v1.14.7

Only slice arguments when necessary - fixes #239

.gitignore

@@ -6,7 +6,7 @@ test/tmp
 /templates.json
 /tests.json
 /browser.js
-/polyfill.js
+/browser-polyfill.js
 /runtime.js
 coverage
 dist

.npmignore

@@ -8,4 +8,4 @@ Makefile
 .*
 dist
 tests.json
-!README.md
+CHANGELOG.md

CHANGELOG.md

@@ -0,0 +1,239 @@
+# 1.14.6
+
+ * Avoid ensuring a block on non-array node replacements.
+
+# 1.14.5
+
+ * Upgrade `acorn-6to5`.
+ * Fix JSON recursion error for unknown code generator node types.
+ * Ensure that a statement is a block on block/statement types when replacing them with multiple nodes.
+
+# 1.14.4
+
+ * Merge pretzel maps and method binding.
+
+# 1.14.3
+
+ * Add playground pretzel maps.
+
+# 1.14.2
+
+ * Fix `commonInterop` default export handling.
+ * Fix keyworded property key identifiers being turned into computed property key literals.
+
+# 1.14.1
+
+ * Inherit comments from `ClassDeclaration`.
+
+# 1.14.0
+
+ * Add [playground](https://6to5.github.io/playground.html).
+
+# 1.13.13
+
+ * Fix `--debug` in `bin/6to5-node`. Thanks [@timoxley](https://github.com/timoxley).
+
+# 1.13.12
+
+ * Ignore `XJSEmptyExpression`s in `react` transformer output.
+
+# 1.13.11
+
+ * Fix `util.regexify` on falsy values.
+ * Fix `_aliasFunction` with rest parameters.
+ * Export as `module.exports` instead of `exports.default` if there are no other `ExportDeclaration`s in `commonInterop` module formatter.
+ * Add `system` module formatter. Thanks [@douglasduteil](https://github.com/douglasduteil).
+
+# 1.13.10
+
+ * Add support for `AssignmentExpression` destructuring outside of `ExpressionStatement`.
+
+# 1.13.9
+
+ * Fix `VirtualPropertyExpression` visitor keys.
+
+# 1.13.8
+
+ * Only use a single reference in abstract references.
+
+# 1.13.7
+
+ * Upgrade `acorn-6to5`.
+ * Add experimental exponentiation operator support.
+
+# 1.13.6
+
+ * Fix experimental object spread/rest helper.
+
+# 1.13.5
+
+ * Upgrade `acorn-6to5`.
+ * Add experimental support for object spread/rest.
+ * Change `arguments` to array to an additional helper method.
+
+# 1.13.4
+
+ * Fix single spread element returning itself.
+
+# 1.13.3
+
+ * Upgrade `acorn-6to5`.
+ * Add experimental support for abstract references.
+
+# 1.13.2
+
+ * Optimise `Array.from` usage by adding a helper method.
+ * Upgrade `acorn-6to5`.
+
+# 1.13.1
+
+ * Fix constructor spread optimisation. Thanks [@zloirock](https://github.com/zloirock).
+
+# 1.13.0
+
+ * Put experimental ES7 features behind a flag `--experimental` and `experimental` option.
+ * Constructor spread performance increase. Thanks [@RReverser](https://github.com/RReverser).
+ * Use `self` instead of `window` in the optional 6to5 runtime. Thanks [@RReverser](https://github.com/RReverser).
+
+# 1.12.26
+
+ * Support computed property destructuring.
+
+# 1.12.25
+
+ * Update `acorn-6to5`, `ast-types`, `es6-shim`, `chokidar`, `estraverse` and `private`.
+
+# 1.12.24
+
+ * Collect references that haven't been declared in scope.
+
+# 1.12.23
+
+ * Fix generator function export hoisting.
+
+# 1.12.22
+
+ * Update `fs-readdir-recursive` and `chokidar`.
+ * Support array destructuring on iterables.
+ * Make amd module id optional. Thanks [@webpro](https://github.com/webpro).
+
+# 1.12.21
+
+ * Fix unneccesary let scoping replacement.
+ * Add `commonInterop` module formatter. Thanks [@Naddiseo](https://github.com/Naddiseo).
+ * Fix `return` outside of function body bug. Thanks [@brentburg](https://github.com/brentburg).
+ * Add more flexible option types.
+
+# 1.12.20
+
+ * Append `sourceMappingURL` when using `bin/6to5` and output sourcemaps.
+
+# 1.12.19
+
+ * Add `comments` option and `--remove-comments` flag. Thanks [@webpro](htps://github.com/webpro).
+ * Embed `regenerator`.
+
+# 1.12.18
+
+ * Use `global` reference instead of `window`.
+
+# 1.12.17
+
+ * Add `moduleName`, `sourceRoot` and `filenameRelative` options. Thanks [@darvelo](https://github.com/darvelo).
+ * Traversal optimisations.
+
+# 1.12.16
+
+ * Fix comments not being retained from `MethodDefinition` in classes.
+ * Add temporal dead zone in default parameters.
+
+# 1.12.15
+
+ * Update `acorn-6to5`.
+
+# 1.12.14
+
+ * Fix duplicate let scoping in functions.
+ * Make JSX whitespace more React-compliant.
+ * Add `_memberExpressionKeywords` transformer that turns keyword identifiers to computed literals.
+ * Upgrade `regenerator-6to5`.
+
+# 1.12.13
+
+ * Support duplicate constants within different block scopes.
+ * Fix for-head duplication testing and replacement.
+ * Support `raw` property on tagged template literals.
+
+# 1.12.12
+
+ * Make scope tracker more reliable to handle all edgecases.
+
+# 1.12.11
+
+ * Block scope classes.
+ * Fix generation of integer `Literal`s in `MemberExpression`.
+
+# 1.12.10
+
+ * Fix let scoping var hoisting.
+
+# 1.12.9
+
+ * Escape unicode characters when generating string `Literal`s.
+ * Fix semicolons being output for statements in `ExportDeclaration`.
+ * Fix `WithStatement` missing parenthesis.
+
+# 1.12.8
+
+ * Temporarily forbid `AssignmentExpression` destructuring outside of `ExpressionStatement`.
+
+# 1.12.7
+
+ * Update to latest `acorn-6to5`.
+
+# 1.12.6
+
+ * Update to latest `acorn-6to5`.
+
+# 1.12.5
+
+ * Fix excessive whitespace trimming resulting in innaccurate sourcemap line.
+
+# 1.12.4
+
+ * Add `doc` folder for documentation.
+
+# 1.12.3
+
+ * Support generator comprehensions.
+ * Use `Array.from` instead of `Array.prototype.slice` in spread transformer.
+ * Support spread in `NewExpression`s.
+
+# 1.12.2
+
+ * Upgrade `matcha` to `0.6.0` and `browserify` to `6.3.2`.
+ * Add own `trimRight` helper instead of relying on the string instance method.
+ * Support JSX spreads that aren't the first.
+
+# 1.12.1
+
+ * Fix `this` and `arguments` mapping in the `_aliasFunctions` transformer.
+
+# 1.12.0
+
+ * Combine `jsx` and `react` transformers to `react`.
+ * Update `react` syntax output to React v0.12.
+
+# 1.11.15
+
+ * Fix JSX literal whitespace generation.
+
+# 1.11.14
+
+ * Avoid using a switch for let-scoping continue and break statements and use an if statement instead.
+ * Remove excess whitespace and newlines from JSX literals.
+
+# 1.11.13
+
+ * Update regenerator-6to5
+ * Add support for most escodegen formatting options

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing
+
+ * **General**
+   * No ES6 syntax features or methods, exclusively ES5.
+   * Max of five arguments for functions
+   * Max depth of four nested blocks
+   * 2-spaced soft tabs
+ * **Naming**
+   * CamelCase all class names
+   * camelBack all variable names
+ * **Spacing**
+   * Spaces after all keywords
+   * Spaces before all left curly braces
+ * **Comments**
+   * Use JSDoc-style comments for methods
+   * Single-line comments for ambiguous code
+ * **Quotes**
+   * Always use double quotes
+   * Only use single quotes when the string contains a double quote
+ * **Declaration**
+   * No unused variables
+   * No pollution of global variables and prototypes
+
+## Testing
+
+    $ make test
+
+## Linting
+
+    $ make lint

FEATURES.md

@@ -1,162 +0,0 @@
-# Features
-
-## Array comprehension
-
-```javascript
-[for (i of [1, 2, 3]) i * i]; // [1, 4, 9]
-```
-
-## Arrow functions
-
-```javascript
-arr.map(x => x * x);
-```
-
-## Let scoping
-
-```javascript
-for (let i in arr) {
-  let v = arr[i];
-}
-```
-
-## Classes
-
-```javascript
-class Foo extends Bar {
-  constructor() { }
-
-  foo() { }
-
-  get bar() { }
-
-  set bar() { }
-}
-```
-
-## Computed property names
-
-```javascript
-var foo = "foo";
-var bar = "bar";
-var obj = {
-  ["foo" + bar]: "heh",
-  ["bar" + foo]: "noo",
-  foo: "foo",
-  bar: "bar"
-};
-```
-
-## Constants
-
-```javascript
-const MULTIPLIER = 5;
-console.log(2 * MULTIPLIER);
-
-MULTIPLIER = 6; // error
-var MULTIPLIER; // error
-```
-
-## Default parameters
-
-```javascript
-function foo(bar = "foo") {
-  return bar + "bar";
-}
-```
-
-## Destructuring
-
-```javascript
-var [a, [b], c, d] = ["hello", [", ", "junk"], ["world"]];
-console.log(a + b + c); // hello, world
-```
-
-## For-of
-
-```javascript
-for (var i of [1, 2, 3]) {
-  console.log(i * i);
-}
-```
-
-## Generators
-
-```javascript
-```
-
-## Modules
-
-```javascript
-```
-
-## Numeric literals
-
-```javascript
-0b111110111 === 503; // true
-0o767 === 503; // true
-```
-
-## Property method assignment
-
-```javascript
-var obj = {
-  foo() {
-    return "foobar";
-  },
-
-  get bar() {
-    return this._bar;
-  },
-
-  set bar(val) {
-    this._bar = val;
-  }
-};
-```
-
-## Property name shorthand
-
-```javascript
-function f(x, y) {
-  return { x, y };
-}
-```
-
-## Rest parameters
-
-```javascript
-function printList(name, ...items) {
-  console.log("list %s has the following items", name);
-  items.forEach(function (item) {
-    console.log(item);
-  });
-}
-```
-
-## Spread
-
-```javascript
-function add(x, y) {
-  return x + y;
-}
-
-var numbers = [5, 10];
-add(...numbers); // 15
-```
-
-## Template literals
-
-```javascript
-var x = 5;
-var y = 10;
-console.log(`${x} + ${y} = ${x + y}`); // "5 + 10 = 15"
-```
-
-## Unicode regex
-
-```javascript
-var string = 'foo💩bar';
-var match = string.match(/foo(.)bar/u);
-console.log(match[1]);
-```

Makefile

@@ -6,7 +6,7 @@ MOCHA_CMD = node_modules/mocha/bin/_mocha
 
 export NODE_ENV = test
 
-.PHONY: clean test test-cov tlint est-travis test-appveyor test-browser publish bench build
+.PHONY: clean test test-cov test-clean lint test-travis test-spec test-browser publish bench build
 
 clean:
 	rm -rf coverage templates.json test/tmp dist
@@ -18,19 +18,23 @@ bench:
 lint:
 	$(JSHINT_CMD) lib bin benchmark/index.js
 
+test-clean:
+	rm -rf test/tmp
+
 test:
 	make lint
 	$(MOCHA_CMD)
+	make test-clean
 
 test-cov:
 	rm -rf coverage
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 
-test-appveyor:
+test-spec:
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) -- --reporter spec
 
 test-travis:
-	make test-appveyor
+	make test-spec
 	if test -n "$$CODECLIMATE_REPO_TOKEN"; then codeclimate < coverage/lcov.info; fi
 
 test-browser:
@@ -66,7 +70,7 @@ publish:
 
 	make build
 	cp dist/6to5.min.js browser.js
-	cp dist/polyfill.min.js polyfill.js
+	cp dist/polyfill.min.js browser-polyfill.js
 	cp dist/runtime.min.js runtime.js
 
 	node bin/cache-templates
@@ -78,4 +82,4 @@ publish:
 
 	git push --follow-tags
 
-	rm -rf templates.json browser.js runtime.js polyfill.js
+	rm -rf templates.json browser.js runtime.js browser-polyfill.js

README.md

@@ -4,7 +4,7 @@
 
 <p align="center">
   <a href="https://travis-ci.org/6to5/6to5">
-    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5.svg?branch=master&amp;style=flat&amp;label=travis">
+    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
   </a>
 
   <a href="https://ci.appveyor.com/project/sebmck/6to5">
@@ -24,479 +24,7 @@
   </a>
 </p>
 
-**6to5** turns ES6 code into vanilla ES5, so you can use ES6 features **today.**
+**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
 
- - **Readable** - formatting is retained if possible so your generated code is as similar as possible.
- - **Extensible** - with a large range of [plugins](#plugins) and **browser support**.
- - **Lossless** - **source map support** so you can debug your compiled code with ease.
- - **Compact** - maps directly to the equivalent ES5 with **no runtime**[\*](#generators).
-
-## Installation
-
-It's as easy as:
-
-    $ npm install -g 6to5
-
-## Table of Contents
-
-- [Features](#features)
-- [Usage](#usage)
-  - [Plugins](#plugins)
-  - [CLI](#cli)
-  - [Node](#node-1)
-  - [Browser](#browser)
-- [Modules](#modules)
-- [Caveats](#caveats)
-- [Polyfill](#polyfill)
-- [Optional runtime](#optional-runtime)
-- [Differences](#differences)
-
-## [Features](FEATURES.md)
-
- - [Array comprehension](FEATURES.md#array-comprehension)
- - [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)
- - [For-of](FEATURES.md#for-of)
- - [Generators](FEATURES.md#generators) via [regenerator](https://github.com/facebook/regenerator)
- - [Let scoping](FEATURES.md#let-scoping)
- - [Modules](FEATURES.md#modules)
- - [Numeric literals](FEATURES.md#numeric-literals)
- - [Property method assignment](FEATURES.md#property-method-assignment)
- - [Property name shorthand](FEATURES.md#property-name-shorthand)
- - [Rest parameters](FEATURES.md#rest-parameters)
- - [Spread](FEATURES.md#spread)
- - [Template literals](FEATURES.md#template-literals)
- - [Unicode regex](FEATURES.md#unicode-regex)
-
-## Usage
-
-### 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)
- - [Gulp](https://github.com/sindresorhus/gulp-6to5)
- - [Grunt](https://github.com/sindresorhus/grunt-6to5)
- - [Jade](https://github.com/Apoxx/jade-6to5)
- - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
- - [webpack](https://github.com/Couto/6to5-loader)
-
-### CLI
-
-Compile the file `script.js` and output it to stdout.
-
-    $ 6to5 script.js
-
-Compile the file `script.js` and output it to `script-compiled.js`.
-
-    $ 6to5 script.js --out-file script-compiled.js
-
-Compile the file `script.js` and output it to `script-compiled.js` and save a
-source map to `script-compiled.js.map`.
-
-    $ 6to5 script.js --source-maps --out-file script-compiled.js
-
-Compile the file `script.js` and output it to `script-compiled.js` with a source
-map embedded in a comment at the bottom.
-
-    $ 6to5 script.js --source-maps-inline --out-file script-compiled.js
-
-Compile the entire `src` directory and output it to the `lib` directory.
-
-    $ 6to5 src --out-dir lib
-
-Compile the entire `src` directory and output it to the one concatenated file.
-
-    $ 6to5 src --out-file script-compiled.js
-
-Pipe a file in via stdin and output it to `script-compiled.js`
-
-    $ 6to5 --out-file script-compiled.js < script.js
-
-#### Node
-
-Launch a repl.
-
-    $ 6to5-node
-
-Evaluate code.
-
-    $ 6to5-node -e "class Test { }"
-
-Compile and run `test.js`.
-
-    $ 6to5-node test
-
-### Node
-
-```javascript
-var to5 = require("6to5");
-
-var result = to5.transform("code();", options);
-result.code;
-result.map;
-result.ast;
-
-to5.transformFileSync("filename.js", options).code;
-
-to5.transformFile("filename.js", options, function (err, result) {
-
-});
-```
-
-##### Options
-
-```javascript
-{
-  // Filename for use in errors etc.
-  // Default: "unknown"
-  filename: "filename",
-
-  // List of transformers to EXCLUDE.
-  // Run `6to5 --help` to see a full list of transformers.
-  blacklist: [],
-
-  // List of transformers to ONLY use.
-  // Run `6to5 --help` to see a full list of transformers.
-  whitelist: [],
-
-  // Module formatter to use
-  // Run `6to5 --help` to see a full list of module formatters.
-  // Default: "common"
-  modules: "common",
-
-  // If truthy, adds a `map` property to returned output.
-  // If set to "inline", a comment with a sourceMappingURL directive is added to
-  // the bottom of the returned code.
-  // Default: false
-  sourceMap: true,
-
-  // Set `file` on returned source map.
-  // Default: `filename` option.
-  sourceMapName: "filename",
-
-  // Set `sources[0]` on returned source map.
-  // Default: `filename` option.
-  sourceFileName: "filename",
-
-  // Optionally replace all 6to5 helper declarations with a referenece to this
-  // variable. If set to `true` then the default namespace is used "to5Runtime".
-  // Default: false
-  runtime: true
-}
-```
-
-#### Require hook
-
-All subsequent files required by node with the extensions `.es6` and `.js` will
-be transformed by 6to5. The polyfill specified in [Polyfill](#polyfill) is also
-required.
-
-```javascript
-require("6to5/register");
-```
-
-**NOTE:** By default all requires to `node_modules` will be ignored. You can
-override this by passing an ignore regex via:
-
-```javascript
-require("6to5/register")({
-  // This will override `node_modules` ignoring - you can alternatively pass
-  // a regex
-  ignore: false
-});
-```
-
-##### Options
-
-```javascript
-require("6to5/register")({
-  // Optional ignore regex - if any filenames **do** match this regex then they
-  // aren't compiled
-  ignore: /regex/,
-
-  // Optional only regex - if any filenames **don't** match this regex then they
-  // aren't compiled
-  only: /my_es6_folder/,
-
-  // See options above for usage
-  whitelist: [],
-  blacklist: [],
-
-  // This will remove the currently hooked extensions of .es6 and .js so you'll
-  // have to add them back if you want them to be used again.
-  extensions: [".js", ".es6"]
-});
-```
-
-### Browser
-
-A browser version of 6to5 is available from `browser.js` inside the 6to5
-directory in an npm release.
-
-#### Scripts
-
-While it's not recommended for serious use, when the browser version is included
-all scripts with the type `text/ecmascript-6` and `text/6to5` are automatically
-compiled and ran.
-
-For example:
-
-```html
-<script src="node_modules/6to5/browser.js"></script>
-<script type="text/6to5">
-class Test {
-  test() {
-    return "test";
-  }
-}
-
-var test = new Test;
-test.test();
-</script>
-```
-
-#### Build
-
-You can build a browser version of the compiler by running the following in the
-6to5 directory:
-
-    $ make build
-
-This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
-
-#### API
-
-```javascript
-to5.transform("class Test {}").code;
-```
-
-#### Test
-
-To test 6to5 in your browser run:
-
-    $ make test-browser
-
-And open `test/browser.html` in your browser if it doesn't open automatically.
-
-## [Modules](MODULES.md)
-
-See [Modules - Common](MODULES.md#common-default) for documentation on the
-default module formatting.
-
-Alternatively see [Modules](MODULES.md) for all other supported module formatting types.
-
-## Caveats
-
-### For-of
-
-A polyfill is required for for-of functionality that implements `Symbol` and
-adds `prototype[Symbol.iterator]` behaviour to built-ins. Using the polyfills
-specified in [polyfill](#polyfill) suffices.
-
-### Classes
-
-Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
-limitations in ES5 implementations.
-
-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),
-this is widely supported but you may run into problems with much older browsers.
-
-**NOTE:** `__proto__` is not supported on IE <= 9 so static properties
-**will not** be inherited. A possible workaround is to use `super();`:
-
-```javascript
-class Foo {
-  static foo() {
-
-  }
-}
-
-class Bar extends Foo {
-  static foo() {
-    super();
-  }
-}
-```
-
-### Generators
-
-The [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js)
-and an [ES6 polyfill](#polyfill) are required in order for generators to work.
-
-## 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.
-
-### Node
-
-```javascript
-require("6to5/polyfill");
-```
-
-### Browser
-
-Available from the `polyfill.js` file within the 6to5 directory of an npm
-release.
-
-## Optional runtime
-
-6to5 has a few helper functions that'll be placed at the top of the generated
-code if needed so it's not inlined multiple times throughout that file. This may
-become an issue if you have multiple files, especially when you're sending them
-to the browser. gzip alleviates most of this concern but it's still not ideal.
-
-You can tell 6to5 to not place any declarations at the top of your files and
-instead just point them to a reference contained within the runtime.
-
-Simply use the following option if you're using the [Node API](#node-1):
-
-```javascript
-{
-  runtime: true
-}
-```
-
-or the following flag if you're using the [CLI](#cli):
-
-    $ 6to5 --runtime
-
-Then just include the runtime before your generated code.
-
-### Getting the runtime
-
-You can get the runtime via either:
-
-    $ 6to5-runtime
-
-or
-
-```javascript
-require("6to5").runtime();
-```
-
-or from an npm release in `runtime.js` from the 6to5 directory.
-
-### Customising namespace
-
-You can also customise the runtime namespace by passing an optional namespace
-argument:
-
-```javascript
-require("6to5").runtime("myCustomNamespace");
-```
-
-    $ 6to5-runtime myCustomNamespace
-
-See [Options - runtime](#options) for documentation on changing the reference in
-generated code.
-
-## Differences
-
-### Philosophy
-
-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.
-
-Many other transpilers are just concerned with making the code work while 6to5
-is concerned with making sure it works **and** is readable at the same time.
-
-For example, given the following array comprehension:
-
-```javascript
-var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }];
-```
-
-is generated to the following with 6to5:
-
-```javascript
-var seattlers = customers.filter(function (c) {
-  return c.city == "Seattle";
-}).map(function (c) {
-  return {
-    name: c.name,
-    age: c.age
-  };
-});
-```
-
-The following is what Traceur generates:
-
-```javascript
-var seattlers = (function() {
-  var c;
-  var $__20 = 0,
-      $__21 = [];
-  for (var $__22 = customers[$traceurRuntime.toProperty(Symbol.iterator)](),
-      $__23; !($__23 = $__22.next()).done; ) {
-    c = $__23.value;
-    if (c.city == "Seattle")
-      $traceurRuntime.setProperty($__21, $__20++, {
-        name: c.name,
-        age: c.age
-      });
-  }
-  return $__21;
-}());
-```
-
-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.
-
-I'm not saying 6to5 is for everyone or even suited for everything. Traceur is
-better suited if you'd like a full ES6 environment with polyfills and all.
-
-### Comparison to other transpilers
-
-|                              | 6to5 | Traceur | esnext | es6now | es6-transpiler | jstransform |
-| ---------------------------- | ---- | ------- | ------ | ------ | -------------- | ----------- |
-| No runtime                   | ✓    |         |        |        | ✓              | ✓           |
-| Source maps                  | ✓    | ✓       | ✓      |        | ✓              | ✓           |
-| No compiler global pollution | ✓    |         | ✓      |        | ✓              | ✓           |
-| Arrow functions              | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Classes                      | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Computed property names      | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Constants                    | ✓    | ✓       |        |        | ✓              |             |
-| Default parameters           | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Destructuring                | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| For-of                       | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Generators                   | ✓    | ✓       | ✓      |        |                |             |
-| Let scoping                  | ✓    | ✓       |        |        | ✓              |             |
-| Modules                      | ✓    | ✓       |        | ✓      |                |             |
-| Property method assignment   | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Property name shorthand      | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Rest parameters              | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| 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 runtime can be eliminated entirely.
-
-#### [es6now](https://github.com/zenparsing/es6now)
-
-es6now doesn't output sourcemaps. This is cited as a positive as line-to-line
-mapping is the goal. This however obviously doesn't retain column mapping
-resulting in the output code not being very pleasant.
-
-#### [es6-transpiler](https://github.com/termi/es6-transpiler)
-
-The es6-transpiler compiler requires shims to operate which pollutes the global
-scope resulting in possible collisions.
-
-es6-transpiler maps line-by-line, just like es6now, this results in the same
-issues such as lack of column information and unpleasant code output.
+For more information view the [documentation](https://6to5.github.io). For
+support visit the [gitter room](https://gitter.im/6to5/6to5).

appveyor.yml

@@ -10,7 +10,7 @@ install:
 test_script:
  - "node --version"
  - "npm --version"
- - "make test-appveyor"
+ - "make test-spec"
 
 build: "off"
 

bin/6to5-node

@@ -14,13 +14,11 @@ process.argv.slice(2).forEach(function(arg){
   switch (flag) {
     case "-d":
       args.unshift("--debug");
-      args.push("--no-timeouts");
       break;
     case "debug":
     case "--debug":
     case "--debug-brk":
       args.unshift(arg);
-      args.push("--no-timeouts");
       break;
     case "-gc":
     case "--expose-gc":

bin/6to5/dir.js

@@ -19,7 +19,9 @@ module.exports = function (commander, filenames, opts) {
     mkdirp.sync(up);
 
     if (commander.sourceMaps) {
-      fs.writeFileSync(dest + ".map", JSON.stringify(data.map));
+      var mapLoc = dest + ".map";
+      data.code = util.addSourceMappingUrl(data.code, mapLoc);
+      fs.writeFileSync(mapLoc, JSON.stringify(data.map));
     }
 
     fs.writeFileSync(dest, data.code);

bin/6to5/file.js

@@ -56,7 +56,9 @@ module.exports = function (commander, filenames) {
 
     if (commander.outFile) {
       if (commander.sourceMaps) {
-        fs.writeFileSync(commander.outFile + ".map", JSON.stringify(result.map));
+        var mapLoc = commander.outFile + ".map";
+        result.code = util.addSourceMappingUrl(result.code, mapLoc);
+        fs.writeFileSync(mapLoc, JSON.stringify(result.map));
       }
 
       fs.writeFileSync(commander.outFile, result.code);

bin/6to5/index.js

@@ -11,12 +11,16 @@ commander.option("-s, --source-maps", "Save source map alongside the compiled co
 commander.option("-f, --filename [filename]", "Filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]", "stdin");
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
+commander.option("-e, --experimental", "Enable experimental support for proposed ES7 features");
+commander.option("-p, --playground", "Enable playground support");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
 commander.option("-b, --blacklist [blacklist]", "Blacklist of transformers to NOT use", util.list);
 commander.option("-o, --out-file [out]", "Compile all input files into a single file");
 commander.option("-d, --out-dir [out]", "Compile an input directory of modules into an output directory");
+commander.option("-c, --remove-comments", "Remove comments from the compiled code", false);
+commander.option("-a, --amd-module-ids", "Insert module id in AMD modules", false);
 
 commander.on("--help", function(){
   var outKeys = function (title, obj) {
@@ -85,9 +89,13 @@ if (errors.length) {
 
 exports.opts = {
   sourceMapName: commander.outFile,
+  amdModuleIds:  commander.amdModuleIds,
+  experimental:  commander.experimental,
+  playground:    commander.playground,
   blacklist:     commander.blacklist,
   whitelist:     commander.whitelist,
   sourceMap:     commander.sourceMaps || commander.sourceMapsInline,
+  comments:      !commander.removeComments,
   runtime:       commander.runtime,
   modules:       commander.modules
 };

bin/6to5/util.js

@@ -1,6 +1,7 @@
 var readdir = require("fs-readdir-recursive");
 var index   = require("./index");
 var util    = require("../../lib/6to5/util");
+var path    = require("path");
 var to5     = require("../../lib/6to5");
 var fs      = require("fs");
 var _       = require("lodash");
@@ -11,6 +12,10 @@ exports.readdirFilter = function (filename) {
   });
 };
 
+exports.addSourceMappingUrl = function (code, loc) {
+  return code + "\n//# sourceMappingURL=" + path.basename(loc);
+};
+
 exports.transform = function (filename, code, opts) {
   opts = _.extend(opts || {}, index.opts);
   opts.filename = filename;

bin/_6to5-node

@@ -1,17 +1,19 @@
 #!/usr/bin/env node
 
 var commander = require("commander");
-var util      = require("../lib/6to5/util");
 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");
-commander.option("-i, --ignore [regex]", "ignore all files that match this regex when using the require hook");
-commander.option("-x, --extensions [extensions]", "list of extensions to hook into [.es6,.js]", util.list);
+commander.option("-e, --eval [script]", "Evaluate script");
+commander.option("-p, --print", "Evaluate script and print result");
+commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
+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");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
@@ -20,22 +22,21 @@ commander.parse(process.argv);
 
 //
 
-var registerOpts = {};
-
-if (commander.ignore) {
-  registerOpts.ignoreRegex = new RegExp(commander.ignore);
-}
-
-if (commander.extensions && commander.extensions.length) {
-  registerOpts.extensions = commander.extensions;
-}
-
-to5.register(registerOpts);
+to5.register({
+  experimental: commander.experimental,
+  extensions:   commander.extensions,
+  ignore:       commander.ignore
+});
 
 //
 
 var _eval = function (code, filename) {
-  code = to5.transform(code, { filename: filename, blacklist: ["useStrict"] }).code;
+  code = to5.transform(code, {
+    modules: "commonInterop",
+    filename: filename,
+    blacklist: ["useStrict"],
+    experimental: commander.experimental
+  }).code;
   return vm.runInThisContext(code, filename);
 };
 

doc/browser.md

@@ -0,0 +1,65 @@
+# Browser
+
+A browser version of 6to5 is available from `browser.js` inside the 6to5
+directory in an npm release.
+
+## Scripts
+
+While it's not recommended for serious use, when the browser version is included
+all scripts with the type `text/ecmascript-6` and `text/6to5` are automatically
+compiled and ran.
+
+For example:
+
+```html
+<script src="node_modules/6to5/browser.js"></script>
+<script type="text/6to5">
+class Test {
+  test() {
+    return "test";
+  }
+}
+
+var test = new Test;
+test.test();
+</script>
+```
+
+## Build
+
+You can build a browser version of the compiler by running the following in the
+6to5 directory:
+
+```sh
+$ make build
+```
+
+This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
+
+## Test
+
+To test 6to5 in your browser run:
+
+```sh
+$ make test-browser
+```
+
+And open `test/browser.html` in your browser if it doesn't open automatically.
+
+## API
+
+### to5.transform(code, [opts])
+
+See [options](usage.md#options) for additional documentation.
+
+```javascript
+to5.transform("class Test {}").code;
+```
+
+### to5.run(code, [opts])
+
+See [options](usage.md#options) for additional documentation.
+
+```javascript
+to5.run("class Test {}");
+```

doc/caveats.md

@@ -0,0 +1,41 @@
+# Caveats
+
+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:
+
+| 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`                                                                                                |
+
+## Classes
+
+Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
+limitations in ES5 implementations.
+
+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),
+this is widely supported but you may run into problems with much older browsers.
+
+**NOTE:** `__proto__` is not supported on IE <= 9 so static properties
+**will not** be inherited. A possible workaround is to use `super();`:
+
+```javascript
+class Foo {
+  static foo() {
+
+  }
+}
+
+class Bar extends Foo {
+  static foo() {
+    super();
+  }
+}
+```

doc/differences.md

@@ -0,0 +1,113 @@
+# Differences
+
+## Philosophy
+
+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.
+
+Many other transpilers are just concerned with making the code work while 6to5
+is concerned with making sure it works **and** is readable at the same time.
+
+For example, given the following array comprehension:
+
+```javascript
+var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }];
+```
+
+is generated to the following with 6to5:
+
+```javascript
+var seattlers = customers.filter(function (c) {
+  return c.city == "Seattle";
+}).map(function (c) {
+  return {
+    name: c.name,
+    age: c.age
+  };
+});
+```
+
+The following is what Traceur generates:
+
+```javascript
+var seattlers = (function() {
+  var c;
+  var $__20 = 0,
+      $__21 = [];
+  for (var $__22 = customers[$traceurRuntime.toProperty(Symbol.iterator)](),
+      $__23; !($__23 = $__22.next()).done; ) {
+    c = $__23.value;
+    if (c.city == "Seattle")
+      $traceurRuntime.setProperty($__21, $__20++, {
+        name: c.name,
+        age: c.age
+      });
+  }
+  return $__21;
+}());
+```
+
+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.
+
+I'm not saying 6to5 is for everyone or even suited for everything. Traceur is
+better suited if you'd like a full ES6 environment with polyfills and all.
+
+## Comparison to other transpilers
+
+### Features
+
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Source maps                  | ✓    | ✓       | ✓              | ✓      |        | ✓           |
+| No compiler global pollution | ✓    |         | ✓              | ✓      |        | ✓           |
+| Optional runtime             | ✓    |         | ✓              |        |        | ✓           |
+| Browser support              | ✓    | ✓       |                | ✓      |        |             |
+
+### 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                | ✓     | ✓       | ✓              |        |        |             |
+
+### [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.
+
+### [es6now](https://github.com/zenparsing/es6now)
+
+es6now doesn't output sourcemaps. This is cited as a positive as line-to-line
+mapping is the goal. This however obviously doesn't retain column mapping
+resulting in the output code not being very pleasant.
+
+### [es6-transpiler](https://github.com/termi/es6-transpiler)
+
+The es6-transpiler compiler requires shims to operate which pollutes the global
+scope resulting in possible collisions.
+
+es6-transpiler maps line-by-line, just like es6now, this results in the same
+issues such as lack of column information and unpleasant code output.

doc/features.md

@@ -0,0 +1,277 @@
+# Features
+
+## Abstract references ([experimental](usage.md#experimental)) ([spec](https://github.com/zenparsing/es-abstract-refs))
+
+```javascript
+foo::bar;
+foo::bar = baz;
+delete foo::bar;
+```
+
+## Array comprehensions ([experimental](usage.md#experimental))
+
+```javascript
+var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
+```
+
+## Arrow functions
+
+```javascript
+// Expression bodies
+var odds = evens.map(v => v + 1);
+var nums = evens.map((v, i) => v + i);
+
+// Statement bodies
+nums.forEach(v => {
+  if (v % 5 === 0)
+    fives.push(v);
+});
+
+// Lexical this
+var bob = {
+  _name: "Bob",
+  _friends: [],
+  printFriends() {
+    this._friends.forEach(f => {
+      console.log(this._name + " knows " + f);
+    });
+  }
+};
+```
+
+## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
+
+```javascript
+async function chainAnimationsAsync(elem, animations) {
+  for (var anim of animations) {
+    await anim(elem);
+  }
+}
+```
+
+## Classes
+
+```javascript
+class SkinnedMesh extends THREE.Mesh {
+  constructor(geometry, materials) {
+    super(geometry, materials);
+
+    this.idMatrix = SkinnedMesh.defaultMatrix();
+    this.bones = [];
+    this.boneMatrices = [];
+    //...
+  }
+
+  update(camera) {
+    //...
+    super.update();
+  }
+
+  static defaultMatrix() {
+    return new THREE.Matrix4();
+  }
+}
+```
+
+## Computed property names
+
+```javascript
+var foo = "foo";
+var bar = "bar";
+var obj = {
+  ["foo" + bar]: "heh",
+  ["bar" + foo]: "noo",
+  foo: "foo",
+  bar: "bar"
+};
+```
+
+## Constants
+
+```javascript
+const MULTIPLIER = 5;
+console.log(2 * MULTIPLIER);
+
+MULTIPLIER = 6; // error
+var MULTIPLIER; // error
+```
+
+## Default parameters
+
+```javascript
+function f(x, y = 12) {
+  // y is 12 if not passed (or passed as undefined)
+  return x + y;
+}
+f(3) == 15
+```
+
+## Destructuring
+
+```javascript
+// list matching
+var [a, , b] = [1,2,3];
+
+// object matching
+var { op: a, lhs: { op: b }, rhs: c } = getASTNode();
+
+// object matching shorthand
+// binds `op`, `lhs` and `rhs` in scope
+var { op, lhs, rhs } = getASTNode();
+
+// Can be used in parameter position
+function g({ name: x }) {
+  console.log(x);
+}
+g({ name: 5 });
+
+// Fail-soft destructuring
+var [a] = [];
+a === undefined;
+```
+
+## Exponentiation operator ([experimental](usage.md#experimental)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+
+```javascript
+var a = 2;
+a **= 2;
+
+var squared = 2 ** 2;
+```
+
+## For-of
+
+```javascript
+for (var i of [1, 2, 3]) {
+  console.log(i * i);
+}
+```
+
+## Generators
+
+```javascript
+function* fibonacci() {
+  var pre = 0, cur = 1;
+  for (;;) {
+    var temp = pre;
+    pre = cur;
+    cur += temp;
+    yield cur;
+  }
+}
+
+for (var n of fibonacci()) {
+  // truncate the sequence at 1000
+  if (n > 1000) break;
+  console.log(n);
+}
+```
+
+## Generator comprehensions ([experimental](usage.md#experimental))
+
+```javascript
+var nums = [1, 2, 3, 4, 5, 6];
+var multiples = (for (i of nums) if (i % 2) i * i);
+assert.equal(multiples.next().value, 1);
+assert.equal(multiples.next().value, 9);
+assert.equal(multiples.next().value, 25);
+```
+
+## Let scoping
+
+```javascript
+for (let i in arr) {
+  let v = arr[i];
+}
+```
+
+## Modules
+
+```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 function test() {}
+
+export default test;
+```
+
+## Numeric literals
+
+```javascript
+0b111110111 === 503; // true
+0o767 === 503; // true
+```
+
+## Object spread/rest ([experimental](usage.md#experimental)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
+
+```javascript
+var n = { x, y, ...z };
+var { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
+```
+
+## Property method assignment
+
+```javascript
+var obj = {
+  foo() {
+    return "foobar";
+  },
+
+  get bar() {
+    return this._bar;
+  },
+
+  set bar(val) {
+    this._bar = val;
+  }
+};
+```
+
+## Property name shorthand
+
+```javascript
+function f(x, y) {
+  return { x, y };
+}
+```
+
+## Rest parameters
+
+```javascript
+function f(x, ...y) {
+  // y is an Array
+  return x * y.length;
+}
+f(3, "hello", true) == 6
+```
+
+## Spread
+
+```javascript
+function f(x, y, z) {
+  return x + y + z;
+}
+// Pass each elem of array as argument
+f(...[1,2,3]) == 6
+```
+
+## Template literals
+
+```javascript
+var x = 5;
+var y = 10;
+console.log(`${x} + ${y} = ${x + y}`); // "5 + 10 = 15"
+```
+## Unicode regex
+
+```javascript
+var string = 'foo💩bar';
+var match = string.match(/foo(.)bar/u);
+console.log(match[1]);
+```

doc/index.md

@@ -0,0 +1,61 @@
+**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
+
+ - **Readable** - formatting is retained if possible so your generated code is as similar as possible.
+ - **Extensible** - with a large range of [plugins](plugins.md) and **browser support**.
+ - **Lossless** - **source map support** so you can debug your compiled code with ease.
+ - **Compact** - maps directly to the equivalent ES5 with **no runtime**[\*](caveats.md).
+
+## Installation
+
+It's as easy as:
+
+    $ npm install -g 6to5
+
+## Usage
+
+Once you've installed 6to5, there are multiple paths you can take depending on
+how you want to use it.
+
+6to5 will simply compile your ES6+ script to ES5 if you pass it as an argument
+to the command-line tool `6to5`:
+
+```sh
+$ 6to5 script.js
+```
+
+If you have a file written using ES6+ and you just want to run it, `6to5-node`
+has you covered:
+
+```sh
+$ 6to5-node script.js
+```
+
+And it doesn't end here! To see all the ways you can use 6to5, check out the
+[Usage](http://6to5.github.io/usage.html) page.
+
+## [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))
+ - [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))
+ - [For-of](features.md#for-of)
+ - [Generators](features.md#generators)
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
+ - [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))
+ - [Property method assignment](features.md#property-method-assignment)
+ - [Property name shorthand](features.md#property-name-shorthand)
+ - [React/JSX](react.md)
+ - [Rest parameters](features.md#rest-parameters)
+ - [Spread](features.md#spread)
+ - [Template literals](features.md#template-literals)
+ - [Unicode regex](features.md#unicode-regex)

doc/modules.md

@@ -4,7 +4,9 @@
 
 ### CLI
 
-    $ 6to5 --modules common script.js
+```sh
+$ 6to5 --modules common script.js
+```
 
 ### Node
 
@@ -15,8 +17,19 @@ to5.transform('import "foo";', { modules: "common" });
 
 ## Formats
 
+ * [AMD](#amd)
+ * [Common (Default)](#common-default)
+ * [Common Interop](#common-interop)
+ * [Ignore](#ignore)
+ * [System](#system)
+ * [UMD](#umd)
+
 ### Common (Default)
 
+```sh
+$ 6to5 --modules common
+```
+
 **In**
 
 ```javascript
@@ -51,8 +64,79 @@ 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.test = test;
+var test = exports.test = 5;
+
+exports["default"] = test;
+```
+
+#### module.exports behaviour
+
+If there exist no other non-default `export`s then `default exports` are
+exported as `module.exports` instead of `exports.default`.
+
+**In**
+
+```javascript
+export default function foo() {
+
+}
+```
+
+**Out**
+
+```javascript
+module.exports = foo;
+
+function foo() {
+
+}
+```
+
 ### AMD
 
+```sh
+$ 6to5 --modules amd
+```
+
 **In**
 
 ```javascript
@@ -77,8 +161,18 @@ define(["exports", "foo"], function (exports, _foo) {
 });
 ```
 
+You can optionally specify to include the module id (using the `--amd-module-id` argument):
+
+```javascript
+define("filename", ["exports", "foo"], function (exports, _foo) {})
+```
+
 ### UMD
 
+```sh
+$ 6to5 --modules umd
+```
+
 **In**
 
 ```javascript
@@ -111,6 +205,9 @@ export function bar() {
 
 ### Ignore
 
+```sh
+$ 6to5 --modules ignore
+```
 
 **In**
 
@@ -130,11 +227,52 @@ function bar() {
 }
 ```
 
+### System
+
+```sh
+$ 6to5 --modules system
+```
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+System.register("bar", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "bar";
+
+  var foo;
+  function bar() {
+    return foo("foobar");
+  }
+  return {
+    setters: [function (m) {
+      foo = m.default;
+    }],
+    execute: function () {
+      _export("bar", bar);
+    }
+  };
+});
+```
+
 ## Custom
 
 You can alternatively specify module names instead of one of the built-in types.
 
-    $ 6to5 --modules custom-module-formatter
+```sh
+$ 6to5 --modules custom-module-formatter
+```
 
 **node_modules/custom-module-formatter/index.js**
 

doc/optional-runtime.md

@@ -0,0 +1,57 @@
+# Optional runtime
+
+6to5 has a few helper functions that'll be placed at the top of the generated
+code if needed so it's not inlined multiple times throughout that file. This may
+become an issue if you have multiple files, especially when you're sending them
+to the browser. gzip alleviates most of this concern but it's still not ideal.
+
+You can tell 6to5 to not place any declarations at the top of your files and
+instead just point them to a reference contained within the runtime.
+
+Simply use the following option if you're using the [Node API](usage.md#node):
+
+```javascript
+{
+  runtime: true
+}
+```
+
+or the following flag if you're using the [CLI](usage.md#cli):
+
+```ssh
+$ 6to5 --runtime
+```
+
+Then just include the runtime before your generated code.
+
+## Getting the runtime
+
+You can get the runtime via either:
+
+```sh
+$ 6to5-runtime
+```
+
+or
+
+```javascript
+require("6to5").runtime();
+```
+
+or from an npm release in `runtime.js` from the 6to5 directory.
+
+## Customising namespace
+
+You can also customise the runtime namespace by passing an optional namespace
+argument:
+
+```javascript
+require("6to5").runtime("myCustomNamespace");
+```
+
+```sh
+$ 6to5-runtime myCustomNamespace
+```
+
+See [Options - runtime](usage.md#options) for documentation on changing the
+reference in generated code.

doc/playground.md

@@ -0,0 +1,68 @@
+# Playground
+
+Playground is a proving ground for **possible** ES7 proposals.
+
+**NOTE: These features are in no way endorsed by Ecma International and are not a part of ES6. They might become a part of ECMAScript in the future.**
+
+## Usage
+
+    $ 6to5 --playground
+
+```javascript
+to5.transform("code", { playground: true });
+```
+
+**NOTE:** Enabling `playground` also enables [experimental support](usage.md#experimental).
+
+## Features
+
+ * [Memoization operator](#memoization-operator)
+ * [Method binding](#method-binding)
+
+### Memoization assignment operator
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+obj.x; // 2
+
+obj = { x: 1 };
+obj.x ?= 2;
+obj.x; // 1
+
+obj = { x: undefined }
+obj.x ?= 2;
+obj.x; // undefined
+```
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+```
+
+equivalent to:
+
+```javascript
+var obj = {};
+if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
+```
+
+### Method binding
+
+```javascript
+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"]
+```
+
+equivalent to:
+
+```javascript
+var fn = obj.method.bind(obj);
+var fn = obj.method.bind(obj, "foob");
+
+["foo", "bar"].map(function (val) { return val.toUpperCase(); });
+[1.1234, 23.53245, 3].map(function (val) { return val.toFixed(2); });
+```

doc/plugins.md

@@ -0,0 +1,18 @@
+# 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)
+ - [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)
+ - [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)

doc/polyfill.md

@@ -0,0 +1,27 @@
+# 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.
+
+This will emulate a full ES6 environment. This polyfill is automatically loaded
+when using [6to5-node](usage.md#node).
+
+## Usage
+
+### Node
+
+You need to include the polyfill require at the top the **entry point** to your
+application.
+
+```javascript
+require("6to5/polyfill");
+```
+
+### Browser
+
+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.

doc/react.md

@@ -0,0 +1,17 @@
+# React/JSX
+
+6to5 has built-in support for React v0.12. Tags are automatically transformed to
+their equivalent `React.createElement(...)` and `displayName` is automatically
+inferred and added to all `React.createClass` calls.
+
+## Blacklist
+
+To disable this behaviour add `react` to your blacklist:
+
+```javascript
+to5.transform("code", { blacklist: ["react"] });
+```
+
+```sh
+$ 6to5 --blacklist react
+```

doc/usage.md

@@ -0,0 +1,216 @@
+# Usage
+
+## CLI
+
+Compile the file `script.js` and output it to stdout.
+
+```sh
+$ 6to5 script.js
+```
+
+Compile the file `script.js` and output it to `script-compiled.js`.
+
+```sh
+$ 6to5 script.js --out-file script-compiled.js
+```
+
+Compile the file `script.js` and output it to `script-compiled.js` and save a
+source map to `script-compiled.js.map`.
+
+```sh
+$ 6to5 script.js --source-maps --out-file script-compiled.js
+```
+
+Compile the file `script.js` and output it to `script-compiled.js` with a source
+map embedded in a comment at the bottom.
+
+```sh
+$ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```
+
+Compile the entire `src` directory and output it to the `lib` directory.
+
+```sh
+$ 6to5 src --out-dir lib
+```
+
+Compile the entire `src` directory and output it to the one concatenated file.
+
+```sh
+$ 6to5 src --out-file script-compiled.js
+```
+
+Pipe a file in via stdin and output it to `script-compiled.js`
+
+```sh
+$ 6to5 --out-file script-compiled.js < script.js
+```
+
+### Node
+
+Launch a repl.
+
+```sh
+$ 6to5-node
+```
+
+Evaluate code.
+
+```sh
+$ 6to5-node -e "class Test { }"
+```
+
+Compile and run `test.js`.
+
+```sh
+$ 6to5-node test
+```
+
+## Node
+
+```javascript
+var to5 = require("6to5");
+```
+
+### to5.transform(code, [opts]);
+
+```javascript
+var result = to5.transform("code();", options);
+result.code;
+result.map;
+result.ast;
+```
+
+### to5.transformFileSync(filename, [opts])
+
+```javascript
+to5.transformFileSync("filename.js", options).code;
+```
+
+### to5.transformFile(filename, [opts], callback)
+
+```javascript
+to5.transformFile("filename.js", options, function (err, result) {
+  result.code;
+});
+```
+
+#### Options
+
+```javascript
+{
+  // Filename for use in errors etc.
+  // Default: "unknown"
+  filename: "filename",
+
+  // Filename relative to `sourceRoot`
+  // Default: `filename` option.
+  filenameRelative: "",
+
+  // List of transformers to EXCLUDE.
+  // Run `6to5 --help` to see a full list of transformers.
+  blacklist: [],
+
+  // List of transformers to ONLY use.
+  // Run `6to5 --help` to see a full list of transformers.
+  whitelist: [],
+
+  // Module formatter to use
+  // Run `6to5 --help` to see a full list of module formatters.
+  // Default: "common"
+  modules: "common",
+
+  // If truthy, adds a `map` property to returned output.
+  // If set to "inline", a comment with a sourceMappingURL directive is added to
+  // the bottom of the returned code.
+  // Default: false
+  sourceMap: true,
+
+  // Set `file` on returned source map.
+  // Default: `filenameRelative` option.
+  sourceMapName: "filename",
+
+  // Set `sources[0]` on returned source map.
+  // Default: `filenameRelative` option.
+  sourceFileName: "filename",
+
+  // The root from which all sources are relative
+  // Default: `moduleRoot` option.
+  sourceRoot: "assets/scripts",
+
+  // Optional prefix for the AMD module formatter that will be prepend to the
+  // filename on module definitions
+  // Default: `sourceRoot` option.
+  moduleRoot: "my-app",
+
+  // If truthy, insert an explicit id for each defined AMD module.
+  // By default, AMD modules are anonymous.
+  // Default: false
+  amdModuleIds: true,
+
+  // Optionally replace all 6to5 helper declarations with a referenece to this
+  // variable. If set to `true` then the default namespace is used "to5Runtime".
+  // Default: false
+  runtime: true,
+
+  // Output comments in generated output
+  // Default: true
+  comments: false,
+
+  // Enable support for experimental ES7 features
+  // Default: false
+  experimental: true
+}
+```
+
+### Require hook
+
+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.
+
+```javascript
+require("6to5/register");
+```
+
+**NOTE:** By default all requires to `node_modules` will be ignored. You can
+override this by passing an ignore regex via:
+
+```javascript
+require("6to5/register")({
+  // This will override `node_modules` ignoring - you can alternatively pass
+  // a regex
+  ignore: false
+});
+```
+
+#### Options
+
+```javascript
+require("6to5/register")({
+  // Optional ignore regex - if any filenames **do** match this regex then they
+  // aren't compiled
+  ignore: /regex/,
+
+  // Optional only regex - if any filenames **don't** match this regex then they
+  // aren't compiled
+  only: /my_es6_folder/,
+
+  // See options above for usage
+  whitelist: [],
+  blacklist: [],
+
+  // This will remove the currently hooked extensions of .es6 and .js so you'll
+  // have to add them back if you want them to be used again.
+  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**.

lib/6to5/browser.js

@@ -2,13 +2,6 @@ var transform = module.exports = require("./transformation/transform");
 
 transform.transform = transform;
 
-transform.eval = function (code, opts) {
-  opts = opts || {};
-  opts.filename = opts.filename || "eval";
-  opts.sourceMap = "inline";
-  return eval(transform(code, opts).code);
-};
-
 transform.run = function (code, opts) {
   opts = opts || {};
   opts.sourceMap = "inline";
@@ -19,7 +12,7 @@ transform.load = function (url, callback, opts, hold) {
   opts = opts || {};
   opts.filename = opts.filename || url;
 
-  var xhr = window.ActiveXObject ? new window.ActiveXObject("Microsoft.XMLHTTP") : new window.XMLHttpRequest();
+  var xhr = global.ActiveXObject ? new global.ActiveXObject("Microsoft.XMLHTTP") : new global.XMLHttpRequest();
   xhr.open("GET", url, true);
   if ("overrideMimeType" in xhr) xhr.overrideMimeType("text/plain");
 
@@ -67,7 +60,7 @@ var runScripts = function () {
     }
   };
 
-  var _scripts = window.document.getElementsByTagName("script");
+  var _scripts = global.document.getElementsByTagName("script");
   for (var i in _scripts) {
     var _script = _scripts[i];
     if (types.indexOf(_script.type) >= 0) scripts.push(_script);
@@ -80,8 +73,8 @@ var runScripts = function () {
   exec();
 };
 
-if (window.addEventListener) {
-  window.addEventListener("DOMContentLoaded", runScripts, false);
-} else {
-  window.attachEvent("onload", runScripts);
+if (global.addEventListener) {
+  global.addEventListener("DOMContentLoaded", runScripts, false);
+} else if (global.attachEvent) {
+  global.attachEvent("onload", runScripts);
 }

lib/6to5/file.js

@@ -10,46 +10,89 @@ var t         = require("./types");
 var _         = require("lodash");
 
 function File(opts) {
-  this.opts            = File.normaliseOptions(opts);
-  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
-
-  this.declarations = {};
-  this.uids         = {};
-  this.ast          = {};
+  this.opts = File.normaliseOptions(opts);
+  this.uids = {};
+  this.ast  = {};
 }
 
-File.declarations = ["extends", "class-props", "slice"];
+File.declarations = [
+  "extends",
+  "class-props",
+  "apply-constructor",
+  "tagged-template-literal",
+  "interop-require",
+  "to-array",
+  "object-spread",
+  "has-own",
+  "slice"
+];
 
 File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
-    whitespace: true,
-    blacklist:  [],
-    whitelist:  [],
-    sourceMap:  false,
-    filename:   "unknown",
-    modules:    "common",
-    runtime:    false
+    experimental: false,
+    playground:   false,
+    whitespace:   true,
+    blacklist:    [],
+    whitelist:    [],
+    sourceMap:    false,
+    comments:     true,
+    filename:     "unknown",
+    modules:      "common",
+    runtime:      false,
+    code:         true
+  });
+
+  // normalise windows path separators to unix
+  opts.filename = opts.filename.replace(/\\/g, "/");
+
+  opts.blacklist = util.arrayify(opts.blacklist);
+  opts.whitelist = util.arrayify(opts.whitelist);
+
+  _.defaults(opts, {
+    moduleRoot: opts.sourceRoot
   });
 
   _.defaults(opts, {
-    sourceFileName: opts.filename,
-    sourceMapName:  opts.filename
+    sourceRoot: opts.moduleRoot
+  });
+
+  _.defaults(opts, {
+    filenameRelative: opts.filename
+  });
+
+  _.defaults(opts, {
+    sourceFileName: opts.filenameRelative,
+    sourceMapName:  opts.filenameRelative
   });
 
   if (opts.runtime === true) {
     opts.runtime = "to5Runtime";
   }
 
+  if (opts.playground) {
+    opts.experimental = true;
+  }
+
   transform._ensureTransformerNames("blacklist", opts.blacklist);
   transform._ensureTransformerNames("whitelist", opts.whitelist);
 
   return opts;
 };
 
+File.prototype.toArray = function (node) {
+  if (t.isArrayExpression(node)) {
+    return node;
+  } else if (t.isIdentifier(node) && node.name === "arguments") {
+    return t.callExpression(t.memberExpression(this.addDeclaration("slice"), t.identifier("call")), [node]);
+  } else {
+    return t.callExpression(this.addDeclaration("to-array"), [node]);
+  }
+};
+
 File.prototype.getModuleFormatter = function (type) {
-  var ModuleFormatter = transform.moduleFormatters[type];
+  var ModuleFormatter = _.isFunction(type) ? type : transform.moduleFormatters[type];
 
   if (!ModuleFormatter) {
     var loc = util.resolve(type);
@@ -80,8 +123,10 @@ File.prototype.addDeclaration = function (name) {
     throw new ReferenceError("unknown declaration " + name);
   }
 
-  var declar = this.declarations[name];
-  if (declar) return declar.uid;
+  var program = this.ast.program;
+
+  var declar = program._declarations && program._declarations[name];
+  if (declar) return declar.id;
 
   var ref;
   var runtimeNamespace = this.opts.runtime;
@@ -92,11 +137,12 @@ File.prototype.addDeclaration = function (name) {
     ref = util.template(name);
   }
 
-  var uid = t.identifier(this.generateUid(name));
-  this.declarations[name] = {
-    uid: uid,
-    node: ref
-  };
+  var uid = this.generateUidIdentifier(name);
+  this.scope.push({
+    key: name,
+    id: uid,
+    init: ref
+  });
   return uid;
 };
 
@@ -126,7 +172,8 @@ File.prototype.parse = function (code) {
 
 File.prototype.transform = function (ast) {
   this.ast = ast;
-  this.scope = new Scope(null, ast.program);
+  this.scope = new Scope(ast.program);
+  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
 
   var self = this;
 
@@ -139,17 +186,27 @@ File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;
 
+  if (!opts.code) {
+    return {
+      code: "",
+      map:  null,
+      ast:  ast
+    };
+  }
+
   var result = generate(ast, opts, this.code);
 
   if (this.shebang) {
     // add back shebang
-    result.code = this.shebang + result.code;
+    result.code = this.shebang + "\n" + result.code;
   }
 
   if (opts.sourceMap === "inline") {
     result.code += "\n" + util.sourceMapToComment(result.map);
   }
 
+  result.ast = result;
+
   return result;
 };
 
@@ -165,6 +222,10 @@ File.prototype.generateUid = function (name, scope) {
   return uid;
 };
 
+File.prototype.generateUidIdentifier = function (name, scope) {
+  return t.identifier(this.generateUid(name, scope));
+};
+
 File.prototype._generateUid = function (name) {
   var uids = this.uids;
   var i = uids[name] || 1;

lib/6to5/generation/buffer.js

@@ -0,0 +1,125 @@
+module.exports = Buffer;
+
+var util = require("../util");
+var _    = require("lodash");
+
+function Buffer(position, format) {
+  this.position = position;
+  this._indent  = format.indent.base;
+  this.format   = format;
+  this.buf      = "";
+}
+
+Buffer.prototype.get = function () {
+  return util.trimRight(this.buf);
+};
+
+Buffer.prototype.getIndent = function () {
+  if (this.format.compact) {
+    return "";
+  } else {
+    return util.repeat(this._indent, this.format.indent.style);
+  }
+};
+
+Buffer.prototype.indentSize = function () {
+  return this.getIndent().length;
+};
+
+Buffer.prototype.indent = function () {
+  this._indent++;
+};
+
+Buffer.prototype.dedent = function () {
+  this._indent--;
+};
+
+Buffer.prototype.semicolon = function () {
+  if (this.format.semicolons) this.push(";");
+};
+
+Buffer.prototype.ensureSemicolon = function () {
+  if (!this.isLast(";")) this.semicolon();
+};
+
+Buffer.prototype.rightBrace = function () {
+  this.newline(true);
+  this.push("}");
+};
+
+Buffer.prototype.keyword = function (name) {
+  this.push(name);
+  this.push(" ");
+};
+
+Buffer.prototype.space = function () {
+  if (this.buf && !this.isLast([" ", "\n"])) {
+    this.push(" ");
+  }
+};
+
+Buffer.prototype.removeLast = function (cha) {
+  if (!this.isLast(cha)) return;
+
+  this.buf = this.buf.slice(0, -1);
+  this.position.unshift(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;
+    i = null;
+  }
+
+  if (_.isNumber(i)) {
+    if (this.endsWith(util.repeat(i, "\n"))) return;
+
+    var self = this;
+    _.times(i, function () {
+      self.newline(null, removeLast);
+    });
+    return;
+  }
+
+  if (removeLast && this.isLast("\n")) this.removeLast("\n");
+
+  this.removeLast(" ");
+  this.buf = this.buf.replace(/\n +$/, "\n");
+  this._push("\n");
+};
+
+Buffer.prototype.push = function (str, noIndent) {
+  if (this._indent && !noIndent && str !== "\n") {
+    // we have an indent level and we aren't pushing a newline
+    var indent = this.getIndent();
+
+    // replace all newlines with newlines with the indentation
+    str = str.replace(/\n/g, "\n" + indent);
+
+    // we've got a newline before us so prepend on the indentation
+    if (this.isLast("\n")) str = indent + str;
+  }
+
+  this._push(str);
+};
+
+Buffer.prototype._push = function (str) {
+  this.position.push(str);
+  this.buf += str;
+};
+
+Buffer.prototype.endsWith = function (str) {
+  return this.buf.slice(-str.length) === str;
+};
+
+Buffer.prototype.isLast = function (cha, trimRight) {
+  var buf = this.buf;
+  if (trimRight) buf = util.trimRight(buf);
+
+  var chars = [].concat(cha);
+  return _.contains(chars, _.last(buf));
+};

lib/6to5/generation/generator.js

@@ -8,6 +8,7 @@ module.exports.CodeGenerator = CodeGenerator;
 var Whitespace = require("./whitespace");
 var SourceMap  = require("./source-map");
 var Position   = require("./position");
+var Buffer     = require("./buffer");
 var util       = require("../util");
 var n          = require("./node");
 var t          = require("../types");
@@ -16,165 +17,63 @@ var _          = require("lodash");
 function CodeGenerator(ast, opts, code) {
   opts = opts || {};
 
-  this.style = {
-    semicolons: true,
-    comments: true,
-    compact: false,
-    indent: {
-      char: " ",
-      width: 2
-    }
-  };
-
   this.comments = ast.comments || [];
   this.tokens   = ast.tokens || [];
-  this.opts     = opts;
+  this.format   = CodeGenerator.normaliseOptions(opts);
   this.ast      = ast;
-  this.buf      = "";
-
-  this._indent = 0;
 
   this.whitespace = new Whitespace(this.tokens, this.comments);
   this.position   = new Position;
   this.map        = new SourceMap(this.position, opts, code);
+  this.buffer     = new Buffer(this.position, this.format);
 }
 
+_.each(Buffer.prototype, function (fn, key) {
+  CodeGenerator.prototype[key] = function () {
+    return fn.apply(this.buffer, arguments);
+  };
+});
+
+CodeGenerator.normaliseOptions = function (opts) {
+  return _.merge({
+    parentheses: true,
+    semicolons: true,
+    comments: opts.comments == null || opts.comments,
+    compact: false,
+    indent: {
+      adjustMultilineComment: true,
+      style: "  ",
+      base: 0
+    }
+  }, opts.format || {});
+};
+
 CodeGenerator.generators = {
-  arrayComprehensions: require("./generators/array-comprehensions"),
-  templateLiterals:    require("./generators/template-literals"),
-  expressions:         require("./generators/expressions"),
-  statements:          require("./generators/statements"),
-  classes:             require("./generators/classes"),
-  methods:             require("./generators/methods"),
-  modules:             require("./generators/modules"),
-  types:               require("./generators/types"),
-  base:                require("./generators/base"),
-  jsx:                 require("./generators/jsx")
+  templateLiterals: require("./generators/template-literals"),
+  comprehensions:   require("./generators/comprehensions"),
+  expressions:      require("./generators/expressions"),
+  statements:       require("./generators/statements"),
+  playground:       require("./generators/playground"),
+  classes:          require("./generators/classes"),
+  methods:          require("./generators/methods"),
+  modules:          require("./generators/modules"),
+  types:            require("./generators/types"),
+  base:             require("./generators/base"),
+  jsx:              require("./generators/jsx")
 };
 
 _.each(CodeGenerator.generators, function (generator) {
   _.extend(CodeGenerator.prototype, generator);
 });
 
-CodeGenerator.prototype.newline = function (i, removeLast) {
-  if (!this.buf) return;
-  if (this.style.compact) return;
-  if (this.endsWith("{\n")) return;
-
-  if (_.isBoolean(i)) {
-    removeLast = i;
-    i = null;
-  }
-
-  if (_.isNumber(i)) {
-    var self = this;
-    _.times(i, function () {
-      self.newline(null, removeLast);
-    });
-    return;
-  }
-
-  if (removeLast && this.isLast("\n")) this.removeLast("\n");
-
-  this.removeLast(" ");
-  this.buf = this.buf.replace(/\n(\s+)$/, "\n");
-  this._push("\n");
-};
-
-CodeGenerator.prototype.removeLast = function (cha) {
-  if (!this.isLast(cha)) return;
-
-  this.buf = this.buf.slice(0, -1);
-  this.position.unshift(cha);
-};
-
-CodeGenerator.prototype.semicolon = function () {
-  if (this.style.semicolons) this.push(";");
-};
-
-CodeGenerator.prototype.ensureSemicolon = function () {
-  if (!this.isLast(";")) this.semicolon();
-};
-
-CodeGenerator.prototype.rightBrace = function () {
-  this.newline(true);
-  this.push("}");
-};
-
-CodeGenerator.prototype.keyword = function (name) {
-  this.push(name);
-  this.push(" ");
-};
-
-CodeGenerator.prototype.space = function () {
-  if (this.buf && !this.isLast([" ", "\n"])) {
-    this.push(" ");
-  }
-};
-
-CodeGenerator.prototype.push = function (str, noIndent) {
-  if (this._indent && !noIndent && str !== "\n") {
-    // we have an indent level and we aren't pushing a newline
-    var indent = this.getIndent();
-
-    // replace all newlines with newlines with the indentation
-    str = str.replace(/\n/g, "\n" + indent);
-
-    // we've got a newline before us so prepend on the indentation
-    if (this.isLast("\n")) str = indent + str;
-  }
-
-  this._push(str);
-};
-
-CodeGenerator.prototype._push = function (str) {
-  this.position.push(str);
-  this.buf += str;
-};
-
-CodeGenerator.prototype.endsWith = function (str) {
-  return this.buf.slice(-str.length) === str;
-};
-
-CodeGenerator.prototype.isLast = function (cha, trimRight) {
-  var buf = this.buf;
-  if (trimRight) buf = buf.trimRight();
-
-  var chars = [].concat(cha);
-  return _.contains(chars, _.last(buf));
-};
-
-CodeGenerator.prototype.getIndent = function () {
-  if (this.style.compact) {
-    return "";
-  } else {
-    return util.repeat(this.indentSize(), this.style.indent.char);
-  }
-};
-
-CodeGenerator.prototype.indentSize = function () {
-  return this._indent * this.style.indent.width;
-};
-
-CodeGenerator.prototype.indent = function () {
-  this._indent++;
-};
-
-CodeGenerator.prototype.dedent = function () {
-  this._indent--;
-};
-
 CodeGenerator.prototype.generate = function () {
   var ast = this.ast;
 
   this.print(ast);
 
-  this.buf = this.buf.trimRight();
-
   return {
     map:  this.map.get(),
-    ast:  ast,
-    code: this.buf
+    code: this.buffer.get()
   };
 };
 
@@ -213,8 +112,6 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
   opts = opts || {};
 
   var newline = function (leading) {
-    var ignoreDuplicates = false;
-
     if (!opts.statement && !n.isUserWhitespacable(node, parent)) {
       return;
     }
@@ -237,7 +134,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
       lines += needs(node, parent);
     }
 
-    self.newline(lines, ignoreDuplicates);
+    self.newline(lines);
   };
 
   if (this[node.type]) {
@@ -264,11 +161,13 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     this.printTrailingComments(node, parent);
   } else {
-    throw new ReferenceError("unknown node " + node.type + " " + JSON.stringify(node));
+    throw new ReferenceError("unknown node " + node.type);
   }
 };
 
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
+  if (!nodes || !nodes.length) return;
+
   opts = opts || {};
 
   var self = this;
@@ -353,8 +252,8 @@ CodeGenerator.prototype._getComments = function (key, node) {
 };
 
 CodeGenerator.prototype._printComments = function (comments) {
-  if (this.style.compact) return;
-  if (!this.style.comments) return;
+  if (this.format.compact) return;
+  if (!this.format.comments) return;
   if (!comments || !comments.length) return;
 
   var self = this;
@@ -373,14 +272,16 @@ CodeGenerator.prototype._printComments = function (comments) {
 
     //
 
-    var offset = comment.loc.start.column;
-    if (offset) {
-      var newlineRegex = new RegExp("\\n\\s{1," + offset + "}", "g");
-      val = val.replace(newlineRegex, "\n");
-    }
+    if (comment.type === "Block" && self.format.indent.adjustMultilineComment) {
+      var offset = comment.loc.start.column;
+      if (offset) {
+        var newlineRegex = new RegExp("\\n\\s{1," + offset + "}", "g");
+        val = val.replace(newlineRegex, "\n");
+      }
 
-    var indent = Math.max(self.indentSize(), column);
-    val = val.replace(/\n/g, "\n" + util.repeat(indent));
+      var indent = Math.max(self.indentSize(), column);
+      val = val.replace(/\n/g, "\n" + util.repeat(indent));
+    }
 
     if (column === 0) {
       val = self.getIndent() + val;

lib/6to5/generation/generators/classes.js

@@ -30,3 +30,11 @@ exports.ClassBody = function (node, print) {
     this.rightBrace();
   }
 };
+
+exports.MethodDefinition = function (node, print) {
+  if (node.static) {
+    this.push("static ");
+  }
+
+  this._method(node, print);
+};

lib/6to5/generation/generators/comprehensions.js

@@ -8,7 +8,8 @@ exports.ComprehensionBlock = function (node, print) {
 };
 
 exports.ComprehensionExpression = function (node, print) {
-  this.push("[");
+  this.push(node.generator ? "(" : "[");
+
   print.join(node.blocks, { separator: " " });
   this.space();
 
@@ -21,5 +22,6 @@ exports.ComprehensionExpression = function (node, print) {
   }
 
   print(node.body);
-  this.push("]");
+
+  this.push(node.generator ? ")" : "]");
 };

lib/6to5/generation/generators/expressions.js

@@ -1,4 +1,5 @@
-var t = require("../../types");
+var util = require("../../util");
+var t    = require("../../types");
 
 exports.UnaryExpression = function (node, print) {
   var hasSpace = /[a-z]$/.test(node.operator);
@@ -44,9 +45,11 @@ exports.ConditionalExpression = function (node, print) {
 exports.NewExpression = function (node, print) {
   this.push("new ");
   print(node.callee);
-  this.push("(");
-  print.join(node.arguments, { separator: ", " });
-  this.push(")");
+  if (node.arguments.length || this.format.parentheses) {
+    this.push("(");
+    print.join(node.arguments, { separator: ", " });
+    this.push(")");
+  }
 };
 
 exports.SequenceExpression = function (node, print) {
@@ -64,15 +67,20 @@ exports.CallExpression = function (node, print) {
   this.push(")");
 };
 
-exports.YieldExpression = function (node, print) {
-  this.push("yield");
-  if (node.delegate) this.push("*");
-  if (node.argument) {
-    this.space();
-    print(node.argument);
-  }
+var buildYieldAwait = function (keyword) {
+  return function (node, print) {
+    this.push(keyword);
+    if (node.delegate) this.push("*");
+    if (node.argument) {
+      this.space();
+      print(node.argument);
+    }
+  };
 };
 
+exports.YieldExpression = buildYieldAwait("yield");
+exports.AwaitExpression = buildYieldAwait("await");
+
 exports.EmptyStatement = function () {
   this.semicolon();
 };
@@ -98,6 +106,11 @@ exports.MemberExpression = function (node, print) {
     print(node.property);
     this.push("]");
   } else {
+    // 5..toFixed(2);
+    if (t.isLiteral(node.object) && util.isInteger(node.object.value)) {
+      this.push(".");
+    }
+
     this.push(".");
     print(node.property);
   }

lib/6to5/generation/generators/jsx.js

@@ -46,15 +46,11 @@ exports.XJSElement = function (node, print) {
 
   this.indent();
   _.each(node.children, function (child) {
-    if (t.isLiteral(child) && typeof child.value === "string") {
-      if (/\S/.test(child.value)) {
-        return self.push(child.value.replace(/^\s+|\s+$/g, ""));
-      } else if (/\n/.test(child.value)) {
-        return self.newline();
-      }
+    if (t.isLiteral(child)) {
+      self.push(child.value);
+    } else {
+      print(child);
     }
-
-    print(child);
   });
   this.dedent();
 
@@ -78,5 +74,5 @@ exports.XJSClosingElement = function (node, print) {
 };
 
 exports.XJSEmptyExpression = function () {
-  this.push("null");
+
 };

lib/6to5/generation/generators/methods.js

@@ -41,6 +41,8 @@ exports._method = function (node, print) {
     this.push(kind + " ");
   }
 
+  if (value.async) this.push("async ");
+
   if (node.computed) {
     this.push("[");
     print(key);
@@ -54,16 +56,9 @@ exports._method = function (node, print) {
   print(value.body);
 };
 
-exports.MethodDefinition = function (node, print) {
-  if (node.static) {
-    this.push("static ");
-  }
-
-  this._method(node, print);
-};
-
 exports.FunctionDeclaration =
 exports.FunctionExpression = function (node, print) {
+  if (node.async) this.push("async ");
   this.push("function");
   if (node.generator) this.push("*");
   this.space();
@@ -74,6 +69,8 @@ exports.FunctionExpression = function (node, print) {
 };
 
 exports.ArrowFunctionExpression = function (node, print) {
+  if (node.async) this.push("async ");
+
   if (node.params.length === 1 && !node.defaults.length && !node.rest && t.isIdentifier(node.params[0])) {
     print(node.params[0]);
   } else {

lib/6to5/generation/generators/modules.js

@@ -25,9 +25,10 @@ exports.ExportDeclaration = function (node, print) {
 
   if (node.declaration) {
     print(node.declaration);
+    if (t.isStatement(node.declaration)) return;
   } else {
     if (specifiers.length === 1 && t.isExportBatchSpecifier(specifiers[0])) {
-      this.push("*");
+      print(specifiers[0]);
     } else {
       this.push("{");
       if (specifiers.length) {

lib/6to5/generation/generators/playground.js

@@ -0,0 +1,7 @@
+var _ = require("lodash");
+
+_.each(["BindMemberExpression", "BindFunctionExpression"], function (type) {
+  exports[type] = function () {
+    throw new ReferenceError("Trying to render non-standard playground node " + JSON.stringify(type));
+  };
+});

lib/6to5/generation/generators/statements.js

@@ -4,6 +4,7 @@ exports.WithStatement = function (node, print) {
   this.keyword("with");
   this.push("(");
   print(node.object);
+  this.push(")");
   print.block(node.body);
 };
 
@@ -134,15 +135,6 @@ exports.SwitchStatement = function (node, print) {
   this.push(") {");
   print.sequence(node.cases, { indent: true });
   this.push("}");
-
-  //if (node.cases.length) {
-  //  this.newline();
-  //  print.sequence(node.cases, { indent: true });
-  //  this.newline();
-  //  this.rightBrace();
-  //} else {
-  //  this.push("}");
-  //}
 };
 
 exports.SwitchCase = function (node, print) {
@@ -154,13 +146,8 @@ exports.SwitchCase = function (node, print) {
     this.push("default:");
   }
 
-  if (node.consequent.length === 1) {
-    this.space();
-    print(node.consequent[0]);
-  } else if (node.consequent.length > 1) {
-    this.newline();
-    print.sequence(node.consequent, { indent: true });
-  }
+  this.space();
+  print.sequence(node.consequent, { indent: true });
 };
 
 exports.DebuggerStatement = function () {

lib/6to5/generation/generators/types.js

@@ -4,11 +4,18 @@ exports.Identifier = function (node) {
   this.push(node.name);
 };
 
-exports.SpreadElement = function (node, print) {
+exports.SpreadElement =
+exports.SpreadProperty = function (node, print) {
   this.push("...");
   print(node.argument);
 };
 
+exports.VirtualPropertyExpression = function (node, print) {
+  print(node.object);
+  this.push("::");
+  print(node.property);
+};
+
 exports.ObjectExpression =
 exports.ObjectPattern = function (node, print) {
   var props = node.properties;
@@ -74,13 +81,20 @@ exports.Literal = function (node) {
   var val  = node.value;
   var type = typeof val;
 
-  if (type === "boolean" || type === "number" || type === "string") {
+  if (type === "string") {
+    val = JSON.stringify(val);
+
+    // escape unicode characters
+    val = val.replace(/[\u007f-\uffff]/g, function (c) {
+      return "\\u" + ("0000" + c.charCodeAt(0).toString(16)).slice(-4);
+    });
+
+    this.push(val);
+  } else if (type === "boolean" || type === "number") {
     this.push(JSON.stringify(val));
   } else if (node.regex) {
     this.push("/" + node.regex.pattern + "/" + node.regex.flags);
   } else if (val === null) {
     this.push("null");
-  } else if (node.raw) {
-    this.push(node.raw);
   }
 };

lib/6to5/generation/node.js

@@ -1,290 +0,0 @@
-module.exports = Node;
-
-var t = require("../types");
-var _ = require("lodash");
-
-function Node(node, parent) {
-  this.parent = parent;
-  this.node   = node;
-}
-
-//
-
-Node.whitespace = {
-  FunctionExpression: 1,
-  FunctionStatement: 1,
-  ClassExpression: 1,
-  ClassStatement: 1,
-  ForOfStatement: 1,
-  ForInStatement: 1,
-  ForStatement: 1,
-  SwitchStatement: 1,
-  IfStatement: { before: 1 },
-  //Property: { before: 1 },
-  Literal: { after: 1 }
-};
-
-_.each(Node.whitespace, function (amounts, type) {
-  if (_.isNumber(amounts)) amounts = { after: amounts, before: amounts };
-  Node.whitespace[type] = amounts;
-});
-
-//
-
-Node.PRECEDENCE = {};
-
-_.each([
-  ["||"],
-  ["&&"],
-  ["|"],
-  ["^"],
-  ["&"],
-  ["==", "===", "!=", "!=="],
-  ["<", ">", "<=", ">=", "in", "instanceof"],
-  [">>", "<<", ">>>"],
-  ["+", "-"],
-  ["*", "/", "%"]
-], function (tier, i) {
-  _.each(tier, function (op) {
-    Node.PRECEDENCE[op] = i;
-  });
-});
-
-//
-
-Node.prototype.isUserWhitespacable = function () {
-  //var parent = this.parent;
-  var node = this.node;
-
-  if (t.isUserWhitespacable(node)) {
-    return true;
-  }
-
-  //if (t.isArrayExpression(parent)) {
-  //  return true;
-  //}
-
-  return false;
-};
-
-Node.prototype.needsWhitespace = function (type) {
-  var parent = this.parent;
-  var node   = this.node;
-  if (!node) return 0;
-
-  if (t.isExpressionStatement(node)) {
-    node = node.expression;
-  }
-
-  if (type === "before") {
-    if (t.isProperty(node) && parent.properties[0] === node) {
-      return 1;
-    }
-  }
-
-  if (type === "after") {
-    if (t.isCallExpression(node)) {
-      return 1;
-    }
-
-    var exprs = [];
-
-    if (t.isVariableDeclaration(node)) {
-      exprs = _.map(node.declarations, "init");
-    }
-
-    if (t.isArrayExpression(node)) {
-      exprs = node.elements;
-    }
-
-    if (t.isObjectExpression(node)) {
-      exprs = node.properties;
-    }
-
-    var lines = 0;
-
-    _.each(exprs, function (expr) {
-      lines = Node.needsWhitespace(expr, node, type);
-      if (lines) return false;
-    });
-
-    if (lines) return lines;
-  }
-
-  if (t.isCallExpression(node) && t.isFunction(node.callee)) {
-    return 1;
-  }
-
-  var opts = Node.whitespace[node.type];
-  return (opts && opts[type]) || 0;
-};
-
-Node.prototype.needsWhitespaceBefore = function () {
-  return this.needsWhitespace("before");
-};
-
-Node.prototype.needsWhitespaceAfter = function () {
-  return this.needsWhitespace("after");
-};
-
-Node.prototype.needsParens = function () {
-  var parent = this.parent;
-  var node = this.node;
-
-  if (!parent) return false;
-
-  //
-  if (t.isUnaryLike(node)) {
-    return t.isMemberExpression(parent) && parent.object === node;
-  }
-
-  if (t.isBinary(node)) {
-    //
-    if (t.isCallExpression(parent) && parent.callee === node) {
-      return true;
-    }
-
-    //
-    if (t.isUnaryLike(parent)) {
-      return true;
-    }
-
-    //
-    if (t.isMemberExpression(parent) && parent.object === node) {
-      return true;
-    }
-
-    if (t.isBinary(parent)) {
-      var parentOp  = parent.operator;
-      var parentPos = Node.PRECEDENCE[parentOp];
-
-      var nodeOp = node.operator;
-      var nodePos = Node.PRECEDENCE[nodeOp];
-
-      if (parentPos > nodePos) {
-        return true;
-      }
-
-      if (parentPos === nodePos && parent.right === node) {
-        return true;
-      }
-    }
-  }
-
-  if (t.isBinaryExpression(node) && node.operator === "in") {
-    // var i = (1 in []);
-    if (t.isVariableDeclarator(parent)) {
-      return true;
-    }
-
-    // for ((1 in []);;);
-    if (t.isFor(parent)) {
-      return true;
-    }
-  }
-
-  // (class {});
-  if (t.isClassExpression(node) && t.isExpressionStatement(parent)) {
-    return true;
-  }
-
-  if (t.isSequenceExpression(node)) {
-    if (t.isForStatement(parent)) {
-      // Although parentheses wouldn't hurt around sequence
-      // expressions in the head of for loops, traditional style
-      // dictates that e.g. i++, j++ should not be wrapped with
-      // parentheses.
-      return false;
-    }
-
-    if (t.isExpressionStatement(parent) && parent.expression === node) {
-      return false;
-    }
-
-    // Otherwise err on the side of overparenthesization, adding
-    // explicit exceptions above if this proves overzealous.
-    return true;
-  }
-
-  //
-  if (t.isYieldExpression(node)) {
-    return t.isBinary(parent) ||
-           t.isUnaryLike(parent) ||
-           t.isCallExpression(parent) ||
-           t.isMemberExpression(parent) ||
-           t.isNewExpression(parent) ||
-           t.isConditionalExpression(parent) ||
-           t.isYieldExpression(parent);
-  }
-
-  if (t.isNewExpression(parent) && parent.callee === node) {
-    return t.isCallExpression(node) || _.some(node, function (val) {
-      return t.isCallExpression(val);
-    });
-  }
-
-  // (1).valueOf()
-  if (t.isLiteral(node) && _.isNumber(node.value) && t.isMemberExpression(parent) && parent.object === node) {
-    return true;
-  }
-
-  if (t.isAssignmentExpression(node) || t.isConditionalExpression(node)) {
-    //
-    if (t.isUnaryLike(parent)) {
-      return true;
-    }
-
-    //
-    if (t.isBinary(parent)) {
-      return true;
-    }
-
-    //
-    if (t.isCallExpression(parent) && parent.callee === node) {
-      return true;
-    }
-
-    //
-    if (t.isConditionalExpression(parent) && parent.test === node) {
-      return true;
-    }
-
-    //
-    if (t.isMemberExpression(parent) && parent.object === node) {
-      return true;
-    }
-  }
-
-  if (t.isFunctionExpression(node)) {
-    // function () {};
-    if (t.isExpressionStatement(parent)) {
-      return true;
-    }
-
-    // (function test() {}).name;
-    if (t.isMemberExpression(parent) && parent.object === node) {
-      return true;
-    }
-
-    // (function () {})();
-    if (t.isCallExpression(parent) && parent.callee === node) {
-      return true;
-    }
-  }
-
-  // ({ x, y }) = { x: 5, y: 6 };
-  if (t.isObjectPattern(node) && t.isAssignmentExpression(parent) && parent.left == node) {
-    return true;
-  }
-
-  return false;
-};
-
-_.each(Node.prototype, function (fn, key) {
-  Node[key] = function (node, parent) {
-    var n = new Node(node, parent);
-
-    var args = _.toArray(arguments).slice(2);
-    return n[key].apply(n, args);
-  };
-});

lib/6to5/generation/node/index.js

@@ -0,0 +1,79 @@
+module.exports = Node;
+
+var whitespace = require("./whitespace");
+var parens     = require("./parentheses");
+var t          = require("../../types");
+var _          = require("lodash");
+
+var find = function (obj, node, parent) {
+  var result;
+
+  _.each(obj, function (fn, type) {
+    if (t["is" + type](node)) {
+      result = fn(node, parent);
+      if (result != null) return false;
+    }
+  });
+
+  return result;
+};
+
+function Node(node, parent) {
+  this.parent = parent;
+  this.node   = node;
+}
+
+Node.prototype.isUserWhitespacable = function () {
+  return t.isUserWhitespacable(this.node);
+};
+
+Node.prototype.needsWhitespace = function (type) {
+  var parent = this.parent;
+  var node   = this.node;
+  if (!node) return 0;
+
+  if (t.isExpressionStatement(node)) {
+    node = node.expression;
+  }
+
+  var lines = find(whitespace[type].nodes, node, parent);
+  if (lines) return lines;
+
+  _.each(find(whitespace[type].list, node, parent), function (expr) {
+    lines = Node.needsWhitespace(expr, node, type);
+    if (lines) return false;
+  });
+  return lines || 0;
+};
+
+Node.prototype.needsWhitespaceBefore = function () {
+  return this.needsWhitespace("before");
+};
+
+Node.prototype.needsWhitespaceAfter = function () {
+  return this.needsWhitespace("after");
+};
+
+Node.prototype.needsParens = function () {
+  var parent = this.parent;
+  var node   = this.node;
+
+  if (!parent) return false;
+
+  if (t.isNewExpression(parent) && parent.callee === node) {
+    return t.isCallExpression(node) || _.some(node, function (val) {
+      return t.isCallExpression(val);
+    });
+  }
+
+  return find(parens, node, parent);
+};
+
+_.each(Node.prototype, function (fn, key) {
+  Node[key] = function (node, parent) {
+    var n = new Node(node, parent);
+
+    var args = _.toArray(arguments).slice(2);
+    return n[key].apply(n, args);
+  };
+});

lib/6to5/generation/node/parentheses.js

@@ -0,0 +1,150 @@
+var t = require("../../types");
+var _ = require("lodash");
+
+var PRECEDENCE = {};
+
+_.each([
+  ["||"],
+  ["&&"],
+  ["|"],
+  ["^"],
+  ["&"],
+  ["==", "===", "!=", "!=="],
+  ["<", ">", "<=", ">=", "in", "instanceof"],
+  [">>", "<<", ">>>"],
+  ["+", "-"],
+  ["*", "/", "%"]
+], function (tier, i) {
+  _.each(tier, function (op) {
+    PRECEDENCE[op] = i;
+  });
+});
+
+exports.Binary = function (node, parent) {
+  if (t.isCallExpression(parent) && parent.callee === node) {
+    return true;
+  }
+
+  if (t.isUnaryLike(parent)) {
+    return true;
+  }
+
+  if (t.isMemberExpression(parent) && parent.object === node) {
+    return true;
+  }
+
+  if (t.isBinary(parent)) {
+    var parentOp  = parent.operator;
+    var parentPos = PRECEDENCE[parentOp];
+
+    var nodeOp = node.operator;
+    var nodePos = PRECEDENCE[nodeOp];
+
+    if (parentPos > nodePos) {
+      return true;
+    }
+
+    if (parentPos === nodePos && parent.right === node) {
+      return true;
+    }
+  }
+};
+
+exports.BinaryExpression = function (node, parent) {
+  if (node.operator === "in") {
+    // var i = (1 in []);
+    if (t.isVariableDeclarator(parent)) {
+      return true;
+    }
+
+    // for ((1 in []);;);
+    if (t.isFor(parent)) {
+      return true;
+    }
+  }
+};
+
+exports.SequenceExpression = function (node, parent) {
+  if (t.isForStatement(parent)) {
+    // Although parentheses wouldn't hurt around sequence
+    // expressions in the head of for loops, traditional style
+    // dictates that e.g. i++, j++ should not be wrapped with
+    // parentheses.
+    return false;
+  }
+
+  if (t.isExpressionStatement(parent) && parent.expression === node) {
+    return false;
+  }
+
+  // Otherwise err on the side of overparenthesization, adding
+  // explicit exceptions above if this proves overzealous.
+  return true;
+};
+
+exports.YieldExpression = function (node, parent) {
+  return t.isBinary(parent) ||
+         t.isUnaryLike(parent) ||
+         t.isCallExpression(parent) ||
+         t.isMemberExpression(parent) ||
+         t.isNewExpression(parent) ||
+         t.isConditionalExpression(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);
+};
+
+exports.UnaryLike = function (node, parent) {
+  return t.isMemberExpression(parent) && parent.object === node;
+};
+
+exports.FunctionExpression = function (node, parent) {
+  // function () {};
+  if (t.isExpressionStatement(parent)) {
+    return true;
+  }
+
+  // (function test() {}).name;
+  if (t.isMemberExpression(parent) && parent.object === node) {
+    return true;
+  }
+
+  // (function () {})();
+  if (t.isCallExpression(parent) && parent.callee === node) {
+    return true;
+  }
+};
+
+exports.AssignmentExpression =
+exports.ConditionalExpression = function (node, parent) {
+  if (t.isUnaryLike(parent)) {
+    return true;
+  }
+
+  if (t.isBinary(parent)) {
+    return true;
+  }
+
+  if (t.isCallExpression(parent) && parent.callee === node) {
+    return true;
+  }
+
+  if (t.isConditionalExpression(parent) && parent.test === node) {
+    return true;
+  }
+
+  if (t.isMemberExpression(parent) && parent.object === node) {
+    return true;
+  }
+
+  return false;
+};

lib/6to5/generation/node/whitespace.js

@@ -0,0 +1,64 @@
+var _ = require("lodash");
+var t = require("../../types");
+
+exports.before = {
+  nodes: {
+    Property: function (node, parent) {
+      if (parent.properties[0] === node) {
+        return 1;
+      }
+    },
+
+    SpreadProperty: function (node, parent) {
+      return exports.before.nodes.Property(node, parent);
+    },
+
+    SwitchCase: function (node, parent) {
+      if (parent.cases[0] === node) {
+        return 1;
+      }
+    },
+
+    CallExpression: function (node) {
+      if (t.isFunction(node.callee)) {
+        return 1;
+      }
+    }
+  }
+};
+
+exports.after = {
+  nodes: {},
+
+  list: {
+    VariableDeclaration: function (node) {
+      return _.map(node.declarations, "init");
+    },
+
+    ArrayExpression: function (node) {
+      return node.elements;
+    },
+
+    ObjectExpression: function (node) {
+      return node.properties;
+    }
+  }
+};
+
+_.each({
+  Function: 1,
+  Class: 1,
+  For: 1,
+  SwitchStatement: 1,
+  IfStatement: { before: 1 },
+  CallExpression: { after: 1 },
+  Literal: { after: 1 }
+}, function (amounts, type) {
+  if (_.isNumber(amounts)) amounts = { after: amounts, before: amounts };
+
+  _.each(amounts, function (amount, key) {
+    exports[key].nodes[type] = function () {
+      return amount;
+    };
+  });
+});

lib/6to5/generation/source-map.js

@@ -9,7 +9,8 @@ function SourceMap(position, opts, code) {
 
   if (opts.sourceMap) {
     this.map = new sourceMap.SourceMapGenerator({
-      file: opts.sourceMapName
+      file: opts.sourceMapName,
+      sourceRoot: opts.sourceRoot
     });
 
     this.map.setSourceContent(opts.sourceFileName, code);

lib/6to5/index.js

@@ -17,6 +17,9 @@ exports.polyfill = function () {
 
 exports.canCompile = util.canCompile;
 
+// do not use this - this is for use by official maintained 6to5 plugins
+exports._util = util;
+
 exports.transform = transform;
 
 exports.transformFile = function (filename, opts, callback) {

lib/6to5/patch.js

@@ -3,6 +3,7 @@ var _ = require("lodash");
 
 var types = require("ast-types");
 var def   = types.Type.def;
+var or    = types.Type.or;
 
 // Program wrapper
 def("File")
@@ -16,12 +17,33 @@ def("ParenthesizedExpression")
   .build("expression")
   .field("expression", def("Expression"));
 
-// Same as ImportNamespaceSpecifier but `id` is `name`
+// Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
   .bases("Specifier")
   .build("name")
   .field("name", def("Identifier"));
 
+// Abstract references
+def("VirtualPropertyExpression")
+  .bases("Expression")
+  .build("object", "property")
+  .field("object", def("Expression"))
+  .field("property", or(def("Identifier"), def("Expression")));
+
+// Playground
+def("BindMemberExpression")
+  .bases("Expression")
+  .build("object", "property", "arguments")
+  .field("object", def("Expression"))
+  .field("property", or(def("Identifier"), def("Expression")))
+  .field("arguments", [def("Expression")]);
+
+def("BindFunctionExpression")
+  .bases("Expression")
+  .build("callee", "arguments")
+  .field("callee", def("Expression"))
+  .field("arguments", [def("Expression")]);
+
 types.finalize();
 
 var estraverse = require("estraverse");

lib/6to5/polyfill.js

@@ -1,6 +1,37 @@
+/* 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("regenerator-6to5/runtime");
+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);
+}

lib/6to5/register.js

@@ -1,7 +1,10 @@
 require("./polyfill");
 
 var sourceMapSupport = require("source-map-support");
+var roadrunner       = require('roadrunner');
+var util             = require("./util");
 var to5              = require("./index");
+var fs               = require("fs");
 var _                = require("lodash");
 
 sourceMapSupport.install({
@@ -36,6 +39,7 @@ var blacklistTest = function (transformer, code) {
 };
 
 blacklistTest("arrayComprehension", "var foo = [for (foo of bar) foo * foo];");
+//blacklistTest("generatorComprehension", "");
 blacklistTest("arrowFunctions", "var foo = x => x * x;");
 blacklistTest("classes", "class Foo {}");
 blacklistTest("computedPropertyNames", "var foo = { [foo]: bar };");
@@ -55,23 +59,41 @@ blacklistTest("unicodeRegex", function () { new RegExp("foo", "u"); });
 
 //
 
-var ignoreRegex = /node_modules/;
+var transformOpts = {};
+var ignoreRegex   = /node_modules/;
 var onlyRegex;
-var whitelist   = [];
-var exts        = {};
-var maps        = {};
-var old         = require.extensions[".js"];
+var whitelist     = [];
+var cache;
+var exts          = {};
+var maps          = {};
+var old           = require.extensions[".js"];
+
+var mtime = function (filename) {
+  return +fs.statSync(filename).mtime;
+};
 
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, {
+  var result;
+
+  if (cache && cache[filename].mtime === mtime(filename)) {
+    result = cache[filename];
+  }
+
+  result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
-    sourceMap: true
-  });
+    sourceMap: true,
+    modules:   "commonInterop"
+  }, transformOpts));
+
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
 
   maps[filename] = result.map;
 
@@ -99,11 +121,13 @@ module.exports = function (opts) {
   if (_.isRegExp(opts)) opts = { ignore: opts };
   if (opts.ignoreRegex != null) opts.ignore = opts.ignoreRegex;
 
-  if (opts.only != null) onlyRegex = opts.only;
-  if (opts.ignore != null) ignoreRegex = opts.ignore;
+  if (opts.only != null) onlyRegex = util.regexify(opts.only);
+  if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);
 
-  if (opts.extensions) hookExtensions(opts.extensions);
+  if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 
-  if (opts.blacklist) blacklist = opts.blacklist;
-  if (opts.whitelist) whitelist = opts.whitelist;
+  if (opts.cache) cache = roadrunner.get('6to5');
+  if (opts.cache === false) cache = null;
+
+  _.extend(transformOpts, opts);
 };

lib/6to5/runtime.js

@@ -5,18 +5,16 @@ var t         = require("./types");
 var _         = require("lodash");
 
 module.exports = function (namespace) {
-  namespace = t.identifier(namespace || "to5Runtime");
+  namespace = t.identifier(t.toIdentifier(namespace || "to5Runtime"));
 
   var body      = [];
-  var container = t.functionExpression(null, [], t.blockStatement(body));
-  var tree      = t.program([t.expressionStatement(t.callExpression(container, []))]);
-
-  body.push(util.template("self-global", true));
+  var container = t.functionExpression(null, [t.identifier("global")], t.blockStatement(body));
+  var tree      = t.program([t.expressionStatement(t.callExpression(container, [util.template("self-global")]))]);
 
   body.push(t.variableDeclaration("var", [
     t.variableDeclarator(
       namespace,
-      t.assignmentExpression("=", t.memberExpression(t.identifier("self"), namespace), t.objectExpression([]))
+      t.assignmentExpression("=", t.memberExpression(t.identifier("global"), namespace), t.objectExpression([]))
     )
   ]));
 

lib/6to5/templates/abstract-expression-call.js

@@ -0,0 +1 @@
+PROPERTY[Symbol.referenceGet](OBJECT).call(OBJECT)

lib/6to5/templates/abstract-expression-delete.js

@@ -0,0 +1 @@
+PROPERTY[Symbol.referenceDelete](OBJECT)

lib/6to5/templates/abstract-expression-get.js

@@ -0,0 +1 @@
+PROPERTY[Symbol.referenceGet](OBJECT)

lib/6to5/templates/abstract-expression-set.js

@@ -0,0 +1 @@
+PROPERTY[Symbol.referenceSet](OBJECT, VALUE)

lib/6to5/templates/apply-constructor.js

@@ -0,0 +1,5 @@
+(function (Constructor, args) {
+  var instance = Object.create(Constructor.prototype);
+  var result = Constructor.apply(instance, args);
+  return result != null && (typeof result == "object" || typeof result == "function") ? result : instance;
+});

lib/6to5/templates/arguments-slice-assign-arg.js

@@ -1 +0,0 @@
-var VARIABLE_NAME = SLICE_KEY.call(arguments, SLICE_ARG);

lib/6to5/templates/arguments-slice-assign.js

@@ -1 +0,0 @@
-var VARIABLE_NAME = SLICE_KEY.call(arguments);

lib/6to5/templates/arguments-slice.js

@@ -1 +0,0 @@
-SLICE_KEY.call(arguments);

lib/6to5/templates/array-from.js

@@ -0,0 +1 @@
+Array.from(VALUE);

lib/6to5/templates/exports-default-module.js

@@ -0,0 +1 @@
+module.exports = VALUE;

lib/6to5/templates/has-own.js

@@ -0,0 +1 @@
+Object.prototype.hasOwnProperty;

lib/6to5/templates/interop-require.js

@@ -0,0 +1,3 @@
+(function (obj) {
+  return obj && (obj["default"] || obj);
+})

lib/6to5/templates/object-spread.js

@@ -0,0 +1,9 @@
+(function (obj, keys) {
+  var target = {};
+  for (var i in obj) {
+    if (keys.indexOf(i) >= 0) continue;
+    if (!Object.prototype.hasOwnProperty.call(obj, i)) continue;
+    target[i] = obj[i];
+  }
+  return target;
+})

lib/6to5/templates/register.js

@@ -0,0 +1 @@
+System.register(MODULE_NAME, MODULE_DEPENDENCIES, MODULE_BODY);

lib/6to5/templates/self-global.js

@@ -1 +1 @@
-var self = typeof global === "undefined" ? window : global;
+typeof global === "undefined" ? self : global

lib/6to5/templates/tagged-template-literal.js

@@ -0,0 +1,4 @@
+(function (strings, raw) {
+  return Object.defineProperties(strings, { raw: { value: raw } });
+});
+

lib/6to5/templates/to-array.js

@@ -0,0 +1,3 @@
+(function (arr) {
+  return Array.isArray(arr) ? arr : Array.from(arr);
+});

lib/6to5/transformation/modules/amd.js

@@ -30,11 +30,24 @@ AMDFormatter.prototype.transform = function (ast) {
   params.unshift(t.identifier("exports"));
 
   var container = t.functionExpression(null, params, t.blockStatement(body));
-  var call = t.callExpression(t.identifier("define"), [names, container]);
+
+  var defineArgs = [names, container];
+  var moduleName = this.getModuleName();
+  if (moduleName) defineArgs.unshift(t.literal(moduleName));
+
+  var call = t.callExpression(t.identifier("define"), defineArgs);
 
   program.body = [t.expressionStatement(call)];
 };
 
+AMDFormatter.prototype.getModuleName = function () {
+  if (this.file.opts.amdModuleIds) {
+    return CommonJSFormatter.prototype.getModuleName.apply(this, arguments);
+  } else {
+    return null;
+  }
+};
+
 AMDFormatter.prototype._push = function (node) {
   var id  = node.source.value;
   var ids = this.ids;
@@ -42,7 +55,7 @@ AMDFormatter.prototype._push = function (node) {
   if (ids[id]) {
     return ids[id];
   } else {
-    return this.ids[id] = t.identifier(this.file.generateUid(id));
+    return this.ids[id] = this.file.generateUidIdentifier(id);
   }
 };
 

lib/6to5/transformation/modules/common-interop.js

@@ -0,0 +1,56 @@
+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);
+};

lib/6to5/transformation/modules/common.js

@@ -7,6 +7,33 @@ function CommonJSFormatter(file) {
   this.file = file;
 }
 
+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", {
@@ -38,23 +65,32 @@ CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes)
   }));
 };
 
+CommonJSFormatter.prototype._hoistExport = function (declar, assign) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = true;
+  }
+
+  return assign;
+};
+
+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;
 
   if (node.default) {
-    var ref = declar;
-
-    if (t.isClass(ref) || t.isFunction(ref)) {
-      if (ref.id) {
-        nodes.push(t.toStatement(ref));
-        ref = ref.id;
-      }
-    }
-
     nodes.push(util.template("exports-default", {
       //inherits: node,
 
-      VALUE: ref
+      VALUE: this._pushStatement(declar, nodes)
     }, true));
   } else {
     var assign;
@@ -83,9 +119,7 @@ CommonJSFormatter.prototype.export = function (node, nodes) {
       nodes.push(t.toStatement(declar));
       nodes.push(assign);
 
-      if (t.isFunctionDeclaration(declar)) {
-        assign._blockHoist = true;
-      }
+      this._hoistExport(declar, assign);
     }
   }
 };
@@ -126,7 +160,7 @@ CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node
 };
 
 CommonJSFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  return this._exportSpecifier(function () {
+  this._exportSpecifier(function () {
     return t.callExpression(t.identifier("require"), [node.source]);
   }, specifier, node, nodes);
 };

lib/6to5/transformation/modules/system.js

@@ -0,0 +1,202 @@
+module.exports = SystemFormatter;
+
+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);
+
+function SystemFormatter(file) {
+  this.exportedStatements = [];
+  this.importedModule     = {};
+
+  this.exportIdentifier   = file.generateUidIdentifier("export");
+  this.file               = file;
+}
+
+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(/\..*$/, "");
+
+  // 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));
+  }
+
+  // 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);
+  }
+};

lib/6to5/transformation/modules/umd.js

@@ -5,9 +5,8 @@ var util         = require("../../util");
 var t            = require("../../types");
 var _            = require("lodash");
 
-function UMDFormatter(file) {
-  this.file = file;
-  this.ids  = {};
+function UMDFormatter() {
+  AMDFormatter.apply(this, arguments);
 }
 
 util.inherits(UMDFormatter, AMDFormatter);
@@ -32,8 +31,12 @@ UMDFormatter.prototype.transform = function (ast) {
 
   // runner
 
+  var defineArgs = [t.arrayExpression([t.literal("exports")].concat(names))];
+  var moduleName = this.getModuleName();
+  if (moduleName) defineArgs.unshift(t.literal(moduleName));
+
   var runner = util.template("umd-runner-body", {
-    AMD_ARGUMENTS: t.arrayExpression([t.literal("exports")].concat(names)),
+    AMD_ARGUMENTS: defineArgs,
 
     COMMON_ARGUMENTS: names.map(function (name) {
       return t.callExpression(t.identifier("require"), [name]);

lib/6to5/transformation/transform.js

@@ -20,45 +20,55 @@ transform._ensureTransformerNames = function (type, keys) {
 transform.transformers = {};
 
 transform.moduleFormatters = {
-  common: require("./modules/common"),
-  ignore: require("./modules/ignore"),
-  amd:    require("./modules/amd"),
-  umd:    require("./modules/umd")
+  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")
 };
 
 _.each({
-  modules:                  require("./transformers/modules"),
-  propertyNameShorthand:    require("./transformers/property-name-shorthand"),
-  constants:                require("./transformers/constants"),
-  arrayComprehension:       require("./transformers/array-comprehension"),
-  arrowFunctions:           require("./transformers/arrow-functions"),
-  classes:                  require("./transformers/classes"),
+  modules:                   require("./transformers/es6-modules"),
+  propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
+  arrayComprehension:        require("./transformers/es7-array-comprehension"),
+  generatorComprehension:    require("./transformers/es7-generator-comprehension"),
+  arrowFunctions:            require("./transformers/es6-arrow-functions"),
+  classes:                   require("./transformers/es6-classes"),
 
-  _propertyLiterals:        require("./transformers/_property-literals"),
-  computedPropertyNames:    require("./transformers/computed-property-names"),
+  computedPropertyNames:     require("./transformers/es6-computed-property-names"),
 
-  spread:                   require("./transformers/spread"),
-  templateLiterals:         require("./transformers/template-literals"),
-  propertyMethodAssignment: require("./transformers/property-method-assignment"),
-  defaultParameters:        require("./transformers/default-parameters"),
-  restParameters:           require("./transformers/rest-parameters"),
-  destructuring:            require("./transformers/destructuring"),
-  letScoping:               require("./transformers/let-scoping"),
-  forOf:                    require("./transformers/for-of"),
-  unicodeRegex:             require("./transformers/unicode-regex"),
-  generators:               require("./transformers/generators"),
-  numericLiterals:          require("./transformers/numeric-literals"),
+  objectSpread:              require("./transformers/es7-object-spread"),
+  exponentiationOperator:    require("./transformers/es7-exponentiation-operator"),
+  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"),
+  forOf:                     require("./transformers/es6-for-of"),
+  unicodeRegex:              require("./transformers/es6-unicode-regex"),
+  abstractReferences:        require("./transformers/es7-abstract-references"),
+  react:                     require("./transformers/react"),
 
-  react:                    require("./transformers/react"),
-  jsx:                      require("./transformers/jsx"),
+  constants:                 require("./transformers/es6-constants"),
+  letScoping:                require("./transformers/es6-let-scoping"),
 
-  _aliasFunctions:          require("./transformers/_alias-functions"),
-  _blockHoist:              require("./transformers/_block-hoist"),
-  _declarations:            require("./transformers/_declarations"),
+  generators:                require("./transformers/es6-generators"),
 
-  useStrict:                require("./transformers/use-strict"),
+  // plyground
+  methodBinding:             require("./transformers/playground-method-binding"),
+  memoizationOperator:       require("./transformers/playground-memoization-operator"),
 
-  _moduleFormatter:         require("./transformers/_module-formatter")
+  _blockHoist:               require("./transformers/_block-hoist"),
+  _declarations:             require("./transformers/_declarations"),
+  _aliasFunctions:           require("./transformers/_alias-functions"),
+
+  useStrict:                 require("./transformers/use-strict"),
+
+  _propertyLiterals:         require("./transformers/_property-literals"),
+  _memberExpressioLiterals:  require("./transformers/_member-expression-literals"),
+  _moduleFormatter:          require("./transformers/_module-formatter")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });

lib/6to5/transformation/transformer.js

@@ -15,6 +15,7 @@ Transformer.normalise = function (transformer) {
   }
 
   _.each(transformer, function (fns, type) {
+    if (type[0] === "_") return;
     if (_.isFunction(fns)) fns = { enter: fns };
     transformer[type] = fns;
   });

lib/6to5/transformation/transformers/_alias-functions.js

@@ -6,18 +6,17 @@ var go = function (getBody, node, file, scope) {
   var thisId;
 
   var getArgumentsId = function () {
-    return argumentsId = argumentsId || t.identifier(file.generateUid("arguments", scope));
+    return argumentsId = argumentsId || file.generateUidIdentifier("arguments", scope);
   };
 
   var getThisId = function () {
-    return thisId = thisId || t.identifier(file.generateUid("this", scope));
+    return thisId = thisId || file.generateUidIdentifier("this", scope);
   };
 
   // traverse the function and find all alias functions so we can alias
-  // arguments and this if necessary
+  // `arguments` and `this` if necessary
   traverse(node, function (node) {
-    var _aliasFunction = node._aliasFunction;
-    if (!_aliasFunction) {
+    if (!node._aliasFunction) {
       if (t.isFunction(node)) {
         // stop traversal of this node as it'll be hit again by this transformer
         return false;
@@ -26,15 +25,13 @@ var go = function (getBody, node, file, scope) {
       }
     }
 
-    // traverse all child nodes of this function and find arguments and this
+    // traverse all child nodes of this function and find `arguments` and `this`
     traverse(node, function (node, parent) {
-      if (_aliasFunction === "arrows") {
-        if (t.isFunction(node) && node._aliasFunction !== "arrows") {
-          return false;
-        }
+      if (t.isFunction(node) && !node._aliasFunction) {
+        return false;
       }
 
-      if (node._ignoreAliasFunctions) return;
+      if (node._ignoreAliasFunctions) return false;
 
       var getId;
 

lib/6to5/transformation/transformers/_declarations.js

@@ -1,12 +1,23 @@
 var t = require("../../types");
 var _ = require("lodash");
 
-module.exports = function (ast, file) {
-  var body = ast.program.body;
+exports.BlockStatement =
+exports.Program = function (node) {
+  var kinds = {};
 
-  _.each(file.declarations, function (declar) {
-    body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(declar.uid, declar.node)
-    ]));
+  _.each(node._declarations, function (declar) {
+    var kind = declar.kind || "var";
+    var declarNode = t.variableDeclarator(declar.id, declar.init);
+
+    if (!declar.init) {
+      kinds[kind] = kinds[kind] || [];
+      kinds[kind].push(declarNode);
+    } else {
+      node.body.unshift(t.variableDeclaration(kind, [declarNode]));
+    }
+  });
+
+  _.each(kinds, function (declars, kind) {
+    node.body.unshift(t.variableDeclaration(kind, declars));
   });
 };

lib/6to5/transformation/transformers/_member-expression-literals.js

@@ -0,0 +1,14 @@
+var esutils = require("esutils");
+var t       = require("../../types");
+
+exports.MemberExpression = function (node) {
+  var prop = node.property;
+  if (node.computed && t.isLiteral(prop) && t.isValidIdentifier(prop.value)) {
+    // computed literal that is a valid identifier
+    node.property = t.identifier(prop.value);
+    node.computed = false;
+  } else if (!node.computed && t.isIdentifier(prop) && esutils.keyword.isKeywordES6(prop.name, true)) {
+    node.property = t.literal(prop.name);
+    node.computed = true;
+  }
+};

lib/6to5/transformation/transformers/_property-literals.js

@@ -1,15 +1,14 @@
 var esutils = require("esutils");
 var t       = require("../../types");
-var _       = require("lodash");
 
 exports.Property = function (node) {
-  // ignore key literals that are valid identifiers
   var key = node.key;
-  if (t.isLiteral(key) && _.isString(key.value) && esutils.keyword.isIdentifierName(key.value)) {
-    key.type = "Identifier";
-    key.name = key.value;
-    delete key.value;
-
+  if (t.isLiteral(key) && t.isValidIdentifier(key.value)) {
+    // property key is a literal but a valid identifier
+    node.key = t.identifier(key.value);
     node.computed = false;
+  } else if (!node.computed && t.isIdentifier(key) && esutils.keyword.isKeywordES6(key.name, true)) {
+    // property key is a keyword
+    node.key = t.literal(key.name);
   }
 };

lib/6to5/transformation/transformers/array-comprehension.js

@@ -1,71 +0,0 @@
-var util = require("../../util");
-var t    = require("../../types");
-
-var singleArrayExpression = function (node) {
-  var block = node.blocks[0];
-
-  var templateName = "array-expression-comprehension-map";
-  if (node.filter) templateName = "array-expression-comprehension-filter";
-
-  var result = util.template(templateName, {
-    STATEMENT: node.body,
-    FILTER:    node.filter,
-    ARRAY:     block.right,
-    KEY:       block.left
-  });
-  result._aliasFunction = true;
-  return result;
-};
-
-var multiple = function (node, file) {
-  var uid = file.generateUid("arr");
-
-  var container = util.template("array-comprehension-container", {
-    KEY: uid
-  });
-  container._aliasFunction = true;
-
-  var block = container.callee.expression.body;
-  var body  = block.body;
-
-  var returnStatement = body.pop();
-
-  var build = function () {
-    var self = node.blocks.shift();
-    if (!self) return;
-
-    var child = build();
-    if (!child) {
-      // last item
-
-      child = util.template("array-push", {
-        STATEMENT: node.body,
-        KEY:       uid
-      }, true);
-
-      // add a filter as this is our final stop
-      if (node.filter) {
-        child = t.ifStatement(node.filter, t.blockStatement([child]));
-      }
-    }
-
-    return t.forOfStatement(
-      t.variableDeclaration("var", [t.variableDeclarator(self.left)]),
-      self.right,
-      t.blockStatement([child])
-    );
-  };
-
-  body.push(build());
-  body.push(returnStatement);
-
-  return container;
-};
-
-exports.ComprehensionExpression = function (node, parent, file) {
-  if (node.blocks.length === 1 && t.isArrayExpression(node.blocks[0].right)) {
-    return singleArrayExpression(node);
-  } else {
-    return multiple(node, file);
-  }
-};

lib/6to5/transformation/transformers/classes.js

@@ -1,209 +0,0 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
-var _        = require("lodash");
-
-exports.ClassDeclaration = function (node, parent, file, scope) {
-  return t.variableDeclaration("var", [
-    t.variableDeclarator(node.id, buildClass(node, file, scope))
-  ]);
-};
-
-exports.ClassExpression = function (node, parent, file, scope) {
-  return buildClass(node, file, scope);
-};
-
-var getMemberExpressionObject = function (node) {
-  while (t.isMemberExpression(node)) {
-    node = node.object;
-  }
-  return node;
-};
-
-var buildClass = function (node, file, scope) {
-  var superName = node.superClass;
-  var className = node.id || t.identifier(file.generateUid("class", scope));
-
-  var superClassArgument = node.superClass;
-  var superClassCallee   = node.superClass;
-
-  if (superName) {
-    if (t.isMemberExpression(superName)) {
-      superClassArgument = superClassCallee = getMemberExpressionObject(superName);
-    } else if (!t.isIdentifier(superName)) {
-      superClassArgument = superName;
-      superClassCallee   = superName = t.identifier(file.generateUid("ref", scope));
-    }
-  }
-
-  var container = util.template("class", {
-    CLASS_NAME: className
-  });
-
-  var block       = container.callee.expression.body;
-  var body        = block.body;
-  var constructor = body[0].declarations[0].init;
-
-  if (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);
-  }
-
-  buildClassBody({
-    file:        file,
-    body:        body,
-    node:        node,
-    className:   className,
-    superName:   superName,
-    constructor: constructor,
-  });
-
-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    return constructor;
-  } else {
-    body.push(returnStatement);
-    return container;
-  }
-};
-
-var buildClassBody = function (opts) {
-  var file        = opts.file;
-  var body        = opts.body;
-  var node        = opts.node;
-  var constructor = opts.constructor;
-  var className   = opts.className;
-  var superName   = opts.superName;
-
-  var instanceMutatorMap = {};
-  var staticMutatorMap   = {};
-  var hasConstructor     = false;
-
-  var classBody = node.body.body;
-
-  _.each(classBody, function (node) {
-    var methodName = node.key;
-    var method     = node.value;
-
-    replaceInstanceSuperReferences(superName, node);
-
-    if (node.key.name === "constructor") {
-      if (node.kind === "") {
-        hasConstructor = true;
-        addConstructor(constructor, method);
-      } else {
-        throw file.errorWithNode(node, "illegal kind for constructor method");
-      }
-    } else {
-      var mutatorMap = instanceMutatorMap;
-      if (node.static) mutatorMap = staticMutatorMap;
-
-      var kind = node.kind;
-
-      if (kind === "") {
-        kind = "value";
-        util.pushMutatorMap(mutatorMap, methodName, "writable", t.identifier("true"));
-      }
-
-      util.pushMutatorMap(mutatorMap, methodName, kind, node);
-    }
-  });
-
-  if (!hasConstructor && superName) {
-    constructor.body.body.push(util.template("class-super-constructor-call", {
-      SUPER_NAME: superName
-    }, true));
-  }
-
-  var instanceProps;
-  var staticProps;
-
-  if (!_.isEmpty(instanceMutatorMap)) {
-    var protoId = util.template("prototype-identifier", {
-      CLASS_NAME: className
-    });
-
-    instanceProps = util.buildDefineProperties(instanceMutatorMap, protoId);
-  }
-
-  if (!_.isEmpty(staticMutatorMap)) {
-    staticProps = util.buildDefineProperties(staticMutatorMap, className);
-  }
-
-  if (instanceProps || staticProps) {
-    staticProps = staticProps || t.literal(null);
-
-    var args = [className, staticProps];
-    if (instanceProps) args.push(instanceProps);
-
-    body.push(t.expressionStatement(
-      t.callExpression(file.addDeclaration("class-props"), args)
-    ));
-  }
-};
-
-var superIdentifier = function (superName, methodNode, node, parent) {
-  var methodName = methodNode.key;
-
-  if (parent.property === node) {
-    return;
-  } else if (t.isCallExpression(parent, { callee: node })) {
-    // super(); -> ClassName.prototype.MethodName.call(this);
-    parent.arguments.unshift(t.thisExpression());
-
-    if (methodName.name === "constructor") {
-      // constructor() { super(); }
-      return t.memberExpression(superName, t.identifier("call"));
-    } else {
-      node = superName;
-
-      // foo() { super(); }
-      if (!methodNode.static) {
-        node = t.memberExpression(node, t.identifier("prototype"));
-      }
-
-      node = t.memberExpression(node, methodName, methodNode.computed);
-      return t.memberExpression(node, t.identifier("call"));
-    }
-  } else if (t.isMemberExpression(parent) && !methodNode.static) {
-    // super.test -> ClassName.prototype.test
-    return t.memberExpression(superName, t.identifier("prototype"));
-  } else {
-    return superName;
-  }
-};
-
-var replaceInstanceSuperReferences = function (superName, methodNode) {
-  var method = methodNode.value;
-
-  superName = superName || t.identifier("Function");
-
-  traverse(method, function (node, parent) {
-    if (t.isIdentifier(node, { name: "super" })) {
-      return superIdentifier(superName, 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.name = callee.property.name + ".call";
-      node.arguments.unshift(t.thisExpression());
-    }
-  });
-};
-
-var addConstructor = function (construct, method) {
-  construct.defaults = method.defaults;
-  construct.params   = method.params;
-  construct.body     = method.body;
-  construct.rest     = method.rest;
-
-  t.inherits(construct, method);
-};

lib/6to5/transformation/transformers/constants.js

@@ -1,49 +0,0 @@
-var traverse = require("../../traverse");
-var t        = require("../../types");
-var _        = require("lodash");
-
-exports.Program =
-exports.BlockStatement =
-exports.ForInStatement =
-exports.ForOfStatement =
-exports.ForStatement = function (node, parent, file) {
-  var constants = [];
-
-  var check = function (node, names) {
-    _.each(names, function (name) {
-      if (constants.indexOf(name) >= 0) {
-        throw file.errorWithNode(node, name + " is read-only");
-      }
-    });
-  };
-
-  var getIds = function (node) {
-    return t.getIds(node, false, ["MemberExpression"]);
-  };
-
-  _.each(node.body, function (child) {
-    if (child && t.isVariableDeclaration(child, { kind: "const" })) {
-      _.each(child.declarations, function (declar) {
-        _.each(getIds(declar), function (name) {
-          check(declar, [name]);
-          constants.push(name);
-        });
-
-        declar._ignoreConstant = true;
-      });
-
-      child._ignoreConstant = true;
-      child.kind = "let";
-    }
-  });
-
-  if (!constants.length) return;
-
-  traverse(node, function (child) {
-    if (child._ignoreConstant) return;
-
-    if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-      check(child, getIds(child));
-    }
-  });
-};

lib/6to5/transformation/transformers/default-parameters.js

@@ -1,21 +0,0 @@
-var util = require("../../util");
-var t    = require("../../types");
-var _    = require("lodash");
-
-exports.Function = function (node) {
-  if (!node.defaults.length) return;
-  t.ensureBlock(node);
-
-  _.each(node.defaults, function (def, i) {
-    if (!def) return;
-
-    var param = node.params[i];
-
-    node.body.body.unshift(util.template("if-undefined-set-to", {
-      VARIABLE: param,
-      DEFAULT: def
-    }, true));
-  });
-
-  node.defaults = [];
-};

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 = "arrows";
+  node._aliasFunction = true;
   node.expression = false;
   node.type = "FunctionExpression";
 

lib/6to5/transformation/transformers/es6-classes.js

@@ -0,0 +1,267 @@
+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 declar = t.variableDeclaration("let", [
+    t.variableDeclarator(node.id, built)
+  ]);
+  t.inheritsComments(declar, node);
+  return declar;
+};
+
+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;
+};
+
+/**
+ * Description
+ *
+ * @param {Node} node
+ * @param {File} file
+ * @param {Scope} scope
+ */
+
+function Class(node, file, scope) {
+  this.scope = scope;
+  this.node  = node;
+  this.file  = file;
+
+  this.instanceMutatorMap = {};
+  this.staticMutatorMap   = {};
+  this.hasConstructor     = false;
+  this.className          = node.id || file.generateUidIdentifier("class", scope);
+  this.superName          = node.superClass;
+}
+
+/**
+ * Description
+ *
+ * @returns {Array}
+ */
+
+Class.prototype.run = function () {
+  var superClassArgument = this.superName;
+  var superClassCallee   = this.superName;
+  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);
+    }
+  }
+
+  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);
+  }
+
+  this.buildBody();
+
+  if (body.length === 1) {
+    // only a constructor so no need for a closure container
+    return constructor;
+  } else {
+    body.push(returnStatement);
+    return container;
+  }
+};
+
+/**
+ * Description
+ */
+
+Class.prototype.buildBody = function () {
+  var constructor = this.constructor;
+  var className   = this.className;
+  var superName   = this.superName;
+  var classBody   = this.node.body.body;
+  var body        = this.body;
+  var self        = this;
+
+  _.each(classBody, function (node) {
+    self.replaceInstanceSuperReferences(node);
+
+    if (node.key.name === "constructor") {
+      self.pushConstructor(node);
+    } else {
+      self.pushMethod(node);
+    }
+  });
+
+  if (!this.hasConstructor && superName) {
+    constructor.body.body.push(util.template("class-super-constructor-call", {
+      SUPER_NAME: superName
+    }, true));
+  }
+
+  var instanceProps;
+  var staticProps;
+
+  if (!_.isEmpty(this.instanceMutatorMap)) {
+    var protoId = util.template("prototype-identifier", {
+      CLASS_NAME: className
+    });
+
+    instanceProps = util.buildDefineProperties(this.instanceMutatorMap, protoId);
+  }
+
+  if (!_.isEmpty(this.staticMutatorMap)) {
+    staticProps = util.buildDefineProperties(this.staticMutatorMap, className);
+  }
+
+  if (instanceProps || staticProps) {
+    staticProps = staticProps || t.literal(null);
+
+    var args = [className, staticProps];
+    if (instanceProps) args.push(instanceProps);
+
+    body.push(t.expressionStatement(
+      t.callExpression(this.file.addDeclaration("class-props"), args)
+    ));
+  }
+};
+
+/**
+ * Push a method to it's respective mutatorMap.
+ *
+ * @param {Node} node MethodDefinition
+ */
+
+Class.prototype.pushMethod = function (node) {
+  var methodName = node.key;
+
+  var mutatorMap = this.instanceMutatorMap;
+  if (node.static) mutatorMap = this.staticMutatorMap;
+
+  var kind = node.kind;
+
+  if (kind === "") {
+    kind = "value";
+    util.pushMutatorMap(mutatorMap, methodName, "writable", t.identifier("true"));
+  }
+
+  util.pushMutatorMap(mutatorMap, methodName, kind, node);
+};
+
+/**
+ * Given a `methodNode`, produce a `MemberExpression` super class reference.
+ *
+ * @param {Node} methodNode MethodDefinition
+ * @param {Node} node Identifier
+ * @param {Node} parent
+ *
+ * @returns {Node}
+ */
+
+Class.prototype.superIdentifier = function (methodNode, id, parent) {
+  var methodName = methodNode.key;
+  var superName  = this.superName || t.identifier("Function");
+
+  if (parent.property === id) {
+    return;
+  } else if (t.isCallExpression(parent, { callee: id })) {
+    // super(); -> ClassName.prototype.MethodName.call(this);
+    parent.arguments.unshift(t.thisExpression());
+
+    if (methodName.name === "constructor") {
+      // constructor() { super(); }
+      return t.memberExpression(superName, t.identifier("call"));
+    } else {
+      id = superName;
+
+      // foo() { super(); }
+      if (!methodNode.static) {
+        id = t.memberExpression(id, t.identifier("prototype"));
+      }
+
+      id = t.memberExpression(id, methodName, methodNode.computed);
+      return t.memberExpression(id, t.identifier("call"));
+    }
+  } else if (t.isMemberExpression(parent) && !methodNode.static) {
+    // super.test -> ClassName.prototype.test
+    return t.memberExpression(superName, t.identifier("prototype"));
+  } else {
+    return superName;
+  }
+};
+
+/**
+ * Replace all `super` references with a reference to our `superClass`.
+ *
+ * @param {Node} methodNode MethodDefinition
+ */
+
+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;
+
+      // super.test(); -> ClassName.prototype.MethodName.call(this);
+      callee.property = t.memberExpression(callee.property, t.identifier("call"));
+      node.arguments.unshift(t.thisExpression());
+    }
+  });
+};
+
+/**
+ * Replace the constructor body of our class.
+ *
+ * @param {Node} method MethodDefinition
+ */
+
+Class.prototype.pushConstructor = function (method) {
+  if (method.kind !== "") {
+    throw this.file.errorWithNode(method, "illegal kind for constructor method");
+  }
+
+  var construct = this.constructor;
+  var fn        = method.value;
+
+  this.hasConstructor = true;
+  t.inherits(construct, fn);
+  t.inheritsComments(construct, method);
+
+  construct.defaults = fn.defaults;
+  construct.params   = fn.params;
+  construct.body     = fn.body;
+  construct.rest     = fn.rest;
+};

lib/6to5/transformation/transformers/es6-computed-property-names.js

@@ -29,7 +29,7 @@ exports.ObjectExpression = function (node, parent, file) {
   var containerCallee = container.callee.expression;
   var containerBody = containerCallee.body.body;
 
-  containerCallee._aliasFunction = "arrows";
+  containerCallee._aliasFunction = true;
 
   _.each(computed, function (prop) {
     containerBody.unshift(

lib/6to5/transformation/transformers/es6-constants.js

@@ -0,0 +1,54 @@
+var traverse = require("../../traverse");
+var t        = require("../../types");
+var _        = require("lodash");
+
+exports.Program =
+exports.BlockStatement =
+exports.ForInStatement =
+exports.ForOfStatement =
+exports.ForStatement = function (node, parent, file) {
+  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;
+
+      throw file.errorWithNode(nameNode, name + " is read-only");
+    });
+  };
+
+  var getIds = function (node) {
+    return t.getIds(node, true, ["MemberExpression"]);
+  };
+
+  _.each(node.body, function (child, parent) {
+    if (child && t.isVariableDeclaration(child, { kind: "const" })) {
+      _.each(child.declarations, function (declar) {
+        _.each(getIds(declar), function (nameNode, name) {
+          var names = {};
+          names[name] = nameNode;
+          check(parent, names);
+
+          constants[name] = parent;
+        });
+
+        declar._ignoreConstant = true;
+      });
+
+      child._ignoreConstant = true;
+      child.kind = "let";
+    }
+  });
+
+  if (_.isEmpty(constants)) return;
+
+  traverse(node, function (child, parent) {
+    if (child._ignoreConstant) return;
+    if (t.isVariableDeclaration(child)) return;
+
+    if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
+      check(parent, getIds(child));
+    }
+  });
+};

lib/6to5/transformation/transformers/es6-default-parameters.js

@@ -0,0 +1,70 @@
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+exports.Function = function (node, parent, file, scope) {
+  if (!node.defaults || !node.defaults.length) return;
+  t.ensureBlock(node);
+
+  var ids = node.params.map(function (param) {
+    return t.getIds(param);
+  });
+
+  var closure = false;
+
+  _.each(node.defaults, function (def, i) {
+    if (!def) return;
+
+    var param = node.params[i];
+
+    // temporal dead zone check - here we prevent accessing of params that
+    // are to the right - ie. uninitialized parameters
+    _.each(ids.slice(i), function (ids) {
+      var check = function (node, parent) {
+        if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;
+
+        if (_.contains(ids, node.name)) {
+          throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+        }
+
+        if (scope.has(node.name)) {
+          closure = true;
+        }
+      };
+
+      check(def, node);
+      traverse(def, 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)) {
+      closure = true;
+    }
+  });
+
+  var body = [];
+
+  _.each(node.defaults, function (def, i) {
+    if (!def) return;
+
+    body.push(util.template("if-undefined-set-to", {
+      VARIABLE: node.params[i],
+      DEFAULT:  def
+    }, true));
+  });
+
+  if (closure) {
+    var container = t.functionExpression(null, [], node.body, node.generator);
+    container._aliasFunction = true;
+
+    body.push(t.returnStatement(t.callExpression(container, [])));
+
+    node.body = t.blockStatement(body);
+  } else {
+    node.body.body = body.concat(node.body.body);
+  }
+
+  node.defaults = [];
+};

lib/6to5/transformation/transformers/es6-destructuring.js

@@ -1,60 +1,92 @@
+// TODO: Clean up
+
 var t = require("../../types");
 var _ = require("lodash");
 
-var buildVariableAssign = function (kind, id, init) {
-  if (kind === false) {
+var buildVariableAssign = function (opts, id, init) {
+  var op = opts.operator;
+  if (t.isMemberExpression(id)) op = "=";
+
+  if (op) {
     return t.expressionStatement(t.assignmentExpression("=", id, init));
   } else {
-    return t.variableDeclaration(kind, [
+    return t.variableDeclaration(opts.kind, [
       t.variableDeclarator(id, init)
     ]);
   }
 };
 
-var push = function (kind, nodes, elem, parentId) {
+var push = function (opts, nodes, elem, parentId) {
   if (t.isObjectPattern(elem)) {
-    pushObjectPattern(kind, nodes, elem, parentId);
+    pushObjectPattern(opts, nodes, elem, parentId);
   } else if (t.isArrayPattern(elem)) {
-    pushArrayPattern(kind, nodes, elem, parentId);
-  } else if (t.isMemberExpression(elem)) {
-    nodes.push(buildVariableAssign(false, elem, parentId));
+    pushArrayPattern(opts, nodes, elem, parentId);
   } else {
-    nodes.push(buildVariableAssign(kind, elem, parentId));
+    nodes.push(buildVariableAssign(opts, elem, parentId));
   }
 };
 
-var pushObjectPattern = function (kind, nodes, pattern, parentId) {
-  _.each(pattern.properties, function (prop) {
-    var pattern2   = prop.value;
-    var patternId2 = t.memberExpression(parentId, prop.key);
+var pushObjectPattern = function (opts, nodes, pattern, parentId) {
+  _.each(pattern.properties, function (prop, 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;
 
-    if (t.isPattern(pattern2)) {
-      push(kind, nodes, pattern2, patternId2);
+          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]);
+        nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
-      nodes.push(buildVariableAssign(kind, pattern2, patternId2));
+      var pattern2   = prop.value;
+      var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
+
+      if (t.isPattern(pattern2)) {
+        push(opts, nodes, pattern2, patternId2);
+      } else {
+        nodes.push(buildVariableAssign(opts, pattern2, patternId2));
+      }
     }
   });
 };
 
-var pushArrayPattern = function (kind, nodes, pattern, parentId) {
+var pushArrayPattern = function (opts, nodes, pattern, parentId) {
+  var _parentId = opts.file.generateUidIdentifier("ref", opts.scope);
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(_parentId, opts.file.toArray(parentId))
+  ]));
+  parentId = _parentId;
+
   _.each(pattern.elements, function (elem, i) {
     if (!elem) return;
 
     var newPatternId;
 
     if (t.isSpreadElement(elem)) {
-      newPatternId = t.callExpression(t.memberExpression(parentId, t.identifier("slice")), [t.literal(i)]);
+      newPatternId = opts.file.toArray(parentId);
+
+      if (+i > 0) {
+        newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
+      }
+
       elem = elem.argument;
     } else {
       newPatternId = t.memberExpression(parentId, t.literal(i), true);
     }
 
-    push(kind, nodes, elem, newPatternId);
+    push(opts, nodes, elem, newPatternId);
   });
 };
 
 var pushPattern = function (opts) {
-  var kind = opts.kind;
   var nodes = opts.nodes;
   var pattern = opts.pattern;
   var parentId = opts.id;
@@ -62,7 +94,7 @@ var pushPattern = function (opts) {
   var scope = opts.scope;
 
   if (!t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = t.identifier(file.generateUid("ref", scope));
+    var key = file.generateUidIdentifier("ref", scope);
 
     nodes.push(t.variableDeclaration("var", [
       t.variableDeclarator(key, parentId)
@@ -71,7 +103,7 @@ var pushPattern = function (opts) {
     parentId = key;
   }
 
-  push(kind, nodes, pattern, parentId);
+  push(opts, nodes, pattern, parentId);
 };
 
 exports.ForInStatement =
@@ -82,14 +114,18 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   var pattern = declar.declarations[0].id;
   if (!t.isPattern(pattern)) return;
 
-  var key = t.identifier(file.generateUid("ref", scope));
+  var key = file.generateUidIdentifier("ref", scope);
   node.left = t.variableDeclaration(declar.kind, [
     t.variableDeclarator(key, null)
   ]);
 
   var nodes = [];
 
-  push(declar.kind, nodes, pattern, key);
+  push({
+    kind: declar.kind,
+    file: file,
+    scope: scope
+  }, nodes, pattern, key);
 
   t.ensureBlock(node);
 
@@ -106,7 +142,7 @@ exports.Function = function (node, parent, file, scope) {
     if (!t.isPattern(pattern)) return pattern;
 
     hasDestructuring = true;
-    var parentId = t.identifier(file.generateUid("ref", scope));
+    var parentId = file.generateUidIdentifier("ref", scope);
 
     pushPattern({
       kind:    "var",
@@ -136,16 +172,45 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
 
   var nodes = [];
 
-  var ref = t.identifier(file.generateUid("ref", scope));
+  var ref = file.generateUidIdentifier("ref", scope);
   nodes.push(t.variableDeclaration("var", [
     t.variableDeclarator(ref, expr.right)
   ]));
 
-  push(false, nodes, expr.left, ref);
+  push({
+    operator: expr.operator,
+    file: file,
+    scope: scope
+  }, nodes, expr.left, ref);
 
   return nodes;
 };
 
+exports.AssignmentExpression = function (node, parent, file, scope) {
+  if (parent.type === "ExpressionStatement") return;
+  if (!t.isPattern(node.left)) return;
+
+  var tempName = file.generateUid("temp", scope);
+  var ref = t.identifier(tempName);
+  scope.push({
+    key: tempName,
+    id: ref
+  });
+
+  var nodes = [];
+  nodes.push(t.assignmentExpression("=", ref, node.right));
+
+  push({
+    operator: node.operator,
+    file: file,
+    scope: scope
+  }, nodes, node.left, ref);
+
+  nodes.push(ref);
+
+  return t.toSequenceExpression(nodes, scope);
+};
+
 exports.VariableDeclaration = function (node, parent, file, scope) {
   if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
 
@@ -163,17 +228,18 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   _.each(node.declarations, function (declar) {
     var patternId = declar.init;
     var pattern   = declar.id;
+    var opts = {
+      kind:    node.kind,
+      nodes:   nodes,
+      pattern: pattern,
+      id:      patternId,
+      file:    file,
+      scope:   scope
+    };
     if (t.isPattern(pattern) && patternId) {
-      pushPattern({
-        kind:    node.kind,
-        nodes:   nodes,
-        pattern: pattern,
-        id:      patternId,
-        file:    file,
-        scope:   scope
-      });
+      pushPattern(opts);
     } else {
-      nodes.push(buildVariableAssign(node.kind, declar.id, declar.init));
+      nodes.push(buildVariableAssign(opts, declar.id, declar.init));
     }
   });
 
@@ -195,4 +261,3 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
 
   return nodes;
 };
-

lib/6to5/transformation/transformers/es6-for-of.js

@@ -5,21 +5,21 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   var left = node.left;
   var declar;
 
-  var stepKey = t.identifier(file.generateUid("step", scope));
-  var stepValueId = t.memberExpression(stepKey, t.identifier("value"));
+  var stepKey   = file.generateUidIdentifier("step", scope);
+  var stepValue = t.memberExpression(stepKey, t.identifier("value"));
 
   if (t.isIdentifier(left)) {
-    declar = t.expressionStatement(t.assignmentExpression("=", left, stepValueId));
+    declar = t.expressionStatement(t.assignmentExpression("=", left, stepValue));
   } else if (t.isVariableDeclaration(left)) {
     declar = t.variableDeclaration(left.kind, [
-      t.variableDeclarator(left.declarations[0].id, stepValueId)
+      t.variableDeclarator(left.declarations[0].id, stepValue)
     ]);
   } else {
-    return;
+    throw file.errorWithNode(left, "Unknown node type " + left.type + " in ForOfStatement");
   }
 
   var node2 = util.template("for-of", {
-    ITERATOR_KEY: file.generateUid("iterator", scope),
+    ITERATOR_KEY: file.generateUidIdentifier("iterator", scope),
     STEP_KEY:     stepKey,
     OBJECT:       node.right
   });

lib/6to5/transformation/transformers/es6-generators/emit/explode-expressions.js

@@ -0,0 +1,204 @@
+/**
+ * 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");
+};

lib/6to5/transformation/transformers/es6-generators/emit/explode-statements.js

@@ -0,0 +1,334 @@
+/**
+ * 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"))
+  ));
+};

lib/6to5/transformation/transformers/es6-generators/emit/index.js

@@ -0,0 +1,611 @@
+/**
+ * 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));
+  }
+};

lib/6to5/transformation/transformers/es6-generators/hoist.js

@@ -0,0 +1,151 @@
+/**
+ * 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);
+};

lib/6to5/transformation/transformers/es6-generators/index.js

@@ -0,0 +1 @@
+module.exports = require("./visit").transform;

lib/6to5/transformation/transformers/es6-generators/leap.js

@@ -0,0 +1,163 @@
+/**
+ * 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);
+};

lib/6to5/transformation/transformers/es6-generators/meta.js

@@ -0,0 +1,98 @@
+/**
+ * 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);

lib/6to5/transformation/transformers/es6-generators/runtime.js

@@ -0,0 +1,454 @@
+/**
+* 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.
+var GF = function GeneratorFunction() {};
+var GFp = function GeneratorFunctionPrototype() {};
+var Gp = GFp.prototype = Generator.prototype;
+(GFp.constructor = GF).prototype =
+  Gp.constructor = GFp;
+
+// Ensure isGeneratorFunction works when Function#name not supported.
+var GFName = "GeneratorFunction";
+if (GF.name !== GFName) GF.name = GFName;
+if (GF.name !== GFName) throw new Error(GFName + " renamed?");
+
+runtime.isGeneratorFunction = function (genFun) {
+  var ctor = genFun && genFun.constructor;
+  return ctor ? GF.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;
+  }
+};

lib/6to5/transformation/transformers/es6-generators/util.js

@@ -0,0 +1,28 @@
+/**
+ * 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);
+};

lib/6to5/transformation/transformers/es6-generators/visit.js

@@ -0,0 +1,221 @@
+/**
+ * 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);
+  }
+});

lib/6to5/transformation/transformers/es6-let-scoping.js

@@ -0,0 +1,474 @@
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+var isLet = function (node) {
+  if (!t.isVariableDeclaration(node)) return false;
+  if (node._let) return true;
+  if (node.kind !== "let") return false;
+
+  node._let = true;
+  node.kind = "var";
+  return true;
+};
+
+var isVar = function (node) {
+  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node);
+};
+
+var standardiseLets = function (declars) {
+  _.each(declars, function (declar) {
+    delete declar._let;
+  });
+};
+
+exports.VariableDeclaration = function (node) {
+  isLet(node);
+};
+
+exports.For = function (node, parent, file, scope) {
+  var init = node.left || node.init;
+  if (isLet(init)) {
+    t.ensureBlock(node);
+    node.body._letDeclars = [init];
+  }
+
+  if (t.isLabeledStatement(parent)) {
+    // set label so `run` has access to it
+    node.label = parent.label;
+  }
+
+  var letScoping = new LetScoping(node, node.body, parent, file, scope);
+  letScoping.run();
+
+  if (node.label && !t.isLabeledStatement(parent)) {
+    // we've been given a label so let's wrap ourselves
+    return t.labeledStatement(node.label, node);
+  }
+};
+
+exports.BlockStatement = function (block, parent, file, scope) {
+  if (!t.isFor(parent)) {
+    var letScoping = new LetScoping(false, block, parent, file, scope);
+    letScoping.run();
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Boolean|Node} forParent
+ * @param {Node} block
+ * @param {Node} parent
+ * @param {File} file
+ * @param {Scope} scope
+ */
+
+function LetScoping(forParent, block, parent, file, scope) {
+  this.forParent = forParent;
+  this.parent    = parent;
+  this.scope     = scope;
+  this.block     = block;
+  this.file      = file;
+
+  this.letReferences = {};
+  this.body          = [];
+}
+
+/**
+ * Start the ball rolling.
+ */
+
+LetScoping.prototype.run = function () {
+  var block = this.block;
+
+  if (block._letDone) return;
+  block._letDone = true;
+
+  this.info = this.getInfo();
+
+  // remap all let references that exist in upper scopes to their uid
+  this.remap();
+
+  // this is a block within a `Function` so we can safely leave it be
+  if (t.isFunction(this.parent)) return this.noClosure();
+
+  // this block has no let references so let's clean up
+  if (!this.info.keys.length) return this.noClosure();
+
+  // returns whether or not there are any outside let references within any
+  // functions
+  var referencesInClosure = this.getLetReferences();
+
+  // no need for a closure so let's clean up
+  if (!referencesInClosure) return this.noClosure();
+
+  // if we're inside of a for loop then we search to see if there are any
+  // `break`s, `continue`s, `return`s etc
+  this.has = this.checkFor();
+
+  // hoist var references to retain scope
+  this.hoistVarDeclarations();
+
+  // set let references to plain var references
+  standardiseLets(this.info.declarators);
+
+  // turn letReferences into an array
+  var letReferences = _.values(this.letReferences);
+
+  // build the closure that we're going to wrap the block with
+  var fn = t.functionExpression(null, letReferences, t.blockStatement(block.body));
+  fn._aliasFunction = true;
+
+  // replace the current block body with the one we're going to build
+  block.body = this.body;
+
+  // change upper scope references with their uid if they have one
+  var params = this.getParams(letReferences);
+
+  // build a call and a unique id that we can assign the return value to
+  var call = t.callExpression(fn, params);
+  var ret  = this.file.generateUidIdentifier("ret", this.scope);
+
+  var hasYield = traverse.hasType(fn.body, "YieldExpression", t.FUNCTION_TYPES);
+  if (hasYield) {
+    fn.generator = true;
+    call = t.yieldExpression(call, true);
+  }
+
+  this.build(ret, call);
+};
+
+/**
+ * There are no let references accessed within a closure so we can just turn the
+ * lets into vars.
+ */
+
+LetScoping.prototype.noClosure = function () {
+  standardiseLets(this.info.declarators);
+};
+
+/**
+ * Traverse through block and replace all references that exist in a higher
+ * scope to their uids.
+ */
+
+LetScoping.prototype.remap = function () {
+  var replacements = this.info.duplicates;
+  var block        = this.block;
+
+  if (_.isEmpty(replacements)) return;
+
+  var replace = function (node, parent, scope) {
+    if (!t.isIdentifier(node)) return;
+    if (!t.isReferenced(node, parent)) return;
+    if (scope && scope.hasOwn(node.name)) return;
+    node.name = replacements[node.name] || node.name;
+  };
+
+  var traverseReplace = function (node, parent) {
+    replace(node, parent);
+    traverse(node, replace);
+  };
+
+  var forParent = this.forParent;
+  if (forParent) {
+    traverseReplace(forParent.right, forParent);
+    traverseReplace(forParent.test, forParent);
+    traverseReplace(forParent.update, forParent);
+  }
+
+  traverse(block, replace);
+};
+
+/**
+ * Description
+ *
+ * @returns {Object}
+ */
+
+LetScoping.prototype.getInfo = function () {
+  var block = this.block;
+  var scope = this.scope;
+  var file  = this.file;
+
+  var opts = {
+    // array of `Identifier` names of let variables that appear lexically out of
+    // this scope but should be accessible - eg. `ForOfStatement`.left
+    outsideKeys: [],
+
+    // array of let `VariableDeclarator`s that are a part of this block
+    declarators: block._letDeclars || [],
+
+    // object of duplicate ids and their aliases - if there's an `Identifier`
+    // name that's used in an upper scope we generate a unique id and replace
+    // all references with it
+    duplicates:  {},
+
+    // array of `Identifier` names of let variables that are accessible within
+    // the current block
+    keys:        []
+  };
+
+  var duplicates = function (id, key) {
+    var has = scope.parentGet(key);
+
+    if (has && has !== id) {
+      // 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);
+    }
+  };
+
+  _.each(opts.declarators, function (declar) {
+    opts.declarators.push(declar);
+
+    var keys = t.getIds(declar, true);
+    _.each(keys, duplicates);
+    keys = _.keys(keys);
+
+    opts.outsideKeys = opts.outsideKeys.concat(keys);
+    opts.keys = opts.keys.concat(keys);
+  });
+
+  _.each(block.body, function (declar) {
+    if (!isLet(declar)) return;
+
+    _.each(t.getIds(declar, true), function (id, key) {
+      duplicates(id, key);
+      opts.keys.push(key);
+    });
+  });
+
+  return opts;
+};
+
+/**
+ * If we're inside of a `For*Statement` 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.
+ *
+ * @returns {Object}
+ */
+
+LetScoping.prototype.checkFor = function () {
+  var has = {
+    hasContinue: false,
+    hasReturn:   false,
+    hasBreak:    false,
+  };
+
+  var forParent = this.forParent;
+
+  traverse(this.block, function (node) {
+    var replace;
+
+    if (t.isFunction(node) || t.isFor(node)) {
+      return false;
+    }
+
+    if (forParent && node && !node.label) {
+      if (t.isBreakStatement(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;
+};
+
+/**
+ * Hoist all var declarations in this block to before it so they retain scope
+ * once we wrap everything in a closure.
+ */
+
+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));
+      }
+    } 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;
+    }
+  });
+};
+
+/**
+ * Build up a parameter list that we'll call our closure wrapper with, replacing
+ * all duplicate ids with their uid.
+ *
+ * @param {Array} params
+ * @returns {Array}
+ */
+
+LetScoping.prototype.getParams = function (params) {
+  var info = this.info;
+  params = _.cloneDeep(params);
+  _.each(params, function (param) {
+    param.name = info.duplicates[param.name] || param.name;
+  });
+  return params;
+};
+
+/**
+ * Get all let references within this block. Stopping whenever we reach another
+ * block.
+ */
+
+LetScoping.prototype.getLetReferences = function () {
+  var closurify = false;
+  var self = this;
+
+  // 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;
+
+        // 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;
+
+        closurify = true;
+
+        // 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;
+      });
+
+      return false;
+    } else if (t.isFor(node)) {
+      return false;
+    }
+  });
+
+  return closurify;
+};
+
+/**
+ * Turn a `VariableDeclaration` into an array of `AssignmentExpressions` with
+ * their declarations hoisted to before the closure wrapper.
+ *
+ * @param {Node} node VariableDeclaration
+ * @returns {Array}
+ */
+
+LetScoping.prototype.pushDeclar = function (node) {
+  this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
+    return t.variableDeclarator(declar.id);
+  })));
+
+  var replace = [];
+
+  _.each(node.declarations, function (declar) {
+    if (!declar.init) return;
+
+    var expr = t.assignmentExpression("=", declar.id, declar.init);
+    replace.push(t.inherits(expr, declar));
+  });
+
+  return replace;
+};
+
+/**
+ * Push the closure to the body.
+ *
+ * @param {Node} ret Identifier
+ * @param {Node} call CallExpression
+ */
+
+LetScoping.prototype.build = function (ret, call) {
+  var has = this.has;
+  if (has.hasReturn || has.hasBreak || has.hasContinue) {
+    this.buildHas(ret, call);
+  } else {
+    this.body.push(t.expressionStatement(call));
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Node} ret Identifier
+ * @param {Node} call CallExpression
+ */
+
+LetScoping.prototype.buildHas = function (ret, call) {
+  var body = this.body;
+
+  body.push(t.variableDeclaration("var", [
+    t.variableDeclarator(ret, call)
+  ]));
+
+  var forParent = this.forParent;
+  var retCheck;
+  var has = this.has;
+  var cases = [];
+
+  if (has.hasReturn) {
+    // typeof ret === "object"
+    retCheck = util.template("let-scoping-return", {
+      RETURN: ret
+    });
+  }
+
+  if (has.hasBreak || has.hasContinue) {
+    // ensure that the parent has a label as we're building a switch and we
+    // need to be able to access it
+    var label = forParent.label = forParent.label || this.file.generateUidIdentifier("loop", this.scope);
+
+    if (has.hasBreak) {
+      cases.push(t.switchCase(t.literal("break"), [t.breakStatement(label)]));
+    }
+
+    if (has.hasContinue) {
+      cases.push(t.switchCase(t.literal("continue"), [t.continueStatement(label)]));
+    }
+
+    if (has.hasReturn) {
+      cases.push(t.switchCase(null, [retCheck]));
+    }
+
+    if (cases.length === 1) {
+      var single = cases[0];
+      body.push(t.ifStatement(
+        t.binaryExpression("===", ret, single.test),
+        single.consequent[0]
+      ));
+    } else {
+      body.push(t.switchStatement(ret, cases));
+    }
+  } else {
+    if (has.hasReturn) body.push(retCheck);
+  }
+};