v2.0.2

Correct system format base support tests

.hound.yml

@@ -1,3 +0,0 @@
-java_script:
-  enabled: true
-  config_file: .jshintrc

CHANGELOG.md

@@ -1,42 +1,330 @@
-# 1.12.5
+# Changelog
+
+Gaps between patch versions are faulty/broken releases.
+
+## 2.0.2
+
+ * Inherit comments in `for-of` transformer.
+ * Remove `interopRequire` from `system` module formatter.
+
+## 2.0.1
+
+ * Remap `UpdateExpression` module export binding.
+ * Fix automatic closure on `PrivateDeclaration` in classes.
+
+## 2.0.0
+
+ * Make string literal generation only escapes unicode that it has to.
+ * Internal code generation format options have been exposed.
+ * Change playground method binding operator from `:` to `#` removing ambiguous syntax with terns.
+ * Fix rest parameters in async and generator functions.
+ * Export/import declarations replace by the modules transformer now inherit comments.
+ * Added playground flag to `6to5-node`.
+ * `6to5-node` now behaves the same as `node`.
+ * `6to5-node` now uses `kexec` to become the forked process to correctly propagate signals on unix.
+ * Constants are now block scoped.
+ * Exposed ast transformer.
+ * Merged `commonInterop` and `common` module formatters.
+ * Fix generator comprehensions not inheriting `arguments`, `this` etc.
+ * Object and class mutator shorthand are now enumerable.
+ * Remove regenerator `Generator has already finished` error which isn't spec-compliant.
+ * Expose internal `spec` transformers that nicen up code output.
+ * Add export variable declaration default initializers.
+ * Propagate export declaration reassignments.
+ * Add initializer default to block scoped variable declarations within a loop.
+ * Flow type support.
+ * Make async/await contextual keywords.
+ * Allow `yield`ing of non-objects.
+ * Class declarations now lack an IIFE.
+ * Support falsy and `null` super classes.
+ * Add support for experimental abstract references `private` declarations.
+ * Leave out IIFE for class declarations.
+ * Switched to [core-js](https://github.com/zloirock/core-js) from [es6-symbol](https://github.com/medikoo/es6-symbol) and [es6-shim](https://github.com/paulmillr/es6-shim/) for built-in polyfill.
+ * `amd` and `umd` module formatters now behave the same as `common` with `interopRequire`.
+ * Micro-optimizations to boost performance by 200%.
+ * Rename module formatter methods `import` to `importDeclaration` and `export` to `exportDeclaration`.
+ * Support multiple declarators in export variable declarations.
+ * Freeze tagged template literal object.
+ * Remove inlined `regenerator` fork.
+ * Remove `ParenthesizedExpression`.
+ * Rename `object-spread` helper to `object-without-properties`.
+ * Rename `class-props` helper to `prototype-properties`.
+ * Rename `extends` helper to `inherits`.
+ * Completely rewritten `system` module formatter.
+
+## 1.15.0
+
+ * Don't alias `GeneratorFunction` and check the name which causes minifiers to remove the name and throw an error later on when we check if it's set.
+
+## 1.14.18
+
+ * Fix files only containg comments not being output.
+ * Fix duplicate comments on property key shorthands.
+
+## 1.14.17
+
+ * Add default initializer to let variables within loop bodies.
+ * Fix excessive `break` replacement inside of switches in let scoping.
+
+## 1.14.16
+
+ * Add object getter memos and this shorthand to playground.
+ * Fix while loops in let scoping.
+ * Upgrade `acorn-6to5`.
+
+## 1.14.14
+
+ * Fix template literals escaping.
+
+## 1.14.13
+
+ * Fix let scoping of `while` loops.
+ * Make class methods enumerable.
+
+## 1.14.12
+
+ * Fix duplicate dynamic expressions in call spread.
+
+## 1.14.10
+
+ * Fix let scoping unneccesary override.
+
+## 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
+## 1.12.4
 
  * Add `doc` folder for documentation.
 
-# 1.12.3
+## 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
+## 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
+## 1.12.1
 
  * Fix `this` and `arguments` mapping in the `_aliasFunctions` transformer.
 
-# 1.12.0
+## 1.12.0
 
  * Combine `jsx` and `react` transformers to `react`.
  * Update `react` syntax output to React v0.12.
 
-# 1.11.15
+## 1.11.15
 
  * Fix JSX literal whitespace generation.
 
-# 1.11.14
+## 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
+## 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

Makefile

@@ -16,7 +16,7 @@ bench:
 	node node_modules/matcha/bin/_matcha
 
 lint:
-	$(JSHINT_CMD) lib bin benchmark/index.js
+	$(JSHINT_CMD) --reporter node_modules/jshint-stylish/stylish.js lib bin benchmark/index.js
 
 test-clean:
 	rm -rf test/tmp

README.md

@@ -3,8 +3,12 @@
 </p>
 
 <p align="center">
+  <a href="https://gratipay.com/sebmck">
+    <img alt="Gratipay" src="https://img.shields.io/gratipay/sebmck.svg?style=flat">
+  </a>
+
   <a href="https://travis-ci.org/6to5/6to5">
-    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5.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">
@@ -24,6 +28,11 @@
   </a>
 </p>
 
-**6to5** turns ES6 code into vanilla ES5, so you can use ES6 features **today.**
+<p align="center">
+  <strong>6to5</strong> turns ES6+ code into vanilla ES5, so you can use next generation features <strong>today.</strong>
+</p>
 
-For more information view the [documentation](https://6to5.github.io).
+<p align="center">
+  For more information view the <a href="https://6to5.github.io">documentation</a>. For
+  support visit the <a href="https://gitter.im/6to5/6to5">gitter room</a>.
+</p>

benchmark/index.js

@@ -2,9 +2,9 @@ Error.stackTraceLimit = Infinity;
 
 var jsTrans = require("jstransform");
 var traceur = require("traceur");
-var es6tr   = require("es6-transpiler");
+//var es6tr   = require("es6-transpiler");
 var es6now  = require("es6now");
-var esnext  = require("esnext");
+//var esnext  = require("esnext");
 var to5     = require("../lib/6to5");
 
 //var uglify  = require("uglify-js");
@@ -56,12 +56,12 @@ var compilers = {
     }
   },
 
-  esnext: {
+  /*esnext: {
     runtime: readResolve("esnext/node_modules/regenerator/runtime.js") || readResolve("regenerator/runtime.js"),
     compile: function (code) {
       return esnext.compile(code).code;
     }
-  },
+  },*/
 
   es6now: {
     runtime: readResolve("es6now/runtime/ES6.js"),
@@ -70,13 +70,13 @@ var compilers = {
     }
   },
 
-  "es6-transpiler": {
+  /*"es6-transpiler": {
     compile: function (code) {
       var result = es6tr.run({ src: code });
       if (result.errors.length) throw new Error(result.join("; "));
       return result.src;
     }
-  },
+  },*/
 
   jstransform: {
     compile: function (code) {

bin/6to5-node

@@ -5,7 +5,6 @@
  * when found, before invoking the "real" _6to5-node(1) executable.
  */
 
-var spawn = require("child_process").spawn;
 var args  = ["--harmony", __dirname + "/_6to5-node"];
 
 process.argv.slice(2).forEach(function(arg){
@@ -14,18 +13,19 @@ 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":
       args.unshift("--expose-gc");
       break;
+
     case "--gc-global":
     case "--harmony":
     case "--harmony-proxies":
@@ -37,20 +37,32 @@ process.argv.slice(2).forEach(function(arg){
     case "--trace-deprecation":
       args.unshift(arg);
       break;
+
     default:
-      if (0 == arg.indexOf("--trace")) args.unshift(arg);
-      else args.push(arg);
+      if (arg.indexOf("--trace") === 0) {
+        args.unshift(arg);
+      } else {
+        args.push(arg);
+      }
       break;
   }
 });
 
-var proc = spawn(process.argv[0], args, { stdio: "inherit" });
-proc.on("exit", function (code, signal) {
-  process.on("exit", function (){
-    if (signal) {
-      process.kill(process.pid, signal);
-    } else {
-      process.exit(code);
-    }
+try {
+  var kexec = require("kexec");
+  kexec(process.argv[0], args);
+} catch (err) {
+  if (err.code !== "MODULE_NOT_FOUND") throw err;
+
+  var child_process = require("child_process");
+  var proc = child_process.spawn(process.argv[0], args, { stdio: "inherit" });
+  proc.on("exit", function (code, signal) {
+    process.on("exit", function () {
+      if (signal) {
+        process.kill(process.pid, signal);
+      } else {
+        process.exit(code);
+      }
+    })
   });
-});
+}

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);
@@ -111,16 +113,14 @@ module.exports = function (commander, filenames) {
     walk();
 
     if (commander.watch) {
-      var watcher = chokidar.watch(filenames, {
+      chokidar.watch(filenames, {
         persistent: true,
         ignoreInitial: true
-      });
-
-      _.each(["add", "change", "unlink"], function (type) {
-        watcher.on(type, function (filename) {
+      }).on("all", function (type, filename) {
+        if (type === "add" || type === "change" || type === "unlink" ) {
           console.log(type, filename);
           walk();
-        });
+        }
       });
     }
   };

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

@@ -1,41 +1,49 @@
 #!/usr/bin/env node
 
-var commander = require("commander");
-var path      = require("path");
-var repl      = require("repl");
-var to5       = require("../lib/6to5");
-var util      = require("../lib/6to5/util");
-var vm        = require("vm");
-var _         = require("lodash");
+var roadrunner = require("roadrunner");
+var commander  = require("commander");
+var Module     = require("module");
+var path       = require("path");
+var repl       = require("repl");
+var to5        = require("../lib/6to5");
+var util       = require("../lib/6to5/util");
+var vm         = require("vm");
+var _          = require("lodash");
 
-commander.option("-e, --eval [script]", "evaluate script");
-commander.option("-p, --print", "evaluate script and print result");
-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");
+commander.option("-c, --cache", "Cache compiled files and require paths");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
 commander.usage("[options] [ -e script | script.js ] [arguments]");
 commander.parse(process.argv);
 
+if (commander.cache) roadrunner.load();
+
 //
 
-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,
+  playground:   commander.playground,
+  ignore:       commander.ignore,
+  cache:        commander.cache && roadrunner.get("6to5")
+});
 
 //
 
 var _eval = function (code, filename) {
-  code = to5.transform(code, { filename: filename, blacklist: ["useStrict"] }).code;
+  code = to5.transform(code, {
+    filename: filename,
+    blacklist: ["useStrict"],
+    experimental: commander.experimental,
+    playground: commander.playground
+  }).code;
   return vm.runInThisContext(code, filename);
 };
 
@@ -43,21 +51,34 @@ if (commander.eval) {
   var result = _eval(commander.eval, "eval");
   if (commander.print) console.log(result);
 } else {
-  var filenames = commander.args;
+  if (commander.args.length) {
+    // slice all arguments up to the first filename since they're 6to5 args that we handle
+    var args = process.argv.slice(2);
 
-  if (filenames.length) {
-    _.each(filenames, function (filename) {
-      if (!util.isAbsolute(filename)) {
-        filename = path.join(process.cwd(), filename);
+    var i = 0;
+    _.each(args, function (arg, i2) {
+      if (arg[0] !== "-") {
+        i = i2;
+        return false;
       }
-
-      require(require.resolve(filename));
     });
+    args = args.slice(i);
+
+    // make the filename absolute
+    var filename = args[0]
+    if (!util.isAbsolute(filename)) args[0] = path.join(process.cwd(), filename);
+
+    // add back on node and concat the sliced args
+    process.argv = ["node"].concat(args);
+
+    Module.runMain();
   } else {
     replStart();
   }
 }
 
+if (commander.cache) roadrunner.save();
+
 function replStart() {
   repl.start({
     prompt: "> ",

doc/browser.md

@@ -3,12 +3,6 @@
 A browser version of 6to5 is available from `browser.js` inside the 6to5
 directory in an npm release.
 
-## API
-
-```javascript
-to5.transform("class Test {}").code;
-```
-
 ## Scripts
 
 While it's not recommended for serious use, when the browser version is included
@@ -36,7 +30,9 @@ test.test();
 You can build a browser version of the compiler by running the following in the
 6to5 directory:
 
-    $ make build
+```sh
+$ make build
+```
 
 This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
@@ -44,6 +40,26 @@ This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
 To test 6to5 in your browser run:
 
-    $ make test-browser
+```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

@@ -1,9 +1,32 @@
 # Caveats
 
-## Classes
+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).
 
-Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
-limitations in ES5 implementations.
+You may alternatively selectively include what you need:
+
+| Feature                     | Requirements                                                                                                           |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | [experimental](experimental.md), `Symbol`                                                                              |
+| Array destructuring         | `Array.isArray`, `Array.from`                                                                                          |
+| Async functions, Generators | [experimental](experimental.md), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
+| Comprehensions              | [experimental](experimental.md), `Array.isArray`, `Array.from`                                                         |
+| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                 |
+| Object spread/rest          | [experimental](experimental.md), `Object.assign`                                                                       |
+| Spread                      | `Array.isArray`, `Array.from`                                                                                          |
+
+## ES5
+
+Since 6to5 assumes that your code will be ran in an ES5 environment it uses ES5
+functions. So if you're using an environment that has limited or no support for
+ES5 such as lower versions of IE then using the
+[es5-shim](https://github.com/es-shims/es5-shim) along with the
+[6to5 polyfill](polyfill.md) will add support for these methods.
+
+## Internet Explorer
+
+### Classes (9 and below)
 
 If you're inheriting from a class then static properties are inherited from it
 via [\_\_proto\_\_](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto),
@@ -26,18 +49,11 @@ class Bar extends Foo {
 }
 ```
 
-## For-of
+## Getters/setters (8 and below)
 
-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.md) suffices.
+In IE8 `Object.defineProperty` can only be used on DOM objects. This is
+unfortunate as it's required to set getters and setters. Due to this if
+you plan on supporting IE8 or below then the user of getters and setters
+isn't recommended.
 
-## Generators
-
-The [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js)
-and an [ES6 polyfill](polyfill.md) are required in order for generators to work.
-
-## Spread
-
-An [ES6 polyfill](polyfill.md) is required in order for spread to work. More
-specifically a polyfill for `Array.from`.
+Reference: [MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty#Internet_Explorer_8_specific_notes).

doc/differences.md

@@ -1,6 +1,8 @@
 # Differences
 
-## Philosophy
+There are three main points that separate 6to5 from all other transpilers.
+
+### Readable code
 
 The fundamental concept behind 6to5 is that the generated code must be close as
 possible to the original, retaining all the same formatting and readability.
@@ -17,7 +19,7 @@ var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, a
 is generated to the following with 6to5:
 
 ```javascript
-var seattlers = customers.filter(function (c) {
+var seattlers = Array.from(customers).filter(function (c) {
   return c.city == "Seattle";
 }).map(function (c) {
   return {
@@ -51,42 +53,75 @@ 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.
+Sometimes there are little inline functions that 6to5 needs. These are
+placed at the top of your file much like coffee-script does. If these
+are bother you then you can use the [optional runtime](optional-runtime.md).
+We promise that these inline functions will never be significant and will
+always be used as little as possible.
+
+### Static analysis
+
+6to5 uses a lot of static analysis to simplify code as much as possible.
+Not many other transpilers do this, and those that do don't do it nearly
+as much as 6to5. This process is pretty intensive but it leads to higher
+quality code.
+
+### Spec compliancy
+
+6to5 prides itself on
+[spec compliancy](https://kangax.github.io/compat-table/es6/). We have
+excellent support for edgecases, something that many other transpilers
+suffer from, including Traceur. When you use 6to5 you can be confident
+that when you turn it off and use your code in a full ES6 environment
+**it'll just work**.
 
 ## Comparison to other transpilers
 
-|                              | 6to5 | Traceur | esnext | es6now | es6-transpiler | jstransform |
-| ---------------------------- | ---- | ------- | ------ | ------ | -------------- | ----------- |
-| No runtime                   | ✓    |         |        |        | ✓              | ✓           |
-| Source maps                  | ✓    | ✓       | ✓      |        | ✓              | ✓           |
-| No compiler global pollution | ✓    |         | ✓      |        | ✓              | ✓           |
-| Browser support              | ✓    | ✓       | ✓      |        |                |             |
-| Array comprehension          | ✓    | ✓       |        |        | ✓              |             |
-| Arrow functions              | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Async functions              | ✓    |         | ✓      |        |                |             |
-| Classes                      | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Computed property names      | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Constants                    | ✓    | ✓       |        |        | ✓              |             |
-| Default parameters           | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Destructuring                | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| For-of                       | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Generators                   | ✓    | ✓       | ✓      |        |                |             |
-| Generator comprehension      | ✓    | ✓       |        |        |                |             |
-| Let scoping                  | ✓    | ✓       |        |        | ✓              |             |
-| Modules                      | ✓    | ✓       |        | ✓      |                |             |
-| Property method assignment   | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Property name shorthand      | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Rest parameters              | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Spread                       | ✓    | ✓       | ✓      | ✓      | ✓              |             |
-| Template literals            | ✓    | ✓       | ✓      | ✓      | ✓              | ✓           |
-| Unicode regex                | ✓    | ✓       |        |        | ✓              |             |
+### Features
+
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Source maps                  | ✓    | ✓       | ✓              | ✓      |        | ✓           |
+| No compiler global pollution | ✓    |         | ✓              | ✓      |        | ✓           |
+| Optional runtime             | ✓    |         | ✓              |        |        | ✓           |
+| Browser compiler             | ✓    | ✓       |                | ✓      |        |             |
+
+### Language Support
+
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓    |         |                |        |        |             |
+| Array comprehension          | ✓    | ✓       | ✓              |        |        |             |
+| Arrow functions              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Async functions              | ✓    | ✓       |                | ✓      |        |             |
+| Async generator functions    | ✓    | ✓       |                |        |        |             |
+| Classes                      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Computed property names      | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Constants                    | ✓    | ✓       | ✓              |        |        |             |
+| Default parameters           | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Destructuring                | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓    | ✓       |                |        |        |             |
+| Flow types                   | ✓    |         |                |        |        | ✓           |
+| For-of                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Generators                   | ✓    | ✓       |                | ✓      |        |             |
+| Generator comprehension      | ✓    | ✓       |                |        |        |             |
+| JSX                          | ✓    |         |                |        |        |             |
+| Let scoping                  | ✓    | ✓       | ✓              |        |        |             |
+| Modules                      | ✓    | ✓       |                |        | ✓      |             |
+| Object rest/spread           | ✓    |         |                |        |        | ✓           |
+| Property method assignment   | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Property name shorthand      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Rest parameters              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| React                        | ✓    |         |                |        |        |             |
+| Spread                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Template literals            | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Unicode regex                | ✓    | ✓       | ✓              |        |        |             |
 
 ### [Traceur](https://github.com/google/traceur-compiler)
 
 Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
 While this can be trimmed down by selectively building the runtime, it's an
-unneccesary step when a runtime can be eliminated entirely.
+unnecessary step when a large runtime can be eliminated entirely.
 
 ### [es6now](https://github.com/zenparsing/es6now)
 

doc/experimental.md

@@ -0,0 +1,8 @@
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
+
+**WARNING:** These proposals are subject to change so use with
+**extreme caution**.

doc/features.md

@@ -1,12 +1,45 @@
 # Features
 
-## Array comprehension
+## Abstract references ([experimental](experimental.md)) ([spec](https://github.com/zenparsing/es-abstract-refs))
 
 ```javascript
-[for (i of [1, 2, 3]) i * i]; // [1, 4, 9]
+foo::bar;
+foo::bar = baz;
+delete foo::bar;
 ```
 
-## Async functions
+## Array comprehensions ([experimental](experimental.md))
+
+```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](experimental.md)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -16,31 +49,33 @@ async function chainAnimationsAsync(elem, animations) {
 }
 ```
 
-## Arrow functions
+## Async generator functions ([experimental](experimental.md)) ([spec](https://github.com/jhusain/asyncgenerator))
 
 ```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() { }
+class SkinnedMesh extends THREE.Mesh {
+  constructor(geometry, materials) {
+    super(geometry, materials);
 
-  foo() { }
+    this.idMatrix = SkinnedMesh.defaultMatrix();
+    this.bones = [];
+    this.boneMatrices = [];
+    //...
+  }
 
-  get bar() { }
+  update(camera) {
+    //...
+    super.update();
+  }
 
-  set bar() { }
+  static defaultMatrix() {
+    return new THREE.Matrix4();
+  }
 }
 ```
 
@@ -70,16 +105,44 @@ var MULTIPLIER; // error
 ## Default parameters
 
 ```javascript
-function foo(bar = "foo") {
-  return bar + "bar";
+function f(x, y = 12) {
+  // y is 12 if not passed (or passed as undefined)
+  return x + y;
 }
+f(3) == 15
 ```
 
 ## Destructuring
 
 ```javascript
-var [a, [b], c, d] = ["hello", [", ", "junk"], ["world"]];
-console.log(a + b + c); // hello, world
+// 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](experimental.md)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+
+```javascript
+var a = 2;
+a **= 2;
+
+var squared = 2 ** 2;
 ```
 
 ## For-of
@@ -93,16 +156,55 @@ for (var i of [1, 2, 3]) {
 ## 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 comprehension
+## Generator comprehensions ([experimental](experimental.md))
 
 ```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
@@ -112,6 +214,13 @@ for (var i of [1, 2, 3]) {
 0o767 === 503; // true
 ```
 
+## Object spread/rest ([experimental](experimental.md)) ([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
@@ -141,23 +250,21 @@ function f(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);
-  });
+function f(x, ...y) {
+  // y is an Array
+  return x * y.length;
 }
+f(3, "hello", true) == 6
 ```
 
 ## Spread
 
 ```javascript
-function add(x, y) {
-  return x + y;
+function f(x, y, z) {
+  return x + y + z;
 }
-
-var numbers = [5, 10];
-add(...numbers); // 15
+// Pass each elem of array as argument
+f(...[1,2,3]) == 6
 ```
 
 ## Template literals
@@ -167,7 +274,6 @@ var x = 5;
 var y = 10;
 console.log(`${x} + ${y} = ${x + y}`); // "5 + 10 = 15"
 ```
-
 ## Unicode regex
 
 ```javascript

doc/index.md

@@ -1,9 +1,9 @@
-**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.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#generators).
+ - **Compact** - maps directly to the equivalent ES5 with **no runtime**[\*](caveats.md).
 
 ## Installation
 
@@ -11,22 +11,48 @@ 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)
 
- - [Array comprehension](features.md#array-comprehension)
- - [Async functions](features.md#async-functions) via [regenerator](https://github.com/facebook/regenerator)
+ - [Abstract references](features.md#abstract-references) ([experimental](experimental.md))
+ - [Array comprehension](features.md#array-comprehension) ([experimental](experimental.md))
+ - [Async functions](features.md#async-functions) ([experimental](experimental.md))
+ - [Async generator functions](features.md#async-generator-functions) ([experimental](experimental.md))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
  - [Constants](features.md#constants)
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](experimental.md))
  - [For-of](features.md#for-of)
- - [Generators](features.md#generators) via [regenerator](https://github.com/facebook/regenerator)
- - [Generator comprehension](features.md#generator-comprehension)
+ - [Generators](features.md#generators)
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](experimental.md))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)
+ - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](experimental.md))
  - [Property method assignment](features.md#property-method-assignment)
  - [Property name shorthand](features.md#property-name-shorthand)
  - [React/JSX](react.md)

doc/modules.md

@@ -4,7 +4,9 @@
 
 ### CLI
 
-    $ 6to5 --modules common script.js
+```sh
+$ 6to5 --modules common script.js
+```
 
 ### Node
 
@@ -15,11 +17,26 @@ to5.transform('import "foo";', { modules: "common" });
 
 ## Formats
 
-### Common (Default)
+ * [AMD](#amd)
+ * [Common (Default)](#common-default)
+ * [Ignore](#ignore)
+ * [System](#system)
+ * [UMD](#umd)
+
+### Common
+
+```sh
+$ 6to5 --modules common
+```
 
 **In**
 
 ```javascript
+export default test;
+
+export {test};
+export var test = 5;
+
 import "foo";
 
 import foo from "foo";
@@ -27,32 +44,38 @@ 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
+"use strict";
+
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
+exports = module.exports = test;
+
+exports.test = test;
+var test = exports.test = 5;
+
 require("foo");
 
-var foo = require("foo").default;
+var foo = _interopRequire(require("foo"));
+
 var foo = require("foo");
 
 var bar = require("foo").bar;
 var bar = require("foo").foo;
-
-exports.test = test;
-var test = 5; exports.test = test;
-
-exports.default = test;
 ```
 
 ### AMD
 
+```sh
+$ 6to5 --modules amd
+```
+
 **In**
 
 ```javascript
@@ -67,9 +90,14 @@ export function bar() {
 
 ```javascript
 define(["exports", "foo"], function (exports, _foo) {
-  exports.bar = bar;
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -77,8 +105,18 @@ 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
@@ -98,10 +136,15 @@ export function bar() {
   } else if (typeof exports !== "undefined") {
     factory(exports, require("foo"));
   }
-})(function (exports) {
-  exports.bar = bar;
+})(function (exports, _foo) {
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -111,6 +154,9 @@ export function bar() {
 
 ### Ignore
 
+```sh
+$ 6to5 --modules ignore
+```
 
 **In**
 
@@ -130,11 +176,52 @@ 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**
 
@@ -150,7 +237,7 @@ ModuleFormatter.prototype.transform = function (ast) {
   // feel free to modify this however
 };
 
-ModuleFormatter.prototype.import = function (node, nodes) {
+ModuleFormatter.prototype.importDeclaration = function (node, nodes) {
   // node is an ImportDeclaration
 };
 
@@ -159,7 +246,7 @@ ModuleFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   // node is an ImportDeclaration
 };
 
-ModuleFormatter.prototype.export = function (node, nodes) {
+ModuleFormatter.prototype.exportDeclaration = function (node, nodes) {
   // node is an ExportDeclaration
 };
 

doc/optional-runtime.md

@@ -18,7 +18,9 @@ Simply use the following option if you're using the [Node API](usage.md#node):
 
 or the following flag if you're using the [CLI](usage.md#cli):
 
-    $ 6to5 --runtime
+```ssh
+$ 6to5 --runtime
+```
 
 Then just include the runtime before your generated code.
 
@@ -26,7 +28,9 @@ Then just include the runtime before your generated code.
 
 You can get the runtime via either:
 
-    $ 6to5-runtime
+```sh
+$ 6to5-runtime
+```
 
 or
 
@@ -45,7 +49,9 @@ argument:
 require("6to5").runtime("myCustomNamespace");
 ```
 
-    $ 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 +1,120 @@
+# 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](experimental.md).
+
+## Features
+
+ * [Memoization operator](#memoization-operator)
+ * [Method binding](#method-binding)
+ * [Object getter memoization](#object-getter-memoization)
+ * [This shorthand](#this-shorthand)
+
+### 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); });
+```
+
+### Object getter memoization
+
+```javascript
+var foo = {
+  memo bar() {
+    return complex();
+  }
+};
+
+class Foo {
+  memo bar() {
+    return complex();
+  }
+}
+```
+
+equivalent to
+
+```javascript
+var foo = {
+  get bar() {
+    if (this._barRan) return this._bar;
+    this._barRan = true;
+    return this._bar = complex();
+  }
+};
+
+class Foo {
+  get bar() {
+    if (this._barRan) return this._bar;
+    this._barRan = true;
+    return this._bar = complex();
+  }
+}
+```
+
+**NOTE:** Memoised functions will return the result of the **first** execution, regardless of arguments.
+
+### This shorthand
+
+```javascript
+@foo
+```
+
+equivalent to
+
+```javascirpt
+this.foo
+```

doc/plugins.md

@@ -1,15 +1,33 @@
 # Plugins
 
- - [Broccoli](https://github.com/very-geek/broccoli-6to5-transpiler)
- - [Browserify](https://github.com/6to5/6to5-browserify)
- - [Brunch](https://github.com/es128/6to5-brunch)
- - [Duo](https://github.com/bdo-labs/duo6to5)
- - [Connect](https://github.com/6to5/6to5-connect)
- - [Gulp](https://github.com/sindresorhus/gulp-6to5)
- - [Grunt](https://github.com/sindresorhus/grunt-6to5)
- - [Jade](https://github.com/Apoxx/jade-6to5)
+## Build systems
+
+ - [Broccoli](https://github.com/6to5/broccoli-6to5-transpiler)
+ - [Browserify](https://github.com/6to5/6to5ify)
+ - [Brunch](https://github.com/6to5/6to5-brunch)
+ - [Duo](https://github.com/6to5/duo6to5)
+ - [Gobble](https://github.com/6to5/gobble-6to5)
+ - [Gulp](https://github.com/6to5/gulp-6to5)
+ - [Grunt](https://github.com/6to5/grunt-6to5)
+ - [Sprockets](https://github.com/josh/sprockets-es6) or via [Browserify](https://github.com/6to5/6to5-rails)
+ - [webpack](https://github.com/6to5/6to5-loader)
+
+## Integrations
+
+ - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
+ - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
+
+## Bridges
+
+ - [Ruby](https://github.com/6to5/6to5-ruby)
+
+## Testing
+
  - [Jest](https://github.com/6to5/6to5-jest)
- - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
+ - [Karma](https://github.com/6to5/karma-6to5-preprocessor)
  - [Mocha](https://github.com/6to5/6to5-mocha)
- - [Rails](https://github.com/6to5/6to5-rails)
- - [webpack](https://github.com/Couto/6to5-loader)
+
+## Misc
+
+ - [Connect](https://github.com/6to5/6to5-connect)
+ - [Jade](https://github.com/6to5/jade-6to5)

doc/polyfill.md

@@ -1,17 +1,34 @@
 # Polyfill
 
-6to5 includes a polyfill that includes the
-[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and the
-[es6-shim](https://github.com/paulmillr/es6-shim) and
-[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
+6to5 includes a polyfill that includes a custom
+[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and
+[core.js](https://github.com/zloirock/core-js).
 
-## Node
+This will emulate a full ES6 environment. This polyfill is automatically loaded
+when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).
+
+## Usage
+
+### Node/Browserify
+
+You need to include the polyfill require at the top the **entry point** to your
+application.
 
 ```javascript
 require("6to5/polyfill");
 ```
 
-## Browser
+Fortunately, this is automatically loaded when using:
+
+```javascript
+require("6to5/register");
+```
+
+### Browser
 
 Available from the `browser-polyfill.js` file within the 6to5 directory of an
-npm release.
+npm release. This needs to be included **before** all your compiled 6to5 code.
+You can either prepend it to your compiled code or include it in a `<script>`
+before it.
+
+**NOTE:** Do not `require` this via browserify etc, use `6to5/polyfill`.

doc/react.md

@@ -12,5 +12,6 @@ To disable this behaviour add `react` to your blacklist:
 to5.transform("code", { blacklist: ["react"] });
 ```
 
-
-    $ 6to5 --blacklist react
+```sh
+$ 6to5 --blacklist react
+```

doc/usage.md

@@ -4,65 +4,106 @@
 
 Compile the file `script.js` and output it to stdout.
 
-    $ 6to5 script.js
+```sh
+$ 6to5 script.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js`.
 
-    $ 6to5 script.js --out-file 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`.
 
-    $ 6to5 script.js --source-maps --out-file script-compiled.js
+```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.
 
-    $ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```sh
+$ 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
+```sh
+$ 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
+```sh
+$ 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
+```sh
+$ 6to5 --out-file script-compiled.js < script.js
+```
 
 ### Node
 
 Launch a repl.
 
-    $ 6to5-node
+```sh
+$ 6to5-node
+```
 
 Evaluate code.
 
-    $ 6to5-node -e "class Test { }"
+```sh
+$ 6to5-node -e "class Test { }"
+```
 
 Compile and run `test.js`.
 
-    $ 6to5-node test
+```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;
 });
 ```
 
+### to5.transform.fromAst(ast, [code], [opts])
+
+```javascript
+var result = to5.transform.fromAst(ast, "var a = 2;", opts);
+result.code;
+result.map;
+result.ast;
+```
+
 #### Options
 
 ```javascript
@@ -71,6 +112,10 @@ to5.transformFile("filename.js", options, function (err, result) {
   // 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: [],
@@ -91,17 +136,73 @@ to5.transformFile("filename.js", options, function (err, result) {
   sourceMap: true,
 
   // Set `file` on returned source map.
-  // Default: `filename` option.
+  // Default: `filenameRelative` option.
   sourceMapName: "filename",
 
   // Set `sources[0]` on returned source map.
-  // Default: `filename` option.
+  // 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
+  runtime: true,
+
+  // Enable support for experimental ES7 features
+  // Default: false
+  experimental: true,
+
+  // Set this to `false` if you don't want the transformed AST in the returned
+  // result
+  // Default: true
+  ast: true,
+
+  // Set this to `false` if you don't want the transformed code in the returned
+  // result
+  // Default: true
+  code: true,
+
+  format: {
+    // Output comments in generated output
+    // Default: true
+    comments: true,
+
+    // Do not include superfluous whitespace characters and line terminators
+    // Default: false
+    compact: false,
+
+    indent: {
+      // Preserve parentheses in new expressions that have no arguments
+      // Default: true
+      parentheses: true,
+
+      // Adjust the indentation of multiline comments to keep asterisks vertically aligned
+      // Default: true
+      adjustMultilineComment: true,
+
+      // Indent string
+      // Default: "  "
+      style: "  ",
+
+      // Base indent level
+      // Default: 0
+      base: 0
+    }
+  }
 }
 ```
 
@@ -109,7 +210,10 @@ to5.transformFile("filename.js", options, function (err, result) {
 
 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.
+also required; but this is automatically loaded when using:
+
+Source maps are automatically configured so if any errors a thrown then line
+number info is mapped and you'll get the correct source location.
 
 ```javascript
 require("6to5/register");
@@ -126,6 +230,8 @@ require("6to5/register")({
 });
 ```
 
+**NOTE:** Using 6to5-node or `require("6to5/register")`, 6to5 will check what features are available in the current environment and blacklists them if they're supported.
+
 #### Options
 
 ```javascript

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

@@ -10,50 +10,90 @@ 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", "apply-constructor"];
+File.declarations = [
+  "inherits",
+  "prototype-properties",
+  "apply-constructor",
+  "tagged-template-literal",
+  "interop-require",
+  "to-array",
+  "object-without-properties",
+  "has-own",
+  "slice"
+];
 
 File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
-    whitespace: true,
-    blacklist:  [],
-    whitelist:  [],
-    sourceMap:  false,
-    filename:   "unknown",
-    modules:    "common",
-    runtime:    false,
-    code:       true
+    experimental: false,
+    playground:   false,
+    whitespace:   true,
+    blacklist:    [],
+    whitelist:    [],
+    sourceMap:    false,
+    comments:     true,
+    filename:     "unknown",
+    modules:      "common",
+    runtime:      false,
+    code:         true,
+    ast:          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, {
-    sourceFileName: opts.filename,
-    sourceMapName:  opts.filename
+    moduleRoot: opts.sourceRoot
+  });
+
+  _.defaults(opts, {
+    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);
@@ -61,7 +101,7 @@ File.prototype.getModuleFormatter = function (type) {
   }
 
   if (!ModuleFormatter) {
-    throw new ReferenceError("unknown module formatter type " + type);
+    throw new ReferenceError("Unknown module formatter type " + JSON.stringify(type));
   }
 
   return new ModuleFormatter(this);
@@ -84,8 +124,10 @@ 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;
@@ -96,11 +138,12 @@ 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;
 };
 
@@ -113,14 +156,16 @@ File.prototype.errorWithNode = function (node, msg, Error) {
   return err;
 };
 
-File.prototype.parse = function (code) {
+File.prototype.addCode = function (code) {
   code = (code || "") + "";
+  this.code = code;
+  return this.parseShebang(code);
+};
 
+File.prototype.parse = function (code) {
   var self = this;
 
-  this.code = code;
-
-  code = this.parseShebang(code);
+  code = this.addCode(code);
 
   return util.parse(this.opts, code, function (tree) {
     self.transform(tree);
@@ -130,7 +175,8 @@ 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;
 
@@ -143,15 +189,18 @@ File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;
 
-  if (!opts.code) {
-    return {
-      code: "",
-      map:  null,
-      ast:  ast
-    };
-  }
+  var result = {
+    code: "",
+    map: null,
+    ast: null
+  };
 
-  var result = generate(ast, opts, this.code);
+  if (opts.ast) result.ast = ast;
+  if (!opts.code) return result;
+
+  var _result = generate(ast, opts, this.code);
+  result.code = _result.code;
+  result.map  = _result.map;
 
   if (this.shebang) {
     // add back shebang
@@ -162,8 +211,6 @@ File.prototype.generate = function () {
     result.code += "\n" + util.sourceMapToComment(result.map);
   }
 
-  result.ast = result;
-
   return result;
 };
 
@@ -179,6 +226,10 @@ 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

@@ -35,7 +35,7 @@ Buffer.prototype.dedent = function () {
 };
 
 Buffer.prototype.semicolon = function () {
-  if (this.format.semicolons) this.push(";");
+  this.push(";");
 };
 
 Buffer.prototype.ensureSemicolon = function () {
@@ -66,9 +66,7 @@ Buffer.prototype.removeLast = function (cha) {
 };
 
 Buffer.prototype.newline = function (i, removeLast) {
-  if (!this.buf) return;
   if (this.format.compact) return;
-  if (this.endsWith("{\n")) return;
 
   if (_.isBoolean(i)) {
     removeLast = i;
@@ -76,6 +74,7 @@ Buffer.prototype.newline = function (i, removeLast) {
   }
 
   if (_.isNumber(i)) {
+    if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
     var self = this;
@@ -88,7 +87,10 @@ Buffer.prototype.newline = function (i, removeLast) {
   if (removeLast && this.isLast("\n")) this.removeLast("\n");
 
   this.removeLast(" ");
+
+  // remove whitespace if last character was a newline
   this.buf = this.buf.replace(/\n +$/, "\n");
+
   this._push("\n");
 };
 

lib/6to5/generation/generator.js

@@ -35,21 +35,16 @@ _.each(Buffer.prototype, function (fn, key) {
 });
 
 CodeGenerator.normaliseOptions = function (opts) {
-  opts = opts.format || {};
-
-  opts = _.merge({
+  return _.merge({
     parentheses: true,
-    semicolons: true,
-    comments: true,
+    comments: opts.comments == null || opts.comments,
     compact: false,
     indent: {
       adjustMultilineComment: true,
       style: "  ",
       base: 0
     }
-  }, opts);
-
-  return opts;
+  }, opts.format || {});
 };
 
 CodeGenerator.generators = {
@@ -57,10 +52,12 @@ CodeGenerator.generators = {
   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"),
+  flow:             require("./generators/flow"),
   base:             require("./generators/base"),
   jsx:              require("./generators/jsx")
 };
@@ -74,6 +71,12 @@ CodeGenerator.prototype.generate = function () {
 
   this.print(ast);
 
+  var comments = [];
+  _.each(ast.comments, function (comment) {
+    if (!comment._displayed) comments.push(comment);
+  });
+  this._printComments(comments);
+
   return {
     map:  this.map.get(),
     code: this.buffer.get()
@@ -135,6 +138,9 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
       var needs = n.needsWhitespaceAfter;
       if (leading) needs = n.needsWhitespaceBefore;
       lines += needs(node, parent);
+
+      // generated nodes can't add starting file whitespace
+      if (!self.buffer.get()) lines = 0;
     }
 
     self.newline(lines);
@@ -150,7 +156,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     // only compute if this node needs parens if our parent has been changed
     // since acorn would've wrapped us in a ParanthesizedExpression
-    var needsParens = parent !== node._parent && n.needsParens(node, parent);
+    var needsParens = n.needsParens(node, parent);
     if (needsParens) this.push("(");
 
     this[node.type](node, this.buildPrint(node), parent);
@@ -164,11 +170,13 @@ 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;
@@ -260,6 +268,14 @@ CodeGenerator.prototype._printComments = function (comments) {
   var self = this;
 
   _.each(comments, function (comment) {
+    // find the original comment in the ast and set it as displayed
+    _.each(self.ast.comments, function (origComment) {
+      if (origComment.start === comment.start) {
+        origComment._displayed = true;
+        return false;
+      }
+    });
+
     // whitespace before
     self.newline(self.whitespace.getNewlinesBefore(comment));
 

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/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);
@@ -17,12 +18,6 @@ exports.UnaryExpression = function (node, print) {
   print(node.argument);
 };
 
-exports.ParenthesizedExpression = function (node, print) {
-  this.push("(");
-  print(node.expression);
-  this.push(")");
-};
-
 exports.UpdateExpression = function (node, print) {
   if (node.prefix) {
     this.push(node.operator);
@@ -97,14 +92,22 @@ exports.AssignmentExpression = function (node, print) {
   print(node.right);
 };
 
+var SCIENTIFIC_NOTATION = /e/i;
+
 exports.MemberExpression = function (node, print) {
-  print(node.object);
+  var obj = node.object;
+  print(obj);
 
   if (node.computed) {
     this.push("[");
     print(node.property);
     this.push("]");
   } else {
+    // 5..toFixed(2);
+    if (t.isLiteral(obj) && util.isInteger(obj.value) && !SCIENTIFIC_NOTATION.test(obj.value.toString())) {
+      this.push(".");
+    }
+
     this.push(".");
     print(node.property);
   }

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

@@ -0,0 +1,3 @@
+exports.ClassProperty = function () {
+  throw new Error("not implemented");
+};

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

@@ -74,5 +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

@@ -1,7 +1,14 @@
 var t = require("../../types");
 var _ = require("lodash");
 
-exports.ImportSpecifier =
+exports.ImportSpecifier = function (node, print) {
+  if (node.id && node.id.name === "default") {
+    print(node.name);
+  } else {
+    return exports.ExportSpecifier.apply(this, arguments);
+  }
+};
+
 exports.ExportSpecifier = function (node, print) {
   print(node.id);
   if (node.name) {
@@ -25,9 +32,10 @@ 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) {
@@ -61,7 +69,9 @@ exports.ImportDeclaration = function (node, print) {
         self.push(", ");
       }
 
-      if (!spec.default && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
+      var isDefault = spec.id && spec.id.name === "default";
+
+      if (!isDefault && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
         foundImportSpecifier = true;
         self.push("{ ");
       }

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 () {
@@ -177,6 +164,12 @@ exports.VariableDeclaration = function (node, print, parent) {
   }
 };
 
+exports.PrivateDeclaration = function (node, print) {
+  this.push("private ");
+  print.join(node.declarations, { separator: ", " });
+  this.semicolon();
+};
+
 exports.VariableDeclarator = function (node, print) {
   if (node.init) {
     print(node.id);

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 illegal js but valid json unicode characters
+    val = val.replace(/[\u000A\u000D\u2028\u2029]/g, function (c) {
+      return "\\u" + ("0000" + c.charCodeAt(0).toString(16)).slice(-4);
+    });
+
+    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/index.js

@@ -2,8 +2,8 @@ module.exports = Node;
 
 var whitespace = require("./whitespace");
 var parens     = require("./parentheses");
-var t           = require("../../types");
-var _           = require("lodash");
+var t          = require("../../types");
+var _          = require("lodash");
 
 var find = function (obj, node, parent) {
   var result;
@@ -24,18 +24,7 @@ function Node(node, parent) {
 }
 
 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;
+  return t.isUserWhitespacable(this.node);
 };
 
 Node.prototype.needsWhitespace = function (type) {

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

@@ -92,13 +92,6 @@ exports.YieldExpression = function (node, parent) {
          t.isYieldExpression(parent);
 };
 
-exports.Literal = function (node, parent) {
-  // (1).valueOf()
-  if (_.isNumber(node.value) && t.isMemberExpression(parent) && parent.object === node) {
-    return true;
-  }
-};
-
 exports.ClassExpression = function (node, parent) {
   return t.isExpressionStatement(parent);
 };

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

@@ -9,6 +9,10 @@ exports.before = {
       }
     },
 
+    SpreadProperty: function (node, parent) {
+      return exports.before.nodes.Property(node, parent);
+    },
+
     SwitchCase: function (node, parent) {
       if (parent.cases[0] === node) {
         return 1;
@@ -24,7 +28,13 @@ exports.before = {
 };
 
 exports.after = {
-  nodes: {},
+  nodes: {
+    AssignmentExpression: function (node) {
+      if (t.isFunction(node.right)) {
+        return 1;
+      }
+    }
+  },
 
   list: {
     VariableDeclaration: function (node) {

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/generation/whitespace.js

@@ -38,7 +38,11 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
     }
   });
 
-  return this.getNewlinesBetween(startToken, endToken);
+  if (endToken.type.type === "eof") {
+    return 1;
+  } else {
+    return this.getNewlinesBetween(startToken, endToken);
+  }
 };
 
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {

lib/6to5/index.js

@@ -3,6 +3,10 @@ var util      = require("./util");
 var fs        = require("fs");
 var _         = require("lodash");
 
+exports.Transformer = require("./transformation/transformer");
+
+exports.types = require("./types");
+
 exports.runtime = require("./runtime");
 
 exports.register = function (opts) {
@@ -17,6 +21,9 @@ 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

@@ -1,28 +1,47 @@
 var t = require("./types");
 var _ = require("lodash");
 
+// estraverse
+
+var estraverse = require("estraverse");
+_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+
+// regenerator/recast/ast-types
+
 var types = require("ast-types");
 var def   = types.Type.def;
+var or    = types.Type.or;
 
-// Program wrapper
-def("File")
-  .bases("Node")
-  .build("program")
-  .field("program", def("Program"));
-
-// Non-standard Acorn type
-def("ParenthesizedExpression")
-  .bases("Expression")
-  .build("expression")
-  .field("expression", def("Expression"));
-
-// 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"));
 
-types.finalize();
+// Abstract references
+def("VirtualPropertyExpression")
+  .bases("Expression")
+  .build("object", "property")
+  .field("object", def("Expression"))
+  .field("property", or(def("Identifier"), def("Expression")));
 
-var estraverse = require("estraverse");
-_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+def("PrivateDeclaration")
+  .bases("Declaration")
+  .build("declarations")
+  .field("declarations", [def("Identifier")]);
+
+// 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();

lib/6to5/polyfill.js

@@ -1,6 +1,2 @@
-if (typeof Symbol === "undefined") {
-  require("es6-symbol/implement");
-}
-
-require("es6-shim");
-require("regenerator-6to5/runtime");
+require("core-js/shim");
+require("regenerator/runtime");

lib/6to5/register.js

@@ -1,7 +1,9 @@
 require("./polyfill");
 
 var sourceMapSupport = require("source-map-support");
+var util             = require("./util");
 var to5              = require("./index");
+var fs               = require("fs");
 var _                = require("lodash");
 
 sourceMapSupport.install({
@@ -56,23 +58,44 @@ 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) {
+    var cached = cache[filename];
+    if (cached && cached.mtime === mtime(filename)) {
+      result = cached;
+    }
+  }
+
+  result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
-    sourceMap: true
-  });
+    sourceMap: true,
+    ast:       false
+  }, transformOpts));
+
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
 
   maps[filename] = result.map;
 
@@ -100,11 +123,13 @@ 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 = opts.cache;
+  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

@@ -1,5 +1,5 @@
 (function (Constructor, args) {
-  var bindArgs = [null].concat(args);
-  var Factory = Constructor.bind.apply(Constructor, bindArgs);
-  return new Factory;
+  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/class-super-constructor-call.js

@@ -1,2 +1,3 @@
-SUPER_NAME.apply(this, arguments);
-
+if (SUPER_NAME) {
+  SUPER_NAME.apply(this, arguments);
+}

lib/6to5/templates/class.js

@@ -1,7 +0,0 @@
-(function () {
-  var CLASS_NAME = function () {
-
-  };
-
-  return CLASS_NAME;
-})()

lib/6to5/templates/exports-assign-key.js

@@ -1 +0,0 @@
-exports.VARIABLE_NAME = OBJECT.KEY;

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

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

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

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

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

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

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

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

lib/6to5/templates/inherits.js

@@ -1,5 +1,5 @@
 (function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -7,5 +7,5 @@
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 })

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

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

lib/6to5/templates/object-without-properties.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/self-global.js

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

lib/6to5/templates/system.js

@@ -0,0 +1,6 @@
+System.register(MODULE_NAME, MODULE_DEPENDENCIES, function (EXPORT_IDENTIFIER) {
+  return {
+    setters: SETTERS,
+    execute: EXECUTE
+  };
+});

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

@@ -0,0 +1,6 @@
+(function (strings, raw) {
+  return Object.freeze(Object.defineProperties(strings, {
+      raw: { value: Object.freeze(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/_default.js

@@ -0,0 +1,198 @@
+module.exports = DefaultFormatter;
+
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+function DefaultFormatter(file) {
+  this.file = file;
+
+  this.localExports = this.getLocalExports();
+  this.remapAssignments();
+}
+
+DefaultFormatter.prototype.getLocalExports = function () {
+  var localExports = {};
+
+  traverse(this.file.ast, {
+    enter: function (node) {
+      var declar = node && node.declaration;
+      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
+        _.extend(localExports, t.getIds(declar, true));
+      }
+    }
+  });
+
+  return localExports;
+};
+
+DefaultFormatter.prototype.remapExportAssignment = function (node) {
+  return t.assignmentExpression(
+    "=",
+    node.left,
+    t.assignmentExpression(
+      node.operator,
+      t.memberExpression(t.identifier("exports"), node.left),
+      node.right
+    )
+  );
+};
+
+DefaultFormatter.prototype.remapAssignments = function () {
+  var localExports = this.localExports;
+  var self = this;
+
+  var isLocalReference = function (node, scope) {
+    var name = node.name;
+    return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
+  };
+
+  traverse(this.file.ast, {
+    enter: function (node, parent, scope) {
+      if (t.isUpdateExpression(node) && isLocalReference(node.argument, scope)) {
+        this.stop();
+
+        // expand to long file assignment expression
+        var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
+
+        // remap this assignment expression
+        var remapped = self.remapExportAssignment(assign);
+
+        // we don't need to change the result
+        if (t.isExpressionStatement(parent) || node.prefix) {
+          return remapped;
+        }
+
+        var nodes = [];
+        nodes.push(remapped);
+
+        var operator;
+        if (node.operator === "--") {
+          operator = "+";
+        } else { // "++"
+          operator = "-";
+        }
+        nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
+
+        return t.sequenceExpression(nodes);
+      }
+
+      if (t.isAssignmentExpression(node) && isLocalReference(node.left, scope)) {
+        this.stop();
+        return self.remapExportAssignment(node);
+      }
+    }
+  });
+};
+
+DefaultFormatter.prototype.getModuleName = function () {
+  var opts = this.file.opts;
+  var filenameRelative = opts.filenameRelative;
+  var moduleName = "";
+
+  if (opts.moduleRoot) {
+    moduleName = opts.moduleRoot + "/";
+  }
+
+  if (!opts.filenameRelative) {
+    return moduleName + opts.filename.replace(/^\//, "");
+  }
+
+  if (opts.sourceRoot) {
+    // remove sourceRoot from filename
+    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
+    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
+  }
+
+  // remove extension
+  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+
+  moduleName += filenameRelative;
+
+  return moduleName;
+};
+
+DefaultFormatter.prototype._pushStatement = function (ref, nodes) {
+  if (t.isClass(ref) || t.isFunction(ref)) {
+    if (ref.id) {
+      nodes.push(t.toStatement(ref));
+      ref = ref.id;
+    }
+  }
+
+  return ref;
+};
+
+DefaultFormatter.prototype._hoistExport = function (declar, assign) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = true;
+  }
+
+  return assign;
+};
+
+DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
+  var inherits = false;
+  if (node.specifiers.length === 1) inherits = node;
+
+  if (node.source) {
+    if (t.isExportBatchSpecifier(specifier)) {
+      // export * from "foo";
+      nodes.push(this._exportsWildcard(getRef()));
+    } else {
+      // export { foo } from "test";
+      nodes.push(this._exportsAssign(
+        t.getSpecifierName(specifier),
+        t.memberExpression(getRef(), specifier.id)
+      ));
+    }
+  } else {
+    // export { foo };
+    nodes.push(this._exportsAssign(t.getSpecifierName(specifier), specifier.id));
+  }
+};
+
+DefaultFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  return util.template("exports-wildcard", {
+    OBJECT: objectIdentifier
+  }, true);
+};
+
+DefaultFormatter.prototype._exportsAssign = function (id, init) {
+  return util.template("exports-assign", {
+    VALUE: init,
+    KEY:   id
+  }, true);
+};
+
+DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
+  var declar = node.declaration;
+
+  if (node.default) {
+    nodes.push(
+      this._exportsAssign(t.identifier("default"), this._pushStatement(declar, nodes))
+    );
+  } else {
+    var assign;
+
+    if (t.isVariableDeclaration(declar)) {
+      for (var i in declar.declarations) {
+        var decl = declar.declarations[i];
+
+        decl.init = this._exportsAssign(decl.id, decl.init).expression;
+
+        var newDeclar = t.variableDeclaration(declar.kind, [decl]);
+        if (i === "0") t.inherits(newDeclar, declar);
+        nodes.push(newDeclar);
+      }
+    } else {
+      assign = this._exportsAssign(declar.id, declar.id);
+
+      nodes.push(t.toStatement(declar));
+      nodes.push(assign);
+
+      this._hoistExport(declar, assign);
+    }
+  }
+};

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

@@ -1,16 +1,28 @@
 module.exports = AMDFormatter;
 
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
+var DefaultFormatter = require("./_default");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");
 
-function AMDFormatter(file) {
-  this.file = file;
+function AMDFormatter() {
+  DefaultFormatter.apply(this, arguments);
   this.ids  = {};
 }
 
-util.inherits(AMDFormatter, CommonJSFormatter);
+util.inherits(AMDFormatter, DefaultFormatter);
+
+AMDFormatter.prototype.buildDependencyLiterals = function () {
+  var names = [];
+  for (var name in this.ids) {
+    names.push(t.literal(name));
+  }
+  return names;
+};
+
+/**
+ * Wrap the entire body in a `define` wrapper.
+ */
 
 AMDFormatter.prototype.transform = function (ast) {
   var program = ast.program;
@@ -18,10 +30,7 @@ AMDFormatter.prototype.transform = function (ast) {
 
   // build an array of module names
 
-  var names = [t.literal("exports")];
-  _.each(this.ids, function (id, name) {
-    names.push(t.literal(name));
-  });
+  var names = [t.literal("exports")].concat(this.buildDependencyLiterals());
   names = t.arrayExpression(names);
 
   // build up define container
@@ -30,11 +39,29 @@ 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)];
 };
 
+/**
+ * Get the AMD module name that we'll prepend to the wrapper
+ * to define this module
+ */
+
+AMDFormatter.prototype.getModuleName = function () {
+  if (this.file.opts.amdModuleIds) {
+    return DefaultFormatter.prototype.getModuleName.apply(this, arguments);
+  } else {
+    return null;
+  }
+};
+
 AMDFormatter.prototype._push = function (node) {
   var id  = node.source.value;
   var ids = this.ids;
@@ -42,31 +69,26 @@ 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);
   }
 };
 
-AMDFormatter.prototype.import = function (node) {
+AMDFormatter.prototype.importDeclaration = function (node) {
   this._push(node);
 };
 
 AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var key = t.getSpecifierName(specifier);
-  var id  = specifier.id;
-
-  // import foo from "foo";
-  if (specifier.default) {
-    id = t.identifier("default");
-  }
-
-  var ref;
+  var ref = this._push(node);
 
   if (t.isImportBatchSpecifier(specifier)) {
     // import * as bar from "foo";
-    ref = this._push(node);
-  } else {
+  } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
     // import foo from "foo";
-    ref = t.memberExpression(this._push(node), id, false);
+    ref = t.callExpression(this.file.addDeclaration("interop-require"), [ref]);
+  } else {
+    // import {foo} from "foo";
+    ref = t.memberExpression(ref, specifier.id, false);
   }
 
   nodes.push(t.variableDeclaration("var", [

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

@@ -1,132 +1,82 @@
 module.exports = CommonJSFormatter;
 
-var util = require("../../util");
-var t    = require("../../types");
+var DefaultFormatter = require("./_default");
+var traverse         = require("../../traverse");
+var util             = require("../../util");
+var t                = require("../../types");
 
 function CommonJSFormatter(file) {
-  this.file = file;
+  DefaultFormatter.apply(this, arguments);
+
+  var hasNonDefaultExports = false;
+  traverse(file.ast, {
+    enter: function (node) {
+      if (t.isExportDeclaration(node) && !node.default) hasNonDefaultExports = true;
+    }
+  });
+  this.hasNonDefaultExports = hasNonDefaultExports;
 }
 
-CommonJSFormatter.prototype.import = function (node, nodes) {
-  // import "foo";
-  nodes.push(util.template("require", {
-    //inherits: node,
-
-    MODULE_NAME: node.source.raw
-  }, true));
-};
+util.inherits(CommonJSFormatter, DefaultFormatter);
 
 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var variableName = t.getSpecifierName(specifier);
 
   // import foo from "foo";
-  if (specifier.default) {
-    specifier.id = t.identifier("default");
+  if (t.isSpecifierDefault(specifier)) {
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(variableName,
+        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
+          MODULE_NAME: node.source
+        })])
+      )
+    ]));
+  } else {
+    // import foo from "foo";
+
+    var templateName = "require-assign";
+
+    // import * as bar from "foo";
+    if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
+
+    nodes.push(util.template(templateName, {
+      VARIABLE_NAME: variableName,
+      MODULE_NAME:   node.source,
+      KEY:           specifier.id
+    }));
   }
-
-  var templateName = "require-assign";
-
-  // import * as bar from "foo";
-  if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
-
-  nodes.push(util.template(templateName, {
-    //inherits: node.specifiers.length === 1 && node,
-
-    VARIABLE_NAME: variableName,
-    MODULE_NAME:   node.source.raw,
-    KEY:           specifier.id
-  }));
 };
 
-CommonJSFormatter.prototype.export = function (node, nodes) {
-  var declar = node.declaration;
+CommonJSFormatter.prototype.importDeclaration = function (node, nodes) {
+  // import "foo";
+  nodes.push(util.template("require", {
+    MODULE_NAME: node.source
+  }, true));
+};
 
+CommonJSFormatter.prototype.exportDeclaration = function (node, nodes) {
   if (node.default) {
-    var ref = declar;
+    var declar = node.declaration;
 
-    if (t.isClass(ref) || t.isFunction(ref)) {
-      if (ref.id) {
-        nodes.push(t.toStatement(ref));
-        ref = ref.id;
-      }
-    }
+    // module.exports = VALUE;
+    var templateName = "exports-default-module";
 
-    nodes.push(util.template("exports-default", {
-      //inherits: node,
+    // exports = module.exports = VALUE;
+    if (this.hasNonDefaultExports) templateName = "exports-default-module-override";
 
-      VALUE: ref
-    }, true));
+    var assign = util.template(templateName, {
+      VALUE: this._pushStatement(declar, nodes)
+    }, true);
+
+    // hoist to the top if this default is a function
+    nodes.push(this._hoistExport(declar, assign));
   } else {
-    var assign;
-
-    if (t.isVariableDeclaration(declar)) {
-      var decl = declar.declarations[0];
-
-      if (decl.init) {
-        decl.init = util.template("exports-assign", {
-          //inherits: node,
-
-          VALUE: decl.init,
-          KEY:   decl.id
-        });
-      }
-
-      nodes.push(declar);
-    } else {
-      assign = util.template("exports-assign", {
-        //inherits: node,
-
-        VALUE: declar.id,
-        KEY:   declar.id
-      }, true);
-
-      nodes.push(t.toStatement(declar));
-      nodes.push(assign);
-
-      if (t.isFunctionDeclaration(declar)) {
-        assign._blockHoist = true;
-      }
-    }
-  }
-};
-
-CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  var inherits = false;
-  if (node.specifiers.length === 1) inherits = node;
-
-  if (node.source) {
-    if (t.isExportBatchSpecifier(specifier)) {
-      // export * from "foo";
-      nodes.push(util.template("exports-wildcard", {
-        //inherits: inherits,
-
-        OBJECT: getRef()
-      }, true));
-    } else {
-      // export { foo } from "test";
-      nodes.push(util.template("exports-assign-key", {
-        //inherits: inherits,
-
-        VARIABLE_NAME: variableName.name,
-        OBJECT:        getRef(),
-        KEY:           specifier.id
-      }, true));
-    }
-  } else {
-    // export { foo };
-    nodes.push(util.template("exports-assign", {
-      //inherits: inherits,
-
-      VALUE: specifier.id,
-      KEY:   variableName
-    }, true));
+    DefaultFormatter.prototype.exportDeclaration.apply(this, arguments);
   }
 };
 
 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/ignore.js

@@ -6,19 +6,13 @@ function IgnoreFormatter() {
 
 }
 
-IgnoreFormatter.prototype.import = function () {
-
-};
-
-IgnoreFormatter.prototype.importSpecifier = function () {
-
-};
-
-IgnoreFormatter.prototype.export = function (node, nodes) {
+IgnoreFormatter.prototype.exportDeclaration = function (node, nodes) {
   var declar = t.toStatement(node.declaration, true);
   if (declar) nodes.push(t.inherits(declar, node));
 };
 
+IgnoreFormatter.prototype.importDeclaration =
+IgnoreFormatter.prototype.importSpecifier =
 IgnoreFormatter.prototype.exportSpecifier = function () {
 
 };

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

@@ -0,0 +1,85 @@
+module.exports = SystemFormatter;
+
+var DefaultFormatter = require("./_default");
+var AMDFormatter     = require("./amd");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");
+
+function SystemFormatter(file) {
+  this.exportIdentifier  = file.generateUidIdentifier("export");
+  this.noInteropRequire = true;
+
+  AMDFormatter.apply(this, arguments);
+
+  this.moduleNameLiteral = t.literal(this.getModuleName());
+}
+
+util.inherits(SystemFormatter, AMDFormatter);
+
+SystemFormatter.prototype.getModuleName = DefaultFormatter.prototype.getModuleName;
+
+SystemFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  var leftIdentifier = t.identifier("i");
+  var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
+
+  var left = t.variableDeclaration("var", [
+    t.variableDeclarator(leftIdentifier)
+  ]);
+
+  var right = objectIdentifier;
+
+  var block = t.blockStatement([
+    this.buildExportCall(leftIdentifier, valIdentifier)
+  ]);
+
+  return t.forInStatement(left, right, block);
+};
+
+SystemFormatter.prototype._exportsAssign = function (id, init) {
+  return this.buildExportCall(t.literal(id.name), init, true);
+};
+
+SystemFormatter.prototype.remapExportAssignment = function (node) {
+  return this.buildExportCall(t.literal(node.left.name), node);
+};
+
+SystemFormatter.prototype.buildExportCall = function (id, init, isStatement) {
+  var call = t.callExpression(this.exportIdentifier, [id, init]);
+  if (isStatement) {
+    return t.expressionStatement(call);
+  } else {
+    return call;
+  }
+};
+
+SystemFormatter.prototype.buildRunnerSetters = function () {
+  return t.arrayExpression(_.map(this.ids, function (uid) {
+    var moduleIdentifier = t.identifier("m");
+
+    return t.functionExpression(null, [moduleIdentifier], t.blockStatement([
+      t.assignmentExpression("=", uid, moduleIdentifier)
+    ]));
+  }));
+};
+
+SystemFormatter.prototype.transform = function (ast) {
+  var program = ast.program;
+
+  var runner = util.template("system", {
+    MODULE_NAME: this.moduleNameLiteral,
+    MODULE_DEPENDENCIES: t.arrayExpression(this.buildDependencyLiterals()),
+    EXPORT_IDENTIFIER: this.exportIdentifier,
+    SETTERS: this.buildRunnerSetters(),
+    EXECUTE: t.functionExpression(null, [], t.blockStatement(program.body))
+  }, true);
+
+  if (!_.isEmpty(this.ids)) {
+    var handlerBody = runner.expression.arguments[2].body.body;
+    handlerBody.unshift(t.variableDeclaration("var", _.map(this.ids, function (uid) {
+      return t.variableDeclarator(uid);
+    })));
+  }
+
+  program.body = [runner];
+};

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);
@@ -19,9 +18,9 @@ UMDFormatter.prototype.transform = function (ast) {
   // build an array of module names
 
   var names = [];
-  _.each(this.ids, function (id, name) {
+  for (var name in this.ids) {
     names.push(t.literal(name));
-  });
+  }
 
   // factory
 
@@ -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

@@ -2,6 +2,7 @@ module.exports = transform;
 
 var Transformer = require("./transformer");
 var File        = require("../file");
+var util        = require("../util");
 var _           = require("lodash");
 
 function transform(code, opts) {
@@ -9,55 +10,84 @@ function transform(code, opts) {
   return file.parse(code);
 }
 
+transform.fromAst = function (ast, code, opts) {
+  ast = util.normaliseAst(ast);
+
+  var file = new File(opts);
+  file.addCode(code);
+  file.transform(ast);
+  return file.generate();
+};
+
 transform._ensureTransformerNames = function (type, keys) {
-  _.each(keys, function (key) {
+  for (var i in keys) {
+    var key = keys[i];
     if (!_.has(transform.transformers, key)) {
       throw new ReferenceError("unknown transformer " + key + " specified in " + type);
     }
-  });
+  }
 };
 
 transform.transformers = {};
 
 transform.moduleFormatters = {
   common: require("./modules/common"),
+  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"),
-  generatorComprehension:   require("./transformers/generator-comprehension"),
-  arrowFunctions:           require("./transformers/arrow-functions"),
-  classes:                  require("./transformers/classes"),
+  // spec
+  specBlockHoistFunctions:   require("./transformers/spec-block-hoist-functions"),
+  specNoForInOfAssignment:   require("./transformers/spec-no-for-in-of-assignment"),
+  specNoDuplicateProperties: require("./transformers/spec-no-duplicate-properties"),
 
-  _propertyLiterals:        require("./transformers/_property-literals"),
-  computedPropertyNames:    require("./transformers/computed-property-names"),
+  // playground
+  methodBinding:             require("./transformers/playground-method-binding"),
+  memoizationOperator:       require("./transformers/playground-memoization-operator"),
+  objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),
 
-  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"),
+  react:                     require("./transformers/react"),
+  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"),
 
-  react:                    require("./transformers/react"),
+  computedPropertyNames:     require("./transformers/es6-computed-property-names"),
 
-  _aliasFunctions:          require("./transformers/_alias-functions"),
-  _blockHoist:              require("./transformers/_block-hoist"),
-  _declarations:            require("./transformers/_declarations"),
+  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"),
+  destructuring:             require("./transformers/es6-destructuring"),
+  defaultParameters:         require("./transformers/es6-default-parameters"),
+  forOf:                     require("./transformers/es6-for-of"),
+  unicodeRegex:              require("./transformers/es6-unicode-regex"),
+  abstractReferences:        require("./transformers/es7-abstract-references"),
 
-  generators:               require("./transformers/generators"),
-  useStrict:                require("./transformers/use-strict"),
+  constants:                 require("./transformers/es6-constants"),
+  letScoping:                require("./transformers/es6-let-scoping"),
 
-  _moduleFormatter:         require("./transformers/_module-formatter")
+  _blockHoist:               require("./transformers/_block-hoist"),
+
+  generators:                require("./transformers/es6-generators"),
+  restParameters:            require("./transformers/es6-rest-parameters"),
+
+  _declarations:             require("./transformers/_declarations"),
+
+  // wrap up
+  _aliasFunctions:           require("./transformers/_alias-functions"),
+  useStrict:                 require("./transformers/use-strict"),
+  _moduleFormatter:          require("./transformers/_module-formatter"),
+
+  // spec
+  specPropertyLiterals:         require("./transformers/spec-property-literals"),
+  specMemberExpressionLiterals: require("./transformers/spec-member-expression-literals")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });

lib/6to5/transformation/transformer.js

@@ -4,8 +4,9 @@ var traverse = require("../traverse");
 var t        = require("../types");
 var _        = require("lodash");
 
-function Transformer(key, transformer) {
+function Transformer(key, transformer, opts) {
   this.transformer = Transformer.normalise(transformer);
+  this.opts        = opts || {};
   this.key         = key;
 }
 
@@ -18,37 +19,38 @@ Transformer.normalise = function (transformer) {
     if (type[0] === "_") return;
     if (_.isFunction(fns)) fns = { enter: fns };
     transformer[type] = fns;
+
+    var aliases = t.FLIPPED_ALIAS_KEYS[type];
+    if (aliases) {
+      _.each(aliases, function (alias) {
+        transformer[alias] = fns;
+      });
+    }
   });
 
   return transformer;
 };
 
+Transformer.prototype.astRun = function (file, key) {
+  var transformer = this.transformer;
+  var ast         = file.ast;
+
+  if (transformer.ast && transformer.ast[key]) {
+    transformer.ast[key](ast, file);
+  }
+};
+
 Transformer.prototype.transform = function (file) {
   if (!this.canRun(file)) return;
 
   var transformer = this.transformer;
   var ast         = file.ast;
 
-  var astRun = function (key) {
-    if (transformer.ast && transformer.ast[key]) {
-      transformer.ast[key](ast, file);
-    }
-  };
-
-  astRun("enter");
+  this.astRun(file, "enter");
 
   var build = function (exit) {
     return function (node, parent, scope) {
-      // add any node type aliases that exist
-      var types = [node.type].concat(t.ALIAS_KEYS[node.type] || []);
-
-      var fns = transformer.all;
-
-      _.each(types, function (type) {
-        fns = transformer[type] || fns;
-      });
-
-      // this transformer cannot deal with this node type
+      var fns = transformer[node.type];
       if (!fns) return;
 
       var fn = fns.enter;
@@ -64,7 +66,7 @@ Transformer.prototype.transform = function (file) {
     exit:  build(true)
   });
 
-  astRun("exit");
+  this.astRun(file, "exit");
 };
 
 Transformer.prototype.canRun = function (file) {

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

@@ -6,47 +6,51 @@ 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
-  traverse(node, function (node) {
-    if (!node._aliasFunction) {
-      if (t.isFunction(node)) {
-        // stop traversal of this node as it'll be hit again by this transformer
-        return false;
-      } else {
-        return;
+  traverse(node, {
+    enter: function (node) {
+      if (!node._aliasFunction) {
+        if (t.isFunction(node)) {
+          // stop traversal of this node as it'll be hit again by this transformer
+          return false;
+        } else {
+          return;
+        }
       }
+
+      // traverse all child nodes of this function and find `arguments` and `this`
+      traverse(node, {
+        enter: function (node, parent) {
+          if (t.isFunction(node) && !node._aliasFunction) {
+            return false;
+          }
+
+          if (node._ignoreAliasFunctions) return false;
+
+          var getId;
+
+          if (t.isIdentifier(node) && node.name === "arguments") {
+            getId = getArgumentsId;
+          } else if (t.isThisExpression(node)) {
+            getId = getThisId;
+          } else {
+            return;
+          }
+
+          if (t.isReferenced(node, parent)) return getId();
+        }
+      });
+
+      return false;
     }
-
-    // traverse all child nodes of this function and find `arguments` and `this`
-    traverse(node, function (node, parent) {
-      if (t.isFunction(node) && !node._aliasFunction) {
-        return false;
-      }
-
-      if (node._ignoreAliasFunctions) return;
-
-      var getId;
-
-      if (t.isIdentifier(node) && node.name === "arguments") {
-        getId = getArgumentsId;
-      } else if (t.isThisExpression(node)) {
-        getId = getThisId;
-      } else {
-        return;
-      }
-
-      if (t.isReferenced(node, parent)) return getId();
-    });
-
-    return false;
   });
 
   var body;

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

@@ -1,12 +1,25 @@
 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 = {};
+  var kind;
 
-  _.each(file.declarations, function (declar) {
-    body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(declar.uid, declar.node)
-    ]));
-  });
+  for (var i in node._declarations) {
+    var declar = node._declarations[i];
+
+    kind = declar.kind || "var";
+    var declarNode = t.variableDeclarator(declar.id, declar.init);
+
+    if (!declar.init) {
+      kinds[kind] = kinds[kind] || [];
+      kinds[kind].push(declarNode);
+    } else {
+      node.body.unshift(t.variableDeclaration(kind, [declarNode]));
+    }
+  }
+
+  for (kind in kinds) {
+    node.body.unshift(t.variableDeclaration(kind, kinds[kind]));
+  }
 };

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

@@ -1,15 +0,0 @@
-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;
-
-    node.computed = false;
-  }
-};

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 || !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/destructuring.js

@@ -1,198 +0,0 @@
-var t = require("../../types");
-var _ = require("lodash");
-
-var buildVariableAssign = function (kind, id, init) {
-  if (kind === false) {
-    return t.expressionStatement(t.assignmentExpression("=", id, init));
-  } else {
-    return t.variableDeclaration(kind, [
-      t.variableDeclarator(id, init)
-    ]);
-  }
-};
-
-var push = function (kind, nodes, elem, parentId) {
-  if (t.isObjectPattern(elem)) {
-    pushObjectPattern(kind, nodes, elem, parentId);
-  } else if (t.isArrayPattern(elem)) {
-    pushArrayPattern(kind, nodes, elem, parentId);
-  } else if (t.isMemberExpression(elem)) {
-    nodes.push(buildVariableAssign(false, elem, parentId));
-  } else {
-    nodes.push(buildVariableAssign(kind, 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);
-
-    if (t.isPattern(pattern2)) {
-      push(kind, nodes, pattern2, patternId2);
-    } else {
-      nodes.push(buildVariableAssign(kind, pattern2, patternId2));
-    }
-  });
-};
-
-var pushArrayPattern = function (kind, nodes, pattern, 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)]);
-      elem = elem.argument;
-    } else {
-      newPatternId = t.memberExpression(parentId, t.literal(i), true);
-    }
-
-    push(kind, nodes, elem, newPatternId);
-  });
-};
-
-var pushPattern = function (opts) {
-  var kind = opts.kind;
-  var nodes = opts.nodes;
-  var pattern = opts.pattern;
-  var parentId = opts.id;
-  var file = opts.file;
-  var scope = opts.scope;
-
-  if (!t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = t.identifier(file.generateUid("ref", scope));
-
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(key, parentId)
-    ]));
-
-    parentId = key;
-  }
-
-  push(kind, nodes, pattern, parentId);
-};
-
-exports.ForInStatement =
-exports.ForOfStatement = function (node, parent, file, scope) {
-  var declar = node.left;
-  if (!t.isVariableDeclaration(declar)) return;
-
-  var pattern = declar.declarations[0].id;
-  if (!t.isPattern(pattern)) return;
-
-  var key = t.identifier(file.generateUid("ref", scope));
-  node.left = t.variableDeclaration(declar.kind, [
-    t.variableDeclarator(key, null)
-  ]);
-
-  var nodes = [];
-
-  push(declar.kind, nodes, pattern, key);
-
-  t.ensureBlock(node);
-
-  var block = node.body;
-  block.body = nodes.concat(block.body);
-};
-
-exports.Function = function (node, parent, file, scope) {
-  var nodes = [];
-
-  var hasDestructuring = false;
-
-  node.params = node.params.map(function (pattern) {
-    if (!t.isPattern(pattern)) return pattern;
-
-    hasDestructuring = true;
-    var parentId = t.identifier(file.generateUid("ref", scope));
-
-    pushPattern({
-      kind:    "var",
-      nodes:   nodes,
-      pattern: pattern,
-      id:      parentId,
-      file:    file,
-      scope:   scope
-    });
-
-    return parentId;
-  });
-
-  if (!hasDestructuring) return;
-
-  t.ensureBlock(node);
-
-  var block = node.body;
-  block.body = nodes.concat(block.body);
-};
-
-exports.ExpressionStatement = function (node, parent, file, scope) {
-  var expr = node.expression;
-  if (expr.type !== "AssignmentExpression") return;
-
-  if (!t.isPattern(expr.left)) return;
-
-  var nodes = [];
-
-  var ref = t.identifier(file.generateUid("ref", scope));
-  nodes.push(t.variableDeclaration("var", [
-    t.variableDeclarator(ref, expr.right)
-  ]));
-
-  push(false, nodes, expr.left, ref);
-
-  return nodes;
-};
-
-exports.VariableDeclaration = function (node, parent, file, scope) {
-  if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
-
-  var nodes = [];
-
-  var hasPattern = false;
-  _.each(node.declarations, function (declar) {
-    if (t.isPattern(declar.id)) {
-      hasPattern = true;
-      return false;
-    }
-  });
-  if (!hasPattern) return;
-
-  _.each(node.declarations, function (declar) {
-    var patternId = declar.init;
-    var pattern   = declar.id;
-    if (t.isPattern(pattern) && patternId) {
-      pushPattern({
-        kind:    node.kind,
-        nodes:   nodes,
-        pattern: pattern,
-        id:      patternId,
-        file:    file,
-        scope:   scope
-      });
-    } else {
-      nodes.push(buildVariableAssign(node.kind, declar.id, declar.init));
-    }
-  });
-
-  if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
-    var declar;
-
-    _.each(nodes, function (node) {
-      declar = declar || t.variableDeclaration(node.kind, []);
-
-      if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
-        throw file.errorWithNode(node, "Cannot use this node within the current parent");
-      }
-
-      declar.declarations = declar.declarations.concat(node.declarations);
-    });
-
-    return declar;
-  }
-
-  return nodes;
-};
-

lib/6to5/transformation/transformers/es5-property-method-assignment.js

@@ -1,5 +1,4 @@
 var util = require("../../util");
-var _    = require("lodash");
 
 exports.Property = function (node) {
   if (node.method) node.method = false;
@@ -7,9 +6,11 @@ exports.Property = function (node) {
 
 exports.ObjectExpression = function (node, parent, file) {
   var mutatorMap = {};
+  var hasAny = false;
 
   node.properties = node.properties.filter(function (prop) {
     if (prop.kind === "get" || prop.kind === "set") {
+      hasAny = true;
       util.pushMutatorMap(mutatorMap, prop.key, prop.kind, prop.value);
       return false;
     } else {
@@ -17,7 +18,7 @@ exports.ObjectExpression = function (node, parent, file) {
     }
   });
 
-  if (_.isEmpty(mutatorMap)) return;
+  if (!hasAny) return;
 
   var objId = util.getUid(parent, file);
 

lib/6to5/transformation/transformers/es6-arrow-functions.js

@@ -3,7 +3,7 @@ var t = require("../../types");
 exports.ArrowFunctionExpression = function (node) {
   t.ensureBlock(node);
 
-  node._aliasFunction = true;
+  node._aliasFunction = "arrow";
   node.expression = false;
   node.type = "FunctionExpression";
 

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

@@ -1,23 +1,38 @@
 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, new Class(node, file, scope).run())
-  ]);
+  var closure = true;
+  if (t.isProgram(parent) || t.isBlockStatement(parent)) {
+    closure = false;
+  }
+
+  var factory = new Class(node, file, scope, closure);
+  var newNode = factory.run();
+  if (factory.closure) {
+    if (closure) {
+      // declaration in an expression context...
+      // export default class Foo {}
+      scope.push({
+        kind: "var",
+        key: node.id.key,
+        id: node.id
+      });
+      return t.assignmentExpression("=", node.id, newNode);
+    } else {
+      // likely has a PrivateDeclaration etc
+      return t.variableDeclaration("let", [
+        t.variableDeclarator(node.id, newNode)
+      ]);
+    }
+  } else {
+    return newNode;
+  }
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
-  return new Class(node, file, scope).run();
-};
-
-var getMemberExpressionObject = function (node) {
-  while (t.isMemberExpression(node)) {
-    node = node.object;
-  }
-  return node;
+  return new Class(node, file, scope, true).run();
 };
 
 /**
@@ -26,17 +41,22 @@ var getMemberExpressionObject = function (node) {
  * @param {Node} node
  * @param {File} file
  * @param {Scope} scope
+ * @param {Boolean} closure
  */
 
-function Class(node, file, scope) {
-  this.scope = scope;
-  this.node  = node;
-  this.file  = file;
+function Class(node, file, scope, closure) {
+  this.closure = closure;
+  this.scope   = scope;
+  this.node    = node;
+  this.file    = file;
+
+  this.hasInstanceMutators = false;
+  this.hasStaticMutators   = false;
 
   this.instanceMutatorMap = {};
   this.staticMutatorMap   = {};
   this.hasConstructor     = false;
-  this.className          = node.id || t.identifier(file.generateUid("class", scope));
+  this.className          = node.id || file.generateUidIdentifier("class", scope);
   this.superName          = node.superClass;
 }
 
@@ -47,50 +67,61 @@ function Class(node, file, scope) {
  */
 
 Class.prototype.run = function () {
-  var superClassArgument = this.superName;
-  var superClassCallee   = this.superName;
-  var superName          = this.superName;
-  var className          = this.className;
-  var file               = this.file;
+  var superName = this.superName;
+  var className = this.className;
+  var file      = this.file;
 
-  if (superName) {
-    if (t.isMemberExpression(superName)) {
-      superClassArgument = superClassCallee = getMemberExpressionObject(superName);
-    } else if (!t.isIdentifier(superName)) {
-      superClassArgument = superName;
-      superClassCallee   = superName = t.identifier(file.generateUid("ref", this.scope));
-    }
+  //
+
+  var body = this.body = [];
+
+  var constructor = t.functionExpression(null, [], t.blockStatement([]));
+  if (this.node.id) constructor.id = className;
+  this.constructor = constructor;
+
+  body.push(t.variableDeclaration("let", [
+    t.variableDeclarator(className, constructor)
+  ]));
+
+  //
+
+  if (superName && t.isDynamic(superName)) {
+    // so we're only evaluating it once
+    var superRefName = "super";
+    if (className) superRefName = className.name + "Super";
+
+    var superRef = file.generateUidIdentifier(superRefName, this.scope);
+    body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(superRef, superName)
+    ]));
+    superName = superRef;
   }
 
   this.superName = superName;
 
-  var container = util.template("class", {
-    CLASS_NAME: className
-  });
-
-  var block       = container.callee.expression.body;
-  var body        = this.body = block.body;
-  var constructor = this.constructor = body[0].declarations[0].init;
-
-  if (this.node.id) constructor.id = className;
-
-  var returnStatement = body.pop();
+  //
 
   if (superName) {
-    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("extends"), [className, superName])));
-
-    container.arguments.push(superClassArgument);
-    container.callee.expression.params.push(superClassCallee);
+    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("inherits"), [className, superName])));
   }
 
   this.buildBody();
 
-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    return constructor;
+  t.inheritsComments(body[0], this.node);
+
+  if (this.closure) {
+    if (body.length === 1) {
+      // only a constructor so no need for a closure container
+      return constructor;
+    } else {
+      body.push(t.returnStatement(className));
+      return t.callExpression(
+        t.functionExpression(null, [], t.blockStatement(body)),
+        []
+      );
+    }
   } else {
-    body.push(returnStatement);
-    return container;
+    return body;
   }
 };
 
@@ -106,15 +137,21 @@ Class.prototype.buildBody = function () {
   var body        = this.body;
   var self        = this;
 
-  _.each(classBody, function (node) {
-    self.replaceInstanceSuperReferences(node);
+  for (var i in classBody) {
+    var node = classBody[i];
+    if (t.isMethodDefinition(node)) {
+      self.replaceInstanceSuperReferences(node);
 
-    if (node.key.name === "constructor") {
-      self.pushConstructor(node);
-    } else {
-      self.pushMethod(node);
+      if (node.key.name === "constructor") {
+        self.pushConstructor(node);
+      } else {
+        self.pushMethod(node);
+      }
+    } else if (t.isPrivateDeclaration(node)) {
+      self.closure = true;
+      body.unshift(node);
     }
-  });
+  }
 
   if (!this.hasConstructor && superName) {
     constructor.body.body.push(util.template("class-super-constructor-call", {
@@ -125,7 +162,7 @@ Class.prototype.buildBody = function () {
   var instanceProps;
   var staticProps;
 
-  if (!_.isEmpty(this.instanceMutatorMap)) {
+  if (this.hasInstanceMutators) {
     var protoId = util.template("prototype-identifier", {
       CLASS_NAME: className
     });
@@ -133,7 +170,7 @@ Class.prototype.buildBody = function () {
     instanceProps = util.buildDefineProperties(this.instanceMutatorMap, protoId);
   }
 
-  if (!_.isEmpty(this.staticMutatorMap)) {
+  if (this.hasStaticMutators) {
     staticProps = util.buildDefineProperties(this.staticMutatorMap, className);
   }
 
@@ -144,7 +181,7 @@ Class.prototype.buildBody = function () {
     if (instanceProps) args.push(instanceProps);
 
     body.push(t.expressionStatement(
-      t.callExpression(this.file.addDeclaration("class-props"), args)
+      t.callExpression(this.file.addDeclaration("prototype-properties"), args)
     ));
   }
 };
@@ -158,17 +195,29 @@ Class.prototype.buildBody = function () {
 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"));
-  }
+    // method
 
-  util.pushMutatorMap(mutatorMap, methodName, kind, node);
+    var className = this.className;
+    if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
+    methodName = t.memberExpression(className, methodName, node.computed);
+
+    var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
+    t.inheritsComments(expr, node);
+    this.body.push(expr);
+  } else {
+    // mutator
+    var mutatorMap = this.instanceMutatorMap;
+    if (node.static) {
+      this.hasStaticMutators = true;
+      mutatorMap = this.staticMutatorMap;
+    } else {
+      this.hasInstanceMutators = true;
+    }
+    util.pushMutatorMap(mutatorMap, methodName, kind, node);
+  }
 };
 
 /**
@@ -223,17 +272,19 @@ Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
   var method = methodNode.value;
   var self = this;
 
-  traverse(method, function (node, parent) {
-    if (t.isIdentifier(node, { name: "super" })) {
-      return self.superIdentifier(methodNode, node, parent);
-    } else if (t.isCallExpression(node)) {
-      var callee = node.callee;
-      if (!t.isMemberExpression(callee)) return;
-      if (callee.object.name !== "super") return;
+  traverse(method, {
+    enter: function (node, parent) {
+      if (t.isIdentifier(node, { name: "super" })) {
+        return self.superIdentifier(methodNode, node, parent);
+      } else if (t.isCallExpression(node)) {
+        var callee = node.callee;
+        if (!t.isMemberExpression(callee)) return;
+        if (callee.object.name !== "super") return;
 
-      // super.test(); -> ClassName.prototype.MethodName.call(this);
-      callee.property = t.memberExpression(callee.property, t.identifier("call"));
-      node.arguments.unshift(t.thisExpression());
+        // super.test(); -> ClassName.prototype.MethodName.call(this);
+        callee.property = t.memberExpression(callee.property, t.identifier("call"));
+        node.arguments.unshift(t.thisExpression());
+      }
     }
   });
 };
@@ -253,7 +304,9 @@ Class.prototype.pushConstructor = function (method) {
   var fn        = method.value;
 
   this.hasConstructor = true;
+
   t.inherits(construct, fn);
+  t.inheritsComments(construct, method);
 
   construct.defaults = fn.defaults;
   construct.params   = fn.params;

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

@@ -1,6 +1,5 @@
 var util = require("../../util");
 var t    = require("../../types");
-var _    = require("lodash");
 
 exports.ObjectExpression = function (node, parent, file) {
   var hasComputed = false;
@@ -26,12 +25,13 @@ exports.ObjectExpression = function (node, parent, file) {
     OBJECT: node
   });
 
-  var containerCallee = container.callee.expression;
+  var containerCallee = container.callee;
   var containerBody = containerCallee.body.body;
 
   containerCallee._aliasFunction = true;
 
-  _.each(computed, function (prop) {
+  for (var i in computed) {
+    var prop = computed[i];
     containerBody.unshift(
       t.expressionStatement(
         t.assignmentExpression(
@@ -41,7 +41,7 @@ exports.ObjectExpression = function (node, parent, file) {
         )
       )
     );
-  });
+  }
 
   return container;
 };

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

@@ -0,0 +1,82 @@
+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 hasConstants = false;
+  var constants = {};
+
+  /**
+   * Check the results of `util.getIds` as `names` generated from a
+   * node against it's parent.
+   */
+
+  var check = function (parent, names, scope) {
+    for (var name in names) {
+      var nameNode = names[name];
+      if (!_.has(constants, name)) continue;
+      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) continue;
+
+      if (scope) {
+        var defined = scope.get(name);
+        if (defined && defined === nameNode) continue;
+      }
+
+      throw file.errorWithNode(nameNode, name + " is read-only");
+    }
+  };
+
+  var getIds = function (node) {
+    return t.getIds(node, true, ["MemberExpression"]);
+  };
+
+  /**
+   * Collect all constants in this scope.
+   */
+
+  _.each(node.body, function (child, parent) {
+    if (t.isExportDeclaration(child)) {
+      child = child.declaration;
+    }
+
+    if (t.isVariableDeclaration(child, { kind: "const" })) {
+      for (var i in child.declarations) {
+        var declar = child.declarations[i];
+
+        var ids = getIds(declar);
+        for (var name in ids) {
+          var nameNode = ids[name];
+
+          var names = {};
+          names[name] = nameNode;
+          check(parent, names);
+
+          constants[name] = parent;
+          hasConstants = true;
+        }
+
+        declar._ignoreConstant = true;
+      }
+
+      child._ignoreConstant = true;
+      child.kind = "let";
+    }
+  });
+
+  if (!hasConstants) return;
+
+  traverse(node, {
+    enter: function (child, parent, scope) {
+      if (child._ignoreConstant) return;
+      if (t.isVariableDeclaration(child)) return;
+
+      if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
+        check(parent, getIds(child), scope);
+      }
+    }
+  });
+};

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

@@ -0,0 +1,74 @@
+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 iife = false;
+  var i;
+  var def;
+
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;
+
+    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 (ids.indexOf(node.name) >= 0) {
+          throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+        }
+
+        if (scope.has(node.name)) {
+          iife = true;
+        }
+      };
+
+      check(def, node);
+      traverse(def, { enter: check });
+    });
+
+    // we're accessing a variable that's already defined within this function
+    var has = scope.get(param.name);
+    if (has && node.params.indexOf(has) < 0) {
+      iife = true;
+    }
+  }
+
+  var body = [];
+
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;
+
+    body.push(util.template("if-undefined-set-to", {
+      VARIABLE: node.params[i],
+      DEFAULT:  def
+    }, true));
+  }
+
+  if (iife) {
+    var container = t.functionExpression(null, [], node.body, node.generator);
+    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

@@ -0,0 +1,273 @@
+// TODO: Clean up
+
+var t = require("../../types");
+
+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(opts.kind, [
+      t.variableDeclarator(id, init)
+    ]);
+  }
+};
+
+var push = function (opts, nodes, elem, parentId) {
+  if (t.isObjectPattern(elem)) {
+    pushObjectPattern(opts, nodes, elem, parentId);
+  } else if (t.isArrayPattern(elem)) {
+    pushArrayPattern(opts, nodes, elem, parentId);
+  } else {
+    nodes.push(buildVariableAssign(opts, elem, parentId));
+  }
+};
+
+var pushObjectPattern = function (opts, nodes, pattern, parentId) {
+  for (var i in pattern.properties) {
+    var prop = pattern.properties[i];
+    if (t.isSpreadProperty(prop)) {
+        // get all the keys that appear in this object before the current spread
+        var keys = [];
+        for (var i2 in pattern.properties) {
+          var prop2 = pattern.properties[i2];
+
+          if (i2 >= i) break;
+          if (t.isSpreadProperty(prop2)) continue;
+
+          var key = prop2.key;
+          if (t.isIdentifier(key)) {
+            key = t.literal(prop2.key.name);
+          }
+          keys.push(key);
+        }
+        keys = t.arrayExpression(keys);
+
+        var value = t.callExpression(opts.file.addDeclaration("object-without-properties"), [parentId, keys]);
+        nodes.push(buildVariableAssign(opts, prop.argument, value));
+    } else {
+      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 (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;
+
+  for (var i in pattern.elements) {
+    var elem = pattern.elements[i];
+    if (!elem) continue;
+
+    i = +i;
+
+    var newPatternId;
+
+    if (t.isSpreadElement(elem)) {
+      newPatternId = opts.file.toArray(parentId);
+
+      if (i > 0) {
+        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(opts, nodes, elem, newPatternId);
+  }
+};
+
+var pushPattern = function (opts) {
+  var nodes = opts.nodes;
+  var pattern = opts.pattern;
+  var parentId = opts.id;
+  var file = opts.file;
+  var scope = opts.scope;
+
+  if (!t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
+    var key = file.generateUidIdentifier("ref", scope);
+
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(key, parentId)
+    ]));
+
+    parentId = key;
+  }
+
+  push(opts, nodes, pattern, parentId);
+};
+
+exports.ForInStatement =
+exports.ForOfStatement = function (node, parent, file, scope) {
+  var declar = node.left;
+  if (!t.isVariableDeclaration(declar)) return;
+
+  var pattern = declar.declarations[0].id;
+  if (!t.isPattern(pattern)) return;
+
+  var key = file.generateUidIdentifier("ref", scope);
+  node.left = t.variableDeclaration(declar.kind, [
+    t.variableDeclarator(key, null)
+  ]);
+
+  var nodes = [];
+
+  push({
+    kind: declar.kind,
+    file: file,
+    scope: scope
+  }, nodes, pattern, key);
+
+  t.ensureBlock(node);
+
+  var block = node.body;
+  block.body = nodes.concat(block.body);
+};
+
+exports.Function = function (node, parent, file, scope) {
+  var nodes = [];
+
+  var hasDestructuring = false;
+
+  node.params = node.params.map(function (pattern) {
+    if (!t.isPattern(pattern)) return pattern;
+
+    hasDestructuring = true;
+    var parentId = file.generateUidIdentifier("ref", scope);
+
+    pushPattern({
+      kind:    "var",
+      nodes:   nodes,
+      pattern: pattern,
+      id:      parentId,
+      file:    file,
+      scope:   scope
+    });
+
+    return parentId;
+  });
+
+  if (!hasDestructuring) return;
+
+  t.ensureBlock(node);
+
+  var block = node.body;
+  block.body = nodes.concat(block.body);
+};
+
+exports.ExpressionStatement = function (node, parent, file, scope) {
+  var expr = node.expression;
+  if (expr.type !== "AssignmentExpression") return;
+
+  if (!t.isPattern(expr.left)) return;
+
+  var nodes = [];
+
+  var ref = file.generateUidIdentifier("ref", scope);
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(ref, expr.right)
+  ]));
+
+  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;
+
+  var nodes = [];
+  var i;
+  var declar;
+
+  var hasPattern = false;
+  for (i in node.declarations) {
+    declar = node.declarations[i];
+    if (t.isPattern(declar.id)) {
+      hasPattern = true;
+      break;
+    }
+  }
+  if (!hasPattern) return;
+
+  for (i in node.declarations) {
+    declar = node.declarations[i];
+
+    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(opts);
+    } else {
+      nodes.push(buildVariableAssign(opts, declar.id, declar.init));
+    }
+  }
+
+  if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
+
+    for (i in nodes) {
+      node = nodes[i];
+      declar = declar || t.variableDeclaration(node.kind, []);
+
+      if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
+        throw file.errorWithNode(node, "Cannot use this node within the current parent");
+      }
+
+      declar.declarations = declar.declarations.concat(node.declarations);
+    }
+
+    return declar;
+  }
+
+  return nodes;
+};

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

@@ -5,25 +5,26 @@ 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
   });
 
+  t.inheritsComments(node2, node);
   t.ensureBlock(node);
 
   var block = node2.body;

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

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

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

@@ -3,33 +3,40 @@ var util     = require("../../util");
 var t        = require("../../types");
 var _        = require("lodash");
 
-var isLet = function (node) {
+var isLet = function (node, parent) {
   if (!t.isVariableDeclaration(node)) return false;
   if (node._let) return true;
   if (node.kind !== "let") return false;
 
+  // https://github.com/6to5/6to5/issues/255
+  if (!t.isFor(parent) || t.isFor(parent) && parent.left !== node) {
+    _.each(node.declarations, function (declar) {
+      declar.init = declar.init || t.identifier("undefined");
+    });
+  }
+
   node._let = true;
   node.kind = "var";
   return true;
 };
 
-var isVar = function (node) {
-  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node);
+var isVar = function (node, parent) {
+  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node, parent);
 };
 
 var standardiseLets = function (declars) {
-  _.each(declars, function (declar) {
-    delete declar._let;
-  });
+  for (var i in declars) {
+    delete declars[i]._let;
+  }
 };
 
-exports.VariableDeclaration = function (node) {
-  isLet(node);
+exports.VariableDeclaration = function (node, parent) {
+  isLet(node, parent);
 };
 
-exports.For = function (node, parent, file, scope) {
+exports.Loop = function (node, parent, file, scope) {
   var init = node.left || node.init;
-  if (isLet(init)) {
+  if (isLet(init, node)) {
     t.ensureBlock(node);
     node.body._letDeclars = [init];
   }
@@ -49,7 +56,7 @@ exports.For = function (node, parent, file, scope) {
 };
 
 exports.BlockStatement = function (block, parent, file, scope) {
-  if (!t.isFor(parent)) {
+  if (!t.isLoop(parent)) {
     var letScoping = new LetScoping(false, block, parent, file, scope);
     letScoping.run();
   }
@@ -58,23 +65,22 @@ exports.BlockStatement = function (block, parent, file, scope) {
 /**
  * Description
  *
- * @param {Boolean|Node} forParent
+ * @param {Boolean|Node} loopParent
  * @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;
+function LetScoping(loopParent, block, parent, file, scope) {
+  this.loopParent = loopParent;
+  this.parent     = parent;
+  this.scope      = scope;
+  this.block      = block;
+  this.file       = file;
 
   this.letReferences = {};
   this.body          = [];
-  this.info          = this.getInfo();
 }
 
 /**
@@ -87,8 +93,13 @@ LetScoping.prototype.run = function () {
   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;
+  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();
@@ -102,7 +113,7 @@ LetScoping.prototype.run = function () {
 
   // 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();
+  this.has = this.checkLoop();
 
   // hoist var references to retain scope
   this.hoistVarDeclarations();
@@ -125,31 +136,57 @@ LetScoping.prototype.run = function () {
 
   // build a call and a unique id that we can assign the return value to
   var call = t.callExpression(fn, params);
-  var ret  = t.identifier(this.file.generateUid("ret", this.scope));
+  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 traverse
- * through this block and replace all references that exist in a high scope to
- * their uids.
+ * 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 declarators  = this.info.declarators;
   var block        = this.block;
 
-  standardiseLets(declarators);
+  if (!this.info.hasDuplicates) return;
 
-  if (_.isEmpty(replacements)) return;
-
-  traverse(block, function (node, parent) {
+  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, { enter: replace });
+  };
+
+  var loopParent = this.loopParent;
+  if (loopParent) {
+    traverseReplace(loopParent.right, loopParent);
+    traverseReplace(loopParent.test, loopParent);
+    traverseReplace(loopParent.update, loopParent);
+  }
+
+  traverse(block, { enter: replace });
 };
 
 /**
@@ -176,66 +213,89 @@ LetScoping.prototype.getInfo = function () {
     // all references with it
     duplicates:  {},
 
+    hasDuplicates: false,
+
     // array of `Identifier` names of let variables that are accessible within
     // the current block
     keys:        []
   };
 
-  _.each(opts.declarators, function (declar) {
+  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);
+      opts.hasDuplicates = true;
+    }
+  };
+
+  var i;
+  var declar;
+
+  for (i in opts.declarators) {
+    declar = opts.declarators[i];
     opts.declarators.push(declar);
 
-    var keys = t.getIds(declar);
+    var keys = t.getIds(declar, true);
+    _.each(keys, duplicates);
+    keys = Object.keys(keys);
+
     opts.outsideKeys = opts.outsideKeys.concat(keys);
     opts.keys = opts.keys.concat(keys);
-  });
+  }
 
-  _.each(block.body, function (declar) {
-    if (!isLet(declar)) return;
+  for (i in block.body) {
+    declar = block.body[i];
+    if (!isLet(declar, block)) continue;
 
     _.each(t.getIds(declar, true), function (id, key) {
-      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);
-      }
-
+      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 we can track later on.
+ * If we're inside of a loop then traverse it and check if it has one of
+ * the following node types `ReturnStatement`, `BreakStatement`,
+ * `ContinueStatement` and replace it with a return value that we can track
+ * later on.
  *
  * @returns {Object}
  */
 
-LetScoping.prototype.checkFor = function () {
+LetScoping.prototype.checkLoop = function () {
   var has = {
     hasContinue: false,
     hasReturn:   false,
     hasBreak:    false,
   };
 
-  if (this.forParent) {
-    traverse(this.block, function (node) {
+  traverse(this.block, {
+    enter: function (node, parent) {
       var replace;
 
-      if (t.isFunction(node) || t.isFor(node)) {
+      if (t.isFunction(node) || t.isLoop(node)) {
         return false;
-      } else if (t.isBreakStatement(node) && !node.label) {
-        has.hasBreak = true;
-        replace = t.returnStatement(t.literal("break"));
-      } else if (t.isContinueStatement(node) && !node.label) {
-        has.hasContinue = true;
-        replace = t.returnStatement(t.literal("continue"));
-      } else if (t.isReturnStatement(node)) {
+      }
+
+      if (node && !node.label) {
+        if (t.isBreakStatement(node)) {
+          if (t.isSwitchCase(parent)) return;
+
+          has.hasBreak = true;
+          replace = t.returnStatement(t.literal("break"));
+        } else if (t.isContinueStatement(node)) {
+          has.hasContinue = true;
+          replace = t.returnStatement(t.literal("continue"));
+        }
+      }
+
+      if (t.isReturnStatement(node)) {
         has.hasReturn = true;
         replace = t.returnStatement(t.objectExpression([
           t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
@@ -243,32 +303,34 @@ LetScoping.prototype.checkFor = function () {
       }
 
       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 is in a closure.
+ * 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));
+  traverse(this.block, {
+    enter: function (node, parent) {
+      if (t.isForStatement(node)) {
+        if (isVar(node.init, node)) {
+          node.init = t.sequenceExpression(self.pushDeclar(node.init));
+        }
+      } else if (t.isFor(node)) {
+        if (isVar(node.left, node)) {
+          node.left = node.left.declarations[0].id;
+        }
+      } else if (isVar(node, parent)) {
+        return self.pushDeclar(node).map(t.expressionStatement);
+      } else if (t.isFunction(node)) {
+        return false;
       }
-    } else if (t.isFor(node)) {
-      if (isVar(node.left)) {
-        node.left = node.left.declarations[0].id;
-      }
-    } else if (isVar(node)) {
-      return self.pushDeclar(node).map(t.expressionStatement);
-    } else if (t.isFunction(node)) {
-      return false;
     }
   });
 };
@@ -301,31 +363,35 @@ LetScoping.prototype.getLetReferences = function () {
 
   // traverse through this block, stopping on functions and checking if they
   // contain any outside let references
-  traverse(this.block, function (node, parent, scope) {
-    if (t.isFunction(node)) {
-      traverse(node, function (node, parent) {
-        // not an identifier so we have no use
-        if (!t.isIdentifier(node)) return;
+  traverse(this.block, {
+    enter: function (node, parent, scope) {
+      if (t.isFunction(node)) {
+        traverse(node, {
+          enter: function (node, parent) {
+            // not an identifier so we have no use
+            if (!t.isIdentifier(node)) return;
 
-        // not a direct reference
-        if (!t.isReferenced(node, parent)) return;
+            // not a direct reference
+            if (!t.isReferenced(node, parent)) return;
 
-        // this scope has a variable with the same name so it couldn't belong
-        // to our let scope
-        if (scope.hasOwn(node.name)) return;
+            // this scope has a variable with the same name so it couldn't belong
+            // to our let scope
+            if (scope.hasOwn(node.name)) return;
 
-        closurify = true;
+            closurify = true;
 
-        // this key doesn't appear just outside our scope
-        if (!_.contains(self.info.outsideKeys, node.name)) return;
+            // this key doesn't appear just outside our scope
+            if (!_.contains(self.info.outsideKeys, node.name)) return;
 
-        // push this badboy
-        self.letReferences[node.name] = node;
-      });
+            // push this badboy
+            self.letReferences[node.name] = node;
+          }
+        });
 
-      return false;
-    } else if (t.isFor(node)) {
-      return false;
+        return false;
+      } else if (t.isLoop(node)) {
+        return false;
+      }
     }
   });
 
@@ -340,19 +406,20 @@ LetScoping.prototype.getLetReferences = function () {
  * @returns {Array}
  */
 
-LetScoping.prototype.buildPushDeclar = function (node) {
+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;
+  for (var i in node.declarations) {
+    var declar = node.declarations[i];
+    if (!declar.init) continue;
 
     var expr = t.assignmentExpression("=", declar.id, declar.init);
     replace.push(t.inherits(expr, declar));
-  });
+  }
 
   return replace;
 };
@@ -387,7 +454,7 @@ LetScoping.prototype.buildHas = function (ret, call) {
     t.variableDeclarator(ret, call)
   ]));
 
-  var forParent = this.forParent;
+  var loopParent = this.loopParent;
   var retCheck;
   var has = this.has;
   var cases = [];
@@ -402,7 +469,7 @@ LetScoping.prototype.buildHas = function (ret, call) {
   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 || t.identifier(this.file.generateUid("loop", this.scope));
+    var label = loopParent.label = loopParent.label || this.file.generateUidIdentifier("loop", this.scope);
 
     if (has.hasBreak) {
       cases.push(t.switchCase(t.literal("break"), [t.breakStatement(label)]));

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

@@ -0,0 +1,50 @@
+var t = require("../../types");
+
+var inheritsComments = function (node, nodes) {
+  if (nodes.length) {
+    t.inheritsComments(nodes[0], node);
+  }
+};
+
+exports.ImportDeclaration = function (node, parent, file) {
+  var nodes = [];
+
+  if (node.specifiers.length) {
+    if (!file.moduleFormatter.importSpecifier) return;
+    for (var i in node.specifiers) {
+      file.moduleFormatter.importSpecifier(node.specifiers[i], node, nodes, parent);
+    }
+  } else {
+    if (!file.moduleFormatter.importDeclaration) return;
+    file.moduleFormatter.importDeclaration(node, nodes, parent);
+  }
+
+  inheritsComments(node, nodes);
+
+  return nodes;
+};
+
+exports.ExportDeclaration = function (node, parent, file) {
+  var nodes = [];
+
+  if (node.declaration) {
+    // make sure variable exports have an initialiser
+    // this is done here to avoid duplicating it in the module formatters
+    if (t.isVariableDeclaration(node.declaration)) {
+      var declar = node.declaration.declarations[0];
+      declar.init = declar.init || t.identifier("undefined");
+    }
+
+    if (!file.moduleFormatter.exportDeclaration) return;
+    file.moduleFormatter.exportDeclaration(node, nodes, parent);
+  } else {
+    if (!file.moduleFormatter.exportSpecifier) return;
+    for (var i in node.specifiers) {
+      file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, parent);
+    }
+  }
+
+  inheritsComments(node, nodes);
+
+  return nodes;
+};

lib/6to5/transformation/transformers/es6-property-name-shorthand.js

@@ -0,0 +1,8 @@
+var t = require("../../types");
+var _ = require("lodash");
+
+exports.Property = function (node) {
+  if (!node.shorthand) return;
+  node.shorthand = false;
+  node.key = t.removeComments(_.clone(node.key));
+};

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

@@ -0,0 +1,22 @@
+var t = require("../../types");
+
+exports.Function = function (node, parent, file) {
+  if (!node.rest) return;
+
+  var rest = node.rest;
+  delete node.rest;
+
+  t.ensureBlock(node);
+
+  var call = file.toArray(t.identifier("arguments"));
+
+  if (node.params.length) {
+    call.arguments.push(t.literal(node.params.length));
+  }
+
+  call._ignoreAliasFunctions = true;
+
+  node.body.body.unshift(t.variableDeclaration("var", [
+    t.variableDeclarator(rest, call)
+  ]));
+};

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

@@ -1,29 +1,19 @@
 var t = require("../../types");
-var _ = require("lodash");
 
-var getSpreadLiteral = function (spread) {
-  var literal = spread.argument;
-  if (!t.isArrayExpression(literal)) {
-    literal = t.callExpression(
-      t.memberExpression(t.identifier("Array"), t.identifier("from")),
-      [literal]
-    );
-  }
-  return literal;
+var getSpreadLiteral = function (spread, file) {
+  return file.toArray(spread.argument);
 };
 
 var hasSpread = function (nodes) {
-  var has = false;
-  _.each(nodes, function (node) {
-    if (t.isSpreadElement(node)) {
-      has = true;
-      return false;
+  for (var i in nodes) {
+    if (t.isSpreadElement(nodes[i])) {
+      return true;
     }
-  });
-  return has;
+  }
+  return false;
 };
 
-var build = function (props) {
+var build = function (props, file) {
   var nodes = [];
 
   var _props = [];
@@ -34,33 +24,37 @@ var build = function (props) {
     _props = [];
   };
 
-  _.each(props, function (prop) {
+  for (var i in props) {
+    var prop = props[i];
     if (t.isSpreadElement(prop)) {
       push();
-      nodes.push(getSpreadLiteral(prop));
+      nodes.push(getSpreadLiteral(prop, file));
     } else {
       _props.push(prop);
     }
-  });
+  }
 
   push();
 
   return nodes;
 };
 
-exports.ArrayExpression = function (node) {
+exports.ArrayExpression = function (node, parent, file) {
   var elements = node.elements;
   if (!hasSpread(elements)) return;
 
-  var nodes = build(elements);
+  var nodes = build(elements, file);
   var first = nodes.shift();
 
-  if (!nodes.length) return first;
+  if (!t.isArrayExpression(first)) {
+    nodes.unshift(first);
+    first = t.arrayExpression([]);
+  }
 
   return t.callExpression(t.memberExpression(first, t.identifier("concat")), nodes);
 };
 
-exports.CallExpression = function (node) {
+exports.CallExpression = function (node, parent, file, scope) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
@@ -68,7 +62,12 @@ exports.CallExpression = function (node) {
 
   node.arguments = [];
 
-  var nodes = build(args);
+  var nodes;
+  if (args.length === 1 && args[0].argument.name === 'arguments') {
+    nodes = [args[0].argument];
+  } else {
+    nodes = build(args, file);
+  }
   var first = nodes.shift();
 
   if (nodes.length) {
@@ -78,10 +77,16 @@ exports.CallExpression = function (node) {
   }
 
   var callee = node.callee;
+  var temp;
 
   if (t.isMemberExpression(callee)) {
     contextLiteral = callee.object;
 
+    if (t.isDynamic(contextLiteral)) {
+      temp = contextLiteral = scope.generateTemp(file);
+      callee.object = t.assignmentExpression("=", temp, callee.object);
+    }
+
     if (callee.computed) {
       callee.object = t.memberExpression(callee.object, callee.property, true);
       callee.property = t.identifier("apply");
@@ -100,7 +105,7 @@ exports.NewExpression = function (node, parent, file) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
-  var nodes = build(args);
+  var nodes = build(args, file);
   var first = nodes.shift();
 
   if (nodes.length) {