doc/plugins.md
+++ b/doc/plugins.md
@@ -1,18 +1,33 @@
 # Plugins
 
- - [Broccoli](https://github.com/very-geek/broccoli-6to5-transpiler)
- - [Browserify](https://github.com/6to5/6to5-browserify)
- - [Brunch](https://github.com/es128/6to5-brunch)
- - [Duo](https://github.com/bdo-labs/duo6to5)
- - [Connect](https://github.com/6to5/6to5-connect)
- - [Gobble](https://github.com/gobblejs/gobble-6to5)
- - [Gulp](https://github.com/sindresorhus/gulp-6to5)
- - [Grunt](https://github.com/sindresorhus/grunt-6to5)
+## Build systems
+
+ - [Broccoli](https://github.com/6to5/broccoli-6to5-transpiler)
+ - [Browserify](https://github.com/6to5/6to5ify)
+ - [Brunch](https://github.com/6to5/6to5-brunch)
+ - [Duo](https://github.com/6to5/duo6to5)
+ - [Gobble](https://github.com/6to5/gobble-6to5)
+ - [Gulp](https://github.com/6to5/gulp-6to5)
+ - [Grunt](https://github.com/6to5/grunt-6to5)
+ - [Sprockets](https://github.com/josh/sprockets-es6) or via [Browserify](https://github.com/6to5/6to5-rails)
+ - [webpack](https://github.com/6to5/6to5-loader)
+
+## Integrations
+
  - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
- - [Jade](https://github.com/Apoxx/jade-6to5)
- - [Jest](https://github.com/6to5/6to5-jest)
  - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
- - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
+
+## Bridges
+
+ - [Ruby](https://github.com/6to5/6to5-ruby)
+
+## Testing
+
+ - [Jest](https://github.com/6to5/6to5-jest)
+ - [Karma](https://github.com/6to5/karma-6to5-preprocessor)
  - [Mocha](https://github.com/6to5/6to5-mocha)
- - [Rails](https://github.com/josh/sprockets-es6) or via [browserify-rails](https://github.com/6to5/6to5-rails)
- - [webpack](https://github.com/Couto/6to5-loader)
+
+## Misc
+
+ - [Connect](https://github.com/6to5/6to5-connect)
+ - [Jade](https://github.com/6to5/jade-6to5)
diff --git a/doc/polyfill.md b/doc/polyfill.md
index 4249e038dc..a97e334fb7 100644
--- a/doc/polyfill.md
+++ b/doc/polyfill.md
@@ -1,16 +1,15 @@
 # Polyfill
 
-6to5 includes a polyfill that includes the
-[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and the
-[es6-shim](https://github.com/paulmillr/es6-shim) and
-[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
+6to5 includes a polyfill that includes a custom
+[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and
+[core.js](https://github.com/zloirock/core-js).
 
 This will emulate a full ES6 environment. This polyfill is automatically loaded
-when using [6to5-node](usage.md#node).
+when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).
 
 ## Usage
 
-### Node
+### Node/Browserify
 
 You need to include the polyfill require at the top the **entry point** to your
 application.
@@ -31,3 +30,5 @@ Available from the `browser-polyfill.js` file within the 6to5 directory of an
 npm release. This needs to be included **before** all your compiled 6to5 code.
 You can either prepend it to your compiled code or include it in a `<script>`
 before it.
+
+**NOTE:** Do not `require` this via browserify etc, use `6to5/polyfill`.
diff --git a/doc/usage.md b/doc/usage.md
index 19116d3ac7..f49ab482e6 100644
--- a/doc/usage.md
+++ b/doc/usage.md
@@ -95,6 +95,15 @@ to5.transformFile("filename.js", options, function (err, result) {
 });
 ```
 
+### to5.transform.fromAst(ast, [code], [opts])
+
+```javascript
+var result = to5.transform.fromAst(ast, "var a = 2;", opts);
+result.code;
+result.map;
+result.ast;
+```
+
 #### Options
 
 ```javascript
@@ -153,13 +162,47 @@ to5.transformFile("filename.js", options, function (err, result) {
   // Default: false
   runtime: true,
 
-  // Output comments in generated output
-  // Default: true
-  comments: false,
-
   // Enable support for experimental ES7 features
   // Default: false
-  experimental: true
+  experimental: true,
+
+  // Set this to `false` if you don't want the transformed AST in the returned
+  // result
+  // Default: true
+  ast: true,
+
+  // Set this to `false` if you don't want the transformed code in the returned
+  // result
+  // Default: true
+  code: true,
+
+  format: {
+    // Output comments in generated output
+    // Default: true
+    comments: true,
+
+    // Do not include superfluous whitespace characters and line terminators
+    // Default: false
+    compact: false,
+
+    indent: {
+      // Preserve parentheses in new expressions that have no arguments
+      // Default: true
+      parentheses: true,
+
+      // Adjust the indentation of multiline comments to keep asterisks vertically aligned
+      // Default: true
+      adjustMultilineComment: true,
+
+      // Indent string
+      // Default: "  "
+      style: "  ",
+
+      // Base indent level
+      // Default: 0
+      base: 0
+    }
+  }
 }
 ```
 
@@ -169,6 +212,9 @@ All subsequent files required by node with the extensions `.es6` and `.js` will
 be transformed by 6to5. The polyfill specified in [Polyfill](polyfill.md) is
 also required; but this is automatically loaded when using:
 
+Source maps are automatically configured so if any errors a thrown then line
+number info is mapped and you'll get the correct source location.
+
 ```javascript
 require("6to5/register");
 ```
@@ -207,12 +253,3 @@ require("6to5/register")({
   extensions: [".js", ".es6"]
 });
 ```
-
-## Experimental
-
-6to5 also has experimental support for ES7 proposals. You can enable this with
-the `experimental: true` option when using the [Node API](#node) or
-`--experimental` when using the [CLI](#cli).
-
-**WARNING:** These proposals are subject to change so use with
-**extreme caution**.
diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index de9957fe79..b42aac76ee 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -2,12 +2,13 @@ module.exports = File;
 
 var SHEBANG_REGEX = /^\#\!.*/;
 
-var transform = require("./transformation/transform");
-var generate  = require("./generation/generator");
-var Scope     = require("./traverse/scope");
-var util      = require("./util");
-var t         = require("./types");
-var _         = require("lodash");
+var Transformer = require("./transformation/transformer");
+var transform   = require("./transformation/transform");
+var generate    = require("./generation/generator");
+var Scope       = require("./traverse/scope");
+var util        = require("./util");
+var t           = require("./types");
+var _           = require("lodash");
 
 function File(opts) {
   this.opts = File.normaliseOptions(opts);
@@ -16,13 +17,13 @@ function File(opts) {
 }
 
 File.declarations = [
-  "extends",
-  "class-props",
+  "inherits",
+  "prototype-properties",
   "apply-constructor",
   "tagged-template-literal",
   "interop-require",
   "to-array",
-  "object-spread",
+  "object-without-properties",
   "has-own",
   "slice"
 ];
@@ -101,7 +102,7 @@ File.prototype.getModuleFormatter = function (type) {
   }
 
   if (!ModuleFormatter) {
-    throw new ReferenceError("unknown module formatter type " + type);
+    throw new ReferenceError("Unknown module formatter type " + JSON.stringify(type));
   }
 
   return new ModuleFormatter(this);
@@ -156,14 +157,16 @@ File.prototype.errorWithNode = function (node, msg, Error) {
   return err;
 };
 
-File.prototype.parse = function (code) {
+File.prototype.addCode = function (code) {
   code = (code || "") + "";
+  this.code = code;
+  return this.parseShebang(code);
+};
 
+File.prototype.parse = function (code) {
   var self = this;
 
-  this.code = code;
-
-  code = this.parseShebang(code);
+  code = this.addCode(code);
 
   return util.parse(this.opts, code, function (tree) {
     self.transform(tree);
diff --git a/lib/6to5/generation/buffer.js b/lib/6to5/generation/buffer.js
index a3f4756653..afd9c4dd23 100644
--- a/lib/6to5/generation/buffer.js
+++ b/lib/6to5/generation/buffer.js
@@ -35,7 +35,7 @@ Buffer.prototype.dedent = function () {
 };
 
 Buffer.prototype.semicolon = function () {
-  if (this.format.semicolons) this.push(";");
+  this.push(";");
 };
 
 Buffer.prototype.ensureSemicolon = function () {
@@ -66,9 +66,7 @@ Buffer.prototype.removeLast = function (cha) {
 };
 
 Buffer.prototype.newline = function (i, removeLast) {
-  if (!this.buf) return;
   if (this.format.compact) return;
-  if (this.endsWith("{\n")) return;
 
   if (_.isBoolean(i)) {
     removeLast = i;
@@ -76,6 +74,7 @@ Buffer.prototype.newline = function (i, removeLast) {
   }
 
   if (_.isNumber(i)) {
+    if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
     var self = this;
@@ -88,7 +87,10 @@ Buffer.prototype.newline = function (i, removeLast) {
   if (removeLast && this.isLast("\n")) this.removeLast("\n");
 
   this.removeLast(" ");
+
+  // remove whitespace if last character was a newline
   this.buf = this.buf.replace(/\n +$/, "\n");
+
   this._push("\n");
 };
 
diff --git a/lib/6to5/generation/generator.js b/lib/6to5/generation/generator.js
index 18fa9b00a3..b12f235b55 100644
--- a/lib/6to5/generation/generator.js
+++ b/lib/6to5/generation/generator.js
@@ -37,7 +37,6 @@ _.each(Buffer.prototype, function (fn, key) {
 CodeGenerator.normaliseOptions = function (opts) {
   return _.merge({
     parentheses: true,
-    semicolons: true,
     comments: opts.comments == null || opts.comments,
     compact: false,
     indent: {
@@ -58,6 +57,7 @@ CodeGenerator.generators = {
   methods:          require("./generators/methods"),
   modules:          require("./generators/modules"),
   types:            require("./generators/types"),
+  flow:             require("./generators/flow"),
   base:             require("./generators/base"),
   jsx:              require("./generators/jsx")
 };
@@ -71,6 +71,12 @@ CodeGenerator.prototype.generate = function () {
 
   this.print(ast);
 
+  var comments = [];
+  _.each(ast.comments, function (comment) {
+    if (!comment._displayed) comments.push(comment);
+  });
+  this._printComments(comments);
+
   return {
     map:  this.map.get(),
     code: this.buffer.get()
@@ -132,6 +138,9 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
       var needs = n.needsWhitespaceAfter;
       if (leading) needs = n.needsWhitespaceBefore;
       lines += needs(node, parent);
+
+      // generated nodes can't add starting file whitespace
+      if (!self.buffer.get()) lines = 0;
     }
 
     self.newline(lines);
@@ -147,7 +156,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     // only compute if this node needs parens if our parent has been changed
     // since acorn would've wrapped us in a ParanthesizedExpression
-    var needsParens = parent !== node._parent && n.needsParens(node, parent);
+    var needsParens = n.needsParens(node, parent);
     if (needsParens) this.push("(");
 
     this[node.type](node, this.buildPrint(node), parent);
@@ -259,6 +268,14 @@ CodeGenerator.prototype._printComments = function (comments) {
   var self = this;
 
   _.each(comments, function (comment) {
+    // find the original comment in the ast and set it as displayed
+    _.each(self.ast.comments, function (origComment) {
+      if (origComment.start === comment.start) {
+        origComment._displayed = true;
+        return false;
+      }
+    });
+
     // whitespace before
     self.newline(self.whitespace.getNewlinesBefore(comment));
 
diff --git a/lib/6to5/generation/generators/expressions.js b/lib/6to5/generation/generators/expressions.js
index 65d0be8710..b5a583d6bb 100644
--- a/lib/6to5/generation/generators/expressions.js
+++ b/lib/6to5/generation/generators/expressions.js
@@ -18,12 +18,6 @@ exports.UnaryExpression = function (node, print) {
   print(node.argument);
 };
 
-exports.ParenthesizedExpression = function (node, print) {
-  this.push("(");
-  print(node.expression);
-  this.push(")");
-};
-
 exports.UpdateExpression = function (node, print) {
   if (node.prefix) {
     this.push(node.operator);
@@ -98,8 +92,11 @@ exports.AssignmentExpression = function (node, print) {
   print(node.right);
 };
 
+var SCIENTIFIC_NOTATION = /e/i;
+
 exports.MemberExpression = function (node, print) {
-  print(node.object);
+  var obj = node.object;
+  print(obj);
 
   if (node.computed) {
     this.push("[");
@@ -107,7 +104,7 @@ exports.MemberExpression = function (node, print) {
     this.push("]");
   } else {
     // 5..toFixed(2);
-    if (t.isLiteral(node.object) && util.isInteger(node.object.value)) {
+    if (t.isLiteral(obj) && util.isInteger(obj.value) && !SCIENTIFIC_NOTATION.test(obj.value.toString())) {
       this.push(".");
     }
 
diff --git a/lib/6to5/generation/generators/flow.js b/lib/6to5/generation/generators/flow.js
new file mode 100644
index 0000000000..f96e45bde0
--- /dev/null
+++ b/lib/6to5/generation/generators/flow.js
@@ -0,0 +1,3 @@
+exports.ClassProperty = function () {
+  throw new Error("not implemented");
+};
diff --git a/lib/6to5/generation/generators/modules.js b/lib/6to5/generation/generators/modules.js
index 871afe085f..16f6a01d83 100644
--- a/lib/6to5/generation/generators/modules.js
+++ b/lib/6to5/generation/generators/modules.js
@@ -1,7 +1,14 @@
 var t = require("../../types");
 var _ = require("lodash");
 
-exports.ImportSpecifier =
+exports.ImportSpecifier = function (node, print) {
+  if (node.id && node.id.name === "default") {
+    print(node.name);
+  } else {
+    return exports.ExportSpecifier.apply(this, arguments);
+  }
+};
+
 exports.ExportSpecifier = function (node, print) {
   print(node.id);
   if (node.name) {
@@ -62,7 +69,9 @@ exports.ImportDeclaration = function (node, print) {
         self.push(", ");
       }
 
-      if (!spec.default && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
+      var isDefault = spec.id && spec.id.name === "default";
+
+      if (!isDefault && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
         foundImportSpecifier = true;
         self.push("{ ");
       }
diff --git a/lib/6to5/generation/generators/statements.js b/lib/6to5/generation/generators/statements.js
index f96ecb29fa..c6c471b638 100644
--- a/lib/6to5/generation/generators/statements.js
+++ b/lib/6to5/generation/generators/statements.js
@@ -164,6 +164,12 @@ exports.VariableDeclaration = function (node, print, parent) {
   }
 };
 
+exports.PrivateDeclaration = function (node, print) {
+  this.push("private ");
+  print.join(node.declarations, { separator: ", " });
+  this.semicolon();
+};
+
 exports.VariableDeclarator = function (node, print) {
   if (node.init) {
     print(node.id);
diff --git a/lib/6to5/generation/generators/types.js b/lib/6to5/generation/generators/types.js
index b9fa822ce3..4a58375a8d 100644
--- a/lib/6to5/generation/generators/types.js
+++ b/lib/6to5/generation/generators/types.js
@@ -84,8 +84,8 @@ exports.Literal = function (node) {
   if (type === "string") {
     val = JSON.stringify(val);
 
-    // escape unicode characters
-    val = val.replace(/[\u007f-\uffff]/g, function (c) {
+    // escape illegal js but valid json unicode characters
+    val = val.replace(/[\u000A\u000D\u2028\u2029]/g, function (c) {
       return "\\u" + ("0000" + c.charCodeAt(0).toString(16)).slice(-4);
     });
 
diff --git a/lib/6to5/generation/node/parentheses.js b/lib/6to5/generation/node/parentheses.js
index 544da11d7a..bdea11d6d2 100644
--- a/lib/6to5/generation/node/parentheses.js
+++ b/lib/6to5/generation/node/parentheses.js
@@ -92,13 +92,6 @@ exports.YieldExpression = function (node, parent) {
          t.isYieldExpression(parent);
 };
 
-exports.Literal = function (node, parent) {
-  // (1).valueOf()
-  if (_.isNumber(node.value) && t.isMemberExpression(parent) && parent.object === node) {
-    return true;
-  }
-};
-
 exports.ClassExpression = function (node, parent) {
   return t.isExpressionStatement(parent);
 };
diff --git a/lib/6to5/generation/whitespace.js b/lib/6to5/generation/whitespace.js
index ee10a63ca7..e43752c577 100644
--- a/lib/6to5/generation/whitespace.js
+++ b/lib/6to5/generation/whitespace.js
@@ -38,7 +38,11 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
     }
   });
 
-  return this.getNewlinesBetween(startToken, endToken);
+  if (endToken.type.type === "eof") {
+    return 1;
+  } else {
+    return this.getNewlinesBetween(startToken, endToken);
+  }
 };
 
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {
diff --git a/lib/6to5/index.js b/lib/6to5/index.js
index 924e08acb3..d60d457322 100644
--- a/lib/6to5/index.js
+++ b/lib/6to5/index.js
@@ -3,6 +3,10 @@ var util      = require("./util");
 var fs        = require("fs");
 var _         = require("lodash");
 
+exports.Transformer = require("./transformation/transformer");
+
+exports.types = require("./types");
+
 exports.runtime = require("./runtime");
 
 exports.register = function (opts) {
diff --git a/lib/6to5/patch.js b/lib/6to5/patch.js
index b50b96718a..836538b2f8 100644
--- a/lib/6to5/patch.js
+++ b/lib/6to5/patch.js
@@ -1,22 +1,17 @@
 var t = require("./types");
 var _ = require("lodash");
 
+// estraverse
+
+var estraverse = require("estraverse");
+_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+
+// regenerator/recast/ast-types
+
 var types = require("ast-types");
 var def   = types.Type.def;
 var or    = types.Type.or;
 
-// Program wrapper
-def("File")
-  .bases("Node")
-  .build("program")
-  .field("program", def("Program"));
-
-// Non-standard Acorn type
-def("ParenthesizedExpression")
-  .bases("Expression")
-  .build("expression")
-  .field("expression", def("Expression"));
-
 // Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
   .bases("Specifier")
@@ -30,6 +25,11 @@ def("VirtualPropertyExpression")
   .field("object", def("Expression"))
   .field("property", or(def("Identifier"), def("Expression")));
 
+def("PrivateDeclaration")
+  .bases("Declaration")
+  .build("declarations")
+  .field("declarations", [def("Identifier")]);
+
 // Playground
 def("BindMemberExpression")
   .bases("Expression")
@@ -45,6 +45,3 @@ def("BindFunctionExpression")
   .field("arguments", [def("Expression")]);
 
 types.finalize();
-
-var estraverse = require("estraverse");
-_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
diff --git a/lib/6to5/polyfill.js b/lib/6to5/polyfill.js
index 9e98ba264a..c8d5124f2b 100644
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,37 +1,2 @@
-/* jshint newcap: false */
-
-var ensureSymbol = function (key) {
-  Symbol[key] = Symbol[key] || Symbol();
-};
-
-var ensureProto = function (Constructor, key, val) {
-  var proto = Constructor.prototype;
-  proto[key] = proto[key] || val;
-};
-
-//
-
-if (typeof Symbol === "undefined") {
-  require("es6-symbol/implement");
-}
-
-require("es6-shim");
-require("./transformation/transformers/es6-generators/runtime");
-
-// Abstract references
-
-ensureSymbol("referenceGet");
-ensureSymbol("referenceSet");
-ensureSymbol("referenceDelete");
-
-ensureProto(Function, Symbol.referenceGet, function () { return this; });
-
-ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
-ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
-ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
-
-if (global.WeakMap) {
-  ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
-  ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
-  ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);
-}
+require("core-js/shim");
+require("regenerator/runtime");
diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index efdec2ad90..b8203ae462 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -89,7 +89,6 @@ var loader = function (m, filename) {
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
-    modules:   "commonInterop",
     ast:       false
   }, transformOpts));
 
diff --git a/lib/6to5/templates/class-super-constructor-call.js b/lib/6to5/templates/class-super-constructor-call.js
index 3c5be02aab..c50d3a50cc 100644
--- a/lib/6to5/templates/class-super-constructor-call.js
+++ b/lib/6to5/templates/class-super-constructor-call.js
@@ -1,2 +1,3 @@
-SUPER_NAME.apply(this, arguments);
-
+if (SUPER_NAME) {
+  SUPER_NAME.apply(this, arguments);
+}
diff --git a/lib/6to5/templates/class.js b/lib/6to5/templates/class.js
deleted file mode 100644
index b644463235..0000000000
--- a/lib/6to5/templates/class.js
+++ /dev/null
@@ -1,7 +0,0 @@
-(function () {
-  var CLASS_NAME = function () {
-
-  };
-
-  return CLASS_NAME;
-})()
diff --git a/lib/6to5/templates/exports-assign-key.js b/lib/6to5/templates/exports-assign-key.js
deleted file mode 100644
index 4a101bbbdc..0000000000
--- a/lib/6to5/templates/exports-assign-key.js
+++ /dev/null
@@ -1 +0,0 @@
-exports.VARIABLE_NAME = OBJECT.KEY;
diff --git a/lib/6to5/templates/exports-default-module-override.js b/lib/6to5/templates/exports-default-module-override.js
new file mode 100644
index 0000000000..4ce92a4fd1
--- /dev/null
+++ b/lib/6to5/templates/exports-default-module-override.js
@@ -0,0 +1 @@
+exports = module.exports = VALUE;
diff --git a/lib/6to5/templates/exports-default.js b/lib/6to5/templates/exports-default.js
deleted file mode 100644
index a34c07f7dc..0000000000
--- a/lib/6to5/templates/exports-default.js
+++ /dev/null
@@ -1 +0,0 @@
-exports.default = VALUE;
diff --git a/lib/6to5/templates/extends.js b/lib/6to5/templates/inherits.js
similarity index 59%
rename from lib/6to5/templates/extends.js
rename to lib/6to5/templates/inherits.js
index bc950dfd9a..1e8f6b5e8f 100644
--- a/lib/6to5/templates/extends.js
+++ b/lib/6to5/templates/inherits.js
@@ -1,5 +1,5 @@
 (function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -7,5 +7,5 @@
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 })
diff --git a/lib/6to5/templates/object-spread.js b/lib/6to5/templates/object-without-properties.js
similarity index 100%
rename from lib/6to5/templates/object-spread.js
rename to lib/6to5/templates/object-without-properties.js
diff --git a/lib/6to5/templates/class-props.js b/lib/6to5/templates/prototype-properties.js
similarity index 100%
rename from lib/6to5/templates/class-props.js
rename to lib/6to5/templates/prototype-properties.js
diff --git a/lib/6to5/templates/register.js b/lib/6to5/templates/register.js
deleted file mode 100644
index 267c8dad4e..0000000000
--- a/lib/6to5/templates/register.js
+++ /dev/null
@@ -1 +0,0 @@
-System.register(MODULE_NAME, MODULE_DEPENDENCIES, MODULE_BODY);
diff --git a/lib/6to5/templates/system.js b/lib/6to5/templates/system.js
new file mode 100644
index 0000000000..00eb18aca5
--- /dev/null
+++ b/lib/6to5/templates/system.js
@@ -0,0 +1,6 @@
+System.register(MODULE_NAME, MODULE_DEPENDENCIES, function (EXPORT_IDENTIFIER) {
+  return {
+    setters: SETTERS,
+    execute: EXECUTE
+  };
+});
diff --git a/lib/6to5/templates/tagged-template-literal.js b/lib/6to5/templates/tagged-template-literal.js
index 9d3b26a3b7..5a3a997307 100644
--- a/lib/6to5/templates/tagged-template-literal.js
+++ b/lib/6to5/templates/tagged-template-literal.js
@@ -1,4 +1,6 @@
 (function (strings, raw) {
-  return Object.defineProperties(strings, { raw: { value: raw } });
+  return Object.freeze(Object.defineProperties(strings, {
+      raw: { value: Object.freeze(raw) }
+  }));
 });
 
diff --git a/lib/6to5/transformation/modules/_default.js b/lib/6to5/transformation/modules/_default.js
new file mode 100644
index 0000000000..e98efcb641
--- /dev/null
+++ b/lib/6to5/transformation/modules/_default.js
@@ -0,0 +1,178 @@
+module.exports = DefaultFormatter;
+
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+function DefaultFormatter(file) {
+  this.file = file;
+
+  this.localExports = this.getLocalExports();
+  this.remapAssignments();
+}
+
+DefaultFormatter.prototype.getLocalExports = function () {
+  var localExports = {};
+
+  traverse(this.file.ast, {
+    enter: function (node) {
+      var declar = node && node.declaration;
+      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
+        _.extend(localExports, t.getIds(declar, true));
+      }
+    }
+  });
+
+  return localExports;
+};
+
+DefaultFormatter.prototype.remapExportAssignment = function (node) {
+  return t.assignmentExpression(
+    "=",
+    node.left,
+    t.assignmentExpression(
+      node.operator,
+      t.memberExpression(t.identifier("exports"), node.left),
+      node.right
+    )
+  );
+};
+
+DefaultFormatter.prototype.remapAssignments = function () {
+  var localExports = this.localExports;
+  var self = this;
+
+  var throwIllegal = function (node) {
+    // todo!!
+  };
+
+  var isLocalReference = function (node, scope) {
+    var left = node.left;
+    var name = left.name;
+    return t.isIdentifier(left) && localExports[name] && localExports[name] === scope.get(name, true);
+  };
+
+  traverse(this.file.ast, {
+    enter: function (node, parent, scope) {
+      if (t.isExportDeclaration(node)) return false;
+
+      if (t.isAssignmentExpression(node) && isLocalReference(node, scope)) {
+        return self.remapExportAssignment(node);
+      }
+    }
+  });
+};
+
+DefaultFormatter.prototype.getModuleName = function () {
+  var opts = this.file.opts;
+  var filenameRelative = opts.filenameRelative;
+  var moduleName = "";
+
+  if (opts.moduleRoot) {
+    moduleName = opts.moduleRoot + "/";
+  }
+
+  if (!opts.filenameRelative) {
+    return moduleName + opts.filename.replace(/^\//, "");
+  }
+
+  if (opts.sourceRoot) {
+    // remove sourceRoot from filename
+    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
+    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
+  }
+
+  // remove extension
+  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+
+  moduleName += filenameRelative;
+
+  return moduleName;
+};
+
+DefaultFormatter.prototype._pushStatement = function (ref, nodes) {
+  if (t.isClass(ref) || t.isFunction(ref)) {
+    if (ref.id) {
+      nodes.push(t.toStatement(ref));
+      ref = ref.id;
+    }
+  }
+
+  return ref;
+};
+
+DefaultFormatter.prototype._hoistExport = function (declar, assign) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = true;
+  }
+
+  return assign;
+};
+
+DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
+  var variableName = t.getSpecifierName(specifier);
+
+  var inherits = false;
+  if (node.specifiers.length === 1) inherits = node;
+
+  if (node.source) {
+    if (t.isExportBatchSpecifier(specifier)) {
+      // export * from "foo";
+      nodes.push(this._exportsWildcard(getRef()));
+    } else {
+      // export { foo } from "test";
+      nodes.push(this._exportsAssign(
+        t.getSpecifierName(specifier),
+        t.memberExpression(getRef(), specifier.id)
+      ));
+    }
+  } else {
+    // export { foo };
+    nodes.push(this._exportsAssign(t.getSpecifierName(specifier), specifier.id));
+  }
+};
+
+DefaultFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  return util.template("exports-wildcard", {
+    OBJECT: objectIdentifier
+  }, true);
+};
+
+DefaultFormatter.prototype._exportsAssign = function (id, init) {
+  return util.template("exports-assign", {
+    VALUE: init,
+    KEY:   id
+  }, true);
+};
+
+DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
+  var declar = node.declaration;
+
+  if (node.default) {
+    nodes.push(
+      this._exportsAssign(t.identifier("default"), this._pushStatement(declar, nodes))
+    );
+  } else {
+    var assign;
+
+    if (t.isVariableDeclaration(declar)) {
+      for (var i in declar.declarations) {
+        var decl = declar.declarations[i];
+
+        decl.init = this._exportsAssign(decl.id, decl.init).expression;
+
+        var newDeclar = t.variableDeclaration(declar.kind, [decl]);
+        if (i == 0) t.inherits(newDeclar, declar);
+        nodes.push(newDeclar);
+      }
+    } else {
+      assign = this._exportsAssign(declar.id, declar.id);
+
+      nodes.push(t.toStatement(declar));
+      nodes.push(assign);
+
+      this._hoistExport(declar, assign);
+    }
+  }
+};
diff --git a/lib/6to5/transformation/modules/amd.js b/lib/6to5/transformation/modules/amd.js
index 17432a1235..226bdfc937 100644
--- a/lib/6to5/transformation/modules/amd.js
+++ b/lib/6to5/transformation/modules/amd.js
@@ -1,16 +1,28 @@
 module.exports = AMDFormatter;
 
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
+var DefaultFormatter = require("./_default");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");
 
 function AMDFormatter(file) {
   this.file = file;
   this.ids  = {};
 }
 
-util.inherits(AMDFormatter, CommonJSFormatter);
+util.inherits(AMDFormatter, DefaultFormatter);
+
+AMDFormatter.prototype.buildDependencyLiterals = function () {
+  var names = [];
+  for (var name in this.ids) {
+    names.push(t.literal(name));
+  }
+  return names;
+};
+
+/**
+ * Wrap the entire body in a `define` wrapper.
+ */
 
 AMDFormatter.prototype.transform = function (ast) {
   var program = ast.program;
@@ -18,10 +30,7 @@ AMDFormatter.prototype.transform = function (ast) {
 
   // build an array of module names
 
-  var names = [t.literal("exports")];
-  _.each(this.ids, function (id, name) {
-    names.push(t.literal(name));
-  });
+  var names = [t.literal("exports")].concat(this.buildDependencyLiterals());
   names = t.arrayExpression(names);
 
   // build up define container
@@ -40,9 +49,14 @@ AMDFormatter.prototype.transform = function (ast) {
   program.body = [t.expressionStatement(call)];
 };
 
+/**
+ * Get the AMD module name that we'll prepend to the wrapper
+ * to define this module
+ */
+
 AMDFormatter.prototype.getModuleName = function () {
   if (this.file.opts.amdModuleIds) {
-    return CommonJSFormatter.prototype.getModuleName.apply(this, arguments);
+    return DefaultFormatter.prototype.getModuleName.apply(this, arguments);
   } else {
     return null;
   }
@@ -59,7 +73,7 @@ AMDFormatter.prototype._push = function (node) {
   }
 };
 
-AMDFormatter.prototype.import = function (node) {
+AMDFormatter.prototype.importDeclaration = function (node) {
   this._push(node);
 };
 
@@ -69,7 +83,7 @@ AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
 
   if (t.isImportBatchSpecifier(specifier)) {
     // import * as bar from "foo";
-  } else if (specifier.default) {
+  } else if (t.isSpecifierDefault(specifier)) {
     // import foo from "foo";
     ref = t.callExpression(this.file.addDeclaration("interop-require"), [ref]);
   } else {
diff --git a/lib/6to5/transformation/modules/common-interop.js b/lib/6to5/transformation/modules/common-interop.js
deleted file mode 100644
index 9cc4d4bd37..0000000000
--- a/lib/6to5/transformation/modules/common-interop.js
+++ /dev/null
@@ -1,56 +0,0 @@
-module.exports = CommonJSInteropFormatter;
-
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
-
-function CommonJSInteropFormatter(file) {
-  CommonJSFormatter.apply(this, arguments);
-
-  var has = false;
-  _.each(file.ast.program.body, function (node) {
-    if (t.isExportDeclaration(node) && !node.default) has = true;
-  });
-  this.has = has;
-}
-
-util.inherits(CommonJSInteropFormatter, CommonJSFormatter);
-
-CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  // import foo from "foo";
-   if (specifier.default) {
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(variableName,
-        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
-          MODULE_NAME: node.source.raw
-        })])
-      )
-    ]));
-  } else {
-    CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
-  }
-};
-
-CommonJSInteropFormatter.prototype.export = function (node, nodes) {
-  if (node.default && !this.has) {
-    var declar = node.declaration;
-
-    // module.exports = VALUE;
-    var assign = util.template("exports-default-module", {
-      VALUE: this._pushStatement(declar, nodes)
-    }, true);
-
-    // hoist to the top if this default is a function
-    nodes.push(this._hoistExport(declar, assign));
-    return;
-  }
-
-  CommonJSFormatter.prototype.export.apply(this, arguments);
-};
-
-CommonJSInteropFormatter.prototype.exportSpecifier = function () {
-  CommonJSFormatter.prototype.exportSpecifier.apply(this, arguments);
-};
diff --git a/lib/6to5/transformation/modules/common.js b/lib/6to5/transformation/modules/common.js
index 267c4ca677..341846f4a0 100644
--- a/lib/6to5/transformation/modules/common.js
+++ b/lib/6to5/transformation/modules/common.js
@@ -1,161 +1,77 @@
 module.exports = CommonJSFormatter;
 
-var util = require("../../util");
-var t    = require("../../types");
+var DefaultFormatter = require("./_default");
+var traverse         = require("../../traverse");
+var util             = require("../../util");
+var t                = require("../../types");
 
 function CommonJSFormatter(file) {
-  this.file = file;
+  DefaultFormatter.apply(this, arguments);
+
+  var hasNonDefaultExports = false;
+  traverse(file.ast, {
+    enter: function (node) {
+      if (t.isExportDeclaration(node) && !node.default) hasNonDefaultExports = true;
+    }
+  });
+  this.hasNonDefaultExports = hasNonDefaultExports;
 }
 
-CommonJSFormatter.prototype.getModuleName = function () {
-  var opts = this.file.opts;
-  var filenameRelative = opts.filenameRelative;
-  var moduleName = "";
-
-  if (opts.moduleRoot) {
-    moduleName = opts.moduleRoot + "/";
-  }
-
-  if (!opts.filenameRelative) {
-    return moduleName + opts.filename.replace(/^\//, "");
-  }
-
-  if (opts.sourceRoot) {
-    // remove sourceRoot from filename
-    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
-    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
-  }
-
-  // remove extension
-  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
-
-  moduleName += filenameRelative;
-
-  return moduleName;
-};
-
-CommonJSFormatter.prototype.import = function (node, nodes) {
-  // import "foo";
-  nodes.push(util.template("require", {
-    //inherits: node,
-
-    MODULE_NAME: node.source.raw
-  }, true));
-};
+util.inherits(CommonJSFormatter, DefaultFormatter);
 
 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var variableName = t.getSpecifierName(specifier);
 
   // import foo from "foo";
-  if (specifier.default) {
-    specifier.id = t.identifier("default");
+  if (t.isSpecifierDefault(specifier)) {
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(variableName,
+        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
+          MODULE_NAME: node.source
+        })])
+      )
+    ]));
+  } else {
+    // import foo from "foo";
+
+    var templateName = "require-assign";
+
+    // import * as bar from "foo";
+    if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
+
+    nodes.push(util.template(templateName, {
+      VARIABLE_NAME: variableName,
+      MODULE_NAME:   node.source,
+      KEY:           specifier.id
+    }));
   }
-
-  var templateName = "require-assign";
-
-  // import * as bar from "foo";
-  if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
-
-  nodes.push(util.template(templateName, {
-    //inherits: node.specifiers.length === 1 && node,
-
-    VARIABLE_NAME: variableName,
-    MODULE_NAME:   node.source.raw,
-    KEY:           specifier.id
-  }));
 };
 
-CommonJSFormatter.prototype._hoistExport = function (declar, assign) {
-  if (t.isFunctionDeclaration(declar)) {
-    assign._blockHoist = true;
-  }
-
-  return assign;
+CommonJSFormatter.prototype.importDeclaration = function (node, nodes) {
+  // import "foo";
+  nodes.push(util.template("require", {
+    MODULE_NAME: node.source
+  }, true));
 };
 
-CommonJSFormatter.prototype._pushStatement = function (ref, nodes) {
-  if (t.isClass(ref) || t.isFunction(ref)) {
-    if (ref.id) {
-      nodes.push(t.toStatement(ref));
-      ref = ref.id;
-    }
-  }
-  return ref;
-};
-
-CommonJSFormatter.prototype.export = function (node, nodes) {
-  var declar = node.declaration;
-
+CommonJSFormatter.prototype.exportDeclaration = function (node, nodes) {
   if (node.default) {
-    nodes.push(util.template("exports-default", {
-      //inherits: node,
+    var declar = node.declaration;
 
+    // module.exports = VALUE;
+    var templateName = "exports-default-module";
+
+    // exports = module.exports = VALUE;
+    if (this.hasNonDefaultExports) templateName = "exports-default-module-override";
+
+    var assign = util.template(templateName, {
       VALUE: this._pushStatement(declar, nodes)
-    }, true));
+    }, true);
+
+    // hoist to the top if this default is a function
+    nodes.push(this._hoistExport(declar, assign));
   } else {
-    var assign;
-
-    if (t.isVariableDeclaration(declar)) {
-      var decl = declar.declarations[0];
-
-      if (decl.init) {
-        decl.init = util.template("exports-assign", {
-          //inherits: node,
-
-          VALUE: decl.init,
-          KEY:   decl.id
-        });
-      }
-
-      nodes.push(declar);
-    } else {
-      assign = util.template("exports-assign", {
-        //inherits: node,
-
-        VALUE: declar.id,
-        KEY:   declar.id
-      }, true);
-
-      nodes.push(t.toStatement(declar));
-      nodes.push(assign);
-
-      this._hoistExport(declar, assign);
-    }
-  }
-};
-
-CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  var inherits = false;
-  if (node.specifiers.length === 1) inherits = node;
-
-  if (node.source) {
-    if (t.isExportBatchSpecifier(specifier)) {
-      // export * from "foo";
-      nodes.push(util.template("exports-wildcard", {
-        //inherits: inherits,
-
-        OBJECT: getRef()
-      }, true));
-    } else {
-      // export { foo } from "test";
-      nodes.push(util.template("exports-assign-key", {
-        //inherits: inherits,
-
-        VARIABLE_NAME: variableName.name,
-        OBJECT:        getRef(),
-        KEY:           specifier.id
-      }, true));
-    }
-  } else {
-    // export { foo };
-    nodes.push(util.template("exports-assign", {
-      //inherits: inherits,
-
-      VALUE: specifier.id,
-      KEY:   variableName
-    }, true));
+    DefaultFormatter.prototype.exportDeclaration.apply(this, arguments);
   }
 };
 
diff --git a/lib/6to5/transformation/modules/ignore.js b/lib/6to5/transformation/modules/ignore.js
index 28fbb4e026..3753440eed 100644
--- a/lib/6to5/transformation/modules/ignore.js
+++ b/lib/6to5/transformation/modules/ignore.js
@@ -6,19 +6,13 @@ function IgnoreFormatter() {
 
 }
 
-IgnoreFormatter.prototype.import = function () {
-
-};
-
-IgnoreFormatter.prototype.importSpecifier = function () {
-
-};
-
-IgnoreFormatter.prototype.export = function (node, nodes) {
+IgnoreFormatter.prototype.exportDeclaration = function (node, nodes) {
   var declar = t.toStatement(node.declaration, true);
   if (declar) nodes.push(t.inherits(declar, node));
 };
 
+IgnoreFormatter.prototype.importDeclaration =
+IgnoreFormatter.prototype.importSpecifier =
 IgnoreFormatter.prototype.exportSpecifier = function () {
 
 };
diff --git a/lib/6to5/transformation/modules/system.js b/lib/6to5/transformation/modules/system.js
index 73ddc6f107..ae1402c651 100644
--- a/lib/6to5/transformation/modules/system.js
+++ b/lib/6to5/transformation/modules/system.js
@@ -1,202 +1,88 @@
 module.exports = SystemFormatter;
 
-var util = require("../../util");
-var t    = require("../../types");
-var _    = require("lodash");
+var DefaultFormatter = require("./_default");
+var AMDFormatter     = require("./amd");
+var traverse         = require("../../traverse");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");
 
-var SETTER_MODULE_NAMESPACE = t.identifier("m");
-var DEFAULT_IDENTIFIER      = t.identifier("default");
-var NULL_SETTER             = t.literal(null);
+var SETTER_MODULE_NAMESPACE        = t.identifier("m");
+var PRIVATE_MODULE_NAME_IDENTIFIER = t.identifier("__moduleName");
+var NULL_SETTER                    = t.literal(null);
 
 function SystemFormatter(file) {
-  this.exportedStatements = [];
-  this.importedModule     = {};
+  AMDFormatter.apply(this, arguments);
 
-  this.exportIdentifier   = file.generateUidIdentifier("export");
-  this.file               = file;
+  this.moduleNameLiteral = t.literal(this.getModuleName());
+  this.exportIdentifier  = file.generateUidIdentifier("export");
 }
 
+util.inherits(SystemFormatter, AMDFormatter);
+
+SystemFormatter.prototype.getModuleName = DefaultFormatter.prototype.getModuleName;
+
+SystemFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  var leftIdentifier = t.identifier("i");
+  var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
+
+  var left = t.variableDeclaration("var", [
+    t.variableDeclarator(leftIdentifier)
+  ]);
+
+  var right = objectIdentifier;
+
+  var block = t.blockStatement([
+    this.buildExportCall(leftIdentifier, valIdentifier)
+  ]);
+
+  return t.forInStatement(left, right, block);
+};
+
+SystemFormatter.prototype._exportsAssign = function (id, init, isExpression) {
+  return this.buildExportCall(t.literal(id.name), init, true);
+};
+
+SystemFormatter.prototype.remapExportAssignment = function (node) {
+  return this.buildExportCall(t.literal(node.left.name), node);
+};
+
+SystemFormatter.prototype.buildExportCall = function (id, init, isStatement) {
+  var call = t.callExpression(this.exportIdentifier, [id, init]);
+  if (isStatement) {
+    return t.expressionStatement(call);
+  } else {
+    return call;
+  }
+};
+
+SystemFormatter.prototype.buildRunnerSetters = function () {
+  return t.arrayExpression(_.map(this.ids, function (uid) {
+    var moduleIdentifier = t.identifier("m");
+
+    return t.functionExpression(null, [moduleIdentifier], t.blockStatement([
+      t.assignmentExpression("=", uid, moduleIdentifier)
+    ]));
+  }));
+};
+
 SystemFormatter.prototype.transform = function (ast) {
   var program = ast.program;
-  var body    = program.body;
 
-  // extract the module name
-  var moduleName = this.file.opts.filename
-    .replace(/^.*\//, "").replace(/\..*$/, "");
+  var runner = util.template("system", {
+    MODULE_NAME: this.moduleNameLiteral,
+    MODULE_DEPENDENCIES: t.arrayExpression(this.buildDependencyLiterals()),
+    EXPORT_IDENTIFIER: this.exportIdentifier,
+    SETTERS: this.buildRunnerSetters(),
+    EXECUTE: t.functionExpression(null, [], t.blockStatement(program.body))
+  }, true);
 
-  // build an array of module names
-  var dependencies = Object.keys(this.importedModule).map(t.literal);
-
-  // generate the __moduleName variable
-  var moduleNameVariableNode = t.variableDeclaration("var", [
-    t.variableDeclarator(
-      t.identifier("__moduleName"),
-      t.literal(moduleName)
-    )
-  ]);
-  body.splice(1, 0, moduleNameVariableNode);
-
-  // generate an array of import variables
-
-  var declaredSetters = _(this.importedModule)
-    .map()
-    .flatten()
-    .pluck("variableName")
-    .pluck("name")
-    .uniq()
-    .map(t.identifier)
-    .map(function (name) {
-      return t.variableDeclarator(name);
-    })
-    .value();
-
-  if (declaredSetters.length) {
-    body.splice(2, 0, t.variableDeclaration("var", declaredSetters));
+  if (!_.isEmpty(this.ids)) {
+    var handlerBody = runner.expression.arguments[2].body.body;
+    handlerBody.unshift(t.variableDeclaration("var", _.map(this.ids, function (uid) {
+      return t.variableDeclarator(uid);
+    })));
   }
 
-  // generate the execute function expression
-  var executeFunctionExpression = t.functionExpression(
-    null, [], t.blockStatement(this.exportedStatements)
-  );
-
-  // generate the execute function expression
-  var settersArrayExpression = t.arrayExpression(this._buildSetters());
-
-  // generate the return statement
-  var moduleReturnStatement = t.returnStatement(t.objectExpression([
-    t.property("init", t.identifier("setters"), settersArrayExpression),
-    t.property("init", t.identifier("execute"), executeFunctionExpression)
-  ]));
-  body.push(moduleReturnStatement);
-
-  // runner
-  var runner = util.template("register", {
-    MODULE_NAME: t.literal(moduleName),
-    MODULE_DEPENDENCIES: t.arrayExpression(dependencies),
-    MODULE_BODY: t.functionExpression(
-      null,
-      [this.exportIdentifier],
-      t.blockStatement(body)
-    )
-  });
-
-  program.body = [t.expressionStatement(runner)];
-};
-
-SystemFormatter.prototype._buildSetters = function () {
-  // generate setters array expression elements
-  return _.map(this.importedModule, function (specs) {
-    if (!specs.length) {
-      return NULL_SETTER;
-    }
-
-    var expressionStatements = _.map(specs, function (spec) {
-      var right = SETTER_MODULE_NAMESPACE;
-      if (!spec.isBatch) {
-        right = t.memberExpression(right, spec.key);
-      }
-
-      return t.expressionStatement(
-        t.assignmentExpression("=", spec.variableName, right
-        )
-      );
-    });
-
-    return t.functionExpression(
-      null, [SETTER_MODULE_NAMESPACE], t.blockStatement(expressionStatements)
-    );
-  });
-};
-
-SystemFormatter.prototype.import = function (node) {
-  var MODULE_NAME = node.source.value;
-  this.importedModule[MODULE_NAME] = this.importedModule[MODULE_NAME] || [];
-};
-
-SystemFormatter.prototype.importSpecifier = function (specifier, node) {
-  var variableName = t.getSpecifierName(specifier);
-
-  // import foo from "foo";
-  if (specifier.default) {
-    specifier.id = DEFAULT_IDENTIFIER;
-  }
-
-  var MODULE_NAME = node.source.value;
-
-  this.importedModule[MODULE_NAME] = this.importedModule[MODULE_NAME] || [];
-
-  this.importedModule[MODULE_NAME].push({
-    variableName: variableName,
-    isBatch:      specifier.type === "ImportBatchSpecifier",
-    key:          specifier.id
-  });
-};
-
-SystemFormatter.prototype._export = function (name, identifier) {
-  this.exportedStatements.push(t.expressionStatement(
-    t.callExpression(this.exportIdentifier, [t.literal(name), identifier])
-  ));
-};
-
-SystemFormatter.prototype.export = function (node, nodes) {
-  var declar = node.declaration;
-  var variableName, identifier;
-
-  if (node.default) {
-    // export default foo
-    variableName = DEFAULT_IDENTIFIER.name;
-    if (t.isClass(declar) || t.isFunction(declar)) {
-      if (!declar.id) {
-        declar.id = this.file.generateUidIdentifier("anonymous");
-      }
-
-      nodes.push(t.toStatement(declar));
-      declar = declar.id;
-    }
-
-    identifier = declar;
-  } else if (t.isVariableDeclaration(declar)) {
-    // export var foo
-    variableName = declar.declarations[0].id.name;
-    identifier = declar.declarations[0].id;
-
-    nodes.push(declar);
-  } else {
-    // export function foo () {}
-    variableName = declar.id.name;
-    identifier = declar.id;
-
-    nodes.push(declar);
-  }
-
-  this._export(variableName, identifier);
-};
-
-SystemFormatter.prototype.exportSpecifier = function (specifier, node) {
-  var variableName = t.getSpecifierName(specifier);
-
-  if (node.source) {
-    if (t.isExportBatchSpecifier(specifier)) {
-      // export * from "foo";
-      var exportIdentifier = t.identifier("exports");
-      this.exportedStatements.push(
-        t.variableDeclaration("var", [
-          t.variableDeclarator(exportIdentifier, this.exportIdentifier)
-        ])
-      );
-
-      this.exportedStatements.push(util.template("exports-wildcard", {
-        OBJECT: t.identifier(node.source.value)
-      }, true));
-    } else {
-      // export { foo } from "test";
-      this._export(variableName.name, t.memberExpression(
-        t.identifier(node.source.value),
-        specifier.id
-      ));
-    }
-  } else {
-    // export { foo };
-    this._export(variableName.name, specifier.id);
-  }
+  program.body = [runner];
 };
diff --git a/lib/6to5/transformation/modules/umd.js b/lib/6to5/transformation/modules/umd.js
index 199de38024..e23c7c6fc2 100644
--- a/lib/6to5/transformation/modules/umd.js
+++ b/lib/6to5/transformation/modules/umd.js
@@ -18,9 +18,9 @@ UMDFormatter.prototype.transform = function (ast) {
   // build an array of module names
 
   var names = [];
-  _.each(this.ids, function (id, name) {
+  for (var name in this.ids) {
     names.push(t.literal(name));
-  });
+  }
 
   // factory
 
diff --git a/lib/6to5/transformation/transform.js b/lib/6to5/transformation/transform.js
index 4824e44548..d9fa1c90b4 100644
--- a/lib/6to5/transformation/transform.js
+++ b/lib/6to5/transformation/transform.js
@@ -2,6 +2,7 @@ module.exports = transform;
 
 var Transformer = require("./transformer");
 var File        = require("../file");
+var util        = require("../util");
 var _           = require("lodash");
 
 function transform(code, opts) {
@@ -9,31 +10,46 @@ function transform(code, opts) {
   return file.parse(code);
 }
 
+transform.fromAst = function (ast, code, opts) {
+  ast = util.normaliseAst(ast);
+
+  var file = new File(opts);
+  file.addCode(code);
+  file.transform(ast);
+  return file.generate();
+};
+
 transform._ensureTransformerNames = function (type, keys) {
-  _.each(keys, function (key) {
+  for (var i in keys) {
+    var key = keys[i];
     if (!_.has(transform.transformers, key)) {
       throw new ReferenceError("unknown transformer " + key + " specified in " + type);
     }
-  });
+  }
 };
 
 transform.transformers = {};
 
 transform.moduleFormatters = {
-  common:        require("./modules/common"),
-  commonInterop: require("./modules/common-interop"),
-  system:        require("./modules/system"),
-  ignore:        require("./modules/ignore"),
-  amd:           require("./modules/amd"),
-  umd:           require("./modules/umd")
+  common: require("./modules/common"),
+  system: require("./modules/system"),
+  ignore: require("./modules/ignore"),
+  amd:    require("./modules/amd"),
+  umd:    require("./modules/umd")
 };
 
 _.each({
-  // plyground
+  // spec
+  specBlockHoistFunctions:   require("./transformers/spec-block-hoist-functions"),
+  specNoForInOfAssignment:   require("./transformers/spec-no-for-in-of-assignment"),
+  specNoDuplicateProperties: require("./transformers/spec-no-duplicate-properties"),
+
+  // playground
   methodBinding:             require("./transformers/playground-method-binding"),
   memoizationOperator:       require("./transformers/playground-memoization-operator"),
   objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),
 
+  react:                     require("./transformers/react"),
   modules:                   require("./transformers/es6-modules"),
   propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
   arrayComprehension:        require("./transformers/es7-array-comprehension"),
@@ -48,28 +64,30 @@ _.each({
   spread:                    require("./transformers/es6-spread"),
   templateLiterals:          require("./transformers/es6-template-literals"),
   propertyMethodAssignment:  require("./transformers/es5-property-method-assignment"),
-  defaultParameters:         require("./transformers/es6-default-parameters"),
-  restParameters:            require("./transformers/es6-rest-parameters"),
   destructuring:             require("./transformers/es6-destructuring"),
+  defaultParameters:         require("./transformers/es6-default-parameters"),
   forOf:                     require("./transformers/es6-for-of"),
   unicodeRegex:              require("./transformers/es6-unicode-regex"),
   abstractReferences:        require("./transformers/es7-abstract-references"),
-  react:                     require("./transformers/react"),
 
   constants:                 require("./transformers/es6-constants"),
   letScoping:                require("./transformers/es6-let-scoping"),
 
-  generators:                require("./transformers/es6-generators"),
-
   _blockHoist:               require("./transformers/_block-hoist"),
+
+  generators:                require("./transformers/es6-generators"),
+  restParameters:            require("./transformers/es6-rest-parameters"),
+
   _declarations:             require("./transformers/_declarations"),
+
+  // wrap up
   _aliasFunctions:           require("./transformers/_alias-functions"),
-
   useStrict:                 require("./transformers/use-strict"),
+  _moduleFormatter:          require("./transformers/_module-formatter"),
 
-  _propertyLiterals:         require("./transformers/_property-literals"),
-  _memberExpressioLiterals:  require("./transformers/_member-expression-literals"),
-  _moduleFormatter:          require("./transformers/_module-formatter")
+  // spec
+  specPropertyLiterals:         require("./transformers/spec-property-literals"),
+  specMemberExpressionLiterals: require("./transformers/spec-member-expression-literals")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });
diff --git a/lib/6to5/transformation/transformer.js b/lib/6to5/transformation/transformer.js
index 9def8f1912..43f5a1b7c7 100644
--- a/lib/6to5/transformation/transformer.js
+++ b/lib/6to5/transformation/transformer.js
@@ -4,8 +4,9 @@ var traverse = require("../traverse");
 var t        = require("../types");
 var _        = require("lodash");
 
-function Transformer(key, transformer) {
+function Transformer(key, transformer, opts) {
   this.transformer = Transformer.normalise(transformer);
+  this.opts        = opts || {};
   this.key         = key;
 }
 
@@ -18,37 +19,38 @@ Transformer.normalise = function (transformer) {
     if (type[0] === "_") return;
     if (_.isFunction(fns)) fns = { enter: fns };
     transformer[type] = fns;
+
+    var aliases = t.FLIPPED_ALIAS_KEYS[type];
+    if (aliases) {
+      _.each(aliases, function (alias) {
+        transformer[alias] = fns;
+      });
+    }
   });
 
   return transformer;
 };
 
+Transformer.prototype.astRun = function (file, key) {
+  var transformer = this.transformer;
+  var ast         = file.ast;
+
+  if (transformer.ast && transformer.ast[key]) {
+    transformer.ast[key](ast, file);
+  }
+};
+
 Transformer.prototype.transform = function (file) {
   if (!this.canRun(file)) return;
 
   var transformer = this.transformer;
   var ast         = file.ast;
 
-  var astRun = function (key) {
-    if (transformer.ast && transformer.ast[key]) {
-      transformer.ast[key](ast, file);
-    }
-  };
-
-  astRun("enter");
+  this.astRun(file, "enter");
 
   var build = function (exit) {
     return function (node, parent, scope) {
-      // add any node type aliases that exist
-      var types = [node.type].concat(t.ALIAS_KEYS[node.type] || []);
-
-      var fns = transformer.all;
-
-      _.each(types, function (type) {
-        fns = transformer[type] || fns;
-      });
-
-      // this transformer cannot deal with this node type
+      var fns = transformer[node.type];
       if (!fns) return;
 
       var fn = fns.enter;
@@ -64,7 +66,7 @@ Transformer.prototype.transform = function (file) {
     exit:  build(true)
   });
 
-  astRun("exit");
+  this.astRun(file, "exit");
 };
 
 Transformer.prototype.canRun = function (file) {
diff --git a/lib/6to5/transformation/transformers/_alias-functions.js b/lib/6to5/transformation/transformers/_alias-functions.js
index 3ea43351a4..4d4b78ea67 100644
--- a/lib/6to5/transformation/transformers/_alias-functions.js
+++ b/lib/6to5/transformation/transformers/_alias-functions.js
@@ -15,38 +15,42 @@ var go = function (getBody, node, file, scope) {
 
   // traverse the function and find all alias functions so we can alias
   // `arguments` and `this` if necessary
-  traverse(node, function (node) {
-    if (!node._aliasFunction) {
-      if (t.isFunction(node)) {
-        // stop traversal of this node as it'll be hit again by this transformer
-        return false;
-      } else {
-        return;
+  traverse(node, {
+    enter: function (node) {
+      if (!node._aliasFunction) {
+        if (t.isFunction(node)) {
+          // stop traversal of this node as it'll be hit again by this transformer
+          return false;
+        } else {
+          return;
+        }
       }
+
+      // traverse all child nodes of this function and find `arguments` and `this`
+      traverse(node, {
+        enter: function (node, parent) {
+          if (t.isFunction(node) && !node._aliasFunction) {
+            return false;
+          }
+
+          if (node._ignoreAliasFunctions) return false;
+
+          var getId;
+
+          if (t.isIdentifier(node) && node.name === "arguments") {
+            getId = getArgumentsId;
+          } else if (t.isThisExpression(node)) {
+            getId = getThisId;
+          } else {
+            return;
+          }
+
+          if (t.isReferenced(node, parent)) return getId();
+        }
+      });
+
+      return false;
     }
-
-    // traverse all child nodes of this function and find `arguments` and `this`
-    traverse(node, function (node, parent) {
-      if (t.isFunction(node) && !node._aliasFunction) {
-        return false;
-      }
-
-      if (node._ignoreAliasFunctions) return false;
-
-      var getId;
-
-      if (t.isIdentifier(node) && node.name === "arguments") {
-        getId = getArgumentsId;
-      } else if (t.isThisExpression(node)) {
-        getId = getThisId;
-      } else {
-        return;
-      }
-
-      if (t.isReferenced(node, parent)) return getId();
-    });
-
-    return false;
   });
 
   var body;
diff --git a/lib/6to5/transformation/transformers/_declarations.js b/lib/6to5/transformation/transformers/_declarations.js
index 6ccda90a1c..a5eb107e41 100644
--- a/lib/6to5/transformation/transformers/_declarations.js
+++ b/lib/6to5/transformation/transformers/_declarations.js
@@ -1,12 +1,14 @@
 var t = require("../../types");
-var _ = require("lodash");
 
 exports.BlockStatement =
 exports.Program = function (node) {
   var kinds = {};
+  var kind;
 
-  _.each(node._declarations, function (declar) {
-    var kind = declar.kind || "var";
+  for (var i in node._declarations) {
+    var declar = node._declarations[i];
+
+    kind = declar.kind || "var";
     var declarNode = t.variableDeclarator(declar.id, declar.init);
 
     if (!declar.init) {
@@ -15,9 +17,9 @@ exports.Program = function (node) {
     } else {
       node.body.unshift(t.variableDeclaration(kind, [declarNode]));
     }
-  });
+  }
 
-  _.each(kinds, function (declars, kind) {
-    node.body.unshift(t.variableDeclaration(kind, declars));
-  });
+  for (kind in kinds) {
+    node.body.unshift(t.variableDeclaration(kind, kinds[kind]));
+  }
 };
diff --git a/lib/6to5/transformation/transformers/es5-property-method-assignment.js b/lib/6to5/transformation/transformers/es5-property-method-assignment.js
index a6712b6375..0bfe57584c 100644
--- a/lib/6to5/transformation/transformers/es5-property-method-assignment.js
+++ b/lib/6to5/transformation/transformers/es5-property-method-assignment.js
@@ -1,5 +1,4 @@
 var util = require("../../util");
-var _    = require("lodash");
 
 exports.Property = function (node) {
   if (node.method) node.method = false;
@@ -7,9 +6,11 @@ exports.Property = function (node) {
 
 exports.ObjectExpression = function (node, parent, file) {
   var mutatorMap = {};
+  var hasAny = false;
 
   node.properties = node.properties.filter(function (prop) {
     if (prop.kind === "get" || prop.kind === "set") {
+      hasAny = true;
       util.pushMutatorMap(mutatorMap, prop.key, prop.kind, prop.value);
       return false;
     } else {
@@ -17,7 +18,7 @@ exports.ObjectExpression = function (node, parent, file) {
     }
   });
 
-  if (_.isEmpty(mutatorMap)) return;
+  if (!hasAny) return;
 
   var objId = util.getUid(parent, file);
 
diff --git a/lib/6to5/transformation/transformers/es6-arrow-functions.js b/lib/6to5/transformation/transformers/es6-arrow-functions.js
index 80a45e573b..40f9ab9906 100644
--- a/lib/6to5/transformation/transformers/es6-arrow-functions.js
+++ b/lib/6to5/transformation/transformers/es6-arrow-functions.js
@@ -3,7 +3,7 @@ var t = require("../../types");
 exports.ArrowFunctionExpression = function (node) {
   t.ensureBlock(node);
 
-  node._aliasFunction = true;
+  node._aliasFunction = "arrow";
   node.expression = false;
   node.type = "FunctionExpression";
 
diff --git a/lib/6to5/transformation/transformers/es6-classes.js b/lib/6to5/transformation/transformers/es6-classes.js
index d44d6c6f25..86629c0f03 100644
--- a/lib/6to5/transformation/transformers/es6-classes.js
+++ b/lib/6to5/transformation/transformers/es6-classes.js
@@ -1,27 +1,30 @@
 var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
-var _        = require("lodash");
 
 exports.ClassDeclaration = function (node, parent, file, scope) {
-  var built = new Class(node, file, scope).run();
+  var closure = true;
+  if (t.isProgram(parent) || t.isBlockStatement(parent)) {
+    closure = false;
+  }
 
-  var declar = t.variableDeclaration("let", [
-    t.variableDeclarator(node.id, built)
-  ]);
-  t.inheritsComments(declar, node);
-  return declar;
+  var newNode = new Class(node, file, scope, closure).run();
+  if (closure) {
+    // declaration in an expression context...
+    // export default class Foo {}
+    scope.push({
+      kind: "var",
+      key: node.id.key,
+      id: node.id
+    });
+    return t.assignmentExpression("=", node.id, newNode);
+  } else {
+    return newNode;
+  }
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
-  return new Class(node, file, scope).run();
-};
-
-var getMemberExpressionObject = function (node) {
-  while (t.isMemberExpression(node)) {
-    node = node.object;
-  }
-  return node;
+  return new Class(node, file, scope, true).run();
 };
 
 /**
@@ -30,12 +33,17 @@ var getMemberExpressionObject = function (node) {
  * @param {Node} node
  * @param {File} file
  * @param {Scope} scope
+ * @param {Boolean} closure
  */
 
-function Class(node, file, scope) {
-  this.scope = scope;
-  this.node  = node;
-  this.file  = file;
+function Class(node, file, scope, closure) {
+  this.closure = closure;
+  this.scope   = scope;
+  this.node    = node;
+  this.file    = file;
+
+  this.hasInstanceMutators = false;
+  this.hasStaticMutators   = false;
 
   this.instanceMutatorMap = {};
   this.staticMutatorMap   = {};
@@ -51,50 +59,61 @@ function Class(node, file, scope) {
  */
 
 Class.prototype.run = function () {
-  var superClassArgument = this.superName;
-  var superClassCallee   = this.superName;
-  var superName          = this.superName;
-  var className          = this.className;
-  var file               = this.file;
+  var superName = this.superName;
+  var className = this.className;
+  var file      = this.file;
 
-  if (superName) {
-    if (t.isMemberExpression(superName)) {
-      superClassArgument = superClassCallee = getMemberExpressionObject(superName);
-    } else if (!t.isIdentifier(superName)) {
-      superClassArgument = superName;
-      superClassCallee   = superName = file.generateUidIdentifier("ref", this.scope);
-    }
+  //
+
+  var body = this.body = [];
+
+  var constructor = t.functionExpression(null, [], t.blockStatement([]));
+  if (this.node.id) constructor.id = className;
+  this.constructor = constructor;
+
+  body.push(t.variableDeclaration("let", [
+    t.variableDeclarator(className, constructor)
+  ]));
+
+  //
+
+  if (superName && t.isDynamic(superName)) {
+    // so we're only evaluating it once
+    var superRefName = "super";
+    if (className) superRefName = className.name + "Super";
+
+    var superRef = file.generateUidIdentifier(superRefName, this.scope);
+    body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(superRef, superName)
+    ]));
+    superName = superRef;
   }
 
   this.superName = superName;
 
-  var container = util.template("class", {
-    CLASS_NAME: className
-  });
-
-  var block       = container.callee.expression.body;
-  var body        = this.body = block.body;
-  var constructor = this.constructor = body[0].declarations[0].init;
-
-  if (this.node.id) constructor.id = className;
-
-  var returnStatement = body.pop();
+  //
 
   if (superName) {
-    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("extends"), [className, superName])));
-
-    container.arguments.push(superClassArgument);
-    container.callee.expression.params.push(superClassCallee);
+    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("inherits"), [className, superName])));
   }
 
   this.buildBody();
 
-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    return constructor;
+  t.inheritsComments(body[0], this.node);
+
+  if (this.closure) {
+    if (body.length === 1) {
+      // only a constructor so no need for a closure container
+      return constructor;
+    } else {
+      body.push(t.returnStatement(className));
+      return t.callExpression(
+        t.functionExpression(null, [], t.blockStatement(body)),
+        []
+      );
+    }
   } else {
-    body.push(returnStatement);
-    return container;
+    return body;
   }
 };
 
@@ -110,15 +129,21 @@ Class.prototype.buildBody = function () {
   var body        = this.body;
   var self        = this;
 
-  _.each(classBody, function (node) {
-    self.replaceInstanceSuperReferences(node);
+  for (var i in classBody) {
+    var node = classBody[i];
+    if (t.isMethodDefinition(node)) {
+      self.replaceInstanceSuperReferences(node);
 
-    if (node.key.name === "constructor") {
-      self.pushConstructor(node);
-    } else {
-      self.pushMethod(node);
+      if (node.key.name === "constructor") {
+        self.pushConstructor(node);
+      } else {
+        self.pushMethod(node);
+      }
+    } else if (t.isPrivateDeclaration(node)) {
+      self.closure = true;
+      body.unshift(node);
     }
-  });
+  }
 
   if (!this.hasConstructor && superName) {
     constructor.body.body.push(util.template("class-super-constructor-call", {
@@ -129,7 +154,7 @@ Class.prototype.buildBody = function () {
   var instanceProps;
   var staticProps;
 
-  if (!_.isEmpty(this.instanceMutatorMap)) {
+  if (this.hasInstanceMutators) {
     var protoId = util.template("prototype-identifier", {
       CLASS_NAME: className
     });
@@ -137,7 +162,7 @@ Class.prototype.buildBody = function () {
     instanceProps = util.buildDefineProperties(this.instanceMutatorMap, protoId);
   }
 
-  if (!_.isEmpty(this.staticMutatorMap)) {
+  if (this.hasStaticMutators) {
     staticProps = util.buildDefineProperties(this.staticMutatorMap, className);
   }
 
@@ -148,7 +173,7 @@ Class.prototype.buildBody = function () {
     if (instanceProps) args.push(instanceProps);
 
     body.push(t.expressionStatement(
-      t.callExpression(this.file.addDeclaration("class-props"), args)
+      t.callExpression(this.file.addDeclaration("prototype-properties"), args)
     ));
   }
 };
@@ -171,11 +196,18 @@ Class.prototype.pushMethod = function (node) {
     if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
     methodName = t.memberExpression(className, methodName, node.computed);
 
-    this.body.push(t.expressionStatement(t.assignmentExpression("=", methodName, node.value)));
+    var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
+    t.inheritsComments(expr, node);
+    this.body.push(expr);
   } else {
     // mutator
     var mutatorMap = this.instanceMutatorMap;
-    if (node.static) mutatorMap = this.staticMutatorMap;
+    if (node.static) {
+      this.hasStaticMutators = true;
+      mutatorMap = this.staticMutatorMap;
+    } else {
+      this.hasInstanceMutators = true;
+    }
     util.pushMutatorMap(mutatorMap, methodName, kind, node);
   }
 };
@@ -232,17 +264,19 @@ Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
   var method = methodNode.value;
   var self = this;
 
-  traverse(method, function (node, parent) {
-    if (t.isIdentifier(node, { name: "super" })) {
-      return self.superIdentifier(methodNode, node, parent);
-    } else if (t.isCallExpression(node)) {
-      var callee = node.callee;
-      if (!t.isMemberExpression(callee)) return;
-      if (callee.object.name !== "super") return;
+  traverse(method, {
+    enter: function (node, parent) {
+      if (t.isIdentifier(node, { name: "super" })) {
+        return self.superIdentifier(methodNode, node, parent);
+      } else if (t.isCallExpression(node)) {
+        var callee = node.callee;
+        if (!t.isMemberExpression(callee)) return;
+        if (callee.object.name !== "super") return;
 
-      // super.test(); -> ClassName.prototype.MethodName.call(this);
-      callee.property = t.memberExpression(callee.property, t.identifier("call"));
-      node.arguments.unshift(t.thisExpression());
+        // super.test(); -> ClassName.prototype.MethodName.call(this);
+        callee.property = t.memberExpression(callee.property, t.identifier("call"));
+        node.arguments.unshift(t.thisExpression());
+      }
     }
   });
 };
@@ -262,6 +296,7 @@ Class.prototype.pushConstructor = function (method) {
   var fn        = method.value;
 
   this.hasConstructor = true;
+
   t.inherits(construct, fn);
   t.inheritsComments(construct, method);
 
diff --git a/lib/6to5/transformation/transformers/es6-computed-property-names.js b/lib/6to5/transformation/transformers/es6-computed-property-names.js
index 8a8dee808d..3b434abb14 100644
--- a/lib/6to5/transformation/transformers/es6-computed-property-names.js
+++ b/lib/6to5/transformation/transformers/es6-computed-property-names.js
@@ -1,6 +1,5 @@
 var util = require("../../util");
 var t    = require("../../types");
-var _    = require("lodash");
 
 exports.ObjectExpression = function (node, parent, file) {
   var hasComputed = false;
@@ -26,12 +25,13 @@ exports.ObjectExpression = function (node, parent, file) {
     OBJECT: node
   });
 
-  var containerCallee = container.callee.expression;
+  var containerCallee = container.callee;
   var containerBody = containerCallee.body.body;
 
   containerCallee._aliasFunction = true;
 
-  _.each(computed, function (prop) {
+  for (var i in computed) {
+    var prop = computed[i];
     containerBody.unshift(
       t.expressionStatement(
         t.assignmentExpression(
@@ -41,7 +41,7 @@ exports.ObjectExpression = function (node, parent, file) {
         )
       )
     );
-  });
+  }
 
   return container;
 };
diff --git a/lib/6to5/transformation/transformers/es6-constants.js b/lib/6to5/transformation/transformers/es6-constants.js
index 15f2c8c45b..a3021188fb 100644
--- a/lib/6to5/transformation/transformers/es6-constants.js
+++ b/lib/6to5/transformation/transformers/es6-constants.js
@@ -7,48 +7,76 @@ exports.BlockStatement =
 exports.ForInStatement =
 exports.ForOfStatement =
 exports.ForStatement = function (node, parent, file) {
+  var hasConstants = false;
   var constants = {};
 
-  var check = function (parent, names) {
-    _.each(names, function (nameNode, name) {
-      if (!_.has(constants, name)) return;
-      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) return;
+  /**
+   * Check the results of `util.getIds` as `names` generated from a
+   * node against it's parent.
+   */
+
+  var check = function (parent, names, scope) {
+    for (var name in names) {
+      var nameNode = names[name];
+      if (!_.has(constants, name)) continue;
+      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) continue;
+
+      if (scope) {
+        var defined = scope.get(name);
+        if (defined && defined === nameNode) continue;
+      }
 
       throw file.errorWithNode(nameNode, name + " is read-only");
-    });
+    }
   };
 
   var getIds = function (node) {
     return t.getIds(node, true, ["MemberExpression"]);
   };
 
+  /**
+   * Collect all constants in this scope.
+   */
+
   _.each(node.body, function (child, parent) {
-    if (child && t.isVariableDeclaration(child, { kind: "const" })) {
-      _.each(child.declarations, function (declar) {
-        _.each(getIds(declar), function (nameNode, name) {
+    if (t.isExportDeclaration(child)) {
+      child = child.declaration;
+    }
+
+    if (t.isVariableDeclaration(child, { kind: "const" })) {
+      for (var i in child.declarations) {
+        var declar = child.declarations[i];
+
+        var ids = getIds(declar);
+        for (var name in ids) {
+          var nameNode = ids[name];
+
           var names = {};
           names[name] = nameNode;
           check(parent, names);
 
           constants[name] = parent;
-        });
+          hasConstants = true;
+        }
 
         declar._ignoreConstant = true;
-      });
+      }
 
       child._ignoreConstant = true;
       child.kind = "let";
     }
   });
 
-  if (_.isEmpty(constants)) return;
+  if (!hasConstants) return;
 
-  traverse(node, function (child, parent) {
-    if (child._ignoreConstant) return;
-    if (t.isVariableDeclaration(child)) return;
+  traverse(node, {
+    enter: function (child, parent, scope) {
+      if (child._ignoreConstant) return;
+      if (t.isVariableDeclaration(child)) return;
 
-    if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-      check(parent, getIds(child));
+      if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
+        check(parent, getIds(child), scope);
+      }
     }
   });
 };
diff --git a/lib/6to5/transformation/transformers/es6-default-parameters.js b/lib/6to5/transformation/transformers/es6-default-parameters.js
index 3901f6defa..9715c2bbdc 100644
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -12,9 +12,12 @@ exports.Function = function (node, parent, file, scope) {
   });
 
   var iife = false;
+  var i;
+  var def;
 
-  _.each(node.defaults, function (def, i) {
-    if (!def) return;
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;
 
     var param = node.params[i];
 
@@ -24,7 +27,7 @@ exports.Function = function (node, parent, file, scope) {
       var check = function (node, parent) {
         if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;
 
-        if (_.contains(ids, node.name)) {
+        if (ids.indexOf(node.name) >= 0) {
           throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
         }
 
@@ -34,26 +37,27 @@ exports.Function = function (node, parent, file, scope) {
       };
 
       check(def, node);
-      traverse(def, check);
+      traverse(def, { enter: check });
     });
 
     // we're accessing a variable that's already defined within this function
     var has = scope.get(param.name);
-    if (has && !_.contains(node.params, has)) {
+    if (has && node.params.indexOf(has) < 0) {
       iife = true;
     }
-  });
+  }
 
   var body = [];
 
-  _.each(node.defaults, function (def, i) {
-    if (!def) return;
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;
 
     body.push(util.template("if-undefined-set-to", {
       VARIABLE: node.params[i],
       DEFAULT:  def
     }, true));
-  });
+  }
 
   if (iife) {
     var container = t.functionExpression(null, [], node.body, node.generator);
diff --git a/lib/6to5/transformation/transformers/es6-destructuring.js b/lib/6to5/transformation/transformers/es6-destructuring.js
index 29d81afc97..bb563bcb34 100644
--- a/lib/6to5/transformation/transformers/es6-destructuring.js
+++ b/lib/6to5/transformation/transformers/es6-destructuring.js
@@ -1,7 +1,6 @@
 // TODO: Clean up
 
 var t = require("../../types");
-var _ = require("lodash");
 
 var buildVariableAssign = function (opts, id, init) {
   var op = opts.operator;
@@ -27,23 +26,26 @@ var push = function (opts, nodes, elem, parentId) {
 };
 
 var pushObjectPattern = function (opts, nodes, pattern, parentId) {
-  _.each(pattern.properties, function (prop, i) {
+  for (var i in pattern.properties) {
+    var prop = pattern.properties[i];
     if (t.isSpreadProperty(prop)) {
         // get all the keys that appear in this object before the current spread
         var keys = [];
-        _.each(pattern.properties, function (prop2, i2) {
-          if (i2 >= i) return false;
-          if (t.isSpreadProperty(prop2)) return;
+        for (var i2 in pattern.properties) {
+          var prop2 = pattern.properties[i2];
+
+          if (i2 >= i) break;
+          if (t.isSpreadProperty(prop2)) continue;
 
           var key = prop2.key;
           if (t.isIdentifier(key)) {
             key = t.literal(prop2.key.name);
           }
           keys.push(key);
-        });
+        }
         keys = t.arrayExpression(keys);
 
-        var value = t.callExpression(opts.file.addDeclaration("object-spread"), [parentId, keys]);
+        var value = t.callExpression(opts.file.addDeclaration("object-without-properties"), [parentId, keys]);
         nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
       var pattern2   = prop.value;
@@ -55,7 +57,7 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
         nodes.push(buildVariableAssign(opts, pattern2, patternId2));
       }
     }
-  });
+  }
 };
 
 var pushArrayPattern = function (opts, nodes, pattern, parentId) {
@@ -65,15 +67,18 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
   ]));
   parentId = _parentId;
 
-  _.each(pattern.elements, function (elem, i) {
-    if (!elem) return;
+  for (var i in pattern.elements) {
+    var elem = pattern.elements[i];
+    if (!elem) continue;
+
+    i = +i;
 
     var newPatternId;
 
     if (t.isSpreadElement(elem)) {
       newPatternId = opts.file.toArray(parentId);
 
-      if (+i > 0) {
+      if (i > 0) {
         newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
       }
 
@@ -83,7 +88,7 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
     }
 
     push(opts, nodes, elem, newPatternId);
-  });
+  }
 };
 
 var pushPattern = function (opts) {
@@ -215,17 +220,22 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
 
   var nodes = [];
+  var i;
+  var declar;
 
   var hasPattern = false;
-  _.each(node.declarations, function (declar) {
+  for (i in node.declarations) {
+    declar = node.declarations[i];
     if (t.isPattern(declar.id)) {
       hasPattern = true;
-      return false;
+      break;
     }
-  });
+  }
   if (!hasPattern) return;
 
-  _.each(node.declarations, function (declar) {
+  for (i in node.declarations) {
+    declar = node.declarations[i];
+
     var patternId = declar.init;
     var pattern   = declar.id;
     var opts = {
@@ -241,12 +251,12 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
     } else {
       nodes.push(buildVariableAssign(opts, declar.id, declar.init));
     }
-  });
+  }
 
   if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
-    var declar;
 
-    _.each(nodes, function (node) {
+    for (i in nodes) {
+      node = nodes[i];
       declar = declar || t.variableDeclaration(node.kind, []);
 
       if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
@@ -254,7 +264,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
       }
 
       declar.declarations = declar.declarations.concat(node.declarations);
-    });
+    }
 
     return declar;
   }
diff --git a/lib/6to5/transformation/transformers/es6-generators.js b/lib/6to5/transformation/transformers/es6-generators.js
new file mode 100644
index 0000000000..7b7c0a3f0e
--- /dev/null
+++ b/lib/6to5/transformation/transformers/es6-generators.js
@@ -0,0 +1 @@
+module.exports = require("regenerator").transform;
diff --git a/lib/6to5/transformation/transformers/es6-generators/emit/explode-expressions.js b/lib/6to5/transformation/transformers/es6-generators/emit/explode-expressions.js
deleted file mode 100644
index fe28897340..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/emit/explode-expressions.js
+++ /dev/null
@@ -1,204 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var assert = require("assert");
-var loc    = require("../util").loc;
-var t      = require("../../../../types");
-
-exports.ParenthesizedExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(this.explodeExpression(path.get("expression")));
-};
-
-exports.MemberExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.memberExpression(
-    this.explodeExpression(path.get("object")),
-    expr.computed ? explodeViaTempVar(null, path.get("property")) : expr.property,
-    expr.computed
-  ));
-};
-
-exports.CallExpression = function (expr, path, explodeViaTempVar, finish) {
-  var oldCalleePath = path.get("callee");
-  var newCallee = this.explodeExpression(oldCalleePath);
-
-  // If the callee was not previously a MemberExpression, then the
-  // CallExpression was "unqualified," meaning its `this` object should
-  // be the global object. If the exploded expression has become a
-  // MemberExpression, then we need to force it to be unqualified by
-  // using the (0, object.property)(...) trick; otherwise, it will
-  // receive the object of the MemberExpression as its `this` object.
-  if (!t.isMemberExpression(oldCalleePath.node) && t.isMemberExpression(newCallee)) {
-    newCallee = t.sequenceExpression([
-      t.literal(0),
-      newCallee
-    ]);
-  }
-
-  return finish(t.callExpression(
-    newCallee,
-    path.get("arguments").map(function (argPath) {
-      return explodeViaTempVar(null, argPath);
-    })
-  ));
-};
-
-exports.NewExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.newExpression(
-    explodeViaTempVar(null, path.get("callee")),
-    path.get("arguments").map(function (argPath) {
-      return explodeViaTempVar(null, argPath);
-    })
-  ));
-};
-
-exports.ObjectExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.objectExpression(
-    path.get("properties").map(function (propPath) {
-      return t.property(
-        propPath.value.kind,
-        propPath.value.key,
-        explodeViaTempVar(null, propPath.get("value"))
-      );
-    })
-  ));
-};
-
-exports.ArrayExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.arrayExpression(
-    path.get("elements").map(function (elemPath) {
-      return explodeViaTempVar(null, elemPath);
-    })
-  ));
-};
-
-exports.SequenceExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
-  var lastIndex = expr.expressions.length - 1;
-  var self = this;
-  var result;
-
-  path.get("expressions").each(function (exprPath) {
-    if (exprPath.name === lastIndex) {
-      result = self.explodeExpression(exprPath, ignoreResult);
-    } else {
-      self.explodeExpression(exprPath, true);
-    }
-  });
-
-  return result;
-};
-
-exports.LogicalExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
-  var after = loc();
-  var result;
-
-  if (!ignoreResult) {
-    result = this.makeTempVar();
-  }
-
-  var left = explodeViaTempVar(result, path.get("left"));
-
-  if (expr.operator === "&&") {
-    this.jumpIfNot(left, after);
-  } else {
-    assert.strictEqual(expr.operator, "||");
-    this.jumpIf(left, after);
-  }
-
-  explodeViaTempVar(result, path.get("right"), ignoreResult);
-
-  this.mark(after);
-
-  return result;
-};
-
-exports.ConditionalExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
-  var elseLoc = loc();
-  var after = loc();
-  var test = this.explodeExpression(path.get("test"));
-  var result;
-
-  this.jumpIfNot(test, elseLoc);
-
-  if (!ignoreResult) {
-    result = this.makeTempVar();
-  }
-
-  explodeViaTempVar(result, path.get("consequent"), ignoreResult);
-  this.jump(after);
-
-  this.mark(elseLoc);
-  explodeViaTempVar(result, path.get("alternate"), ignoreResult);
-
-  this.mark(after);
-
-  return result;
-};
-
-exports.UnaryExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.unaryExpression(
-    expr.operator,
-    // Can't (and don't need to) break up the syntax of the argument.
-    // Think about delete a[b].
-    this.explodeExpression(path.get("argument")),
-    !!expr.prefix
-  ));
-};
-
-exports.BinaryExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.binaryExpression(
-    expr.operator,
-    explodeViaTempVar(null, path.get("left")),
-    explodeViaTempVar(null, path.get("right"))
-  ));
-};
-
-exports.AssignmentExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.assignmentExpression(
-    expr.operator,
-    this.explodeExpression(path.get("left")),
-    this.explodeExpression(path.get("right"))
-  ));
-};
-
-exports.UpdateExpression = function (expr, path, explodeViaTempVar, finish) {
-  return finish(t.updateExpression(
-    expr.operator,
-    this.explodeExpression(path.get("argument")),
-    expr.prefix
-  ));
-};
-
-exports.YieldExpression = function (expr, path) {
-  var after = loc();
-  var arg = expr.argument && this.explodeExpression(path.get("argument"));
-  var result;
-
-  if (arg && expr.delegate) {
-    result = this.makeTempVar();
-
-    this.emit(t.returnStatement(t.callExpression(
-      this.contextProperty("delegateYield"), [
-        arg,
-        t.literal(result.property.name),
-        after
-      ]
-    )));
-
-    this.mark(after);
-
-    return result;
-  }
-
-  this.emitAssign(this.contextProperty("next"), after);
-  this.emit(t.returnStatement(arg || null));
-  this.mark(after);
-
-  return this.contextProperty("sent");
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/emit/explode-statements.js b/lib/6to5/transformation/transformers/es6-generators/emit/explode-statements.js
deleted file mode 100644
index 9f73681883..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/emit/explode-statements.js
+++ /dev/null
@@ -1,334 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var assert = require("assert");
-var types  = require("ast-types");
-var leap   = require("../leap");
-var util   = require("../util");
-var t      = require("../../../../types");
-
-var runtimeKeysMethod = util.runtimeProperty("keys");
-var loc               = util.loc;
-
-exports.ExpressionStatement = function (path) {
-  this.explodeExpression(path.get("expression"), true);
-};
-
-exports.LabeledStatement = function (path, stmt) {
-  this.explodeStatement(path.get("body"), stmt.label);
-};
-
-exports.WhileStatement = function (path, stmt, labelId) {
-  var before = loc();
-  var after = loc();
-
-  this.mark(before);
-  this.jumpIfNot(this.explodeExpression(path.get("test")), after);
-  this.leapManager.withEntry(
-    new leap.LoopEntry(after, before, labelId),
-    function () { this.explodeStatement(path.get("body")); }
-  );
-  this.jump(before);
-  this.mark(after);
-};
-
-exports.DoWhileStatement = function (path, stmt, labelId) {
-  var first = loc();
-  var test = loc();
-  var after = loc();
-
-  this.mark(first);
-  this.leapManager.withEntry(
-    new leap.LoopEntry(after, test, labelId),
-    function () { this.explode(path.get("body")); }
-  );
-  this.mark(test);
-  this.jumpIf(this.explodeExpression(path.get("test")), first);
-  this.mark(after);
-};
-
-exports.ForStatement = function (path, stmt, labelId) {
-  var head = loc();
-  var update = loc();
-  var after = loc();
-
-  if (stmt.init) {
-    // We pass true here to indicate that if stmt.init is an expression
-    // then we do not care about its result.
-    this.explode(path.get("init"), true);
-  }
-
-  this.mark(head);
-
-  if (stmt.test) {
-    this.jumpIfNot(this.explodeExpression(path.get("test")), after);
-  } else {
-    // No test means continue unconditionally.
-  }
-
-  this.leapManager.withEntry(
-    new leap.LoopEntry(after, update, labelId),
-    function () { this.explodeStatement(path.get("body")); }
-  );
-
-  this.mark(update);
-
-  if (stmt.update) {
-    // We pass true here to indicate that if stmt.update is an
-    // expression then we do not care about its result.
-    this.explode(path.get("update"), true);
-  }
-
-  this.jump(head);
-
-  this.mark(after);
-};
-
-exports.ForInStatement = function (path, stmt, labelId) {
-  t.assertIdentifier(stmt.left);
-
-  var head = loc();
-  var after = loc();
-
-  var keyIterNextFn = this.makeTempVar();
-  this.emitAssign(
-    keyIterNextFn,
-    t.callExpression(
-      runtimeKeysMethod,
-      [this.explodeExpression(path.get("right"))]
-    )
-  );
-
-  this.mark(head);
-
-  var keyInfoTmpVar = this.makeTempVar();
-  this.jumpIf(
-    t.memberExpression(
-      t.assignmentExpression(
-        "=",
-        keyInfoTmpVar,
-        t.callExpression(keyIterNextFn, [])
-      ),
-      t.identifier("done"),
-      false
-    ),
-    after
-  );
-
-  this.emitAssign(
-    stmt.left,
-    t.memberExpression(
-      keyInfoTmpVar,
-      t.identifier("value"),
-      false
-    )
-  );
-
-  this.leapManager.withEntry(
-    new leap.LoopEntry(after, head, labelId),
-    function () { this.explodeStatement(path.get("body")); }
-  );
-
-  this.jump(head);
-
-  this.mark(after);
-};
-
-exports.BreakStatement = function (path, stmt) {
-  this.emitAbruptCompletion({
-    type: "break",
-    target: this.leapManager.getBreakLoc(stmt.label)
-  });
-};
-
-exports.ContinueStatement = function (path, stmt) {
-  this.emitAbruptCompletion({
-    type: "continue",
-    target: this.leapManager.getContinueLoc(stmt.label)
-  });
-};
-
-exports.SwitchStatement = function (path, stmt) {
-  // Always save the discriminant into a temporary variable in case the
-  // test expressions overwrite values like context.sent.
-  var disc = this.emitAssign(
-    this.makeTempVar(),
-    this.explodeExpression(path.get("discriminant"))
-  );
-
-  var after = loc();
-  var defaultLoc = loc();
-  var condition = defaultLoc;
-  var caseLocs = [];
-  var self = this;
-
-  // If there are no cases, .cases might be undefined.
-  var cases = stmt.cases || [];
-
-  for (var i = cases.length - 1; i >= 0; --i) {
-    var c = cases[i];
-    t.assertSwitchCase(c);
-
-    if (c.test) {
-      condition = t.conditionalExpression(
-        t.binaryExpression("===", disc, c.test),
-        caseLocs[i] = loc(),
-        condition
-      );
-    } else {
-      caseLocs[i] = defaultLoc;
-    }
-  }
-
-  this.jump(this.explodeExpression(
-    new types.NodePath(condition, path, "discriminant")
-  ));
-
-  this.leapManager.withEntry(
-    new leap.SwitchEntry(after),
-    function () {
-      path.get("cases").each(function (casePath) {
-        var i = casePath.name;
-
-        self.mark(caseLocs[i]);
-
-        casePath.get("consequent").each(
-          self.explodeStatement,
-          self
-        );
-      });
-    }
-  );
-
-  this.mark(after);
-  if (defaultLoc.value === -1) {
-    this.mark(defaultLoc);
-    assert.strictEqual(after.value, defaultLoc.value);
-  }
-};
-
-exports.IfStatement = function (path, stmt) {
-  var elseLoc = stmt.alternate && loc();
-  var after = loc();
-
-  this.jumpIfNot(
-    this.explodeExpression(path.get("test")),
-    elseLoc || after
-  );
-
-  this.explodeStatement(path.get("consequent"));
-
-  if (elseLoc) {
-    this.jump(after);
-    this.mark(elseLoc);
-    this.explodeStatement(path.get("alternate"));
-  }
-
-  this.mark(after);
-};
-
-exports.ReturnStatement = function (path) {
-  this.emitAbruptCompletion({
-    type: "return",
-    value: this.explodeExpression(path.get("argument"))
-  });
-};
-
-exports.TryStatement = function (path, stmt) {
-  var after = loc();
-  var self = this;
-
-  var handler = stmt.handler;
-  if (!handler && stmt.handlers) {
-    handler = stmt.handlers[0] || null;
-  }
-
-  var catchLoc = handler && loc();
-  var catchEntry = catchLoc && new leap.CatchEntry(
-    catchLoc,
-    handler.param
-  );
-
-  var finallyLoc = stmt.finalizer && loc();
-  var finallyEntry = finallyLoc && new leap.FinallyEntry(finallyLoc);
-
-  var tryEntry = new leap.TryEntry(
-    this.getUnmarkedCurrentLoc(),
-    catchEntry,
-    finallyEntry
-  );
-
-  this.tryEntries.push(tryEntry);
-  this.updateContextPrevLoc(tryEntry.firstLoc);
-
-  this.leapManager.withEntry(tryEntry, function () {
-    this.explodeStatement(path.get("block"));
-
-    if (catchLoc) {
-      if (finallyLoc) {
-        // If we have both a catch block and a finally block, then
-        // because we emit the catch block first, we need to jump over
-        // it to the finally block.
-        this.jump(finallyLoc);
-
-      } else {
-        // If there is no finally block, then we need to jump over the
-        // catch block to the fall-through location.
-        this.jump(after);
-      }
-
-      this.updateContextPrevLoc(self.mark(catchLoc));
-
-      var bodyPath = path.get("handler", "body");
-      var safeParam = this.makeTempVar();
-      this.clearPendingException(tryEntry.firstLoc, safeParam);
-
-      var catchScope = bodyPath.scope;
-      var catchParamName = handler.param.name;
-      t.assertCatchClause(catchScope.node);
-      assert.strictEqual(catchScope.lookup(catchParamName), catchScope);
-
-      types.visit(bodyPath, {
-        visitIdentifier: function (path) {
-          if (path.value.name === catchParamName &&
-              path.scope.lookup(catchParamName) === catchScope) {
-            return safeParam;
-          }
-          this.traverse(path);
-        }
-      });
-
-      this.leapManager.withEntry(catchEntry, function () {
-        this.explodeStatement(bodyPath);
-      });
-    }
-
-    if (finallyLoc) {
-      this.updateContextPrevLoc(this.mark(finallyLoc));
-
-      this.leapManager.withEntry(finallyEntry, function () {
-        this.explodeStatement(path.get("finalizer"));
-      });
-
-      this.emit(t.callExpression(
-        this.contextProperty("finish"),
-        [finallyEntry.firstLoc]
-      ));
-    }
-  });
-
-  this.mark(after);
-};
-
-exports.ThrowStatement = function (path) {
-  this.emit(t.throwStatement(
-    this.explodeExpression(path.get("argument"))
-  ));
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/emit/index.js b/lib/6to5/transformation/transformers/es6-generators/emit/index.js
deleted file mode 100644
index 8df1576721..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/emit/index.js
+++ /dev/null
@@ -1,611 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-exports.Emitter = Emitter;
-
-var explodeExpressions = require("./explode-expressions");
-var explodeStatements  = require("./explode-statements");
-var assert             = require("assert");
-var types              = require("ast-types");
-var leap               = require("../leap");
-var meta               = require("../meta");
-var util               = require("../util");
-var t                  = require("../../../../types");
-var _                  = require("lodash");
-
-var loc = util.loc;
-var n   = types.namedTypes;
-
-function Emitter(contextId) {
-  assert.ok(this instanceof Emitter);
-  t.assertIdentifier(contextId);
-
-  // In order to make sure the context object does not collide with
-  // anything in the local scope, we might have to rename it, so we
-  // refer to it symbolically instead of just assuming that it will be
-  // called "context".
-  this.contextId = contextId;
-
-  // An append-only list of Statements that grows each time this.emit is
-  // called.
-  this.listing = [];
-
-  // A sparse array whose keys correspond to locations in this.listing
-  // that have been marked as branch/jump targets.
-  this.marked = [true];
-
-  // The last location will be marked when this.getDispatchLoop is
-  // called.
-  this.finalLoc = loc();
-
-  // A list of all leap.TryEntry statements emitted.
-  this.tryEntries = [];
-
-  // Each time we evaluate the body of a loop, we tell this.leapManager
-  // to enter a nested loop context that determines the meaning of break
-  // and continue statements therein.
-  this.leapManager = new leap.LeapManager(this);
-}
-
-// Sets the exact value of the given location to the offset of the next
-// Statement emitted.
-Emitter.prototype.mark = function (loc) {
-  t.assertLiteral(loc);
-  var index = this.listing.length;
-  if (loc.value === -1) {
-    loc.value = index;
-  } else {
-    // Locations can be marked redundantly, but their values cannot change
-    // once set the first time.
-    assert.strictEqual(loc.value, index);
-  }
-  this.marked[index] = true;
-  return loc;
-};
-
-Emitter.prototype.emit = function (node) {
-  if (t.isExpression(node)) node = t.expressionStatement(node);
-  t.assertStatement(node);
-  this.listing.push(node);
-};
-
-// Shorthand for emitting assignment statements. This will come in handy
-// for assignments to temporary variables.
-Emitter.prototype.emitAssign = function (lhs, rhs) {
-  this.emit(this.assign(lhs, rhs));
-  return lhs;
-};
-
-// Shorthand for an assignment statement.
-Emitter.prototype.assign = function (lhs, rhs) {
-  return t.expressionStatement(
-    t.assignmentExpression("=", lhs, rhs));
-};
-
-// Convenience function for generating expressions like context.next,
-// context.sent, and context.rval.
-Emitter.prototype.contextProperty = function (name, computed) {
-  return t.memberExpression(
-    this.contextId,
-    computed ? t.literal(name) : t.identifier(name),
-    !!computed
-  );
-};
-
-var volatileContextPropertyNames = {
-  prev: true,
-  next: true,
-  sent: true,
-  rval: true
-};
-
-// A "volatile" context property is a MemberExpression like context.sent
-// that should probably be stored in a temporary variable when there's a
-// possibility the property will get overwritten.
-Emitter.prototype.isVolatileContextProperty = function (expr) {
-  if (t.isMemberExpression(expr)) {
-    if (expr.computed) {
-      // If it's a computed property such as context[couldBeAnything],
-      // assume the worst in terms of volatility.
-      return true;
-    }
-
-    if (t.isIdentifier(expr.object) &&
-        t.isIdentifier(expr.property) &&
-        expr.object.name === this.contextId.name &&
-        _.has(volatileContextPropertyNames, expr.property.name)) {
-      return true;
-    }
-  }
-
-  return false;
-};
-
-// Shorthand for setting context.rval and jumping to `context.stop()`.
-Emitter.prototype.stop = function (rval) {
-  if (rval) {
-    this.setReturnValue(rval);
-  }
-
-  this.jump(this.finalLoc);
-};
-
-Emitter.prototype.setReturnValue = function (valuePath) {
-  t.assertExpression(valuePath.value);
-
-  this.emitAssign(
-    this.contextProperty("rval"),
-    this.explodeExpression(valuePath)
-  );
-};
-
-Emitter.prototype.clearPendingException = function (tryLoc, assignee) {
-  t.assertLiteral(tryLoc);
-
-  var catchCall = t.callExpression(
-    this.contextProperty("catch", true),
-    [tryLoc]
-  );
-
-  if (assignee) {
-    this.emitAssign(assignee, catchCall);
-  } else {
-    this.emit(catchCall);
-  }
-};
-
-// Emits code for an unconditional jump to the given location, even if the
-// exact value of the location is not yet known.
-Emitter.prototype.jump = function (toLoc) {
-  this.emitAssign(this.contextProperty("next"), toLoc);
-  this.emit(t.breakStatement());
-};
-
-// Conditional jump.
-Emitter.prototype.jumpIf = function (test, toLoc) {
-  t.assertExpression(test);
-  t.assertLiteral(toLoc);
-
-  this.emit(t.ifStatement(
-    test,
-    t.blockStatement([
-      this.assign(this.contextProperty("next"), toLoc),
-      t.breakStatement()
-    ])
-  ));
-};
-
-// Conditional jump, with the condition negated.
-Emitter.prototype.jumpIfNot = function (test, toLoc) {
-  t.assertExpression(test);
-  t.assertLiteral(toLoc);
-
-  var negatedTest;
-  if (t.isUnaryExpression(test) && test.operator === "!") {
-    // Avoid double negation.
-    negatedTest = test.argument;
-  } else {
-    negatedTest = t.unaryExpression("!", test);
-  }
-
-  this.emit(t.ifStatement(
-    negatedTest,
-    t.blockStatement([
-      this.assign(this.contextProperty("next"), toLoc),
-      t.breakStatement()
-    ])
-  ));
-};
-
-// Returns a unique MemberExpression that can be used to store and
-// retrieve temporary values. Since the object of the member expression is
-// the context object, which is presumed to coexist peacefully with all
-// other local variables, and since we just increment `nextTempId`
-// monotonically, uniqueness is assured.
-var nextTempId = 0;
-Emitter.prototype.makeTempVar = function () {
-  return this.contextProperty("t" + nextTempId++);
-};
-
-Emitter.prototype.getContextFunction = function (id) {
-  var node = t.functionExpression(
-    id || null,
-    [this.contextId],
-    t.blockStatement([this.getDispatchLoop()]),
-    false, // Not a generator anymore!
-    false // Nor an expression.
-  );
-  node._aliasFunction = true;
-  return node;
-};
-
-// Turns this.listing into a loop of the form
-//
-//   while (1) switch (context.next) {
-//   case 0:
-//   ...
-//   case n:
-//     return context.stop();
-//   }
-//
-// Each marked location in this.listing will correspond to one generated
-// case statement.
-Emitter.prototype.getDispatchLoop = function () {
-  var self = this;
-  var cases = [];
-  var current;
-
-  // If we encounter a break, continue, or return statement in a switch
-  // case, we can skip the rest of the statements until the next case.
-  var alreadyEnded = false;
-
-  self.listing.forEach(function (stmt, i) {
-    if (self.marked.hasOwnProperty(i)) {
-      cases.push(t.switchCase(t.literal(i), current = []));
-      alreadyEnded = false;
-    }
-
-    if (!alreadyEnded) {
-      current.push(stmt);
-      if (isSwitchCaseEnder(stmt))
-        alreadyEnded = true;
-    }
-  });
-
-  // Now that we know how many statements there will be in this.listing,
-  // we can finally resolve this.finalLoc.value.
-  this.finalLoc.value = this.listing.length;
-
-  cases.push(
-    t.switchCase(this.finalLoc, [
-      // Intentionally fall through to the "end" case...
-    ]),
-
-    // So that the runtime can jump to the final location without having
-    // to know its offset, we provide the "end" case as a synonym.
-    t.switchCase(t.literal("end"), [
-      // This will check/clear both context.thrown and context.rval.
-      t.returnStatement(
-        t.callExpression(this.contextProperty("stop"), [])
-      )
-    ])
-  );
-
-  return t.whileStatement(
-    t.literal(true),
-    t.switchStatement(
-      t.assignmentExpression(
-        "=",
-        this.contextProperty("prev"),
-        this.contextProperty("next")
-      ),
-      cases
-    )
-  );
-};
-
-// See comment above re: alreadyEnded.
-function isSwitchCaseEnder(stmt) {
-  return t.isBreakStatement(stmt) ||
-         t.isContinueStatement(stmt) ||
-         t.isReturnStatement(stmt) ||
-         t.isThrowStatement(stmt);
-}
-
-Emitter.prototype.getTryEntryList = function () {
-  if (this.tryEntries.length === 0) {
-    // To avoid adding a needless [] to the majority of runtime.wrap
-    // argument lists, force the caller to handle this case specially.
-    return null;
-  }
-
-  var lastLocValue = 0;
-
-  return t.arrayExpression(
-    this.tryEntries.map(function (tryEntry) {
-      var thisLocValue = tryEntry.firstLoc.value;
-      assert.ok(thisLocValue >= lastLocValue, "try entries out of order");
-      lastLocValue = thisLocValue;
-
-      var ce = tryEntry.catchEntry;
-      var fe = tryEntry.finallyEntry;
-
-      var triple = [
-        tryEntry.firstLoc,
-        // The null here makes a hole in the array.
-        ce ? ce.firstLoc : null
-      ];
-
-      if (fe) {
-        triple[2] = fe.firstLoc;
-      }
-
-      return t.arrayExpression(triple);
-    })
-  );
-};
-
-// All side effects must be realized in order.
-
-// If any subexpression harbors a leap, all subexpressions must be
-// neutered of side effects.
-
-// No destructive modification of AST nodes.
-
-Emitter.prototype.explode = function (path, ignoreResult) {
-  assert.ok(path instanceof types.NodePath);
-
-  var node = path.value;
-  var self = this;
-
-  n.Node.check(node);
-
-  if (t.isStatement(node))
-    return self.explodeStatement(path);
-
-  if (t.isExpression(node))
-    return self.explodeExpression(path, ignoreResult);
-
-  if (t.isDeclaration(node))
-    throw getDeclError(node);
-
-  switch (node.type) {
-  case "Program":
-    return path.get("body").map(self.explodeStatement, self);
-
-  case "VariableDeclarator":
-    throw getDeclError(node);
-
-  // These node types should be handled by their parent nodes
-  // (ObjectExpression, SwitchStatement, and TryStatement, respectively).
-  case "Property":
-  case "SwitchCase":
-  case "CatchClause":
-    throw new Error(node.type + " nodes should be handled by their parents");
-
-  default:
-    throw new Error("unknown Node of type " + JSON.stringify(node.type));
-  }
-};
-
-function getDeclError(node) {
-  return new Error(
-    "all declarations should have been transformed into " +
-    "assignments before the Exploder began its work: " +
-    JSON.stringify(node));
-}
-
-Emitter.prototype.explodeStatement = function (path, labelId) {
-  assert.ok(path instanceof types.NodePath);
-
-  var stmt = path.value;
-  var self = this;
-
-  t.assertStatement(stmt);
-
-  if (labelId) {
-    t.assertIdentifier(labelId);
-  } else {
-    labelId = null;
-  }
-
-  // Explode BlockStatement nodes even if they do not contain a yield,
-  // because we don't want or need the curly braces.
-  if (t.isBlockStatement(stmt)) {
-    return path.get("body").each(
-      self.explodeStatement,
-      self
-    );
-  }
-
-  if (!meta.containsLeap(stmt)) {
-    // Technically we should be able to avoid emitting the statement
-    // altogether if !meta.hasSideEffects(stmt), but that leads to
-    // confusing generated code (for instance, `while (true) {}` just
-    // disappears) and is probably a more appropriate job for a dedicated
-    // dead code elimination pass.
-    self.emit(stmt);
-    return;
-  }
-
-  var fn = explodeStatements[stmt.type];
-  if (fn) {
-    fn.call(this, path, stmt, labelId);
-  } else {
-    throw new Error("unknown Statement of type " + JSON.stringify(stmt.type));
-  }
-};
-
-Emitter.prototype.emitAbruptCompletion = function (record) {
-  if (!isValidCompletion(record)) {
-    assert.ok(
-      false,
-      "invalid completion record: " + JSON.stringify(record)
-    );
-  }
-
-  assert.notStrictEqual(
-    record.type, "normal",
-    "normal completions are not abrupt"
-  );
-
-  var abruptArgs = [t.literal(record.type)];
-
-  if (record.type === "break" || record.type === "continue") {
-    t.assertLiteral(record.target);
-    abruptArgs[1] = record.target;
-  } else if (record.type === "return" || record.type === "throw") {
-    if (record.value) {
-      t.assertExpression(record.value);
-      abruptArgs[1] = record.value;
-    }
-  }
-
-  this.emit(
-    t.returnStatement(
-      t.callExpression(
-        this.contextProperty("abrupt"),
-        abruptArgs
-      )
-    )
-  );
-};
-
-function isValidCompletion(record) {
-  var type = record.type;
-
-  if (type === "normal") {
-    return !_.has(record, "target");
-  }
-
-  if (type === "break" || type === "continue") {
-    return !_.has(record, "value") && t.isLiteral(record.target);
-  }
-
-  if (type === "return" || type === "throw") {
-    return _.has(record, "value") && !_.has(record, "target");
-  }
-
-  return false;
-}
-
-// Not all offsets into emitter.listing are potential jump targets. For
-// example, execution typically falls into the beginning of a try block
-// without jumping directly there. This method returns the current offset
-// without marking it, so that a switch case will not necessarily be
-// generated for this offset (I say "not necessarily" because the same
-// location might end up being marked in the process of emitting other
-// statements). There's no logical harm in marking such locations as jump
-// targets, but minimizing the number of switch cases keeps the generated
-// code shorter.
-Emitter.prototype.getUnmarkedCurrentLoc = function () {
-  return t.literal(this.listing.length);
-};
-
-// The context.prev property takes the value of context.next whenever we
-// evaluate the switch statement discriminant, which is generally good
-// enough for tracking the last location we jumped to, but sometimes
-// context.prev needs to be more precise, such as when we fall
-// successfully out of a try block and into a finally block without
-// jumping. This method exists to update context.prev to the freshest
-// available location. If we were implementing a full interpreter, we
-// would know the location of the current instruction with complete
-// precision at all times, but we don't have that luxury here, as it would
-// be costly and verbose to set context.prev before every statement.
-Emitter.prototype.updateContextPrevLoc = function (loc) {
-  if (loc) {
-    t.assertLiteral(loc);
-
-    if (loc.value === -1) {
-      // If an uninitialized location literal was passed in, set its value
-      // to the current this.listing.length.
-      loc.value = this.listing.length;
-    } else {
-      // Otherwise assert that the location matches the current offset.
-      assert.strictEqual(loc.value, this.listing.length);
-    }
-
-  } else {
-    loc = this.getUnmarkedCurrentLoc();
-  }
-
-  // Make sure context.prev is up to date in case we fell into this try
-  // statement without jumping to it. TODO Consider avoiding this
-  // assignment when we know control must have jumped here.
-  this.emitAssign(this.contextProperty("prev"), loc);
-};
-
-Emitter.prototype.explodeExpression = function (path, ignoreResult) {
-  assert.ok(path instanceof types.NodePath);
-
-  var expr = path.value;
-  if (expr) {
-    t.assertExpression(expr);
-  } else {
-    return expr;
-  }
-
-  var self = this;
-
-  function finish(expr) {
-    t.assertExpression(expr);
-    if (ignoreResult) {
-      self.emit(expr);
-    } else {
-      return expr;
-    }
-  }
-
-  // If the expression does not contain a leap, then we either emit the
-  // expression as a standalone statement or return it whole.
-  if (!meta.containsLeap(expr)) {
-    return finish(expr);
-  }
-
-  // If any child contains a leap (such as a yield or labeled continue or
-  // break statement), then any sibling subexpressions will almost
-  // certainly have to be exploded in order to maintain the order of their
-  // side effects relative to the leaping child(ren).
-  var hasLeapingChildren = meta.containsLeap.onlyChildren(expr);
-
-  // In order to save the rest of explodeExpression from a combinatorial
-  // trainwreck of special cases, explodeViaTempVar is responsible for
-  // deciding when a subexpression needs to be "exploded," which is my
-  // very technical term for emitting the subexpression as an assignment
-  // to a temporary variable and the substituting the temporary variable
-  // for the original subexpression. Think of exploded view diagrams, not
-  // Michael Bay movies. The point of exploding subexpressions is to
-  // control the precise order in which the generated code realizes the
-  // side effects of those subexpressions.
-  function explodeViaTempVar(tempVar, childPath, ignoreChildResult) {
-    assert.ok(childPath instanceof types.NodePath);
-
-    assert.ok(
-      !ignoreChildResult || !tempVar,
-      "Ignoring the result of a child expression but forcing it to " +
-        "be assigned to a temporary variable?"
-    );
-
-    var result = self.explodeExpression(childPath, ignoreChildResult);
-
-    if (ignoreChildResult) {
-      // Side effects already emitted above.
-
-    } else if (tempVar || (hasLeapingChildren &&
-                           (self.isVolatileContextProperty(result) ||
-                            meta.hasSideEffects(result)))) {
-      // If tempVar was provided, then the result will always be assigned
-      // to it, even if the result does not otherwise need to be assigned
-      // to a temporary variable.  When no tempVar is provided, we have
-      // the flexibility to decide whether a temporary variable is really
-      // necessary.  In general, temporary assignment is required only
-      // when some other child contains a leap and the child in question
-      // is a context property like $ctx.sent that might get overwritten
-      // or an expression with side effects that need to occur in proper
-      // sequence relative to the leap.
-      result = self.emitAssign(
-        tempVar || self.makeTempVar(),
-        result
-      );
-    }
-    return result;
-  }
-
-  // If ignoreResult is true, then we must take full responsibility for
-  // emitting the expression with all its side effects, and we should not
-  // return a result.
-
-  var fn = explodeExpressions[expr.type];
-  if (fn) {
-    return fn.call(this, expr, path, explodeViaTempVar, finish, ignoreResult);
-  } else {
-    throw new Error("unknown Expression of type " + JSON.stringify(expr.type));
-  }
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/hoist.js b/lib/6to5/transformation/transformers/es6-generators/hoist.js
deleted file mode 100644
index b9772466ba..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/hoist.js
+++ /dev/null
@@ -1,151 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.githut.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var assert = require("assert");
-var types  = require("ast-types");
-var t      = require("../../../types");
-var _      = require("lodash");
-
-// The hoist function takes a FunctionExpression or FunctionDeclaration
-// and replaces any Declaration nodes in its body with assignments, then
-// returns a VariableDeclaration containing just the names of the removed
-// declarations.
-exports.hoist = function (funPath) {
-  assert.ok(funPath instanceof types.NodePath);
-  t.assertFunction(funPath.value);
-
-  var vars = {};
-
-  function varDeclToExpr(vdec, includeIdentifiers) {
-    t.assertVariableDeclaration(vdec);
-    var exprs = [];
-
-    vdec.declarations.forEach(function (dec) {
-      vars[dec.id.name] = dec.id;
-
-      if (dec.init) {
-        exprs.push(t.assignmentExpression(
-          "=", dec.id, dec.init
-        ));
-      } else if (includeIdentifiers) {
-        exprs.push(dec.id);
-      }
-    });
-
-    if (exprs.length === 0)
-      return null;
-
-    if (exprs.length === 1)
-      return exprs[0];
-
-    return t.sequenceExpression(exprs);
-  }
-
-  types.visit(funPath.get("body"), {
-    visitVariableDeclaration: function (path) {
-      var expr = varDeclToExpr(path.value, false);
-      if (expr === null) {
-        path.replace();
-      } else {
-        // We don't need to traverse this expression any further because
-        // there can't be any new declarations inside an expression.
-        return t.expressionStatement(expr);
-      }
-
-      // Since the original node has been either removed or replaced,
-      // avoid traversing it any further.
-      return false;
-    },
-
-    visitForStatement: function (path) {
-      var init = path.value.init;
-      if (t.isVariableDeclaration(init)) {
-        path.get("init").replace(varDeclToExpr(init, false));
-      }
-      this.traverse(path);
-    },
-
-    visitForInStatement: function (path) {
-      var left = path.value.left;
-      if (t.isVariableDeclaration(left)) {
-        path.get("left").replace(varDeclToExpr(left, true));
-      }
-      this.traverse(path);
-    },
-
-    visitFunctionDeclaration: function (path) {
-      var node = path.value;
-      vars[node.id.name] = node.id;
-
-      var assignment = t.expressionStatement(
-        t.assignmentExpression(
-          "=",
-          node.id,
-          t.functionExpression(
-            node.id,
-            node.params,
-            node.body,
-            node.generator,
-            node.expression
-          )
-        )
-      );
-
-      if (t.isBlockStatement(path.parent.node)) {
-        // Insert the assignment form before the first statement in the
-        // enclosing block.
-        path.parent.get("body").unshift(assignment);
-
-        // Remove the function declaration now that we've inserted the
-        // equivalent assignment form at the beginning of the block.
-        path.replace();
-
-      } else {
-        // If the parent node is not a block statement, then we can just
-        // replace the declaration with the equivalent assignment form
-        // without worrying about hoisting it.
-        path.replace(assignment);
-      }
-
-      // Don't hoist variables out of inner functions.
-      return false;
-    },
-
-    visitFunctionExpression: function () {
-      // Don't descend into nested function expressions.
-      return false;
-    }
-  });
-
-  var paramNames = {};
-  funPath.get("params").each(function (paramPath) {
-    var param = paramPath.value;
-    if (t.isIdentifier(param)) {
-      paramNames[param.name] = param;
-    } else {
-      // Variables declared by destructuring parameter patterns will be
-      // harmlessly re-declared.
-    }
-  });
-
-  var declarations = [];
-
-  Object.keys(vars).forEach(function (name) {
-    if (!_.has(paramNames, name)) {
-      declarations.push(t.variableDeclarator(vars[name], null));
-    }
-  });
-
-  if (declarations.length === 0) {
-    return null; // Be sure to handle this case!
-  }
-
-  return t.variableDeclaration("var", declarations);
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/index.js b/lib/6to5/transformation/transformers/es6-generators/index.js
deleted file mode 100644
index 563781f8b7..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/index.js
+++ /dev/null
@@ -1 +0,0 @@
-module.exports = require("./visit").transform;
diff --git a/lib/6to5/transformation/transformers/es6-generators/leap.js b/lib/6to5/transformation/transformers/es6-generators/leap.js
deleted file mode 100644
index 5cd289b501..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/leap.js
+++ /dev/null
@@ -1,163 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-exports.FunctionEntry = FunctionEntry;
-exports.FinallyEntry  = FinallyEntry;
-exports.SwitchEntry   = SwitchEntry;
-exports.LeapManager   = LeapManager;
-exports.CatchEntry    = CatchEntry;
-exports.LoopEntry     = LoopEntry;
-exports.TryEntry      = TryEntry;
-
-var assert = require("assert");
-var util   = require("util");
-var t      = require("../../../types");
-
-var inherits = util.inherits;
-
-function Entry() {
-  assert.ok(this instanceof Entry);
-}
-
-function FunctionEntry(returnLoc) {
-  Entry.call(this);
-
-  t.assertLiteral(returnLoc);
-
-  this.returnLoc = returnLoc;
-}
-
-inherits(FunctionEntry, Entry);
-
-function LoopEntry(breakLoc, continueLoc, label) {
-  Entry.call(this);
-
-  t.assertLiteral(breakLoc);
-  t.assertLiteral(continueLoc);
-
-  if (label) {
-    t.assertIdentifier(label);
-  } else {
-    label = null;
-  }
-
-  this.breakLoc = breakLoc;
-  this.continueLoc = continueLoc;
-  this.label = label;
-}
-
-inherits(LoopEntry, Entry);
-
-function SwitchEntry(breakLoc) {
-  Entry.call(this);
-
-  t.assertLiteral(breakLoc);
-
-  this.breakLoc = breakLoc;
-}
-
-inherits(SwitchEntry, Entry);
-
-function TryEntry(firstLoc, catchEntry, finallyEntry) {
-  Entry.call(this);
-
-  t.assertLiteral(firstLoc);
-
-  if (catchEntry) {
-    assert.ok(catchEntry instanceof CatchEntry);
-  } else {
-    catchEntry = null;
-  }
-
-  if (finallyEntry) {
-    assert.ok(finallyEntry instanceof FinallyEntry);
-  } else {
-    finallyEntry = null;
-  }
-
-  // Have to have one or the other (or both).
-  assert.ok(catchEntry || finallyEntry);
-
-  this.firstLoc = firstLoc;
-  this.catchEntry = catchEntry;
-  this.finallyEntry = finallyEntry;
-}
-
-inherits(TryEntry, Entry);
-
-function CatchEntry(firstLoc, paramId) {
-  Entry.call(this);
-
-  t.assertLiteral(firstLoc);
-  t.assertIdentifier(paramId);
-
-  this.firstLoc = firstLoc;
-  this.paramId = paramId;
-}
-
-inherits(CatchEntry, Entry);
-
-function FinallyEntry(firstLoc) {
-  Entry.call(this);
-
-  t.assertLiteral(firstLoc);
-
-  this.firstLoc = firstLoc;
-}
-
-inherits(FinallyEntry, Entry);
-
-function LeapManager(emitter) {
-  assert.ok(this instanceof LeapManager);
-
-  var Emitter = require("./emit").Emitter;
-  assert.ok(emitter instanceof Emitter);
-
-  this.emitter = emitter;
-  this.entryStack = [new FunctionEntry(emitter.finalLoc)];
-}
-
-LeapManager.prototype.withEntry = function (entry, callback) {
-  assert.ok(entry instanceof Entry);
-  this.entryStack.push(entry);
-  try {
-    callback.call(this.emitter);
-  } finally {
-    var popped = this.entryStack.pop();
-    assert.strictEqual(popped, entry);
-  }
-};
-
-LeapManager.prototype._findLeapLocation = function (property, label) {
-  for (var i = this.entryStack.length - 1; i >= 0; --i) {
-    var entry = this.entryStack[i];
-    var loc = entry[property];
-    if (loc) {
-      if (label) {
-        if (entry.label &&
-            entry.label.name === label.name) {
-          return loc;
-        }
-      } else {
-        return loc;
-      }
-    }
-  }
-
-  return null;
-};
-
-LeapManager.prototype.getBreakLoc = function (label) {
-  return this._findLeapLocation("breakLoc", label);
-};
-
-LeapManager.prototype.getContinueLoc = function (label) {
-  return this._findLeapLocation("continueLoc", label);
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/meta.js b/lib/6to5/transformation/transformers/es6-generators/meta.js
deleted file mode 100644
index f7bb1248e6..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/meta.js
+++ /dev/null
@@ -1,98 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var assert = require("assert");
-var types  = require("ast-types");
-var m      = require("private").makeAccessor();
-var _      = require("lodash");
-
-var isArray = types.builtInTypes.array;
-var n       = types.namedTypes;
-
-function makePredicate(propertyName, knownTypes) {
-  function onlyChildren(node) {
-    n.Node.check(node);
-
-    // Assume no side effects until we find out otherwise.
-    var result = false;
-
-    function check(child) {
-      if (result) {
-        // Do nothing.
-      } else if (isArray.check(child)) {
-        child.some(check);
-      } else if (n.Node.check(child)) {
-        assert.strictEqual(result, false);
-        result = predicate(child);
-      }
-      return result;
-    }
-
-    types.eachField(node, function (name, child) {
-      check(child);
-    });
-
-    return result;
-  }
-
-  function predicate(node) {
-    n.Node.check(node);
-
-    var meta = m(node);
-    if (_.has(meta, propertyName)) return meta[propertyName];
-
-    // Certain types are "opaque," which means they have no side
-    // effects or leaps and we don't care about their subexpressions.
-    if (_.has(opaqueTypes, node.type)) return meta[propertyName] = false;
-
-    if (_.has(knownTypes, node.type)) return meta[propertyName] = true;
-
-    return meta[propertyName] = onlyChildren(node);
-  }
-
-  predicate.onlyChildren = onlyChildren;
-
-  return predicate;
-}
-
-var opaqueTypes = {
-  FunctionExpression: true
-};
-
-// These types potentially have side effects regardless of what side
-// effects their subexpressions have.
-var sideEffectTypes = {
-  CallExpression: true, // Anything could happen!
-  ForInStatement: true, // Modifies the key variable.
-  UnaryExpression: true, // Think delete.
-  BinaryExpression: true, // Might invoke .toString() or .valueOf().
-  AssignmentExpression: true, // Side-effecting by definition.
-  UpdateExpression: true, // Updates are essentially assignments.
-  NewExpression: true // Similar to CallExpression.
-};
-
-// These types are the direct cause of all leaps in control flow.
-var leapTypes = {
-  YieldExpression: true,
-  BreakStatement: true,
-  ContinueStatement: true,
-  ReturnStatement: true,
-  ThrowStatement: true
-};
-
-// All leap types are also side effect types.
-for (var type in leapTypes) {
-  if (_.has(leapTypes, type)) {
-    sideEffectTypes[type] = leapTypes[type];
-  }
-}
-
-exports.hasSideEffects = makePredicate("hasSideEffects", sideEffectTypes);
-exports.containsLeap = makePredicate("containsLeap", leapTypes);
diff --git a/lib/6to5/transformation/transformers/es6-generators/runtime.js b/lib/6to5/transformation/transformers/es6-generators/runtime.js
deleted file mode 100644
index 0c8f932f1f..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/runtime.js
+++ /dev/null
@@ -1,448 +0,0 @@
-/**
-* Copyright (c) 2014, Facebook, Inc.
-* All rights reserved.
-*
-* This source code is licensed under the BSD-style license found in the
-* https://raw.github.com/facebook/regenerator/master/LICENSE file. An
-* additional grant of patent rights can be found in the PATENTS file in
-* the same directory.
-*/
-
-var iteratorSymbol = typeof Symbol === "function" && Symbol.iterator || "@@iterator";
-var runtime = global.regeneratorRuntime = exports;
-var hasOwn = Object.prototype.hasOwnProperty;
-
-var wrap = runtime.wrap = function wrap(innerFn, outerFn, self, tryList) {
-  return new Generator(innerFn, outerFn, self || null, tryList || []);
-};
-
-var GenStateSuspendedStart = "suspendedStart";
-var GenStateSuspendedYield = "suspendedYield";
-var GenStateExecuting = "executing";
-var GenStateCompleted = "completed";
-
-// Returning this object from the innerFn has the same effect as
-// breaking out of the dispatch switch statement.
-var ContinueSentinel = {};
-
-// Dummy constructor that we use as the .constructor property for
-// functions that return Generator objects.
-function GeneratorFunction() {}
-var GFp = function GeneratorFunctionPrototype() {};
-var Gp = GFp.prototype = Generator.prototype;
-(GFp.constructor = GeneratorFunction).prototype = Gp.constructor = GFp;
-
-runtime.isGeneratorFunction = function (genFun) {
-  var ctor = genFun && genFun.constructor;
-  return ctor ? GeneratorFunction.name === ctor.name : false;
-};
-
-runtime.mark = function (genFun) {
-  genFun.__proto__ = GFp;
-  genFun.prototype = Object.create(Gp);
-  return genFun;
-};
-
-runtime.async = function (innerFn, outerFn, self, tryList) {
-  return new Promise(function (resolve, reject) {
-    var generator = wrap(innerFn, outerFn, self, tryList);
-    var callNext = step.bind(generator.next);
-    var callThrow = step.bind(generator["throw"]);
-
-    function step(arg) {
-      var info;
-      var value;
-
-      try {
-        info = this(arg);
-        value = info.value;
-      } catch (error) {
-        return reject(error);
-      }
-
-      if (info.done) {
-        resolve(value);
-      } else {
-        Promise.resolve(value).then(callNext, callThrow);
-      }
-    }
-
-    callNext();
-  });
-};
-
-function Generator(innerFn, outerFn, self, tryList) {
-  var generator = outerFn ? Object.create(outerFn.prototype) : this;
-  var context = new Context(tryList);
-  var state = GenStateSuspendedStart;
-
-  function invoke(method, arg) {
-    if (state === GenStateExecuting) {
-      throw new Error("Generator is already running");
-    }
-
-    if (state === GenStateCompleted) {
-      throw new Error("Generator has already finished");
-    }
-
-    while (true) {
-      var delegate = context.delegate;
-      var info;
-
-      if (delegate) {
-        try {
-          info = delegate.iterator[method](arg);
-
-          // Delegate generator ran and handled its own exceptions so
-          // regardless of what the method was, we continue as if it is
-          // "next" with an undefined arg.
-          method = "next";
-          arg = undefined;
-
-        } catch (uncaught) {
-          context.delegate = null;
-
-          // Like returning generator.throw(uncaught), but without the
-          // overhead of an extra function call.
-          method = "throw";
-          arg = uncaught;
-
-          continue;
-        }
-
-        if (info.done) {
-          context[delegate.resultName] = info.value;
-          context.next = delegate.nextLoc;
-        } else {
-          state = GenStateSuspendedYield;
-          return info;
-        }
-
-        context.delegate = null;
-      }
-
-      if (method === "next") {
-        if (state === GenStateSuspendedStart &&
-            typeof arg !== "undefined") {
-          // https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorresume
-          throw new TypeError(
-            "attempt to send " + JSON.stringify(arg) + " to newborn generator"
-          );
-        }
-
-        if (state === GenStateSuspendedYield) {
-          context.sent = arg;
-        } else {
-          delete context.sent;
-        }
-
-      } else if (method === "throw") {
-        if (state === GenStateSuspendedStart) {
-          state = GenStateCompleted;
-          throw arg;
-        }
-
-        if (context.dispatchException(arg)) {
-          // If the dispatched exception was caught by a catch block,
-          // then let that catch block handle the exception normally.
-          method = "next";
-          arg = undefined;
-        }
-
-      } else if (method === "return") {
-        context.abrupt("return", arg);
-      }
-
-      state = GenStateExecuting;
-
-      try {
-        var value = innerFn.call(self, context);
-
-        // If an exception is thrown from innerFn, we leave state ===
-        // GenStateExecuting and loop back for another invocation.
-        state = context.done ? GenStateCompleted : GenStateSuspendedYield;
-
-        info = {
-          value: value,
-          done: context.done
-        };
-
-        if (value === ContinueSentinel) {
-          if (context.delegate && method === "next") {
-            // Deliberately forget the last sent value so that we don't
-            // accidentally pass it on to the delegate.
-            arg = undefined;
-          }
-        } else {
-          return info;
-        }
-
-      } catch (thrown) {
-        state = GenStateCompleted;
-
-        if (method === "next") {
-          context.dispatchException(thrown);
-        } else {
-          arg = thrown;
-        }
-      }
-    }
-  }
-
-  generator.next = invoke.bind(generator, "next");
-  generator["throw"] = invoke.bind(generator, "throw");
-  generator["return"] = invoke.bind(generator, "return");
-
-  return generator;
-}
-
-Gp[iteratorSymbol] = function () {
-  return this;
-};
-
-Gp.toString = function () {
-  return "[object Generator]";
-};
-
-function pushTryEntry(triple) {
-  var entry = { tryLoc: triple[0] };
-
-  if (1 in triple) {
-    entry.catchLoc = triple[1];
-  }
-
-  if (2 in triple) {
-    entry.finallyLoc = triple[2];
-  }
-
-  this.tryEntries.push(entry);
-}
-
-function resetTryEntry(entry, i) {
-  var record = entry.completion || {};
-  record.type = i === 0 ? "normal" : "return";
-  delete record.arg;
-  entry.completion = record;
-}
-
-function Context(tryList) {
-  // The root entry object (effectively a try statement without a catch
-  // or a finally block) gives us a place to store values thrown from
-  // locations where there is no enclosing try statement.
-  this.tryEntries = [{ tryLoc: "root" }];
-  tryList.forEach(pushTryEntry, this);
-  this.reset();
-}
-
-runtime.keys = function (object) {
-  var keys = [];
-  for (var key in object) {
-    keys.push(key);
-  }
-  keys.reverse();
-
-  // Rather than returning an object with a next method, we keep
-  // things simple and return the next function itself.
-  return function next() {
-    while (keys.length) {
-      var key = keys.pop();
-      if (key in object) {
-        next.value = key;
-        next.done = false;
-        return next;
-      }
-    }
-
-    // To avoid creating an additional object, we just hang the .value
-    // and .done properties off the next function object itself. This
-    // also ensures that the minifier will not anonymize the function.
-    next.done = true;
-    return next;
-  };
-};
-
-function values(iterable) {
-  var iterator = iterable;
-  if (iteratorSymbol in iterable) {
-    iterator = iterable[iteratorSymbol]();
-  } else if (!isNaN(iterable.length)) {
-    var i = -1;
-    iterator = function next() {
-      while (++i < iterable.length) {
-        if (i in iterable) {
-          next.value = iterable[i];
-          next.done = false;
-          return next;
-        }
-      }
-      next.done = true;
-      return next;
-    };
-    iterator.next = iterator;
-  }
-  return iterator;
-}
-runtime.values = values;
-
-Context.prototype = {
-  constructor: Context,
-
-  reset: function () {
-    this.prev = 0;
-    this.next = 0;
-    this.sent = undefined;
-    this.done = false;
-    this.delegate = null;
-
-    this.tryEntries.forEach(resetTryEntry);
-
-    // Pre-initialize at least 20 temporary variables to enable hidden
-    // class optimizations for simple generators.
-    for (var tempIndex = 0, tempName;
-         hasOwn.call(this, tempName = "t" + tempIndex) || tempIndex < 20;
-         ++tempIndex) {
-      this[tempName] = null;
-    }
-  },
-
-  stop: function () {
-    this.done = true;
-
-    var rootEntry = this.tryEntries[0];
-    var rootRecord = rootEntry.completion;
-    if (rootRecord.type === "throw") {
-      throw rootRecord.arg;
-    }
-
-    return this.rval;
-  },
-
-  dispatchException: function (exception) {
-    if (this.done) {
-      throw exception;
-    }
-
-    var context = this;
-    function handle(loc, caught) {
-      record.type = "throw";
-      record.arg = exception;
-      context.next = loc;
-      return !!caught;
-    }
-
-    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
-      var entry = this.tryEntries[i];
-      var record = entry.completion;
-
-      if (entry.tryLoc === "root") {
-        // Exception thrown outside of any try block that could handle
-        // it, so set the completion value of the entire function to
-        // throw the exception.
-        return handle("end");
-      }
-
-      if (entry.tryLoc <= this.prev) {
-        var hasCatch = hasOwn.call(entry, "catchLoc");
-        var hasFinally = hasOwn.call(entry, "finallyLoc");
-
-        if (hasCatch && hasFinally) {
-          if (this.prev < entry.catchLoc) {
-            return handle(entry.catchLoc, true);
-          } else if (this.prev < entry.finallyLoc) {
-            return handle(entry.finallyLoc);
-          }
-
-        } else if (hasCatch) {
-          if (this.prev < entry.catchLoc) {
-            return handle(entry.catchLoc, true);
-          }
-
-        } else if (hasFinally) {
-          if (this.prev < entry.finallyLoc) {
-            return handle(entry.finallyLoc);
-          }
-
-        } else {
-          throw new Error("try statement without catch or finally");
-        }
-      }
-    }
-  },
-
-  _findFinallyEntry: function (finallyLoc) {
-    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
-      var entry = this.tryEntries[i];
-      if (entry.tryLoc <= this.prev &&
-          hasOwn.call(entry, "finallyLoc") && (
-            entry.finallyLoc === finallyLoc ||
-            this.prev < entry.finallyLoc)) {
-        return entry;
-      }
-    }
-  },
-
-  abrupt: function (type, arg) {
-    var entry = this._findFinallyEntry();
-    var record = entry ? entry.completion : {};
-
-    record.type = type;
-    record.arg = arg;
-
-    if (entry) {
-      this.next = entry.finallyLoc;
-    } else {
-      this.complete(record);
-    }
-
-    return ContinueSentinel;
-  },
-
-  complete: function (record) {
-    if (record.type === "throw") {
-      throw record.arg;
-    }
-
-    if (record.type === "break" || record.type === "continue") {
-      this.next = record.arg;
-    } else if (record.type === "return") {
-      this.rval = record.arg;
-      this.next = "end";
-    }
-
-    return ContinueSentinel;
-  },
-
-  finish: function (finallyLoc) {
-    var entry = this._findFinallyEntry(finallyLoc);
-    return this.complete(entry.completion);
-  },
-
-  "catch": function (tryLoc) {
-    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
-      var entry = this.tryEntries[i];
-      if (entry.tryLoc === tryLoc) {
-        var record = entry.completion;
-        var thrown;
-        if (record.type === "throw") {
-          thrown = record.arg;
-          resetTryEntry(entry, i);
-        }
-        return thrown;
-      }
-    }
-
-    // The context.catch method must only be called with a location
-    // argument that corresponds to a known catch block.
-    throw new Error("illegal catch attempt");
-  },
-
-  delegateYield: function (iterable, resultName, nextLoc) {
-    this.delegate = {
-      iterator: values(iterable),
-      resultName: resultName,
-      nextLoc: nextLoc
-    };
-
-    return ContinueSentinel;
-  }
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/util.js b/lib/6to5/transformation/transformers/es6-generators/util.js
deleted file mode 100644
index 99e7072a19..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/util.js
+++ /dev/null
@@ -1,28 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var t = require("../../../types");
-
-exports.runtimeProperty = function (name) {
-  return t.memberExpression(
-    t.identifier("regeneratorRuntime"),
-    t.identifier(name)
-  );
-};
-
-// Offsets into this.listing that could be used as targets for branches or
-// jumps are represented as numeric Literal nodes. This representation has
-// the amazingly convenient benefit of allowing the exact value of the
-// location to be determined at any time, even after generating code that
-// refers to the location.
-
-exports.loc = function () {
-  return t.literal(-1);
-};
diff --git a/lib/6to5/transformation/transformers/es6-generators/visit.js b/lib/6to5/transformation/transformers/es6-generators/visit.js
deleted file mode 100644
index eaa504fbab..0000000000
--- a/lib/6to5/transformation/transformers/es6-generators/visit.js
+++ /dev/null
@@ -1,221 +0,0 @@
-/**
- * Copyright (c) 2014, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * https://raw.githut.com/facebook/regenerator/master/LICENSE file. An
- * additional grant of patent rights can be found in the PATENTS file in
- * the same directory.
- */
-
-var runtimeProperty = require("./util").runtimeProperty;
-var Emitter         = require("./emit").Emitter;
-var hoist           = require("./hoist").hoist;
-var types           = require("ast-types");
-var t               = require("../../../types");
-
-var runtimeAsyncMethod = runtimeProperty("async");
-var runtimeWrapMethod  = runtimeProperty("wrap");
-var runtimeMarkMethod  = runtimeProperty("mark");
-
-exports.transform = function transform(node, file) {
-  return types.visit(node, {
-    visitFunction: function (path) {
-      return visitor.call(this, path, file);
-    }
-  });
-};
-
-var visitor = function (path, file) {
-  // Calling this.traverse(path) first makes for a post-order traversal.
-  this.traverse(path);
-
-  var node = path.value;
-  var scope; // we need to actually get the current scope
-
-  if (!node.generator && !node.async) {
-    return;
-  }
-
-  node.generator = false;
-
-  if (node.expression) {
-    // Transform expression lambdas into normal functions.
-    node.expression = false;
-    node.body = t.blockStatement([
-      t.returnStatement(node.body)
-    ]);
-  }
-
-  if (node.async) {
-    awaitVisitor.visit(path.get("body"));
-  }
-
-  var outerFnId = node.id || (
-    node.id = file.generateUidIdentifier("callee", scope)
-  );
-
-  var innerFnId = t.identifier(node.id.name + "$");
-  var contextId = file.generateUidIdentifier("context", scope);
-  var vars = hoist(path);
-
-  var emitter = new Emitter(contextId);
-  emitter.explode(path.get("body"));
-
-  var outerBody = [];
-
-  if (vars && vars.declarations.length > 0) {
-    outerBody.push(vars);
-  }
-
-  var wrapArgs = [
-    emitter.getContextFunction(innerFnId),
-    // Async functions don't care about the outer function because they
-    // don't need it to be marked and don't inherit from its .prototype.
-    node.async ? t.literal(null) : outerFnId,
-    t.thisExpression()
-  ];
-
-  var tryEntryList = emitter.getTryEntryList();
-  if (tryEntryList) {
-    wrapArgs.push(tryEntryList);
-  }
-
-  var wrapCall = t.callExpression(
-    node.async ? runtimeAsyncMethod : runtimeWrapMethod,
-    wrapArgs
-  );
-
-  outerBody.push(t.returnStatement(wrapCall));
-  node.body = t.blockStatement(outerBody);
-
-  if (node.async) {
-    node.async = false;
-    return;
-  }
-
-  if (t.isFunctionDeclaration(node)) {
-    var pp = path.parent;
-
-    while (pp && !(t.isBlockStatement(pp.value) || t.isProgram(pp.value))) {
-      pp = pp.parent;
-    }
-
-    if (!pp) {
-      return;
-    }
-
-    // Here we turn the FunctionDeclaration into a named
-    // FunctionExpression that will be assigned to a variable of the
-    // same name at the top of the enclosing block. This is important
-    // for a very subtle reason: named function expressions can refer to
-    // themselves by name without fear that the binding may change due
-    // to code executing outside the function, whereas function
-    // declarations are vulnerable to the following rebinding:
-    //
-    //   function f() { return f }
-    //   var g = f;
-    //   f = "asdf";
-    //   g(); // "asdf"
-    //
-    // One way to prevent the problem illustrated above is to transform
-    // the function declaration thus:
-    //
-    //   var f = function f() { return f };
-    //   var g = f;
-    //   f = "asdf";
-    //   g(); // f
-    //   g()()()()(); // f
-    //
-    // In the code below, we transform generator function declarations
-    // in the following way:
-    //
-    //   gen().next(); // { value: gen, done: true }
-    //   function *gen() {
-    //     return gen;
-    //   }
-    //
-    // becomes something like
-    //
-    //   var gen = runtime.mark(function *gen() {
-    //     return gen;
-    //   });
-    //   gen().next(); // { value: gen, done: true }
-    //
-    // which ensures that the generator body can always reliably refer
-    // to gen by name.
-
-    // Remove the FunctionDeclaration so that we can add it back as a
-    // FunctionExpression passed to runtime.mark.
-    path.replace();
-
-    // Change the type of the function to be an expression instead of a
-    // declaration. Note that all the other fields are the same.
-    node.type = "FunctionExpression";
-
-    var varDecl = t.variableDeclaration("var", [
-      t.variableDeclarator(
-        node.id,
-        t.callExpression(runtimeMarkMethod, [node])
-      )
-    ]);
-
-    // Copy any comments preceding the function declaration to the
-    // variable declaration, to avoid weird formatting consequences.
-    t.inheritsComments(varDecl, node);
-    t.removeComments(node);
-
-    varDecl._blockHoist = true;
-
-    var bodyPath = pp.get("body");
-    var bodyLen = bodyPath.value.length;
-
-    for (var i = 0; i < bodyLen; ++i) {
-      var firstStmtPath = bodyPath.get(i);
-      if (!shouldNotHoistAbove(firstStmtPath)) {
-        firstStmtPath.insertBefore(varDecl);
-        return;
-      }
-    }
-
-    bodyPath.push(varDecl);
-  } else {
-    t.assertFunctionExpression(node);
-    return t.callExpression(runtimeMarkMethod, [node]);
-  }
-};
-
-function shouldNotHoistAbove(stmtPath) {
-  var value = stmtPath.value;
-  t.assertStatement(value);
-
-  // If the first statement is a "use strict" declaration, make sure to
-  // insert hoisted declarations afterwards.
-  if (t.isExpressionStatement(value) &&
-      t.isLiteral(value.expression) &&
-      value.expression.value === "use strict") {
-    return true;
-  }
-
-  if (t.isVariableDeclaration(value)) {
-    for (var i = 0; i < value.declarations.length; ++i) {
-      var decl = value.declarations[i];
-      if (t.isCallExpression(decl.init) && types.astNodesAreEquivalent(decl.init.callee, runtimeMarkMethod)) {
-        return true;
-      }
-    }
-  }
-
-  return false;
-}
-
-var awaitVisitor = types.PathVisitor.fromMethodsObject({
-  visitFunction: function () {
-    return false; // Don't descend into nested function scopes.
-  },
-
-  visitAwaitExpression: function (path) {
-    // Convert await expressions to yield expressions.
-    return t.yieldExpression(path.value.argument, false);
-  }
-});
diff --git a/lib/6to5/transformation/transformers/es6-let-scoping.js b/lib/6to5/transformation/transformers/es6-let-scoping.js
index ce11cde375..7d6fa09b76 100644
--- a/lib/6to5/transformation/transformers/es6-let-scoping.js
+++ b/lib/6to5/transformation/transformers/es6-let-scoping.js
@@ -3,33 +3,40 @@ var util     = require("../../util");
 var t        = require("../../types");
 var _        = require("lodash");
 
-var isLet = function (node) {
+var isLet = function (node, parent) {
   if (!t.isVariableDeclaration(node)) return false;
   if (node._let) return true;
   if (node.kind !== "let") return false;
 
+  // https://github.com/6to5/6to5/issues/255
+  if (!t.isFor(parent) || t.isFor(parent) && parent.left !== node) {
+    _.each(node.declarations, function (declar) {
+      declar.init = declar.init || t.identifier("undefined");
+    });
+  }
+
   node._let = true;
   node.kind = "var";
   return true;
 };
 
-var isVar = function (node) {
-  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node);
+var isVar = function (node, parent) {
+  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node, parent);
 };
 
 var standardiseLets = function (declars) {
-  _.each(declars, function (declar) {
-    delete declar._let;
-  });
+  for (var i in declars) {
+    delete declars[i]._let;
+  }
 };
 
-exports.VariableDeclaration = function (node) {
-  isLet(node);
+exports.VariableDeclaration = function (node, parent) {
+  isLet(node, parent);
 };
 
 exports.Loop = function (node, parent, file, scope) {
   var init = node.left || node.init;
-  if (isLet(init)) {
+  if (isLet(init, node)) {
     t.ensureBlock(node);
     node.body._letDeclars = [init];
   }
@@ -91,9 +98,6 @@ LetScoping.prototype.run = function () {
   // remap all let references that exist in upper scopes to their uid
   this.remap();
 
-  // add default initializer to let variables in loop bodys
-  this.initialiseLoopLets();
-
   // this is a block within a `Function` so we can safely leave it be
   if (t.isFunction(this.parent)) return this.noClosure();
 
@@ -161,7 +165,7 @@ LetScoping.prototype.remap = function () {
   var replacements = this.info.duplicates;
   var block        = this.block;
 
-  if (_.isEmpty(replacements)) return;
+  if (!this.info.hasDuplicates) return;
 
   var replace = function (node, parent, scope) {
     if (!t.isIdentifier(node)) return;
@@ -172,7 +176,7 @@ LetScoping.prototype.remap = function () {
 
   var traverseReplace = function (node, parent) {
     replace(node, parent);
-    traverse(node, replace);
+    traverse(node, { enter: replace });
   };
 
   var loopParent = this.loopParent;
@@ -182,7 +186,7 @@ LetScoping.prototype.remap = function () {
     traverseReplace(loopParent.update, loopParent);
   }
 
-  traverse(block, replace);
+  traverse(block, { enter: replace });
 };
 
 /**
@@ -209,6 +213,8 @@ LetScoping.prototype.getInfo = function () {
     // all references with it
     duplicates:  {},
 
+    hasDuplicates: false,
+
     // array of `Identifier` names of let variables that are accessible within
     // the current block
     keys:        []
@@ -221,59 +227,41 @@ LetScoping.prototype.getInfo = function () {
       // there's a variable with this exact name in an upper scope so we need
       // to generate a new name
       opts.duplicates[key] = id.name = file.generateUid(key, scope);
+      opts.hasDuplicates = true;
     }
   };
 
-  _.each(opts.declarators, function (declar) {
+  var i;
+  var declar;
+
+  for (i in opts.declarators) {
+    declar = opts.declarators[i];
     opts.declarators.push(declar);
 
     var keys = t.getIds(declar, true);
     _.each(keys, duplicates);
-    keys = _.keys(keys);
+    keys = Object.keys(keys);
 
     opts.outsideKeys = opts.outsideKeys.concat(keys);
     opts.keys = opts.keys.concat(keys);
-  });
+  }
 
-  _.each(block.body, function (declar) {
-    if (!isLet(declar)) return;
+  for (i in block.body) {
+    declar = block.body[i];
+    if (!isLet(declar, block)) continue;
 
     _.each(t.getIds(declar, true), function (id, key) {
       duplicates(id, key);
       opts.keys.push(key);
     });
-  });
+  }
 
   return opts;
 };
 
 /**
- * Any let variable declared within a loop body need to have an initializer or
- * else they'll be hoisted and subsequent iterations of the loop will have a
- * previous state. This function adds a default initializer of `undefined` to
- * those variables.
- */
-
-LetScoping.prototype.initialiseLoopLets = function () {
-  var loopParent = this.loopParent;
-  if (!loopParent) return;
-
-  traverse(this.block, function (node) {
-    if (t.isFunction(node) || t.isLoop(node)) {
-      return false;
-    }
-
-    if (isLet(node)) {
-      _.each(node.declarations, function (declar) {
-        declar.init = declar.init || t.identifier("undefined");
-      });
-    }
-  });
-};
-
-/**
- * If we're inside of a `For*Statement` then traverse it and check if it has one
- * of the following node types `ReturnStatement`, `BreakStatement`,
+ * If we're inside of a loop then traverse it and check if it has one of
+ * the following node types `ReturnStatement`, `BreakStatement`,
  * `ContinueStatement` and replace it with a return value that we can track
  * later on.
  *
@@ -287,33 +275,35 @@ LetScoping.prototype.checkLoop = function () {
     hasBreak:    false,
   };
 
-  traverse(this.block, function (node, parent) {
-    var replace;
+  traverse(this.block, {
+    enter: function (node, parent) {
+      var replace;
 
-    if (t.isFunction(node) || t.isLoop(node)) {
-      return false;
-    }
-
-    if (node && !node.label) {
-      if (t.isBreakStatement(node)) {
-        if (t.isSwitchCase(parent)) return;
-
-        has.hasBreak = true;
-        replace = t.returnStatement(t.literal("break"));
-      } else if (t.isContinueStatement(node)) {
-        has.hasContinue = true;
-        replace = t.returnStatement(t.literal("continue"));
+      if (t.isFunction(node) || t.isLoop(node)) {
+        return false;
       }
-    }
 
-    if (t.isReturnStatement(node)) {
-      has.hasReturn = true;
-      replace = t.returnStatement(t.objectExpression([
-        t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
-      ]));
-    }
+      if (node && !node.label) {
+        if (t.isBreakStatement(node)) {
+          if (t.isSwitchCase(parent)) return;
 
-    if (replace) return t.inherits(replace, node);
+          has.hasBreak = true;
+          replace = t.returnStatement(t.literal("break"));
+        } else if (t.isContinueStatement(node)) {
+          has.hasContinue = true;
+          replace = t.returnStatement(t.literal("continue"));
+        }
+      }
+
+      if (t.isReturnStatement(node)) {
+        has.hasReturn = true;
+        replace = t.returnStatement(t.objectExpression([
+          t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
+        ]));
+      }
+
+      if (replace) return t.inherits(replace, node);
+    }
   });
 
   return has;
@@ -326,19 +316,21 @@ LetScoping.prototype.checkLoop = function () {
 
 LetScoping.prototype.hoistVarDeclarations = function () {
   var self = this;
-  traverse(this.block, function (node) {
-    if (t.isForStatement(node)) {
-      if (isVar(node.init)) {
-        node.init = t.sequenceExpression(self.pushDeclar(node.init));
+  traverse(this.block, {
+    enter: function (node, parent) {
+      if (t.isForStatement(node)) {
+        if (isVar(node.init, node)) {
+          node.init = t.sequenceExpression(self.pushDeclar(node.init));
+        }
+      } else if (t.isFor(node)) {
+        if (isVar(node.left, node)) {
+          node.left = node.left.declarations[0].id;
+        }
+      } else if (isVar(node, parent)) {
+        return self.pushDeclar(node).map(t.expressionStatement);
+      } else if (t.isFunction(node)) {
+        return false;
       }
-    } else if (t.isFor(node)) {
-      if (isVar(node.left)) {
-        node.left = node.left.declarations[0].id;
-      }
-    } else if (isVar(node)) {
-      return self.pushDeclar(node).map(t.expressionStatement);
-    } else if (t.isFunction(node)) {
-      return false;
     }
   });
 };
@@ -371,31 +363,35 @@ LetScoping.prototype.getLetReferences = function () {
 
   // traverse through this block, stopping on functions and checking if they
   // contain any outside let references
-  traverse(this.block, function (node, parent, scope) {
-    if (t.isFunction(node)) {
-      traverse(node, function (node, parent) {
-        // not an identifier so we have no use
-        if (!t.isIdentifier(node)) return;
+  traverse(this.block, {
+    enter: function (node, parent, scope) {
+      if (t.isFunction(node)) {
+        traverse(node, {
+          enter: function (node, parent) {
+            // not an identifier so we have no use
+            if (!t.isIdentifier(node)) return;
 
-        // not a direct reference
-        if (!t.isReferenced(node, parent)) return;
+            // not a direct reference
+            if (!t.isReferenced(node, parent)) return;
 
-        // this scope has a variable with the same name so it couldn't belong
-        // to our let scope
-        if (scope.hasOwn(node.name)) return;
+            // this scope has a variable with the same name so it couldn't belong
+            // to our let scope
+            if (scope.hasOwn(node.name)) return;
 
-        closurify = true;
+            closurify = true;
 
-        // this key doesn't appear just outside our scope
-        if (!_.contains(self.info.outsideKeys, node.name)) return;
+            // this key doesn't appear just outside our scope
+            if (!_.contains(self.info.outsideKeys, node.name)) return;
 
-        // push this badboy
-        self.letReferences[node.name] = node;
-      });
+            // push this badboy
+            self.letReferences[node.name] = node;
+          }
+        });
 
-      return false;
-    } else if (t.isLoop(node)) {
-      return false;
+        return false;
+      } else if (t.isLoop(node)) {
+        return false;
+      }
     }
   });
 
@@ -417,12 +413,13 @@ LetScoping.prototype.pushDeclar = function (node) {
 
   var replace = [];
 
-  _.each(node.declarations, function (declar) {
-    if (!declar.init) return;
+  for (var i in node.declarations) {
+    var declar = node.declarations[i];
+    if (!declar.init) continue;
 
     var expr = t.assignmentExpression("=", declar.id, declar.init);
     replace.push(t.inherits(expr, declar));
-  });
+  }
 
   return replace;
 };
diff --git a/lib/6to5/transformation/transformers/es6-modules.js b/lib/6to5/transformation/transformers/es6-modules.js
index cfcd991f5c..039d716aa2 100644
--- a/lib/6to5/transformation/transformers/es6-modules.js
+++ b/lib/6to5/transformation/transformers/es6-modules.js
@@ -1,16 +1,26 @@
-var _ = require("lodash");
+var t = require("../../types");
+
+var inheritsComments = function (node, nodes) {
+  if (nodes.length) {
+    t.inheritsComments(nodes[0], node);
+  }
+};
 
 exports.ImportDeclaration = function (node, parent, file) {
   var nodes = [];
 
   if (node.specifiers.length) {
-    _.each(node.specifiers, function (specifier) {
-      file.moduleFormatter.importSpecifier(specifier, node, nodes, parent);
-    });
+    if (!file.moduleFormatter.importSpecifier) return;
+    for (var i in node.specifiers) {
+      file.moduleFormatter.importSpecifier(node.specifiers[i], node, nodes, parent);
+    }
   } else {
-    file.moduleFormatter.import(node, nodes, parent);
+    if (!file.moduleFormatter.importDeclaration) return;
+    file.moduleFormatter.importDeclaration(node, nodes, parent);
   }
 
+  inheritsComments(node, nodes);
+
   return nodes;
 };
 
@@ -18,12 +28,23 @@ exports.ExportDeclaration = function (node, parent, file) {
   var nodes = [];
 
   if (node.declaration) {
-    file.moduleFormatter.export(node, nodes, parent);
+    // make sure variable exports have an initialiser
+    // this is done here to avoid duplicating it in the module formatters
+    if (t.isVariableDeclaration(node.declaration)) {
+      var declar = node.declaration.declarations[0];
+      declar.init = declar.init || t.identifier("undefined");
+    }
+
+    if (!file.moduleFormatter.exportDeclaration) return;
+    file.moduleFormatter.exportDeclaration(node, nodes, parent);
   } else {
-    _.each(node.specifiers, function (specifier) {
-      file.moduleFormatter.exportSpecifier(specifier, node, nodes, parent);
-    });
+    if (!file.moduleFormatter.exportSpecifier) return;
+    for (var i in node.specifiers) {
+      file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, parent);
+    }
   }
 
+  inheritsComments(node, nodes);
+
   return nodes;
 };
diff --git a/lib/6to5/transformation/transformers/es6-property-name-shorthand.js b/lib/6to5/transformation/transformers/es6-property-name-shorthand.js
index 747cbbd9ec..8614d69c84 100644
--- a/lib/6to5/transformation/transformers/es6-property-name-shorthand.js
+++ b/lib/6to5/transformation/transformers/es6-property-name-shorthand.js
@@ -1,4 +1,8 @@
+var t = require("../../types");
+var _ = require("lodash");
+
 exports.Property = function (node) {
   if (!node.shorthand) return;
   node.shorthand = false;
+  node.key = t.removeComments(_.clone(node.key));
 };
diff --git a/lib/6to5/transformation/transformers/es6-spread.js b/lib/6to5/transformation/transformers/es6-spread.js
index 5e64db73eb..7c8062bcdf 100644
--- a/lib/6to5/transformation/transformers/es6-spread.js
+++ b/lib/6to5/transformation/transformers/es6-spread.js
@@ -1,19 +1,16 @@
 var t = require("../../types");
-var _ = require("lodash");
 
 var getSpreadLiteral = function (spread, file) {
   return file.toArray(spread.argument);
 };
 
 var hasSpread = function (nodes) {
-  var has = false;
-  _.each(nodes, function (node) {
-    if (t.isSpreadElement(node)) {
-      has = true;
-      return false;
+  for (var i in nodes) {
+    if (t.isSpreadElement(nodes[i])) {
+      return true;
     }
-  });
-  return has;
+  }
+  return false;
 };
 
 var build = function (props, file) {
@@ -27,14 +24,15 @@ var build = function (props, file) {
     _props = [];
   };
 
-  _.each(props, function (prop) {
+  for (var i in props) {
+    var prop = props[i];
     if (t.isSpreadElement(prop)) {
       push();
       nodes.push(getSpreadLiteral(prop, file));
     } else {
       _props.push(prop);
     }
-  });
+  }
 
   push();
 
diff --git a/lib/6to5/transformation/transformers/es6-template-literals.js b/lib/6to5/transformation/transformers/es6-template-literals.js
index 116a583609..5a5f4ce445 100644
--- a/lib/6to5/transformation/transformers/es6-template-literals.js
+++ b/lib/6to5/transformation/transformers/es6-template-literals.js
@@ -1,5 +1,4 @@
 var t = require("../../types");
-var _ = require("lodash");
 
 var buildBinaryExpression = function (left, right) {
   return t.binaryExpression("+", left, right);
@@ -12,10 +11,11 @@ exports.TaggedTemplateExpression = function (node, parent, file) {
   var strings = [];
   var raw = [];
 
-  _.each(quasi.quasis, function (elem) {
+  for (var i in quasi.quasis) {
+    var elem = quasi.quasis[i];
     strings.push(t.literal(elem.value.cooked));
     raw.push(t.literal(elem.value.raw));
-  });
+  }
 
   args.push(t.callExpression(file.addDeclaration("tagged-template-literal"), [
     t.arrayExpression(strings),
@@ -29,27 +29,27 @@ exports.TaggedTemplateExpression = function (node, parent, file) {
 
 exports.TemplateLiteral = function (node) {
   var nodes = [];
+  var i;
+
+  for (i in node.quasis) {
+    var elem = node.quasis[i];
 
-  _.each(node.quasis, function (elem) {
     nodes.push(t.literal(elem.value.cooked));
 
     var expr = node.expressions.shift();
-    if (expr) {
-      if (t.isBinary(expr)) expr = t.parenthesizedExpression(expr);
-      nodes.push(expr);
-    }
-  });
+    if (expr) nodes.push(expr);
+  }
 
   if (nodes.length > 1) {
     // remove redundant '' at the end of the expression
-    var last = _.last(nodes);
+    var last = nodes[nodes.length - 1];
     if (t.isLiteral(last, { value: "" })) nodes.pop();
 
     var root = buildBinaryExpression(nodes.shift(), nodes.shift());
 
-    _.each(nodes, function (node) {
-      root = buildBinaryExpression(root, node);
-    });
+    for (i in nodes) {
+      root = buildBinaryExpression(root, nodes[i]);
+    }
 
     return root;
   } else {
diff --git a/lib/6to5/transformation/transformers/es6-unicode-regex.js b/lib/6to5/transformation/transformers/es6-unicode-regex.js
index 14c9c2143c..d85bdf4e3b 100644
--- a/lib/6to5/transformation/transformers/es6-unicode-regex.js
+++ b/lib/6to5/transformation/transformers/es6-unicode-regex.js
@@ -6,7 +6,7 @@ exports.Literal = function (node) {
   if (!regex) return;
 
   var flags = regex.flags.split("");
-  if (!_.contains(regex.flags, "u")) return;
+  if (regex.flags.indexOf("u") < 0) return;
   _.pull(flags, "u");
 
   regex.pattern = rewritePattern(regex.pattern, regex.flags);
diff --git a/lib/6to5/transformation/transformers/es7-abstract-references.js b/lib/6to5/transformation/transformers/es7-abstract-references.js
index 266aa9d09b..2bdf11365c 100644
--- a/lib/6to5/transformation/transformers/es7-abstract-references.js
+++ b/lib/6to5/transformation/transformers/es7-abstract-references.js
@@ -34,6 +34,17 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
     }
   }
 
+  if (node.operator !== "=") {
+    value = t.binaryExpression(
+      node.operator[0],
+      util.template("abstract-expression-get", {
+        PROPERTY: node.property,
+        OBJECT:   node.object
+      }),
+      value
+    );
+  }
+
   var call = util.template("abstract-expression-set", {
     PROPERTY: left.property,
     OBJECT:   left.object,
@@ -96,3 +107,9 @@ exports.VirtualPropertyExpression = function (node) {
     OBJECT:   node.object
   });
 };
+
+exports.PrivateDeclaration = function (node) {
+  return t.variableDeclaration("const", node.declarations.map(function (id) {
+    return t.variableDeclarator(id, t.newExpression(t.identifier("WeakMap"), []));
+  }));
+};
diff --git a/lib/6to5/transformation/transformers/es7-array-comprehension.js b/lib/6to5/transformation/transformers/es7-array-comprehension.js
index 1cd029ac4c..ded4f5a28f 100644
--- a/lib/6to5/transformation/transformers/es7-array-comprehension.js
+++ b/lib/6to5/transformation/transformers/es7-array-comprehension.js
@@ -1,6 +1,5 @@
 var util = require("../../util");
 var t    = require("../../types");
-var _    = require("lodash");
 
 var single = function (node, file) {
   var block = node.blocks[0];
@@ -15,11 +14,13 @@ var single = function (node, file) {
     KEY:       block.left
   });
 
-  _.each([result.callee.object, result], function (call) {
+  var aliasPossibles = [result.callee.object, result];
+  for (var i in aliasPossibles) {
+    var call = aliasPossibles[i];
     if (t.isCallExpression(call)) {
       call.arguments[0]._aliasFunction = true;
     }
-  });
+  }
 
   return result;
 };
@@ -32,7 +33,7 @@ var multiple = function (node, file) {
   });
   container.callee.expression._aliasFunction = true;
 
-  var block = container.callee.expression.body;
+  var block = container.callee.body;
   var body  = block.body;
 
   var returnStatement = body.pop();
diff --git a/lib/6to5/transformation/transformers/es7-generator-comprehension.js b/lib/6to5/transformation/transformers/es7-generator-comprehension.js
index 3a102474c4..2034beef85 100644
--- a/lib/6to5/transformation/transformers/es7-generator-comprehension.js
+++ b/lib/6to5/transformation/transformers/es7-generator-comprehension.js
@@ -6,6 +6,7 @@ exports.ComprehensionExpression = function (node) {
 
   var body = [];
   var container = t.functionExpression(null, [], t.blockStatement(body), true);
+  container._aliasFunction = true;
 
   body.push(arrayComprehension._build(node, function () {
     return t.expressionStatement(t.yieldExpression(node.body));
diff --git a/lib/6to5/transformation/transformers/es7-object-spread.js b/lib/6to5/transformation/transformers/es7-object-spread.js
index 73aecb4283..ec10d971c5 100644
--- a/lib/6to5/transformation/transformers/es7-object-spread.js
+++ b/lib/6to5/transformation/transformers/es7-object-spread.js
@@ -1,16 +1,18 @@
 // https://github.com/sebmarkbage/ecmascript-rest-spread
 
 var t = require("../../types");
-var _ = require("lodash");
 
 exports.ObjectExpression = function (node) {
   var hasSpread = false;
-  _.each(node.properties, function (prop) {
+  var i;
+  var prop;
+  for (i in node.properties) {
+    prop = node.properties[i];
     if (t.isSpreadProperty(prop)) {
       hasSpread = true;
-      return false;
+      break;
     }
-  });
+  }
   if (!hasSpread) return;
 
   var args = [];
@@ -22,14 +24,15 @@ exports.ObjectExpression = function (node) {
     props = [];
   };
 
-  _.each(node.properties, function (prop) {
+  for (i in node.properties) {
+    prop = node.properties[i];
     if (t.isSpreadProperty(prop)) {
       push();
       args.push(prop.argument);
     } else {
       props.push(prop);
     }
-  });
+  }
 
   push();
 
diff --git a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
index 8c3c835023..560f2967c3 100644
--- a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
+++ b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
@@ -21,11 +21,13 @@ exports.MethodDefinition = function (node, parent, file, scope) {
   var memoId = t.memberExpression(t.thisExpression(), t.identifier(key));
   var doneId = t.memberExpression(t.thisExpression(), t.identifier(key + "Done"));
 
-  traverse(value, function (node) {
-    if (t.isFunction(node)) return;
+  traverse(value, {
+    enter: function (node) {
+      if (t.isFunction(node)) return;
 
-    if (t.isReturnStatement(node) && node.argument) {
-      node.argument = t.assignmentExpression("=", memoId, node.argument);
+      if (t.isReturnStatement(node) && node.argument) {
+        node.argument = t.assignmentExpression("=", memoId, node.argument);
+      }
     }
   });
 
diff --git a/lib/6to5/transformation/transformers/react.js b/lib/6to5/transformation/transformers/react.js
index 645e19a744..0f1de5be78 100644
--- a/lib/6to5/transformation/transformers/react.js
+++ b/lib/6to5/transformation/transformers/react.js
@@ -5,7 +5,6 @@
 
 var esutils = require("esutils");
 var t       = require("../../types");
-var _       = require("lodash");
 
 exports.XJSIdentifier = function (node) {
   if (esutils.keyword.isIdentifierName(node.name)) {
@@ -49,7 +48,7 @@ exports.XJSOpeningElement = {
       tagName = tagExpr.value;
     }
 
-    if (tagName && (/[a-z]/.exec(tagName[0]) || _.contains(tagName, "-"))) {
+    if (tagName && (/[a-z]/.exec(tagName[0]) || tagName.indexOf("-") >= 0)) {
       args.push(t.literal(tagName));
     } else {
       args.push(tagExpr);
@@ -105,14 +104,19 @@ exports.XJSOpeningElement = {
 exports.XJSElement = {
   exit: function (node) {
     var callExpr = node.openingElement;
+    var i;
+
+    for (i in node.children) {
+      var child = node.children[i];
 
-    _.each(node.children, function (child) {
       if (t.isLiteral(child)) {
         var lines = child.value.split(/\r\n|\n|\r/);
 
-        _.each(lines, function (line, i) {
-          var isFirstLine = i === 0;
-          var isLastLine = i === lines.length - 1;
+        for (i in lines) {
+          var line = lines[i];
+
+          var isFirstLine = i == 0;
+          var isLastLine = i == lines.length - 1;
 
           // replace rendered whitespace tabs with spaces
           var trimmedLine = line.replace(/\t/g, ' ');
@@ -130,15 +134,15 @@ exports.XJSElement = {
           if (trimmedLine) {
             callExpr.arguments.push(t.literal(trimmedLine));
           }
-        });
+        }
 
-        return;
+        continue;
       } else if (t.isXJSEmptyExpression(child)) {
-        return;
+        continue;
       }
 
       callExpr.arguments.push(child);
-    });
+    }
 
     return t.inherits(callExpr, node);
   }
@@ -171,11 +175,13 @@ var addDisplayName = function (id, call) {
   var props = first.properties;
   var safe = true;
 
-  _.each(props, function (prop) {
+  for (var i in props) {
+    prop = props[i];
     if (t.isIdentifier(prop.key, { name: "displayName" })) {
-      return safe = false;
+      safe = false;
+      break;
     }
-  });
+  }
 
   if (safe) {
     props.unshift(t.property("init", t.identifier("displayName"), t.literal(id)));
diff --git a/lib/6to5/transformation/transformers/spec-block-hoist-functions.js b/lib/6to5/transformation/transformers/spec-block-hoist-functions.js
new file mode 100644
index 0000000000..8d18464de0
--- /dev/null
+++ b/lib/6to5/transformation/transformers/spec-block-hoist-functions.js
@@ -0,0 +1,18 @@
+var t = require("../../types");
+
+exports.BlockStatement = function (node, parent) {
+  if (t.isFunction(parent)) return;
+
+  node.body = node.body.map(function (node) {
+    if (t.isFunction(node)) {
+      node.type = "FunctionExpression";
+      var declar = t.variableDeclaration("let", [
+        t.variableDeclarator(node.id, node)
+      ]);
+      declar._blockHoist = true;
+      return declar;
+    } else {
+      return node;
+    }
+  });
+};
diff --git a/lib/6to5/transformation/transformers/_member-expression-literals.js b/lib/6to5/transformation/transformers/spec-member-expression-literals.js
similarity index 100%
rename from lib/6to5/transformation/transformers/_member-expression-literals.js
rename to lib/6to5/transformation/transformers/spec-member-expression-literals.js
diff --git a/lib/6to5/transformation/transformers/spec-no-duplicate-properties.js b/lib/6to5/transformation/transformers/spec-no-duplicate-properties.js
new file mode 100644
index 0000000000..6c7e93e761
--- /dev/null
+++ b/lib/6to5/transformation/transformers/spec-no-duplicate-properties.js
@@ -0,0 +1,25 @@
+var t = require("../../types");
+
+exports.ObjectExpression = function (node, parent, file) {
+  var keys = [];
+
+  for (var i in node.properties) {
+    var prop = node.properties[i];
+    if (prop.computed || prop.kind !== "init") continue;
+
+    var key = prop.key;
+    if (t.isIdentifier(key)) {
+      key = key.name;
+    } else if (t.isLiteral(key)) {
+      key = key.value;
+    } else {
+      continue;
+    }
+
+    if (keys.indexOf(key) >= 0) {
+      throw file.errorWithNode(prop.key, "Duplicate property key");
+    } else {
+      keys.push(key);
+    }
+  }
+};
diff --git a/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js b/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js
new file mode 100644
index 0000000000..5af12108f1
--- /dev/null
+++ b/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js
@@ -0,0 +1,10 @@
+var t = require("../../types");
+
+exports.ForInStatement =
+exports.ForOfStatement = function (node, parent, file) {
+  var left = node.left;
+  if (t.isVariableDeclaration(left)) {
+    var declar = left.declarations[0];
+    if (declar.init) throw file.errorWithNode(declar, "No assignments allowed in for-in/of head");
+  }
+};
diff --git a/lib/6to5/transformation/transformers/_property-literals.js b/lib/6to5/transformation/transformers/spec-property-literals.js
similarity index 100%
rename from lib/6to5/transformation/transformers/_property-literals.js
rename to lib/6to5/transformation/transformers/spec-property-literals.js
diff --git a/lib/6to5/traverse/index.js b/lib/6to5/traverse/index.js
index 32bad31add..fcbdf1f587 100644
--- a/lib/6to5/traverse/index.js
+++ b/lib/6to5/traverse/index.js
@@ -4,14 +4,14 @@ var Scope = require("./scope");
 var t     = require("../types");
 var _     = require("lodash");
 
-function traverse(parent, callbacks, opts) {
+function traverse(parent, opts, scope) {
   // falsy node
   if (!parent) return;
 
   // array of nodes
   if (_.isArray(parent)) {
     _.each(parent, function (node) {
-      traverse(node, callbacks, opts);
+      traverse(node, opts, scope);
     });
     return;
   }
@@ -21,13 +21,6 @@ function traverse(parent, callbacks, opts) {
   if (!keys) return;
 
   opts = opts || {};
-  if (_.isArray(opts)) opts = { blacklist: opts };
-
-  // blacklist these node types from being traversed
-  var blacklistTypes = opts.blacklist || [];
-
-  // normalise callbacks
-  if (_.isFunction(callbacks)) callbacks = { enter: callbacks };
 
   for (var i in keys) {
     var key = keys[i];
@@ -41,7 +34,7 @@ function traverse(parent, callbacks, opts) {
       if (!node) return;
 
       // type is blacklisted
-      if (blacklistTypes.indexOf(node.type) > -1) return;
+      if (opts.blacklist && opts.blacklist.indexOf(node.type) > -1) return;
 
       // replace node
       var maybeReplace = function (result) {
@@ -58,12 +51,12 @@ function traverse(parent, callbacks, opts) {
       };
 
       //
-      var opts2 = { scope: opts.scope, blacklist: opts.blacklist };
-      if (t.isScope(node)) opts2.scope = new Scope(node, opts.scope);
+      var ourScope = scope;
+      if (t.isScope(node)) ourScope = new Scope(node, scope);
 
       // enter
-      if (callbacks.enter) {
-        var result = callbacks.enter(node, parent, opts2.scope);
+      if (opts.enter) {
+        var result = opts.enter(node, parent, ourScope);
         maybeReplace(result);
 
         // stop iteration
@@ -71,11 +64,11 @@ function traverse(parent, callbacks, opts) {
       }
 
       // traverse node
-      traverse(node, callbacks, opts2);
+      traverse(node, opts, ourScope);
 
       // exit
-      if (callbacks.exit) {
-        maybeReplace(callbacks.exit(node, parent, opts2.scope));
+      if (opts.exit) {
+        maybeReplace(opts.exit(node, parent, ourScope));
       }
     };
 
@@ -93,10 +86,9 @@ function traverse(parent, callbacks, opts) {
 
 traverse.removeProperties = function (tree) {
   var clear = function (node) {
-    delete node._scopeReferences;
     delete node._declarations;
     delete node.extendedRange;
-    delete node._parent;
+    delete node._scopeInfo;
     delete node._scope;
     delete node.tokens;
     delete node.range;
@@ -114,7 +106,7 @@ traverse.removeProperties = function (tree) {
   };
 
   clear(tree);
-  traverse(tree, clear);
+  traverse(tree, { enter: clear });
 
   return tree;
 };
@@ -130,12 +122,15 @@ traverse.hasType = function (tree, type, blacklistTypes) {
   // the type we're looking for is the same as the passed node
   if (tree.type === type) return true;
 
-  traverse(tree, function (node) {
-    if (node.type === type) {
-      has = true;
-      return false;
+  traverse(tree, {
+    blacklist: blacklistTypes,
+    enter: function (node) {
+      if (node.type === type) {
+        has = true;
+        return false;
+      }
     }
-  }, { blacklist: blacklistTypes });
+  });
 
   return has;
 };
diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index 50bb67243c..e5acde3244 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -18,31 +18,39 @@ function Scope(block, parent) {
   this.parent = parent;
   this.block  = block;
 
-  this.references = this.getReferences();
+  var info = this.getInfo();
+  this.references = info.references;
+  this.declarations = info.declarations;
 }
 
+var vars = require("jshint/src/vars");
+Scope.defaultDeclarations = _.flatten([vars.newEcmaIdentifiers, vars.node, vars.ecmaIdentifiers, vars.reservedVars].map(_.keys));
+
 Scope.add = function (node, references) {
   if (!node) return;
   _.defaults(references, t.getIds(node, true));
 };
 
 Scope.prototype.generateTemp = function (file, name) {
-    var id = file.generateUidIdentifier(name || "temp", this);
-    this.push({
-      key: id.name,
-      id: id
-    });
-    return id;
+  var id = file.generateUidIdentifier(name || "temp", this);
+  this.push({
+    key: id.name,
+    id: id
+  });
+  return id;
 };
 
-Scope.prototype.getReferences = function () {
+Scope.prototype.getInfo = function () {
   var block = this.block;
-  if (block._scopeReferences) return block._scopeReferences;
+  if (block._scopeInfo) return block._scopeInfo;
 
-  var references = block._scopeReferences = {};
+  var info = block._scopeInfo = {};
+  var references = info.references = {};
+  var declarations = info.declarations = {};
 
-  var add = function (node) {
+  var add = function (node, reference) {
     Scope.add(node, references);
+    if (!reference) Scope.add(node, declarations);
   };
 
   // ForStatement - left, init
@@ -74,28 +82,33 @@ Scope.prototype.getReferences = function () {
   // Program, Function - var variables
 
   if (t.isProgram(block) || t.isFunction(block)) {
-    traverse(block, function (node, parent, scope) {
-      if (t.isFor(node)) {
-        _.each(FOR_KEYS, function (key) {
-          var declar = node[key];
-          if (t.isVar(declar)) add(declar);
-        });
-      }
+    traverse(block, {
+      enter: function (node, parent, scope) {
+        if (t.isFor(node)) {
+          _.each(FOR_KEYS, function (key) {
+            var declar = node[key];
+            if (t.isVar(declar)) add(declar);
+          });
+        }
 
-      // this block is a function so we'll stop since none of the variables
-      // declared within are accessible
-      if (t.isFunction(node)) return false;
+        // this block is a function so we'll stop since none of the variables
+        // declared within are accessible
+        if (t.isFunction(node)) return false;
 
-      if (t.isIdentifier(node) && t.isReferenced(node, parent) && !scope.has(node.name)) {
-        add(node);
-      }
+        // function identifier doesn't belong to this scope
+        if (block.id && node === block.id) return;
 
-      // we've ran into a declaration!
-      // we'll let the BlockStatement scope deal with `let` declarations
-      if (t.isDeclaration(node) && !t.isLet(node)) {
-        add(node);
+        if (t.isIdentifier(node) && t.isReferenced(node, parent) && !scope.has(node.name)) {
+          add(node, true);
+        }
+
+        // we've ran into a declaration!
+        // we'll let the BlockStatement scope deal with `let` declarations unless
+        if (t.isDeclaration(node) && !t.isLet(node)) {
+          add(node);
+        }
       }
-    }, { scope: this });
+    }, this);
   }
 
   // Function - params, rest
@@ -107,7 +120,7 @@ Scope.prototype.getReferences = function () {
     });
   }
 
-  return references;
+  return info;
 };
 
 Scope.prototype.push = function (opts) {
@@ -134,26 +147,29 @@ Scope.prototype.add = function (node) {
   Scope.add(node, this.references);
 };
 
-Scope.prototype.get = function (id) {
-  return id && (this.getOwn(id) || this.parentGet(id));
+Scope.prototype.get = function (id, decl) {
+  return id && (this.getOwn(id, decl) || this.parentGet(id, decl));
 };
 
-Scope.prototype.getOwn = function (id) {
-  return _.has(this.references, id) && this.references[id];
+Scope.prototype.getOwn = function (id, decl) {
+  var refs = this.references;
+  if (decl) refs = this.declarations;
+  return _.has(refs, id) && refs[id];
 };
 
-Scope.prototype.parentGet = function (id) {
-  return this.parent && this.parent.get(id);
+Scope.prototype.parentGet = function (id, decl) {
+  return this.parent && this.parent.get(id, decl);
 };
 
-Scope.prototype.has = function (id) {
-  return id && (this.hasOwn(id) || this.parentHas(id));
+Scope.prototype.has = function (id, decl) {
+  return (id && (this.hasOwn(id, decl) || this.parentHas(id, decl))) ||
+         _.contains(Scope.defaultDeclarations, id);
 };
 
-Scope.prototype.hasOwn = function (id) {
-  return !!this.getOwn(id);
+Scope.prototype.hasOwn = function (id, decl) {
+  return !!this.getOwn(id, decl);
 };
 
-Scope.prototype.parentHas = function (id) {
-  return this.parent && this.parent.has(id);
+Scope.prototype.parentHas = function (id, decl) {
+  return this.parent && this.parent.has(id, decl);
 };
diff --git a/lib/6to5/types/builder-keys.json b/lib/6to5/types/builder-keys.json
index 45c315a50b..beca94c0e4 100644
--- a/lib/6to5/types/builder-keys.json
+++ b/lib/6to5/types/builder-keys.json
@@ -1,5 +1,6 @@
 {
   "ArrayExpression":         ["elements"],
+  "ArrowFunctionExpression": ["params", "body"],
   "AssignmentExpression":    ["operator", "left", "right"],
   "BinaryExpression":        ["operator", "left", "right"],
   "BlockStatement":          ["body"],
@@ -15,7 +16,6 @@
   "MemberExpression":        ["object", "property", "computed"],
   "NewExpression":           ["callee", "arguments"],
   "ObjectExpression":        ["properties"],
-  "ParenthesizedExpression": ["expression"],
   "Program":                 ["body"],
   "Property":                ["kind", "key", "value", "computed"],
   "ReturnStatement":         ["argument"],
@@ -24,5 +24,6 @@
   "UnaryExpression":         ["operator", "argument", "prefix"],
   "VariableDeclaration":     ["kind", "declarations"],
   "VariableDeclarator":      ["id", "init"],
+  "WithStatement":           ["object", "body"],
   "YieldExpression":         ["argument", "delegate"]
 }
diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index f741debaff..97be33b034 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -45,20 +45,20 @@ _.each(t.BUILDER_KEYS, function (keys, type) {
 
 t.ALIAS_KEYS = require("./alias-keys");
 
-var _aliases = {};
+t.FLIPPED_ALIAS_KEYS = {};
 
 _.each(t.ALIAS_KEYS, function (aliases, type) {
   _.each(aliases, function (alias) {
-    var types = _aliases[alias] = _aliases[alias] || [];
+    var types = t.FLIPPED_ALIAS_KEYS[alias] = t.FLIPPED_ALIAS_KEYS[alias] || [];
     types.push(type);
   });
 });
 
-_.each(_aliases, function (types, type) {
+_.each(t.FLIPPED_ALIAS_KEYS, function (types, type) {
   t[type.toUpperCase() + "_TYPES"] = types;
 
   var is = t["is" + type] = function (node, opts) {
-    return node && _.contains(types, node.type) && t.shallowEqual(node, opts);
+    return node && types.indexOf(node.type) >= 0 && t.shallowEqual(node, opts);
   };
 
   addAssert(type, is);
@@ -116,7 +116,7 @@ t.shallowEqual = function (actual, expected) {
 //
 
 t.isDynamic = function (node) {
-  if (t.isParenthesizedExpression(node) || t.isExpressionStatement(node)) {
+  if (t.isExpressionStatement(node)) {
     return t.isDynamic(node.expression);
   } else if (t.isIdentifier(node) || t.isLiteral(node) || t.isThisExpression(node)) {
     return false;
@@ -127,9 +127,10 @@ t.isDynamic = function (node) {
   }
 };
 
+// todo: https://github.com/eventualbuddha/ast-util/blob/9bf91c5ce8/lib/index.js#L454-L507
 t.isReferenced = function (node, parent) {
-  // we're a property key so we aren't referenced
-  if (t.isProperty(parent) && parent.key === node) return false;
+  // we're a property key and we aren't computed so we aren't referenced
+  if (t.isProperty(parent) && parent.key === node && !parent.computed) return false;
 
   // we're a variable declarator id so we aren't referenced
   if (t.isVariableDeclarator(parent) && parent.id === node) return false;
@@ -256,12 +257,11 @@ t.getIds = function (node, map, ignoreTypes) {
 
 t.getIds.nodes = {
   AssignmentExpression: "left",
-  ImportSpecifier: "id",
-  ExportSpecifier: "id",
+  ImportSpecifier: "name",
+  ExportSpecifier: "name",
   VariableDeclarator: "id",
   FunctionDeclaration: "id",
   ClassDeclaration: "id",
-  ParenthesizedExpression: "expression",
   MemeberExpression: "object",
   SpreadElement: "argument",
   Property: "value"
@@ -295,11 +295,6 @@ t.inheritsComments = function (child, parent) {
   return child;
 };
 
-t.removeComments = function (node) {
-  delete node.leadingComments;
-  delete node.trailingComments;
-};
-
 t.inherits = function (child, parent) {
   child.loc   = parent.loc;
   child.end   = parent.end;
@@ -312,3 +307,7 @@ t.inherits = function (child, parent) {
 t.getSpecifierName = function (specifier) {
   return specifier.name || specifier.id;
 };
+
+t.isSpecifierDefault = function (specifier) {
+  return t.isIdentifier(specifier.id) && specifier.id.name === "default";
+};
diff --git a/lib/6to5/types/visitor-keys.json b/lib/6to5/types/visitor-keys.json
index fc78a716e5..32292aa669 100644
--- a/lib/6to5/types/visitor-keys.json
+++ b/lib/6to5/types/visitor-keys.json
@@ -5,6 +5,7 @@
   "AssignmentExpression":      ["left", "right"],
   "AwaitExpression":           ["argument"],
   "BinaryExpression":          ["left", "right"],
+  "BindFunctionExpression":    ["callee", "arguments"],
   "BindMemberExpression":      ["object", "property", "arguments"],
   "BlockStatement":            ["body"],
   "BreakStatement":            ["label"],
@@ -13,6 +14,7 @@
   "ClassBody":                 ["body"],
   "ClassDeclaration":          ["id", "body", "superClass"],
   "ClassExpression":           ["id", "body", "superClass"],
+  "ClassProperty":             ["key"],
   "ComprehensionBlock":        ["left", "right", "body"],
   "ComprehensionExpression":   ["filter", "blocks", "body"],
   "ConditionalExpression":     ["test", "consequent", "alternate"],
@@ -43,8 +45,7 @@
   "NewExpression":             ["callee", "arguments"],
   "ObjectExpression":          ["properties"],
   "ObjectPattern":             ["properties"],
-  "ParenthesizedExpression":   ["expression"],
-  "BindFunctionExpression":    ["callee", "arguments"],
+  "PrivateDeclaration":        ["declarations"],
   "Program":                   ["body"],
   "Property":                  ["key", "value"],
   "ReturnStatement":           ["argument"],
diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 244ab28cab..cc33a85911 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -117,6 +117,8 @@ exports.buildDefineProperties = function (mutatorMap) {
 
     var propNode = t.property("init", map._key, mapNode, map._computed);
 
+    map.enumerable = t.literal(true);
+
     _.each(map, function (node, key) {
       if (key[0] === "_") return;
 
@@ -148,13 +150,10 @@ exports.template = function (name, nodes, keepExpression) {
   template = _.cloneDeep(template);
 
   if (!_.isEmpty(nodes)) {
-    traverse(template, function (node) {
-      if (t.isIdentifier(node) && _.has(nodes, node.name)) {
-        var newNode = nodes[node.name];
-        if (_.isString(newNode)) {
-          node.name = newNode;
-        } else {
-          return newNode;
+    traverse(template, {
+      enter: function (node) {
+        if (t.isIdentifier(node) && _.has(nodes, node.name)) {
+          return nodes[node.name];
         }
       }
     });
@@ -164,8 +163,6 @@ exports.template = function (name, nodes, keepExpression) {
 
   if (!keepExpression && t.isExpressionStatement(node)) {
     node = node.expression;
-
-    if (t.isParenthesizedExpression(node)) node = node.expression;
   }
 
   return node;
@@ -210,30 +207,34 @@ exports.repeat = function (width, cha) {
   return new Array(width + 1).join(cha);
 };
 
+exports.normaliseAst = function (ast, comments, tokens) {
+  if (ast && ast.type === "Program") {
+    return t.file(ast, comments || [], tokens || []);
+  } else {
+    throw new Error("Not a valid ast?");
+  }
+};
+
 exports.parse = function (opts, code, callback) {
   try {
     var comments = [];
     var tokens   = [];
 
     var ast = acorn.parse(code, {
-      allowReturnOutsideFunction: true,
-      preserveParens:             true,
-      ecmaVersion:                opts.experimental ? 7 : 6,
-      playground:                 opts.playground,
-      strictMode:                 true,
-      onComment:                  comments,
-      locations:                  true,
-      onToken:                    tokens,
-      ranges:                     true
+      allowImportExportEverywhere: true,
+      allowReturnOutsideFunction:  true,
+      ecmaVersion:                 opts.experimental ? 7 : 6,
+      playground:                  opts.playground,
+      strictMode:                  true,
+      onComment:                   comments,
+      locations:                   true,
+      onToken:                     tokens,
+      ranges:                      true
     });
 
     estraverse.attachComments(ast, comments, tokens);
 
-    ast = t.file(ast, comments, tokens);
-
-    traverse(ast, function (node, parent) {
-      node._parent = parent;
-    });
+    ast = exports.normaliseAst(ast, comments, tokens);
 
     if (callback) {
       return callback(ast);
diff --git a/package.json b/package.json
index 6b825114b2..39c62d068a 100644
--- a/package.json
+++ b/package.json
@@ -35,19 +35,21 @@
     "test": "make test"
   },
   "dependencies": {
-    "acorn-6to5": "0.9.1-12",
-    "ast-types": "0.6.5",
+    "acorn-6to5": "0.9.1-16",
+    "ast-types": "~0.6.1",
     "chokidar": "0.11.1",
     "commander": "2.5.0",
-    "es6-shim": "0.21.0",
-    "es6-symbol": "0.1.1",
+    "core-js": "^0.3.2",
     "estraverse": "1.8.0",
     "esutils": "1.1.6",
     "fs-readdir-recursive": "0.1.0",
+    "jshint": "^2.5.10",
     "lodash": "2.4.1",
     "mkdirp": "0.5.0",
     "private": "0.1.6",
+    "regenerator": "^0.8.2",
     "regexpu": "0.3.0",
+    "roadrunner": "^1.0.4",
     "source-map": "0.1.40",
     "source-map-support": "0.2.8"
   },
@@ -55,7 +57,6 @@
     "browserify": "6.3.2",
     "chai": "^1.9.2",
     "istanbul": "0.3.2",
-    "jshint": "2.5.10",
     "jshint-stylish": "^1.0.0",
     "matcha": "0.6.0",
     "mocha": "1.21.4",
diff --git a/test/_generator-helpers.js b/test/_generator-helpers.js
index 4d1a390058..4eef535ee0 100644
--- a/test/_generator-helpers.js
+++ b/test/_generator-helpers.js
@@ -20,14 +20,6 @@ exports.raise = function raise(argument) {
 };
 
 exports.assertAlreadyFinished = function assertAlreadyFinished(generator) {
-  try {
-    generator.next();
-    assert.ok(false, "should have thrown an exception");
-  } catch (err) {
-    assert.ok(err instanceof Error);
-    assert.strictEqual(
-      err.message,
-      "Generator has already finished"
-    );
-  }
+  var item = generator.next();
+  assert.ok(item.done && item.value === undefined, "not finished");
 };
diff --git a/test/api.js b/test/api.js
index 084a9f5c07..260c7f4483 100644
--- a/test/api.js
+++ b/test/api.js
@@ -8,6 +8,11 @@ suite("api", function () {
     assert.ok(!result.code);
   });
 
+  test("{ ast: false }", function () {
+    var result = transform("foo('bar');", { ast: false });
+    assert.ok(!result.ast);
+  });
+
   test("addDeclaration unknown", function () {
     var file = new File;
     assert.throws(function () {
diff --git a/test/bin.js b/test/bin.js
index 6107ad5506..8930fdf05f 100644
--- a/test/bin.js
+++ b/test/bin.js
@@ -1,3 +1,6 @@
+// skip these tests under instanbul since they're useless
+if (process.env.running_under_istanbul === '1') return;
+
 var readdir = require("fs-readdir-recursive");
 var helper  = require("./_helper");
 var assert  = require("assert");
diff --git a/test/fixtures/bin/6to5-node/filenames/in-files/bar.js b/test/fixtures/bin/6to5-node/filenames/in-files/bar.js
deleted file mode 100644
index 5e0f4fd877..0000000000
--- a/test/fixtures/bin/6to5-node/filenames/in-files/bar.js
+++ /dev/null
@@ -1,2 +0,0 @@
-var bar = () => console.log("bar");
-bar();
diff --git a/test/fixtures/bin/6to5-node/filenames/in-files/foo.js b/test/fixtures/bin/6to5-node/filenames/in-files/foo.js
deleted file mode 100644
index 6cbc6fbcfb..0000000000
--- a/test/fixtures/bin/6to5-node/filenames/in-files/foo.js
+++ /dev/null
@@ -1,2 +0,0 @@
-var foo = () => console.log("foo");
-foo();
diff --git a/test/fixtures/bin/6to5-node/filenames/options.json b/test/fixtures/bin/6to5-node/filenames/options.json
deleted file mode 100644
index 4caf67b360..0000000000
--- a/test/fixtures/bin/6to5-node/filenames/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "args": ["foo", "bar"]
-}
diff --git a/test/fixtures/bin/6to5-node/filenames/stdout.txt b/test/fixtures/bin/6to5-node/filenames/stdout.txt
deleted file mode 100644
index 3bd1f0e297..0000000000
--- a/test/fixtures/bin/6to5-node/filenames/stdout.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-foo
-bar
diff --git a/test/fixtures/bin/6to5/stdin --filename/stderr.txt b/test/fixtures/bin/6to5/stdin --filename/stderr.txt
index 40674d06f1..70be01b6f3 100644
--- a/test/fixtures/bin/6to5/stdin --filename/stderr.txt	
+++ b/test/fixtures/bin/6to5/stdin --filename/stderr.txt	
@@ -1 +1 @@
-SyntaxError: test.js: Unexpected character '#'
+SyntaxError: test.js: Unexpected token (2:10)
diff --git a/test/fixtures/bin/6to5/stdin --filename/stdin.txt b/test/fixtures/bin/6to5/stdin --filename/stdin.txt
index 6b84913768..1d931c7e85 100644
--- a/test/fixtures/bin/6to5/stdin --filename/stdin.txt	
+++ b/test/fixtures/bin/6to5/stdin --filename/stdin.txt	
@@ -1,3 +1,3 @@
-arr.map(x => {
-  $#!
+arr.map(function () {
+  return $]!;
 });
diff --git a/test/fixtures/generation/comments/2-space-multi-comment-with-space/actual.js b/test/fixtures/generation/comments/2-space-multi-comment-with-space/actual.js
new file mode 100644
index 0000000000..aa61a9c8fe
--- /dev/null
+++ b/test/fixtures/generation/comments/2-space-multi-comment-with-space/actual.js
@@ -0,0 +1,10 @@
+function test() {
+
+
+  /*
+   * this is comment
+   */
+
+
+  var i = 20;
+}
diff --git a/test/fixtures/generation/comments/2-space-multi-comment-with-space/expected.js b/test/fixtures/generation/comments/2-space-multi-comment-with-space/expected.js
new file mode 100644
index 0000000000..aa61a9c8fe
--- /dev/null
+++ b/test/fixtures/generation/comments/2-space-multi-comment-with-space/expected.js
@@ -0,0 +1,10 @@
+function test() {
+
+
+  /*
+   * this is comment
+   */
+
+
+  var i = 20;
+}
diff --git a/test/fixtures/generation/comments/.comment-only/actual.js b/test/fixtures/generation/comments/comment-only-with-space/actual.js
similarity index 82%
rename from test/fixtures/generation/comments/.comment-only/actual.js
rename to test/fixtures/generation/comments/comment-only-with-space/actual.js
index 2cc6cab81c..befcf38bfa 100644
--- a/test/fixtures/generation/comments/.comment-only/actual.js
+++ b/test/fixtures/generation/comments/comment-only-with-space/actual.js
@@ -1,6 +1,7 @@
+
 // from #23
+
 /**/
+
 /*
 */
-
-test
diff --git a/test/fixtures/generation/comments/comment-only-with-space/expected.js b/test/fixtures/generation/comments/comment-only-with-space/expected.js
new file mode 100644
index 0000000000..befcf38bfa
--- /dev/null
+++ b/test/fixtures/generation/comments/comment-only-with-space/expected.js
@@ -0,0 +1,7 @@
+
+// from #23
+
+/**/
+
+/*
+*/
diff --git a/test/fixtures/generation/comments/.comment-only/expected.js b/test/fixtures/generation/comments/comment-only/actual.js
similarity index 100%
rename from test/fixtures/generation/comments/.comment-only/expected.js
rename to test/fixtures/generation/comments/comment-only/actual.js
diff --git a/test/fixtures/generation/comments/comment-only/expected.js b/test/fixtures/generation/comments/comment-only/expected.js
new file mode 100644
index 0000000000..acfb1b9a7b
--- /dev/null
+++ b/test/fixtures/generation/comments/comment-only/expected.js
@@ -0,0 +1,4 @@
+// from #23
+/**/
+/*
+*/
diff --git a/test/fixtures/generation/comments/return-no-argument/expected.js b/test/fixtures/generation/comments/return-no-argument/expected.js
index c8f39a07a5..0dc96b3a8c 100644
--- a/test/fixtures/generation/comments/return-no-argument/expected.js
+++ b/test/fixtures/generation/comments/return-no-argument/expected.js
@@ -1,3 +1,3 @@
 (function () {
   return; // comment
-}());
+})();
diff --git a/test/fixtures/generation/edgecase/bitwise-precedence/expected.js b/test/fixtures/generation/edgecase/bitwise-precedence/expected.js
index 7c6969bfc8..ffcf91adde 100644
--- a/test/fixtures/generation/edgecase/bitwise-precedence/expected.js
+++ b/test/fixtures/generation/edgecase/bitwise-precedence/expected.js
@@ -1,3 +1,3 @@
 x | y ^ z;
-x | (y ^ z);
+x | y ^ z;
 (x | y) ^ z;
diff --git a/test/fixtures/generation/edgecase/floating-point/expected.js b/test/fixtures/generation/edgecase/floating-point/expected.js
index b38eebf513..f0c3126dbe 100644
--- a/test/fixtures/generation/edgecase/floating-point/expected.js
+++ b/test/fixtures/generation/edgecase/floating-point/expected.js
@@ -1,2 +1,2 @@
 1.1.valueOf();
-(1e+300).valueOf();
+1e+300.valueOf();
diff --git a/test/fixtures/generation/edgecase/for-in-no-in/expected.js b/test/fixtures/generation/edgecase/for-in-no-in/expected.js
index f84b95ae6b..029b11e515 100644
--- a/test/fixtures/generation/edgecase/for-in-no-in/expected.js
+++ b/test/fixtures/generation/edgecase/for-in-no-in/expected.js
@@ -1,12 +1,12 @@
 for (var i = (1 in []) in []);
-for (var i = 1 in [] in []);
+for (var i = 1 in ([] in []));
 for (var i = (10 * 10 in []) in []);
 for (var i = (10 + 10 in []) in []);
 for (var i = 10 + (10 in []) in []);
-for (var i = 10 + 10 in [] in []);
+for (var i = 10 + 10 in ([] in []));
 for (var i = (1 in []);;);
 for ((1 in []);;);
 for (1 * (1 in []);;);
 for (1 * (1 + 1 in []);;);
-for (1 * ((1 + 1) in []);;);
+for (1 * (1 + 1 in []);;);
 for (1 * (1 + (1 in []));;);
diff --git a/test/fixtures/generation/edgecase/new-precedence/actual.js b/test/fixtures/generation/edgecase/new-precedence/actual.js
index 56044a7b99..7100c69c3d 100644
--- a/test/fixtures/generation/edgecase/new-precedence/actual.js
+++ b/test/fixtures/generation/edgecase/new-precedence/actual.js
@@ -1,9 +1,9 @@
 new (a().b)();
 new a().b();
 new (a()).b();
-new (a());
-new new a(a);
-new (new a)(a);
+new (a())();
+new new a(a)();
+new (new a())(a);
 (new a()).test;
 (new a().test);
-(new (a().test));
+(new (a().test)());
diff --git a/test/fixtures/generation/edgecase/new-precedence/expected.js b/test/fixtures/generation/edgecase/new-precedence/expected.js
index 7100c69c3d..646afe94da 100644
--- a/test/fixtures/generation/edgecase/new-precedence/expected.js
+++ b/test/fixtures/generation/edgecase/new-precedence/expected.js
@@ -1,9 +1,9 @@
 new (a().b)();
 new a().b();
-new (a()).b();
+new (a().b)();
 new (a())();
 new new a(a)();
-new (new a())(a);
-(new a()).test;
-(new a().test);
-(new (a().test)());
+new new a()(a);
+new a().test;
+new a().test;
+new (a().test)();
diff --git a/test/fixtures/generation/edgecase/variable-declaration/expected.js b/test/fixtures/generation/edgecase/variable-declaration/expected.js
index 12407627ec..0af0dd6ac0 100644
--- a/test/fixtures/generation/edgecase/variable-declaration/expected.js
+++ b/test/fixtures/generation/edgecase/variable-declaration/expected.js
@@ -1,4 +1,4 @@
-var fact5 = function fact(n) {
+var fact5 = (function fact(n) {
   if (n <= 1) return 1;
   return n * fact(n - 1);
-}(5);
+})(5);
diff --git a/test/fixtures/generation/harmony-edgecase/export-default-declaration/expected.js b/test/fixtures/generation/harmony-edgecase/export-default-declaration/expected.js
index 2dd8e728b3..c33f5633d7 100644
--- a/test/fixtures/generation/harmony-edgecase/export-default-declaration/expected.js
+++ b/test/fixtures/generation/harmony-edgecase/export-default-declaration/expected.js
@@ -1 +1 @@
-export default function a() {};
+export default function a() {}
diff --git a/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/actual.js b/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/actual.js
index 729d7ce58e..1a9597b14b 100644
--- a/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/actual.js
+++ b/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/actual.js
@@ -4,8 +4,8 @@ export default [];
 export default foo;
 export default function () {};
 export default class {};
-export default function foo() {};
-export default class Foo {};
+export default function foo() {}
+export default class Foo {}
 export * from "foo";
 export { foo } from "foo";
 export { foo, bar } from "foo";
diff --git a/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/expected.js b/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/expected.js
index 729d7ce58e..1a9597b14b 100644
--- a/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/expected.js
+++ b/test/fixtures/generation/types/ExportDeclaration-ExportSpecifier-ExportBatchSpecifier/expected.js
@@ -4,8 +4,8 @@ export default [];
 export default foo;
 export default function () {};
 export default class {};
-export default function foo() {};
-export default class Foo {};
+export default function foo() {}
+export default class Foo {}
 export * from "foo";
 export { foo } from "foo";
 export { foo, bar } from "foo";
diff --git a/test/fixtures/generation/types/ImportDeclaration-ImportSpecifier-ImportBatchSpecifier/expected.js b/test/fixtures/generation/types/ImportDeclaration-ImportSpecifier-ImportBatchSpecifier/expected.js
index b7a4a4b9fd..ed9cfef590 100644
--- a/test/fixtures/generation/types/ImportDeclaration-ImportSpecifier-ImportBatchSpecifier/expected.js
+++ b/test/fixtures/generation/types/ImportDeclaration-ImportSpecifier-ImportBatchSpecifier/expected.js
@@ -1,6 +1,6 @@
 import "foo";
 import foo from "foo";
-import { default as foo } from "foo";
+import foo from "foo";
 import * as foo from "foo";
 import foo, { baz as xyz } from "foo";
 import { bar } from "foo";
diff --git a/test/fixtures/generation/types/ParenthesizedExpression/actual.js b/test/fixtures/generation/types/ParenthesizedExpression/actual.js
deleted file mode 100644
index 5d7b0fd7c0..0000000000
--- a/test/fixtures/generation/types/ParenthesizedExpression/actual.js
+++ /dev/null
@@ -1,2 +0,0 @@
-(foo());
-(5 * 6);
diff --git a/test/fixtures/generation/types/ParenthesizedExpression/expected.js b/test/fixtures/generation/types/ParenthesizedExpression/expected.js
deleted file mode 100644
index 5d7b0fd7c0..0000000000
--- a/test/fixtures/generation/types/ParenthesizedExpression/expected.js
+++ /dev/null
@@ -1,2 +0,0 @@
-(foo());
-(5 * 6);
diff --git a/test/fixtures/generation/types/PrivateDeclaration/actual.js b/test/fixtures/generation/types/PrivateDeclaration/actual.js
new file mode 100644
index 0000000000..c9c6b03ef6
--- /dev/null
+++ b/test/fixtures/generation/types/PrivateDeclaration/actual.js
@@ -0,0 +1,7 @@
+private A;
+private B, C;
+
+class Test {
+  private A;
+  private B, C;
+}
diff --git a/test/fixtures/generation/types/PrivateDeclaration/expected.js b/test/fixtures/generation/types/PrivateDeclaration/expected.js
new file mode 100644
index 0000000000..c9c6b03ef6
--- /dev/null
+++ b/test/fixtures/generation/types/PrivateDeclaration/expected.js
@@ -0,0 +1,7 @@
+private A;
+private B, C;
+
+class Test {
+  private A;
+  private B, C;
+}
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-default/expected.js b/test/fixtures/transformation/.es6-modules-system/exports-default/expected.js
deleted file mode 100644
index 7e90c983cb..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/exports-default/expected.js
+++ /dev/null
@@ -1,32 +0,0 @@
-System.register("actual", [], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  function _anonymous() {}
-  var _anonymous2;
-
-  function foo() {}
-  var Foo;
-
-  return {
-    setters: [],
-    execute: function () {
-      _export("default", 42);
-
-      _export("default", {});
-
-      _export("default", []);
-
-      _export("default", foo);
-
-      _export("default", _anonymous);
-
-      _export("default", _anonymous2 = function _anonymous2() {});
-
-      _export("default", foo);
-
-      _export("default", Foo = function Foo() {});
-    }
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-from/expected.js b/test/fixtures/transformation/.es6-modules-system/exports-from/expected.js
deleted file mode 100644
index 680bae3c9f..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/exports-from/expected.js
+++ /dev/null
@@ -1,34 +0,0 @@
-System.register("actual", ["foo"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var _localExports = ['foo', 'bar', 'default'];
-
-  return {
-    setters: [
-    function(m) {
-      _export("foo", m.foo);
-
-      _export("foo", m.foo);
-
-      _export("bar", m.bar);
-
-      _export("bar", m.foo);
-
-      _export("default", m.foo);
-
-      _export("default", m.foo);
-
-      _export("bar", m.bar);
-
-      for (var p in m) {
-        if (_localExports.indexOf(i) == -1)
-          _export(p, m[p]);
-      }
-    }
-    ],
-    execute: function () {
-    }
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-named/expected.js b/test/fixtures/transformation/.es6-modules-system/exports-named/expected.js
deleted file mode 100644
index e0f17a11f9..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/exports-named/expected.js
+++ /dev/null
@@ -1,26 +0,0 @@
-System.register("actual", [], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  return {
-    setters: [
-    function(m) {
-      _export("foo", m.foo);
-
-      _export("foo", m.foo);
-
-      _export("bar", m.bar);
-
-      _export("bar", m.foo);
-
-      _export("default", m.foo);
-
-      _export("default", m.foo);
-
-      _export("bar", m.bar);
-    }],
-    execute: function () {
-    }
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-variable/expected.js b/test/fixtures/transformation/.es6-modules-system/exports-variable/expected.js
deleted file mode 100644
index fd8e2dba9e..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/exports-variable/expected.js
+++ /dev/null
@@ -1,37 +0,0 @@
-System.register("actual", [], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var foo;
-  var foo2;
-  var foo3;
-  var foo4;
-  var foo5;
-  var foo6;
-  function foo7() {}
-  _export("foo7", foo7);
-
-  var foo8;
-
-  return {
-    setters: [],
-    execute: function () {
-      _export("foo", foo = 1);
-
-      _export("foo2", foo2 = function () {});
-
-      _export("foo3", foo3);
-
-      _export("foo4", foo4 = 2);
-
-      _export("foo5", foo5);
-
-      _export("foo6", foo6 = 3);
-
-      _export("foo7", foo7);
-
-      _export("foo8", foo8 = function foo8() {});
-    }
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/hoist-function-exports/expected.js b/test/fixtures/transformation/.es6-modules-system/hoist-function-exports/expected.js
deleted file mode 100644
index 6e20c45e3d..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/hoist-function-exports/expected.js
+++ /dev/null
@@ -1,25 +0,0 @@
-System.register("actual", ["./evens"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var isEven;
-  function nextOdd(n) {
-    return isEven(n) ? n + 1 : n + 2;
-  }
-  _export("nextOdd", nextOdd);
-
-  var isOdd;
-  return {
-    setters: [function (m) {
-      isEven = m.isEven;
-    }],
-    execute: function () {
-      _export("isOdd", isOdd = (function (isEven) {
-        return function (n) {
-          return !isEven(n);
-        };
-      })(isEven));
-    }
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-default/expected.js b/test/fixtures/transformation/.es6-modules-system/imports-default/expected.js
deleted file mode 100644
index c2bd28f729..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/imports-default/expected.js
+++ /dev/null
@@ -1,14 +0,0 @@
-System.register("actual", ["foo"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var foo;
-  return {
-    setters: [function (m) {
-      foo = m.default;
-      foo = m.default;
-    }],
-    execute: function () {}
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-glob/expected.js b/test/fixtures/transformation/.es6-modules-system/imports-glob/expected.js
deleted file mode 100644
index cb6d64cc04..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/imports-glob/expected.js
+++ /dev/null
@@ -1,13 +0,0 @@
-System.register("actual", ["foo"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var foo;
-  return {
-    setters: [function (m) {
-      foo = m;
-    }],
-    execute: function () {}
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-mixing/expected.js b/test/fixtures/transformation/.es6-modules-system/imports-mixing/expected.js
deleted file mode 100644
index 77c3348166..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/imports-mixing/expected.js
+++ /dev/null
@@ -1,14 +0,0 @@
-System.register("actual", ["foo"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var foo, xyz;
-  return {
-    setters: [function (m) {
-      foo = m.default;
-      xyz = m.baz;
-    }],
-    execute: function () {}
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-named/expected.js b/test/fixtures/transformation/.es6-modules-system/imports-named/expected.js
deleted file mode 100644
index 1610dafb58..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/imports-named/expected.js
+++ /dev/null
@@ -1,18 +0,0 @@
-System.register("actual", ["foo"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var bar, baz, xyz;
-  return {
-    setters: [function (m) {
-      bar = m.bar;
-      bar = m.bar;
-      baz = m.baz;
-      baz = m.bar;
-      baz = m.bar;
-      xyz = m.xyz;
-    }],
-    execute: function () {}
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/imports/expected.js b/test/fixtures/transformation/.es6-modules-system/imports/expected.js
deleted file mode 100644
index 809982b1c2..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/imports/expected.js
+++ /dev/null
@@ -1,10 +0,0 @@
-System.register("actual", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  return {
-    setters: [null, null, null],
-    execute: function () {}
-  };
-});
diff --git a/test/fixtures/transformation/.es6-modules-system/overview/expected.js b/test/fixtures/transformation/.es6-modules-system/overview/expected.js
deleted file mode 100644
index 420d145069..0000000000
--- a/test/fixtures/transformation/.es6-modules-system/overview/expected.js
+++ /dev/null
@@ -1,24 +0,0 @@
-System.register("actual", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
-  "use strict";
-
-  var __moduleName = "actual";
-
-  var foo, bar;
-  var test;
-
-  return {
-    setters: [function (m) {
-      foo = m.default;
-      foo = m;
-      bar = m.bar;
-      bar = m.foo;
-    }, null, null],
-    execute: function () {
-      _export("test", test);
-
-      _export("test", test = 5);
-
-      _export("default", test);
-    }
-  };
-});
diff --git a/test/fixtures/transformation/api/unknown-module-formatter/options.json b/test/fixtures/transformation/api/unknown-module-formatter/options.json
new file mode 100644
index 0000000000..834f1d0a2e
--- /dev/null
+++ b/test/fixtures/transformation/api/unknown-module-formatter/options.json
@@ -0,0 +1,4 @@
+{
+  "modules": "foobar",
+  "throws": "Unknown module formatter type \"foobar\""
+}
diff --git a/test/fixtures/transformation/errors/syntax/actual.js b/test/fixtures/transformation/errors/syntax/actual.js
index 1ef7cb5d40..1d931c7e85 100644
--- a/test/fixtures/transformation/errors/syntax/actual.js
+++ b/test/fixtures/transformation/errors/syntax/actual.js
@@ -1,3 +1,3 @@
 arr.map(function () {
-  return $#!;
+  return $]!;
 });
diff --git a/test/fixtures/transformation/errors/syntax/options.json b/test/fixtures/transformation/errors/syntax/options.json
index 72ad0f0daf..7c05159f45 100644
--- a/test/fixtures/transformation/errors/syntax/options.json
+++ b/test/fixtures/transformation/errors/syntax/options.json
@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected character '#'"
+  "throws": "Unexpected token (2:10)"
 }
diff --git a/test/fixtures/transformation/es5-property-methods-assignment/getter-and-setter/expected.js b/test/fixtures/transformation/es5-property-methods-assignment/getter-and-setter/expected.js
index 23467f3675..9ef3d3265d 100644
--- a/test/fixtures/transformation/es5-property-methods-assignment/getter-and-setter/expected.js
+++ b/test/fixtures/transformation/es5-property-methods-assignment/getter-and-setter/expected.js
@@ -8,7 +8,8 @@ var obj = (function (_obj) {
       },
       set: function (value) {
         this._foo = value;
-      }
+      },
+      enumerable: true
     }
   });
 
diff --git a/test/fixtures/transformation/es5-property-methods-assignment/getter/expected.js b/test/fixtures/transformation/es5-property-methods-assignment/getter/expected.js
index fda0188e6e..c519a4ee8d 100644
--- a/test/fixtures/transformation/es5-property-methods-assignment/getter/expected.js
+++ b/test/fixtures/transformation/es5-property-methods-assignment/getter/expected.js
@@ -5,7 +5,8 @@ var obj = (function (_obj) {
     foo: {
       get: function () {
         return 5 + 5;
-      }
+      },
+      enumerable: true
     }
   });
 
diff --git a/test/fixtures/transformation/es5-property-methods-assignment/setter/expected.js b/test/fixtures/transformation/es5-property-methods-assignment/setter/expected.js
index 3320d6ee41..780fb983a8 100644
--- a/test/fixtures/transformation/es5-property-methods-assignment/setter/expected.js
+++ b/test/fixtures/transformation/es5-property-methods-assignment/setter/expected.js
@@ -5,7 +5,8 @@ var obj = (function (_obj) {
     foo: {
       set: function (value) {
         this._foo = value;
-      }
+      },
+      enumerable: true
     }
   });
 
diff --git a/test/fixtures/transformation/es6-classes/accessing-super-class/expected.js b/test/fixtures/transformation/es6-classes/accessing-super-class/expected.js
index 0c54fbc4e6..fd7527b70a 100644
--- a/test/fixtures/transformation/es6-classes/accessing-super-class/expected.js
+++ b/test/fixtures/transformation/es6-classes/accessing-super-class/expected.js
@@ -1,8 +1,8 @@
 "use strict";
 
 var _slice = Array.prototype.slice;
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -10,36 +10,32 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var Test = (function (Foo) {
-  var Test = function Test() {
-    woops["super"].test();
-    Foo.call(this);
-    Foo.prototype.test.call(this);
-    foob(Foo);
+var Test = function Test() {
+  woops["super"].test();
+  Foo.call(this);
+  Foo.prototype.test.call(this);
+  foob(Foo);
 
-    Foo.call.apply(Foo, [this].concat(_slice.call(arguments)));
-    Foo.call.apply(Foo, [this, "test"].concat(_slice.call(arguments)));
+  Foo.call.apply(Foo, [this].concat(_slice.call(arguments)));
+  Foo.call.apply(Foo, [this, "test"].concat(_slice.call(arguments)));
 
-    Foo.prototype.test.call.apply(Foo.prototype, [this].concat(_slice.call(arguments)));
-    Foo.prototype.test.call.apply(Foo.prototype, [this, "test"].concat(_slice.call(arguments)));
-  };
+  Foo.prototype.test.call.apply(Foo.prototype, [this].concat(_slice.call(arguments)));
+  Foo.prototype.test.call.apply(Foo.prototype, [this, "test"].concat(_slice.call(arguments)));
+};
 
-  _extends(Test, Foo);
+_inherits(Test, Foo);
 
-  Test.prototype.test = function () {
-    Foo.prototype.test.call(this);
-    Foo.prototype.test.call.apply(Foo.prototype.test, [this].concat(_slice.call(arguments)));
-    Foo.prototype.test.call.apply(Foo.prototype.test, [this, "test"].concat(_slice.call(arguments)));
-  };
+Test.prototype.test = function () {
+  Foo.prototype.test.call(this);
+  Foo.prototype.test.call.apply(Foo.prototype.test, [this].concat(_slice.call(arguments)));
+  Foo.prototype.test.call.apply(Foo.prototype.test, [this, "test"].concat(_slice.call(arguments)));
+};
 
-  Test.foo = function () {
-    Foo.foo.call(this);
-    Foo.foo.call.apply(Foo.foo, [this].concat(_slice.call(arguments)));
-    Foo.foo.call.apply(Foo.foo, [this, "test"].concat(_slice.call(arguments)));
-  };
-
-  return Test;
-})(Foo);
+Test.foo = function () {
+  Foo.foo.call(this);
+  Foo.foo.call.apply(Foo.foo, [this].concat(_slice.call(arguments)));
+  Foo.foo.call.apply(Foo.foo, [this, "test"].concat(_slice.call(arguments)));
+};
diff --git a/test/fixtures/transformation/es6-classes/accessing-super-properties/expected.js b/test/fixtures/transformation/es6-classes/accessing-super-properties/expected.js
index dec479103b..64df221c08 100644
--- a/test/fixtures/transformation/es6-classes/accessing-super-properties/expected.js
+++ b/test/fixtures/transformation/es6-classes/accessing-super-properties/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,16 +9,12 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var Test = (function (Foo) {
-  var Test = function Test() {
-    Foo.prototype.test;
-    Foo.prototype.test.whatever;
-  };
+var Test = function Test() {
+  Foo.prototype.test;
+  Foo.prototype.test.whatever;
+};
 
-  _extends(Test, Foo);
-
-  return Test;
-})(Foo);
+_inherits(Test, Foo);
diff --git a/test/fixtures/transformation/es6-classes/calling-super-properties/expected.js b/test/fixtures/transformation/es6-classes/calling-super-properties/expected.js
index 28aa2cb0ea..d13ee876cd 100644
--- a/test/fixtures/transformation/es6-classes/calling-super-properties/expected.js
+++ b/test/fixtures/transformation/es6-classes/calling-super-properties/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,20 +9,16 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var Test = (function (Foo) {
-  var Test = function Test() {
-    Foo.prototype.test.whatever();
-    Foo.prototype.test.call(this);
-  };
+var Test = function Test() {
+  Foo.prototype.test.whatever();
+  Foo.prototype.test.call(this);
+};
 
-  _extends(Test, Foo);
+_inherits(Test, Foo);
 
-  Test.test = function () {
-    return Foo.wow.call(this);
-  };
-
-  return Test;
-})(Foo);
+Test.test = function () {
+  return Foo.wow.call(this);
+};
diff --git a/test/fixtures/transformation/es6-classes/constructor/expected.js b/test/fixtures/transformation/es6-classes/constructor/expected.js
index 200e36b4c5..00e97931b5 100644
--- a/test/fixtures/transformation/es6-classes/constructor/expected.js
+++ b/test/fixtures/transformation/es6-classes/constructor/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,19 +9,15 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
 var Test = function Test() {
   this.state = "test";
 };
 
-var Foo = (function (Bar) {
-  var Foo = function Foo() {
-    this.state = "test";
-  };
+var Foo = function Foo() {
+  this.state = "test";
+};
 
-  _extends(Foo, Bar);
-
-  return Foo;
-})(Bar);
+_inherits(Foo, Bar);
diff --git a/test/fixtures/transformation/es6-classes/instance-getter-and-setter/expected.js b/test/fixtures/transformation/es6-classes/instance-getter-and-setter/expected.js
index 0fb4c995d3..391423e078 100644
--- a/test/fixtures/transformation/es6-classes/instance-getter-and-setter/expected.js
+++ b/test/fixtures/transformation/es6-classes/instance-getter-and-setter/expected.js
@@ -1,23 +1,20 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var Test = (function () {
-  var Test = function Test() {};
+var Test = function Test() {};
 
-  _classProps(Test, null, {
-    test: {
-      get: function () {
-        return 5 + 5;
-      },
-      set: function (val) {
-        this._test = val;
-      }
-    }
-  });
-
-  return Test;
-})();
+_prototypeProperties(Test, null, {
+  test: {
+    get: function () {
+      return 5 + 5;
+    },
+    set: function (val) {
+      this._test = val;
+    },
+    enumerable: true
+  }
+});
diff --git a/test/fixtures/transformation/es6-classes/instance-getter/expected.js b/test/fixtures/transformation/es6-classes/instance-getter/expected.js
index 0d50b8e732..6fa5d59400 100644
--- a/test/fixtures/transformation/es6-classes/instance-getter/expected.js
+++ b/test/fixtures/transformation/es6-classes/instance-getter/expected.js
@@ -1,20 +1,17 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var Test = (function () {
-  var Test = function Test() {};
+var Test = function Test() {};
 
-  _classProps(Test, null, {
-    test: {
-      get: function () {
-        return 5 + 5;
-      }
-    }
-  });
-
-  return Test;
-})();
+_prototypeProperties(Test, null, {
+  test: {
+    get: function () {
+      return 5 + 5;
+    },
+    enumerable: true
+  }
+});
diff --git a/test/fixtures/transformation/es6-classes/instance-method/expected.js b/test/fixtures/transformation/es6-classes/instance-method/expected.js
index bedd164fe5..8e4305baca 100644
--- a/test/fixtures/transformation/es6-classes/instance-method/expected.js
+++ b/test/fixtures/transformation/es6-classes/instance-method/expected.js
@@ -1,11 +1,7 @@
 "use strict";
 
-var Test = (function () {
-  var Test = function Test() {};
+var Test = function Test() {};
 
-  Test.prototype.test = function () {
-    return 5 + 5;
-  };
-
-  return Test;
-})();
+Test.prototype.test = function () {
+  return 5 + 5;
+};
diff --git a/test/fixtures/transformation/es6-classes/instance-setter/expected.js b/test/fixtures/transformation/es6-classes/instance-setter/expected.js
index 87f8e40dde..2ffe02b551 100644
--- a/test/fixtures/transformation/es6-classes/instance-setter/expected.js
+++ b/test/fixtures/transformation/es6-classes/instance-setter/expected.js
@@ -1,20 +1,17 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var Test = (function () {
-  var Test = function Test() {};
+var Test = function Test() {};
 
-  _classProps(Test, null, {
-    test: {
-      set: function (val) {
-        this._test = val;
-      }
-    }
-  });
-
-  return Test;
-})();
+_prototypeProperties(Test, null, {
+  test: {
+    set: function (val) {
+      this._test = val;
+    },
+    enumerable: true
+  }
+});
diff --git a/test/fixtures/transformation/es6-classes/static/expected.js b/test/fixtures/transformation/es6-classes/static/expected.js
index 1ef2108334..e7d7df4451 100644
--- a/test/fixtures/transformation/es6-classes/static/expected.js
+++ b/test/fixtures/transformation/es6-classes/static/expected.js
@@ -1,21 +1,18 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var A = (function () {
-  var A = function A() {};
+var A = function A() {};
 
-  A.a = function () {};
+A.a = function () {};
 
-  _classProps(A, {
-    b: {
-      get: function () {},
-      set: function (b) {}
-    }
-  });
-
-  return A;
-})();
+_prototypeProperties(A, {
+  b: {
+    get: function () {},
+    set: function (b) {},
+    enumerable: true
+  }
+});
diff --git a/test/fixtures/transformation/es6-classes/super-class-id-member-expression/expected.js b/test/fixtures/transformation/es6-classes/super-class-id-member-expression/expected.js
index bce35e1528..70de0712ea 100644
--- a/test/fixtures/transformation/es6-classes/super-class-id-member-expression/expected.js
+++ b/test/fixtures/transformation/es6-classes/super-class-id-member-expression/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,25 +9,21 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var BaseController = (function (Chaplin) {
-  var BaseController = function BaseController() {
+var BaseController = function BaseController() {
+  if (Chaplin.Controller) {
     Chaplin.Controller.apply(this, arguments);
-  };
+  }
+};
 
-  _extends(BaseController, Chaplin.Controller);
+_inherits(BaseController, Chaplin.Controller);
 
-  return BaseController;
-})(Chaplin);
-
-var BaseController2 = (function (Chaplin) {
-  var BaseController2 = function BaseController2() {
+var BaseController2 = function BaseController2() {
+  if (Chaplin.Controller.Another) {
     Chaplin.Controller.Another.apply(this, arguments);
-  };
+  }
+};
 
-  _extends(BaseController2, Chaplin.Controller.Another);
-
-  return BaseController2;
-})(Chaplin);
+_inherits(BaseController2, Chaplin.Controller.Another);
diff --git a/test/fixtures/transformation/es6-classes/super-class-id-non-identifiers/expected.js b/test/fixtures/transformation/es6-classes/super-class-id-non-identifiers/expected.js
index 353a8c289b..15f2fd75c4 100644
--- a/test/fixtures/transformation/es6-classes/super-class-id-non-identifiers/expected.js
+++ b/test/fixtures/transformation/es6-classes/super-class-id-non-identifiers/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,15 +9,15 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var Q = (function (_ref) {
-  var Q = function Q() {
-    _ref.apply(this, arguments);
-  };
+var _QSuper = function () {};
 
-  _extends(Q, _ref);
+var Q = function Q() {
+  if (_QSuper) {
+    _QSuper.apply(this, arguments);
+  }
+};
 
-  return Q;
-})(function () {});
+_inherits(Q, _QSuper);
diff --git a/test/fixtures/transformation/es6-classes/super-class/expected.js b/test/fixtures/transformation/es6-classes/super-class/expected.js
index c8c1fb516f..d7a906d848 100644
--- a/test/fixtures/transformation/es6-classes/super-class/expected.js
+++ b/test/fixtures/transformation/es6-classes/super-class/expected.js
@@ -1,7 +1,7 @@
 "use strict";
 
-var _extends = function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+var _inherits = function (child, parent) {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -9,15 +9,13 @@ var _extends = function (child, parent) {
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 };
 
-var Test = (function (Foo) {
-  var Test = function Test() {
+var Test = function Test() {
+  if (Foo) {
     Foo.apply(this, arguments);
-  };
+  }
+};
 
-  _extends(Test, Foo);
-
-  return Test;
-})(Foo);
+_inherits(Test, Foo);
diff --git a/test/fixtures/transformation/es6-constants/block-scoped/exec.js b/test/fixtures/transformation/es6-constants/block-scoped/exec.js
new file mode 100644
index 0000000000..c46d684d19
--- /dev/null
+++ b/test/fixtures/transformation/es6-constants/block-scoped/exec.js
@@ -0,0 +1,3 @@
+const bar = 123;
+{ const bar = 456; }
+assert.equal(bar, 123);
diff --git a/test/fixtures/transformation/es6-destructuring/es7-object-rest/expected.js b/test/fixtures/transformation/es6-destructuring/es7-object-rest/expected.js
index 50857a50a3..8a6ade7f6f 100644
--- a/test/fixtures/transformation/es6-destructuring/es7-object-rest/expected.js
+++ b/test/fixtures/transformation/es6-destructuring/es7-object-rest/expected.js
@@ -1,6 +1,6 @@
 "use strict";
 
-var _objectSpread = function (obj, keys) {
+var _objectWithoutProperties = function (obj, keys) {
   var target = {};
   for (var i in obj) {
     if (keys.indexOf(i) >= 0) continue;
@@ -11,12 +11,12 @@ var _objectSpread = function (obj, keys) {
   return target;
 };
 
-var x = _objectSpread(z, []);
+var x = _objectWithoutProperties(z, []);
 
 var x = z.x;
-var y = _objectSpread(z, ["x"]);
+var y = _objectWithoutProperties(z, ["x"]);
 
 (function (_ref) {
   var x = _ref.x;
-  var y = _objectSpread(_ref, ["x"]);
+  var y = _objectWithoutProperties(_ref, ["x"]);
 });
diff --git a/test/fixtures/transformation/es6-generators/function-declaration-hoisting-should-work-even-if-the-declarations-are-out-of-order/exec.js b/test/fixtures/transformation/es6-generators/function-declaration-hoisting-should-work-even-if-the-declarations-are-out-of-order/exec.js
index 202b84a0d1..1b1de7c33b 100644
--- a/test/fixtures/transformation/es6-generators/function-declaration-hoisting-should-work-even-if-the-declarations-are-out-of-order/exec.js
+++ b/test/fixtures/transformation/es6-generators/function-declaration-hoisting-should-work-even-if-the-declarations-are-out-of-order/exec.js
@@ -15,18 +15,10 @@ function *gen(n) {
     function decrement(x) {
       return x - 1;
     }
-  } else {
-    // The behavior of function declarations nested inside conditional
-    // blocks is notoriously underspecified, and in V8 it appears the
-    // halve function is still defined when we take this branch, so
-    // "undefine" it for consistency with regenerator semantics.
-    halve = void 0;
   }
 
-  yield typeof halve;
-
   yield increment(increment(n));
 }
 
-genHelpers.check(gen(3), [4, 1, "function", 5]);
-genHelpers.check(gen(4), [5, "undefined", 6]);
+genHelpers.check(gen(3), [4, 1, 5]);
+genHelpers.check(gen(4), [5, 6]);
diff --git a/test/fixtures/transformation/es6-modules-amd/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-amd/exports-variable/actual.js
index b4629cc731..c9cd5af09c 100644
--- a/test/fixtures/transformation/es6-modules-amd/exports-variable/actual.js
+++ b/test/fixtures/transformation/es6-modules-amd/exports-variable/actual.js
@@ -1,4 +1,5 @@
 export var foo = 1;
+export var foo = 1, bar = 2;
 export var foo2 = function () {};
 export var foo3;
 export let foo4 = 2;
diff --git a/test/fixtures/transformation/es6-modules-amd/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-amd/exports-variable/expected.js
index b94e1dd338..d01bae5920 100644
--- a/test/fixtures/transformation/es6-modules-amd/exports-variable/expected.js
+++ b/test/fixtures/transformation/es6-modules-amd/exports-variable/expected.js
@@ -3,10 +3,12 @@ define(["exports"], function (exports) {
 
   exports.foo7 = foo7;
   var foo = exports.foo = 1;
+  var foo = exports.foo = 1;
+  var bar = exports.bar = 2;
   var foo2 = exports.foo2 = function () {};
-  var foo3;
+  var foo3 = exports.foo3 = undefined;
   var foo4 = exports.foo4 = 2;
-  var foo5;
+  var foo5 = exports.foo5 = undefined;
   var foo6 = exports.foo6 = 3;
   function foo7() {}
   var foo8 = function foo8() {};
diff --git a/test/fixtures/transformation/es6-modules-amd/imports-default/expected.js b/test/fixtures/transformation/es6-modules-amd/imports-default/expected.js
index 43e1ab9d53..b19c21fa34 100644
--- a/test/fixtures/transformation/es6-modules-amd/imports-default/expected.js
+++ b/test/fixtures/transformation/es6-modules-amd/imports-default/expected.js
@@ -7,5 +7,5 @@ define(["exports", "foo"], function (exports, _foo) {
 
   var foo = _interopRequire(_foo);
 
-  var foo = _foo["default"];
+  var foo = _interopRequire(_foo);
 });
diff --git a/test/fixtures/transformation/es6-modules-amd/module-name/actual.js b/test/fixtures/transformation/es6-modules-amd/module-name/actual.js
new file mode 100644
index 0000000000..f3b473756e
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-amd/module-name/actual.js
@@ -0,0 +1 @@
+foobar();
diff --git a/test/fixtures/transformation/es6-modules-amd/module-name/expected.js b/test/fixtures/transformation/es6-modules-amd/module-name/expected.js
new file mode 100644
index 0000000000..8677aed980
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-amd/module-name/expected.js
@@ -0,0 +1,5 @@
+define("es6-modules-amd/module-name/expected", ["exports"], function (exports) {
+  "use strict";
+
+  foobar();
+});
diff --git a/test/fixtures/transformation/es6-modules-amd/module-name/options.json b/test/fixtures/transformation/es6-modules-amd/module-name/options.json
new file mode 100644
index 0000000000..a2868455b4
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-amd/module-name/options.json
@@ -0,0 +1,3 @@
+{
+  "amdModuleIds": true
+}
diff --git a/test/fixtures/transformation/es6-modules-amd/remap/actual.js b/test/fixtures/transformation/es6-modules-amd/remap/actual.js
new file mode 100644
index 0000000000..7345a055a5
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-amd/remap/actual.js
@@ -0,0 +1,7 @@
+export var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-amd/remap/expected.js b/test/fixtures/transformation/es6-modules-amd/remap/expected.js
new file mode 100644
index 0000000000..5fc760fd92
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-amd/remap/expected.js
@@ -0,0 +1,11 @@
+define(["exports"], function (exports) {
+  "use strict";
+
+  var test = exports.test = 2;
+  test = 5;
+
+  (function () {
+    var test = 2;
+    test = 3;
+  })();
+});
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-default/actual.js b/test/fixtures/transformation/es6-modules-common-interop/exports-default/actual.js
deleted file mode 100644
index 62923e5c15..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-default/actual.js
+++ /dev/null
@@ -1,8 +0,0 @@
-export default 42;
-export default {};
-export default [];
-export default foo;
-export default function () {}
-export default class {}
-export default function foo () {}
-export default class Foo {}
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-default/expected.js b/test/fixtures/transformation/es6-modules-common-interop/exports-default/expected.js
deleted file mode 100644
index ef8ba56786..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-default/expected.js
+++ /dev/null
@@ -1,15 +0,0 @@
-"use strict";
-
-module.exports = foo;
-module.exports = 42;
-module.exports = {};
-module.exports = [];
-module.exports = foo;
-module.exports = function () {};
-
-module.exports = function () {};
-
-function foo() {}
-var Foo = function Foo() {};
-
-module.exports = Foo;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-from/actual.js b/test/fixtures/transformation/es6-modules-common-interop/exports-from/actual.js
deleted file mode 100644
index 60857f6542..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-from/actual.js
+++ /dev/null
@@ -1,6 +0,0 @@
-export * from "foo";
-export {foo} from "foo";
-export {foo, bar} from "foo";
-export {foo as bar} from "foo";
-export {foo as default} from "foo";
-export {foo as default, bar} from "foo";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-from/expected.js b/test/fixtures/transformation/es6-modules-common-interop/exports-from/expected.js
deleted file mode 100644
index feaeac94ee..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-from/expected.js
+++ /dev/null
@@ -1,15 +0,0 @@
-"use strict";
-
-(function (obj) {
-  for (var i in obj) {
-    exports[i] = obj[i];
-  }
-})(require("foo"));
-
-exports.foo = require("foo").foo;
-exports.foo = require("foo").foo;
-exports.bar = require("foo").bar;
-exports.bar = require("foo").foo;
-exports["default"] = require("foo").foo;
-exports["default"] = require("foo").foo;
-exports.bar = require("foo").bar;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-named/actual.js b/test/fixtures/transformation/es6-modules-common-interop/exports-named/actual.js
deleted file mode 100644
index 8515ace759..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-named/actual.js
+++ /dev/null
@@ -1,5 +0,0 @@
-export {foo};
-export {foo, bar};
-export {foo as bar};
-export {foo as default};
-export {foo as default, bar};
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-named/expected.js b/test/fixtures/transformation/es6-modules-common-interop/exports-named/expected.js
deleted file mode 100644
index ce378a6fb0..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-named/expected.js
+++ /dev/null
@@ -1,9 +0,0 @@
-"use strict";
-
-exports.foo = foo;
-exports.foo = foo;
-exports.bar = bar;
-exports.bar = foo;
-exports["default"] = foo;
-exports["default"] = foo;
-exports.bar = bar;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-common-interop/exports-variable/actual.js
deleted file mode 100644
index b4629cc731..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-variable/actual.js
+++ /dev/null
@@ -1,8 +0,0 @@
-export var foo = 1;
-export var foo2 = function () {};
-export var foo3;
-export let foo4 = 2;
-export let foo5;
-export const foo6 = 3;
-export function foo7 () {}
-export class foo8 {}
diff --git a/test/fixtures/transformation/es6-modules-common-interop/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-common-interop/exports-variable/expected.js
deleted file mode 100644
index 886cf61824..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/exports-variable/expected.js
+++ /dev/null
@@ -1,13 +0,0 @@
-"use strict";
-
-exports.foo7 = foo7;
-var foo = exports.foo = 1;
-var foo2 = exports.foo2 = function () {};
-var foo3;
-var foo4 = exports.foo4 = 2;
-var foo5;
-var foo6 = exports.foo6 = 3;
-function foo7() {}
-var foo8 = function foo8() {};
-
-exports.foo8 = foo8;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/actual.js b/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/actual.js
deleted file mode 100644
index 3c40b7d1c1..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/actual.js
+++ /dev/null
@@ -1,11 +0,0 @@
-import { isEven } from "./evens";
-
-export function nextOdd(n) {
-  return isEven(n) ? n + 1 : n + 2;
-}
-
-export var isOdd = (function (isEven) {
-  return function (n) {
-    return !isEven(n);
-  };
-})(isEven);
diff --git a/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/expected.js b/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/expected.js
deleted file mode 100644
index 5a074e1496..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/hoist-function-exports/expected.js
+++ /dev/null
@@ -1,13 +0,0 @@
-"use strict";
-
-exports.nextOdd = nextOdd;
-var isEven = require("./evens").isEven;
-function nextOdd(n) {
-  return isEven(n) ? n + 1 : n + 2;
-}
-
-var isOdd = exports.isOdd = (function (isEven) {
-  return function (n) {
-    return !isEven(n);
-  };
-})(isEven);
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-default/actual.js b/test/fixtures/transformation/es6-modules-common-interop/imports-default/actual.js
deleted file mode 100644
index e67418654c..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-default/actual.js
+++ /dev/null
@@ -1,2 +0,0 @@
-import foo from "foo";
-import {default as foo} from "foo";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-default/expected.js b/test/fixtures/transformation/es6-modules-common-interop/imports-default/expected.js
deleted file mode 100644
index a93b2668f9..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-default/expected.js
+++ /dev/null
@@ -1,9 +0,0 @@
-"use strict";
-
-var _interopRequire = function (obj) {
-  return obj && (obj["default"] || obj);
-};
-
-var foo = _interopRequire(require("foo"));
-
-var foo = require("foo")["default"];
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-glob/actual.js b/test/fixtures/transformation/es6-modules-common-interop/imports-glob/actual.js
deleted file mode 100644
index e55c077500..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-glob/actual.js
+++ /dev/null
@@ -1 +0,0 @@
-import * as foo from "foo";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-glob/expected.js b/test/fixtures/transformation/es6-modules-common-interop/imports-glob/expected.js
deleted file mode 100644
index 3293bd0ebd..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-glob/expected.js
+++ /dev/null
@@ -1,3 +0,0 @@
-"use strict";
-
-var foo = require("foo");
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/actual.js b/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/actual.js
deleted file mode 100644
index ef78c95b1c..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/actual.js
+++ /dev/null
@@ -1 +0,0 @@
-import foo, {baz as xyz} from "foo";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/expected.js b/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/expected.js
deleted file mode 100644
index 09ea4cec86..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-mixing/expected.js
+++ /dev/null
@@ -1,9 +0,0 @@
-"use strict";
-
-var _interopRequire = function (obj) {
-  return obj && (obj["default"] || obj);
-};
-
-var foo = _interopRequire(require("foo"));
-
-var xyz = require("foo").baz;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-named/actual.js b/test/fixtures/transformation/es6-modules-common-interop/imports-named/actual.js
deleted file mode 100644
index 83a766c62d..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-named/actual.js
+++ /dev/null
@@ -1,4 +0,0 @@
-import {bar} from "foo";
-import {bar, baz} from "foo";
-import {bar as baz} from "foo";
-import {bar as baz, xyz} from "foo";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports-named/expected.js b/test/fixtures/transformation/es6-modules-common-interop/imports-named/expected.js
deleted file mode 100644
index 9a51dccc06..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports-named/expected.js
+++ /dev/null
@@ -1,8 +0,0 @@
-"use strict";
-
-var bar = require("foo").bar;
-var bar = require("foo").bar;
-var baz = require("foo").baz;
-var baz = require("foo").bar;
-var baz = require("foo").bar;
-var xyz = require("foo").xyz;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports/actual.js b/test/fixtures/transformation/es6-modules-common-interop/imports/actual.js
deleted file mode 100644
index 222b6885ac..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports/actual.js
+++ /dev/null
@@ -1,3 +0,0 @@
-import "foo";
-import "foo-bar";
-import "./directory/foo-bar";
diff --git a/test/fixtures/transformation/es6-modules-common-interop/imports/expected.js b/test/fixtures/transformation/es6-modules-common-interop/imports/expected.js
deleted file mode 100644
index f1a139f51a..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/imports/expected.js
+++ /dev/null
@@ -1,7 +0,0 @@
-"use strict";
-
-require("foo");
-
-require("foo-bar");
-
-require("./directory/foo-bar");
diff --git a/test/fixtures/transformation/es6-modules-common-interop/options.json b/test/fixtures/transformation/es6-modules-common-interop/options.json
deleted file mode 100644
index d5e2792eed..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/options.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "modules": "commonInterop"
-}
diff --git a/test/fixtures/transformation/es6-modules-common-interop/overview/actual.js b/test/fixtures/transformation/es6-modules-common-interop/overview/actual.js
deleted file mode 100644
index a77d4d5dfa..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/overview/actual.js
+++ /dev/null
@@ -1,12 +0,0 @@
-import "foo";
-import "foo-bar";
-import "./directory/foo-bar";
-import foo from "foo";
-import * as foo from "foo";
-import {bar} from "foo";
-import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
diff --git a/test/fixtures/transformation/es6-modules-common-interop/overview/expected.js b/test/fixtures/transformation/es6-modules-common-interop/overview/expected.js
deleted file mode 100644
index 208d3a3d3b..0000000000
--- a/test/fixtures/transformation/es6-modules-common-interop/overview/expected.js
+++ /dev/null
@@ -1,22 +0,0 @@
-"use strict";
-
-var _interopRequire = function (obj) {
-  return obj && (obj["default"] || obj);
-};
-
-require("foo");
-
-require("foo-bar");
-
-require("./directory/foo-bar");
-
-var foo = _interopRequire(require("foo"));
-
-var foo = require("foo");
-
-var bar = require("foo").bar;
-var bar = require("foo").foo;
-exports.test = test;
-var test = exports.test = 5;
-
-exports["default"] = test;
diff --git a/test/fixtures/transformation/es6-modules-common/exports-default/expected.js b/test/fixtures/transformation/es6-modules-common/exports-default/expected.js
index 8c68ab4224..ef8ba56786 100644
--- a/test/fixtures/transformation/es6-modules-common/exports-default/expected.js
+++ b/test/fixtures/transformation/es6-modules-common/exports-default/expected.js
@@ -1,15 +1,15 @@
 "use strict";
 
-exports["default"] = 42;
-exports["default"] = {};
-exports["default"] = [];
-exports["default"] = foo;
-exports["default"] = function () {};
+module.exports = foo;
+module.exports = 42;
+module.exports = {};
+module.exports = [];
+module.exports = foo;
+module.exports = function () {};
 
-exports["default"] = function () {};
+module.exports = function () {};
 
 function foo() {}
-exports["default"] = foo;
 var Foo = function Foo() {};
 
-exports["default"] = Foo;
+module.exports = Foo;
diff --git a/test/fixtures/transformation/es6-modules-common/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-common/exports-variable/actual.js
index b4629cc731..c9cd5af09c 100644
--- a/test/fixtures/transformation/es6-modules-common/exports-variable/actual.js
+++ b/test/fixtures/transformation/es6-modules-common/exports-variable/actual.js
@@ -1,4 +1,5 @@
 export var foo = 1;
+export var foo = 1, bar = 2;
 export var foo2 = function () {};
 export var foo3;
 export let foo4 = 2;
diff --git a/test/fixtures/transformation/es6-modules-common/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-common/exports-variable/expected.js
index 886cf61824..2c13db0878 100644
--- a/test/fixtures/transformation/es6-modules-common/exports-variable/expected.js
+++ b/test/fixtures/transformation/es6-modules-common/exports-variable/expected.js
@@ -2,10 +2,12 @@
 
 exports.foo7 = foo7;
 var foo = exports.foo = 1;
+var foo = exports.foo = 1;
+var bar = exports.bar = 2;
 var foo2 = exports.foo2 = function () {};
-var foo3;
+var foo3 = exports.foo3 = undefined;
 var foo4 = exports.foo4 = 2;
-var foo5;
+var foo5 = exports.foo5 = undefined;
 var foo6 = exports.foo6 = 3;
 function foo7() {}
 var foo8 = function foo8() {};
diff --git a/test/fixtures/transformation/es6-modules-common/imports-default/expected.js b/test/fixtures/transformation/es6-modules-common/imports-default/expected.js
index 32db9b239c..2a84fb6d1e 100644
--- a/test/fixtures/transformation/es6-modules-common/imports-default/expected.js
+++ b/test/fixtures/transformation/es6-modules-common/imports-default/expected.js
@@ -1,4 +1,9 @@
 "use strict";
 
-var foo = require("foo")["default"];
-var foo = require("foo")["default"];
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
+var foo = _interopRequire(require("foo"));
+
+var foo = _interopRequire(require("foo"));
diff --git a/test/fixtures/transformation/es6-modules-common/imports-mixing/expected.js b/test/fixtures/transformation/es6-modules-common/imports-mixing/expected.js
index 57bcfd38fc..09ea4cec86 100644
--- a/test/fixtures/transformation/es6-modules-common/imports-mixing/expected.js
+++ b/test/fixtures/transformation/es6-modules-common/imports-mixing/expected.js
@@ -1,4 +1,9 @@
 "use strict";
 
-var foo = require("foo")["default"];
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
+var foo = _interopRequire(require("foo"));
+
 var xyz = require("foo").baz;
diff --git a/test/fixtures/transformation/es6-modules-common/overview/expected.js b/test/fixtures/transformation/es6-modules-common/overview/expected.js
index 614b23e905..f0d7868fc9 100644
--- a/test/fixtures/transformation/es6-modules-common/overview/expected.js
+++ b/test/fixtures/transformation/es6-modules-common/overview/expected.js
@@ -1,12 +1,17 @@
 "use strict";
 
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
 require("foo");
 
 require("foo-bar");
 
 require("./directory/foo-bar");
 
-var foo = require("foo")["default"];
+var foo = _interopRequire(require("foo"));
+
 var foo = require("foo");
 
 var bar = require("foo").bar;
@@ -14,4 +19,4 @@ var bar = require("foo").foo;
 exports.test = test;
 var test = exports.test = 5;
 
-exports["default"] = test;
+exports = module.exports = test;
diff --git a/test/fixtures/transformation/es6-modules-common/remap/actual.js b/test/fixtures/transformation/es6-modules-common/remap/actual.js
new file mode 100644
index 0000000000..7345a055a5
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/remap/actual.js
@@ -0,0 +1,7 @@
+export var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-common/remap/expected.js b/test/fixtures/transformation/es6-modules-common/remap/expected.js
new file mode 100644
index 0000000000..f4f8f05b7b
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-common/remap/expected.js
@@ -0,0 +1,9 @@
+"use strict";
+
+var test = exports.test = 2;
+test = exports.test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-ignore/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-ignore/exports-variable/actual.js
index b4629cc731..c9cd5af09c 100644
--- a/test/fixtures/transformation/es6-modules-ignore/exports-variable/actual.js
+++ b/test/fixtures/transformation/es6-modules-ignore/exports-variable/actual.js
@@ -1,4 +1,5 @@
 export var foo = 1;
+export var foo = 1, bar = 2;
 export var foo2 = function () {};
 export var foo3;
 export let foo4 = 2;
diff --git a/test/fixtures/transformation/es6-modules-ignore/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-ignore/exports-variable/expected.js
index b9c8a5d690..854aad79f8 100644
--- a/test/fixtures/transformation/es6-modules-ignore/exports-variable/expected.js
+++ b/test/fixtures/transformation/es6-modules-ignore/exports-variable/expected.js
@@ -1,10 +1,11 @@
 "use strict";
 
 var foo = 1;
+var foo = 1, bar = 2;
 var foo2 = function () {};
-var foo3;
+var foo3 = undefined;
 var foo4 = 2;
-var foo5;
+var foo5 = undefined;
 var foo6 = 3;
 function foo7() {}
 var foo8 = function foo8() {};
diff --git a/test/fixtures/transformation/es6-modules-ignore/remap/actual.js b/test/fixtures/transformation/es6-modules-ignore/remap/actual.js
new file mode 100644
index 0000000000..7345a055a5
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-ignore/remap/actual.js
@@ -0,0 +1,7 @@
+export var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-ignore/remap/expected.js b/test/fixtures/transformation/es6-modules-ignore/remap/expected.js
new file mode 100644
index 0000000000..15120d6616
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-ignore/remap/expected.js
@@ -0,0 +1,9 @@
+"use strict";
+
+var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-default/actual.js b/test/fixtures/transformation/es6-modules-system/exports-default/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/exports-default/actual.js
rename to test/fixtures/transformation/es6-modules-system/exports-default/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/exports-default/expected.js b/test/fixtures/transformation/es6-modules-system/exports-default/expected.js
new file mode 100644
index 0000000000..074d3026c8
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/exports-default/expected.js
@@ -0,0 +1,27 @@
+System.register("es6-modules-system/exports-default/expected", [], function (_export) {
+  return {
+    setters: [],
+    execute: function () {
+      "use strict";
+
+      _export("default", 42);
+
+      _export("default", {});
+
+      _export("default", []);
+
+      _export("default", foo);
+
+      _export("default", function () {});
+
+      _export("default", function () {});
+
+      function foo() {}
+      _export("default", foo);
+
+      var Foo = function Foo() {};
+
+      _export("default", Foo);
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-from/actual.js b/test/fixtures/transformation/es6-modules-system/exports-from/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/exports-from/actual.js
rename to test/fixtures/transformation/es6-modules-system/exports-from/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/exports-from/expected.js b/test/fixtures/transformation/es6-modules-system/exports-from/expected.js
new file mode 100644
index 0000000000..e84f56e0c3
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/exports-from/expected.js
@@ -0,0 +1,29 @@
+System.register("es6-modules-system/exports-from/expected", ["foo"], function (_export) {
+  var _foo;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }],
+    execute: function () {
+      "use strict";
+
+      for (var i in _foo) {
+        _export(i, _foo[i])
+      }
+
+      _export("foo", _foo.foo);
+
+      _export("foo", _foo.foo);
+
+      _export("bar", _foo.bar);
+
+      _export("bar", _foo.foo);
+
+      _export("default", _foo.foo);
+
+      _export("default", _foo.foo);
+
+      _export("bar", _foo.bar);
+    }
+  };
+});
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-named/actual.js b/test/fixtures/transformation/es6-modules-system/exports-named/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/exports-named/actual.js
rename to test/fixtures/transformation/es6-modules-system/exports-named/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/exports-named/expected.js b/test/fixtures/transformation/es6-modules-system/exports-named/expected.js
new file mode 100644
index 0000000000..e297af4bfe
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/exports-named/expected.js
@@ -0,0 +1,22 @@
+System.register("es6-modules-system/exports-named/expected", [], function (_export) {
+  return {
+    setters: [],
+    execute: function () {
+      "use strict";
+
+      _export("foo", foo);
+
+      _export("foo", foo);
+
+      _export("bar", bar);
+
+      _export("bar", foo);
+
+      _export("default", foo);
+
+      _export("default", foo);
+
+      _export("bar", bar);
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-system/exports-variable/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/exports-variable/actual.js
rename to test/fixtures/transformation/es6-modules-system/exports-variable/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-system/exports-variable/expected.js
new file mode 100644
index 0000000000..636a73a17d
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/exports-variable/expected.js
@@ -0,0 +1,21 @@
+System.register("es6-modules-system/exports-variable/expected", [], function (_export) {
+  return {
+    setters: [],
+    execute: function () {
+      "use strict";
+
+      _export("foo7", foo7);
+
+      var foo = _export("foo", 1);
+      var foo2 = _export("foo2", function () {});
+      var foo3 = _export("foo3", undefined);
+      var foo4 = _export("foo4", 2);
+      var foo5 = _export("foo5", undefined);
+      var foo6 = _export("foo6", 3);
+      function foo7() {}
+      var foo8 = function foo8() {};
+
+      _export("foo8", foo8);
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/hoist-function-exports/actual.js b/test/fixtures/transformation/es6-modules-system/hoist-function-exports/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/hoist-function-exports/actual.js
rename to test/fixtures/transformation/es6-modules-system/hoist-function-exports/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/hoist-function-exports/expected.js b/test/fixtures/transformation/es6-modules-system/hoist-function-exports/expected.js
new file mode 100644
index 0000000000..ad626fc12d
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/hoist-function-exports/expected.js
@@ -0,0 +1,24 @@
+System.register("es6-modules-system/hoist-function-exports/expected", ["./evens"], function (_export) {
+  var _evens;
+  return {
+    setters: [function (m) {
+      _evens = m
+    }],
+    execute: function () {
+      "use strict";
+
+      _export("nextOdd", nextOdd);
+
+      var isEven = _evens.isEven;
+      function nextOdd(n) {
+        return isEven(n) ? n + 1 : n + 2;
+      }
+
+      var isOdd = _export("isOdd", (function (isEven) {
+        return function (n) {
+          return !isEven(n);
+        };
+      })(isEven));
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-default/actual.js b/test/fixtures/transformation/es6-modules-system/imports-default/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/imports-default/actual.js
rename to test/fixtures/transformation/es6-modules-system/imports-default/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/imports-default/expected.js b/test/fixtures/transformation/es6-modules-system/imports-default/expected.js
new file mode 100644
index 0000000000..c4e481d3d8
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/imports-default/expected.js
@@ -0,0 +1,19 @@
+System.register("es6-modules-system/imports-default/expected", ["foo"], function (_export) {
+  var _foo;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }],
+    execute: function () {
+      "use strict";
+
+      var _interopRequire = function (obj) {
+        return obj && (obj["default"] || obj);
+      };
+
+      var foo = _interopRequire(_foo);
+
+      var foo = _interopRequire(_foo);
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-glob/actual.js b/test/fixtures/transformation/es6-modules-system/imports-glob/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/imports-glob/actual.js
rename to test/fixtures/transformation/es6-modules-system/imports-glob/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/imports-glob/expected.js b/test/fixtures/transformation/es6-modules-system/imports-glob/expected.js
new file mode 100644
index 0000000000..d641fe072e
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/imports-glob/expected.js
@@ -0,0 +1,13 @@
+System.register("es6-modules-system/imports-glob/expected", ["foo"], function (_export) {
+  var _foo;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }],
+    execute: function () {
+      "use strict";
+
+      var foo = _foo;
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-mixing/actual.js b/test/fixtures/transformation/es6-modules-system/imports-mixing/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/imports-mixing/actual.js
rename to test/fixtures/transformation/es6-modules-system/imports-mixing/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/imports-mixing/expected.js b/test/fixtures/transformation/es6-modules-system/imports-mixing/expected.js
new file mode 100644
index 0000000000..79469ef9a7
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/imports-mixing/expected.js
@@ -0,0 +1,19 @@
+System.register("es6-modules-system/imports-mixing/expected", ["foo"], function (_export) {
+  var _foo;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }],
+    execute: function () {
+      "use strict";
+
+      var _interopRequire = function (obj) {
+        return obj && (obj["default"] || obj);
+      };
+
+      var foo = _interopRequire(_foo);
+
+      var xyz = _foo.baz;
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/imports-named/actual.js b/test/fixtures/transformation/es6-modules-system/imports-named/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/imports-named/actual.js
rename to test/fixtures/transformation/es6-modules-system/imports-named/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/imports-named/expected.js b/test/fixtures/transformation/es6-modules-system/imports-named/expected.js
new file mode 100644
index 0000000000..cb3db1ff7a
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/imports-named/expected.js
@@ -0,0 +1,18 @@
+System.register("es6-modules-system/imports-named/expected", ["foo"], function (_export) {
+  var _foo;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }],
+    execute: function () {
+      "use strict";
+
+      var bar = _foo.bar;
+      var bar = _foo.bar;
+      var baz = _foo.baz;
+      var baz = _foo.bar;
+      var baz = _foo.bar;
+      var xyz = _foo.xyz;
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/imports/actual.js b/test/fixtures/transformation/es6-modules-system/imports/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/imports/actual.js
rename to test/fixtures/transformation/es6-modules-system/imports/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/imports/expected.js b/test/fixtures/transformation/es6-modules-system/imports/expected.js
new file mode 100644
index 0000000000..76236eb64e
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/imports/expected.js
@@ -0,0 +1,15 @@
+System.register("es6-modules-system/imports/expected", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
+  var _foo, _fooBar, _directoryFooBar;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }, function (m) {
+      _fooBar = m
+    }, function (m) {
+      _directoryFooBar = m
+    }],
+    execute: function () {
+      "use strict";
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/.es6-modules-system/options.json b/test/fixtures/transformation/es6-modules-system/options.json
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/options.json
rename to test/fixtures/transformation/es6-modules-system/options.json
diff --git a/test/fixtures/transformation/.es6-modules-system/overview/actual.js b/test/fixtures/transformation/es6-modules-system/overview/actual.js
similarity index 100%
rename from test/fixtures/transformation/.es6-modules-system/overview/actual.js
rename to test/fixtures/transformation/es6-modules-system/overview/actual.js
diff --git a/test/fixtures/transformation/es6-modules-system/overview/expected.js b/test/fixtures/transformation/es6-modules-system/overview/expected.js
new file mode 100644
index 0000000000..9bd4fe1f90
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/overview/expected.js
@@ -0,0 +1,30 @@
+System.register("es6-modules-system/overview/expected", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
+  var _foo, _fooBar, _directoryFooBar;
+  return {
+    setters: [function (m) {
+      _foo = m
+    }, function (m) {
+      _fooBar = m
+    }, function (m) {
+      _directoryFooBar = m
+    }],
+    execute: function () {
+      "use strict";
+
+      var _interopRequire = function (obj) {
+        return obj && (obj["default"] || obj);
+      };
+
+      var foo = _interopRequire(_foo);
+
+      var foo = _foo;
+      var bar = _foo.bar;
+      var bar = _foo.foo;
+      _export("test", test);
+
+      var test = _export("test", 5);
+
+      _export("default", test);
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/es6-modules-system/remap/actual.js b/test/fixtures/transformation/es6-modules-system/remap/actual.js
new file mode 100644
index 0000000000..7345a055a5
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/remap/actual.js
@@ -0,0 +1,7 @@
+export var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-system/remap/expected.js b/test/fixtures/transformation/es6-modules-system/remap/expected.js
new file mode 100644
index 0000000000..58803da194
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-system/remap/expected.js
@@ -0,0 +1,16 @@
+System.register("es6-modules-system/remap/expected", [], function (_export) {
+  return {
+    setters: [],
+    execute: function () {
+      "use strict";
+
+      var test = _export("test", 2);
+      test = 5;
+
+      (function () {
+        var test = 2;
+        test = 3;
+      })();
+    }
+  };
+});
\ No newline at end of file
diff --git a/test/fixtures/transformation/es6-modules-umd/exports-variable/actual.js b/test/fixtures/transformation/es6-modules-umd/exports-variable/actual.js
index b4629cc731..c9cd5af09c 100644
--- a/test/fixtures/transformation/es6-modules-umd/exports-variable/actual.js
+++ b/test/fixtures/transformation/es6-modules-umd/exports-variable/actual.js
@@ -1,4 +1,5 @@
 export var foo = 1;
+export var foo = 1, bar = 2;
 export var foo2 = function () {};
 export var foo3;
 export let foo4 = 2;
diff --git a/test/fixtures/transformation/es6-modules-umd/exports-variable/expected.js b/test/fixtures/transformation/es6-modules-umd/exports-variable/expected.js
index d381823150..7cabcda1e3 100644
--- a/test/fixtures/transformation/es6-modules-umd/exports-variable/expected.js
+++ b/test/fixtures/transformation/es6-modules-umd/exports-variable/expected.js
@@ -9,10 +9,12 @@
 
   exports.foo7 = foo7;
   var foo = exports.foo = 1;
+  var foo = exports.foo = 1;
+  var bar = exports.bar = 2;
   var foo2 = exports.foo2 = function () {};
-  var foo3;
+  var foo3 = exports.foo3 = undefined;
   var foo4 = exports.foo4 = 2;
-  var foo5;
+  var foo5 = exports.foo5 = undefined;
   var foo6 = exports.foo6 = 3;
   function foo7() {}
   var foo8 = function foo8() {};
diff --git a/test/fixtures/transformation/es6-modules-umd/imports-default/expected.js b/test/fixtures/transformation/es6-modules-umd/imports-default/expected.js
index b68de76392..83402d6e59 100644
--- a/test/fixtures/transformation/es6-modules-umd/imports-default/expected.js
+++ b/test/fixtures/transformation/es6-modules-umd/imports-default/expected.js
@@ -13,5 +13,5 @@
 
   var foo = _interopRequire(_foo);
 
-  var foo = _foo["default"];
+  var foo = _interopRequire(_foo);
 });
diff --git a/test/fixtures/transformation/es6-modules-umd/module-name/actual.js b/test/fixtures/transformation/es6-modules-umd/module-name/actual.js
new file mode 100644
index 0000000000..f3b473756e
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-umd/module-name/actual.js
@@ -0,0 +1 @@
+foobar();
diff --git a/test/fixtures/transformation/es6-modules-umd/module-name/expected.js b/test/fixtures/transformation/es6-modules-umd/module-name/expected.js
new file mode 100644
index 0000000000..0659537571
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-umd/module-name/expected.js
@@ -0,0 +1,11 @@
+(function (factory) {
+  if (typeof define === "function" && define.amd) {
+    define("es6-modules-umd/module-name/expected", ["exports"], factory);
+  } else if (typeof exports !== "undefined") {
+    factory(exports);
+  }
+})(function (exports) {
+  "use strict";
+
+  foobar();
+});
diff --git a/test/fixtures/transformation/es6-modules-umd/module-name/options.json b/test/fixtures/transformation/es6-modules-umd/module-name/options.json
new file mode 100644
index 0000000000..a2868455b4
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-umd/module-name/options.json
@@ -0,0 +1,3 @@
+{
+  "amdModuleIds": true
+}
diff --git a/test/fixtures/transformation/es6-modules-umd/remap/actual.js b/test/fixtures/transformation/es6-modules-umd/remap/actual.js
new file mode 100644
index 0000000000..7345a055a5
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-umd/remap/actual.js
@@ -0,0 +1,7 @@
+export var test = 2;
+test = 5;
+
+(function () {
+  var test = 2;
+  test = 3;
+})();
diff --git a/test/fixtures/transformation/es6-modules-umd/remap/expected.js b/test/fixtures/transformation/es6-modules-umd/remap/expected.js
new file mode 100644
index 0000000000..0fe2bbd0f4
--- /dev/null
+++ b/test/fixtures/transformation/es6-modules-umd/remap/expected.js
@@ -0,0 +1,17 @@
+(function (factory) {
+  if (typeof define === "function" && define.amd) {
+    define(["exports"], factory);
+  } else if (typeof exports !== "undefined") {
+    factory(exports);
+  }
+})(function (exports) {
+  "use strict";
+
+  var test = exports.test = 2;
+  test = 5;
+
+  (function () {
+    var test = 2;
+    test = 3;
+  })();
+});
diff --git a/test/fixtures/transformation/es6-property-name-shorthand/comments/actual.js b/test/fixtures/transformation/es6-property-name-shorthand/comments/actual.js
new file mode 100644
index 0000000000..a6a10d4689
--- /dev/null
+++ b/test/fixtures/transformation/es6-property-name-shorthand/comments/actual.js
@@ -0,0 +1,4 @@
+const A = 'a';
+const o = {
+  A // comment
+};
diff --git a/test/fixtures/transformation/es6-property-name-shorthand/comments/expected.js b/test/fixtures/transformation/es6-property-name-shorthand/comments/expected.js
new file mode 100644
index 0000000000..bb002dfed6
--- /dev/null
+++ b/test/fixtures/transformation/es6-property-name-shorthand/comments/expected.js
@@ -0,0 +1,6 @@
+"use strict";
+
+var A = "a";
+var o = {
+  A: A // comment
+};
diff --git a/test/fixtures/transformation/es6-template-literals/tag/expected.js b/test/fixtures/transformation/es6-template-literals/tag/expected.js
index 9992ad8f15..c4b5cb6cbb 100644
--- a/test/fixtures/transformation/es6-template-literals/tag/expected.js
+++ b/test/fixtures/transformation/es6-template-literals/tag/expected.js
@@ -1,11 +1,11 @@
 "use strict";
 
 var _taggedTemplateLiteral = function (strings, raw) {
-  return Object.defineProperties(strings, {
+  return Object.freeze(Object.defineProperties(strings, {
     raw: {
-      value: raw
+      value: Object.freeze(raw)
     }
-  });
+  }));
 };
 
 var foo = bar(_taggedTemplateLiteral(["wow\na", "b ", ""], ["wow\\na", "b ", ""]), 42, _.foobar());
diff --git a/test/fixtures/transformation/es6-unicode-regex/basic/expected.js b/test/fixtures/transformation/es6-unicode-regex/basic/expected.js
index d4f30f3911..eb24a69373 100644
--- a/test/fixtures/transformation/es6-unicode-regex/basic/expected.js
+++ b/test/fixtures/transformation/es6-unicode-regex/basic/expected.js
@@ -1,4 +1,4 @@
 "use strict";
 
-var string = "foo\ud83d\udca9bar";
+var string = "foo💩bar";
 var match = string.match(/foo((?:[\0-\t\x0B\f\x0E-\u2027\u202A-\uD7FF\uDC00-\uFFFF]|[\uD800-\uDBFF][\uDC00-\uDFFF]|[\uD800-\uDBFF]))bar/);
diff --git a/test/fixtures/transformation/es6-unicode-regex/ignore-non-unicode/expected.js b/test/fixtures/transformation/es6-unicode-regex/ignore-non-unicode/expected.js
index ab57a7f88e..2a77fc0b65 100644
--- a/test/fixtures/transformation/es6-unicode-regex/ignore-non-unicode/expected.js
+++ b/test/fixtures/transformation/es6-unicode-regex/ignore-non-unicode/expected.js
@@ -1,4 +1,4 @@
 "use strict";
 
-var string = "foo\ud83d\udca9bar";
+var string = "foo💩bar";
 var match = string.match(/foo(.)bar/);
diff --git a/test/fixtures/transformation/es7-abstract-references/private/actual.js b/test/fixtures/transformation/es7-abstract-references/private/actual.js
new file mode 100644
index 0000000000..9643ff19c2
--- /dev/null
+++ b/test/fixtures/transformation/es7-abstract-references/private/actual.js
@@ -0,0 +1,12 @@
+private A;
+private B, C;
+
+class D {
+  private E;
+  private F, G;
+}
+
+var H = class {
+  private I;
+  private J, K;
+};
diff --git a/test/fixtures/transformation/es7-abstract-references/private/expected.js b/test/fixtures/transformation/es7-abstract-references/private/expected.js
new file mode 100644
index 0000000000..91d4b390d1
--- /dev/null
+++ b/test/fixtures/transformation/es7-abstract-references/private/expected.js
@@ -0,0 +1,19 @@
+"use strict";
+
+var A = new WeakMap();
+var B = new WeakMap(), C = new WeakMap();
+(function () {
+  var F = new WeakMap(), G = new WeakMap();
+  var E = new WeakMap();
+  var D = function D() {};
+
+  return D;
+})()
+
+var H = (function () {
+  var J = new WeakMap(), K = new WeakMap();
+  var I = new WeakMap();
+  var _class = function () {};
+
+  return _class;
+})();
diff --git a/test/fixtures/transformation/es7-object-spread/expression/expected.js b/test/fixtures/transformation/es7-object-spread/expression/expected.js
index ae48d06c13..856b5c1f8c 100644
--- a/test/fixtures/transformation/es7-object-spread/expression/expected.js
+++ b/test/fixtures/transformation/es7-object-spread/expression/expected.js
@@ -1,3 +1,3 @@
 "use strict";
 
-(Object.assign({ x: x }, y, { a: a }, b, { c: c }));
+Object.assign({ x: x }, y, { a: a }, b, { c: c });
diff --git a/test/fixtures/transformation/misc/property-literals/actual.js b/test/fixtures/transformation/misc/property-literals/actual.js
deleted file mode 100644
index 229c4e0f42..0000000000
--- a/test/fixtures/transformation/misc/property-literals/actual.js
+++ /dev/null
@@ -1,3 +0,0 @@
-var obj = {
-  "foobar": "lol"
-};
diff --git a/test/fixtures/transformation/misc/property-literals/expected.js b/test/fixtures/transformation/misc/property-literals/expected.js
deleted file mode 100644
index 5222f9aedf..0000000000
--- a/test/fixtures/transformation/misc/property-literals/expected.js
+++ /dev/null
@@ -1,5 +0,0 @@
-"use strict";
-
-var obj = {
-  foobar: "lol"
-};
diff --git a/test/fixtures/transformation/playground/method-binding/actual.js b/test/fixtures/transformation/playground/method-binding/actual.js
index 1457513da0..12185e1a7c 100644
--- a/test/fixtures/transformation/playground/method-binding/actual.js
+++ b/test/fixtures/transformation/playground/method-binding/actual.js
@@ -1,13 +1,13 @@
-var fn = obj:method;
-var fn = obj:method("foob");
-var fn = obj[foo]:method;
-var fn = obj.foo:method;
-var fn = obj[foo()]:method;
+var fn = obj#method;
+var fn = obj#method("foob");
+var fn = obj[foo]#method;
+var fn = obj.foo#method;
+var fn = obj[foo()]#method;
 
-["foo", "bar"].map(:toUpperCase);
-[1.1234, 23.53245, 3].map(:toFixed(2));
+["foo", "bar"].map(#toUpperCase);
+[1.1234, 23.53245, 3].map(#toFixed(2));
 
 var get = function () {
   return 2;
 };
-[1.1234, 23.53245, 3].map(:toFixed(get()));
+[1.1234, 23.53245, 3].map(#toFixed(get()));
diff --git a/test/fixtures/transformation/playground/method-binding/exec.js b/test/fixtures/transformation/playground/method-binding/exec.js
index 77a2949ab4..b83e4b49aa 100644
--- a/test/fixtures/transformation/playground/method-binding/exec.js
+++ b/test/fixtures/transformation/playground/method-binding/exec.js
@@ -12,19 +12,19 @@ var obj = {
   }
 };
 
-var foo = obj:getFoo;
+var foo = obj#getFoo;
 assert.equal(foo(), "foo");
 
-var bar = obj:getBar("foo");
+var bar = obj#getBar("foo");
 assert.equal(bar(), "foo bar");
 
-var zoo = obj:getZoo("foo");
+var zoo = obj#getZoo("foo");
 assert.equal(zoo("bar"), "foo bar foo bar");
 
-assert.deepEqual(["foo", "bar"].map(:toUpperCase), ["FOO", "BAR"]);
-assert.deepEqual([1.1234, 23.53245, 3].map(:toFixed(2)), ["1.12", "23.53", "3.00"]);
+assert.deepEqual(["foo", "bar"].map(#toUpperCase), ["FOO", "BAR"]);
+assert.deepEqual([1.1234, 23.53245, 3].map(#toFixed(2)), ["1.12", "23.53", "3.00"]);
 
 var get = function () {
   return 2;
 }
-assert.deepEqual([1.1234, 23.53245, 3].map(:toFixed(get())), ["1.12", "23.53", "3.00"]);
+assert.deepEqual([1.1234, 23.53245, 3].map(#toFixed(get())), ["1.12", "23.53", "3.00"]);
diff --git a/test/fixtures/transformation/playground/object-getter-memoization/expected.js b/test/fixtures/transformation/playground/object-getter-memoization/expected.js
index 83441a35f4..bc4288930a 100644
--- a/test/fixtures/transformation/playground/object-getter-memoization/expected.js
+++ b/test/fixtures/transformation/playground/object-getter-memoization/expected.js
@@ -1,34 +1,32 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var Foo = (function () {
-  var Foo = function Foo() {};
+var Foo = function Foo() {};
 
-  _classProps(Foo, null, (function (_ref) {
-    _ref[bar] = {
-      get: function () {
-        if (this._memoDone) return this._memo;
-        this._memoDone = true;
-        return this._memo = complex();
-      }
-    };
-    return _ref;
-  })({
-    bar: {
-      get: function () {
-        if (this._barDone) return this._bar;
-        this._barDone = true;
-        return this._bar = complex();
-      }
-    }
-  }));
-
-  return Foo;
-})();
+_prototypeProperties(Foo, null, (function (_ref) {
+  _ref[bar] = {
+    get: function () {
+      if (this._memoDone) return this._memo;
+      this._memoDone = true;
+      return this._memo = complex();
+    },
+    enumerable: true
+  };
+  return _ref;
+})({
+  bar: {
+    get: function () {
+      if (this._barDone) return this._bar;
+      this._barDone = true;
+      return this._bar = complex();
+    },
+    enumerable: true
+  }
+}));
 
 var foo = (function (_foo) {
   _foo[bar] = function () {
@@ -45,7 +43,8 @@ var foo = (function (_foo) {
         if (this._barDone) return this._bar;
         this._barDone = true;
         return this._bar = complex();
-      }
+      },
+      enumerable: true
     }
   });
 
diff --git a/test/fixtures/transformation/react/display-name-object-declaration/actual.js b/test/fixtures/transformation/react/display-name-object-declaration/actual.js
index b00fb85bde..27aa16fb2f 100644
--- a/test/fixtures/transformation/react/display-name-object-declaration/actual.js
+++ b/test/fixtures/transformation/react/display-name-object-declaration/actual.js
@@ -1,7 +1,7 @@
 exports = {
   Component: React.createClass({
-  render: function () {
-    return null;
-  }
+    render: function () {
+      return null;
+    }
   })
 };
diff --git a/test/fixtures/transformation/source-maps/class/expected.js b/test/fixtures/transformation/source-maps/class/expected.js
index 7a04a39640..af92fdbd5c 100644
--- a/test/fixtures/transformation/source-maps/class/expected.js
+++ b/test/fixtures/transformation/source-maps/class/expected.js
@@ -1,23 +1,20 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
+var _prototypeProperties = function (child, staticProps, instanceProps) {
   if (staticProps) Object.defineProperties(child, staticProps);
   if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
 };
 
-var Test = (function () {
-  var Test = function Test() {};
+var Test = function Test() {};
 
-  _classProps(Test, null, {
-    bar: {
-      get: function () {
-        throw new Error("wow");
-      }
-    }
-  });
-
-  return Test;
-})();
+_prototypeProperties(Test, null, {
+  bar: {
+    get: function () {
+      throw new Error("wow");
+    },
+    enumerable: true
+  }
+});
 
 var test = new Test();
 test.bar;
diff --git a/test/fixtures/transformation/source-maps/class/source-mappings.json b/test/fixtures/transformation/source-maps/class/source-mappings.json
index 8b95905776..1fe92711b8 100644
--- a/test/fixtures/transformation/source-maps/class/source-mappings.json
+++ b/test/fixtures/transformation/source-maps/class/source-mappings.json
@@ -4,7 +4,7 @@
     "column": 10
   },
   "generated": {
-    "line": 14,
-    "column": 15
+    "line": 13,
+    "column": 13
   }
 }]
diff --git a/test/fixtures/transformation/spec-no-duplicate-properties/identifiers/actual.js b/test/fixtures/transformation/spec-no-duplicate-properties/identifiers/actual.js
new file mode 100644
index 0000000000..7dd5168e50
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-duplicate-properties/identifiers/actual.js
@@ -0,0 +1 @@
+var obj = { a: 1, a: 2 };
diff --git a/test/fixtures/transformation/spec-no-duplicate-properties/literals/actual.js b/test/fixtures/transformation/spec-no-duplicate-properties/literals/actual.js
new file mode 100644
index 0000000000..85b7f9f02a
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-duplicate-properties/literals/actual.js
@@ -0,0 +1 @@
+var obj = { "a": 1, "a": 2 };
diff --git a/test/fixtures/transformation/spec-no-duplicate-properties/mixed/actual.js b/test/fixtures/transformation/spec-no-duplicate-properties/mixed/actual.js
new file mode 100644
index 0000000000..eace9c1b04
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-duplicate-properties/mixed/actual.js
@@ -0,0 +1 @@
+var obj = { a: 1, "a": 2 };
diff --git a/test/fixtures/transformation/spec-no-duplicate-properties/options.json b/test/fixtures/transformation/spec-no-duplicate-properties/options.json
new file mode 100644
index 0000000000..32dce7785e
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-duplicate-properties/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "Duplicate property key"
+}
diff --git a/test/fixtures/transformation/spec-no-for-in-of-assignment/in/actual.js b/test/fixtures/transformation/spec-no-for-in-of-assignment/in/actual.js
new file mode 100644
index 0000000000..167407a7da
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-for-in-of-assignment/in/actual.js
@@ -0,0 +1,3 @@
+for (var i = 0 in obj) {
+
+}
diff --git a/test/fixtures/transformation/spec-no-for-in-of-assignment/of/actual.js b/test/fixtures/transformation/spec-no-for-in-of-assignment/of/actual.js
new file mode 100644
index 0000000000..56e4dfef82
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-for-in-of-assignment/of/actual.js
@@ -0,0 +1,3 @@
+for (var i = 0 of obj) {
+
+}
diff --git a/test/fixtures/transformation/spec-no-for-in-of-assignment/options.json b/test/fixtures/transformation/spec-no-for-in-of-assignment/options.json
new file mode 100644
index 0000000000..c7ae9b8aa4
--- /dev/null
+++ b/test/fixtures/transformation/spec-no-for-in-of-assignment/options.json
@@ -0,0 +1,3 @@
+{
+  "throws": "No assignments allowed in for-in/of head"
+}
diff --git a/test/fixtures/transformation/spec/block-hoist-functions/exec.js b/test/fixtures/transformation/spec/block-hoist-functions/exec.js
new file mode 100644
index 0000000000..f3475e0a9e
--- /dev/null
+++ b/test/fixtures/transformation/spec/block-hoist-functions/exec.js
@@ -0,0 +1,5 @@
+function f() { return 1; }
+{
+  function f() { return 2; }
+}
+assert.equal(f(), 1);
diff --git a/test/fixtures/transformation/misc/_member-expression-literals/actual.js b/test/fixtures/transformation/spec/member-expression-literals/actual.js
similarity index 100%
rename from test/fixtures/transformation/misc/_member-expression-literals/actual.js
rename to test/fixtures/transformation/spec/member-expression-literals/actual.js
diff --git a/test/fixtures/transformation/misc/_member-expression-literals/expected.js b/test/fixtures/transformation/spec/member-expression-literals/expected.js
similarity index 100%
rename from test/fixtures/transformation/misc/_member-expression-literals/expected.js
rename to test/fixtures/transformation/spec/member-expression-literals/expected.js
diff --git a/test/fixtures/transformation/misc/_property-literals/actual.js b/test/fixtures/transformation/spec/property-literals/actual.js
similarity index 100%
rename from test/fixtures/transformation/misc/_property-literals/actual.js
rename to test/fixtures/transformation/spec/property-literals/actual.js
diff --git a/test/fixtures/transformation/misc/_property-literals/expected.js b/test/fixtures/transformation/spec/property-literals/expected.js
similarity index 100%
rename from test/fixtures/transformation/misc/_property-literals/expected.js
rename to test/fixtures/transformation/spec/property-literals/expected.js
diff --git a/test/transformation.js b/test/transformation.js
index 388097e447..8bed3f56c1 100644
--- a/test/transformation.js
+++ b/test/transformation.js
@@ -7,6 +7,8 @@ var chai       = require("chai");
 var util       = require("../lib/6to5/util");
 var _          = require("lodash");
 
+require("../lib/6to5/polyfill");
+
 var run = function (task, done) {
   var actual = task.actual;
   var expect = task.expect;
@@ -15,8 +17,7 @@ var run = function (task, done) {
 
   var getOpts = function (self) {
     return _.merge({
-      whtiespace: true,
-      filename:   self.loc
+      filename: self.loc
     }, opts);
   };
 
@@ -27,8 +28,6 @@ var run = function (task, done) {
     result = transform(execCode, getOpts(exec));
     execCode = result.code;
 
-    require("../lib/6to5/polyfill");
-
     try {
       var fn = new Function("assert", "done", "genHelpers", execCode);
       fn(assert, done, genHelpers);
@@ -78,7 +77,9 @@ _.each(helper.get("transformation"), function (testSuite) {
           // the options object with useless options
           delete task.options.throws;
 
-          assert.throws(runTask, new RegExp(throwMsg));
+          assert.throws(runTask, function (err) {
+            return err.message.indexOf(throwMsg) >= 0;
+          });
         } else {
           runTask();
         }
diff --git a/test/traverse.js b/test/traverse.js
index aa863d91ee..0c1aa915c7 100644
--- a/test/traverse.js
+++ b/test/traverse.js
@@ -65,24 +65,30 @@ suite("traverse", function () {
 
     var actual = [];
 
-    traverse(ast, function (node) {
-      actual.push(node);
+    traverse(ast, {
+      enter: function (node) {
+        actual.push(node);
+      }
     });
 
     assert.deepEqual(actual, expect);
   });
 
   test("traverse falsy parent", function () {
-    traverse(null, function () {
-      throw new Error("should not be ran");
+    traverse(null, {
+      enter: function () {
+        throw new Error("should not be ran");
+      }
     });
   });
 
   test("traverse unknown type", function () {
     traverse({
       type: "FooBar"
-    }, function () {
-      throw new Error("should not be ran");
+    }, {
+      enter: function () {
+        throw new Error("should not be ran");
+      }
     });
   });
 
@@ -94,9 +100,12 @@ suite("traverse", function () {
 
     var actual = [];
 
-    traverse(ast, function (node) {
-      actual.push(node);
-    }, ["MemberExpression"]);
+    traverse(ast, {
+      blacklist: ["MemberExpression"],
+      enter: function (node) {
+        actual.push(node);
+      }
+    });
 
     assert.deepEqual(actual, expect);
   });
@@ -108,8 +117,10 @@ suite("traverse", function () {
     };
     var ast2 = _.cloneDeep(ast);
 
-    traverse(ast2, function (node) {
-      if (node.type === "ThisExpression") return replacement;
+    traverse(ast2, {
+      enter: function (node) {
+        if (node.type === "ThisExpression") return replacement;
+      }
     });
 
     assert.equal(ast2.body[1].expression.left.object, replacement);