v1.14.12

Only slice arguments when necessary - fixes #239

.hound.yml

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

CHANGELOG.md

@@ -1,3 +1,208 @@
+# 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.

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

README.md

@@ -4,7 +4,7 @@
 
 <p align="center">
   <a href="https://travis-ci.org/6to5/6to5">
-    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5.svg?branch=master&amp;style=flat&amp;label=travis">
+    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
   </a>
 
   <a href="https://ci.appveyor.com/project/sebmck/6to5">
@@ -24,6 +24,7 @@
   </a>
 </p>
 
-**6to5** turns ES6 code into vanilla ES5, so you can use ES6 features **today.**
+**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
 
-For more information view the [documentation](https://6to5.github.io).
+For more information view the [documentation](https://6to5.github.io). For
+support visit the [gitter room](https://gitter.im/6to5/6to5).

bin/6to5-node

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

bin/6to5/dir.js

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

bin/6to5/file.js

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

bin/6to5/index.js

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

bin/6to5/util.js

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

bin/_6to5-node

@@ -8,10 +8,12 @@ var util      = require("../lib/6to5/util");
 var vm        = require("vm");
 var _         = require("lodash");
 
-commander.option("-e, --eval [script]", "evaluate script");
-commander.option("-p, --print", "evaluate script and print result");
-commander.option("-i, --ignore [regex]", "ignore all files that match this regex when using the require hook");
-commander.option("-x, --extensions [extensions]", "list of extensions to hook into [.es6,.js]", util.list);
+commander.option("-e, --eval [script]", "Evaluate script");
+commander.option("-p, --print", "Evaluate script and print result");
+commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
+commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
+commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
+commander.option("-g, --playground", "Enable playground support");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
@@ -20,22 +22,21 @@ commander.parse(process.argv);
 
 //
 
-var registerOpts = {};
-
-if (commander.ignore) {
-  registerOpts.ignoreRegex = new RegExp(commander.ignore);
-}
-
-if (commander.extensions && commander.extensions.length) {
-  registerOpts.extensions = commander.extensions;
-}
-
-to5.register(registerOpts);
+to5.register({
+  experimental: commander.experimental,
+  extensions:   commander.extensions,
+  ignore:       commander.ignore
+});
 
 //
 
 var _eval = function (code, filename) {
-  code = to5.transform(code, { filename: filename, blacklist: ["useStrict"] }).code;
+  code = to5.transform(code, {
+    modules: "commonInterop",
+    filename: filename,
+    blacklist: ["useStrict"],
+    experimental: commander.experimental
+  }).code;
   return vm.runInThisContext(code, filename);
 };
 

doc/browser.md

@@ -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

@@ -1,5 +1,19 @@
 # Caveats
 
+In order for certain features to work they require certain polyfills. You can
+satisfy **all** 6to5 feature requirements by using the included
+[polyfill](polyfill.md). You may alternatively selectively include what you need:
+
+| Feature                     | Requirements                                                                                                                 |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | [experimental](usage.md#experimental), `Symbol`                                                                              |
+| Array destructuring         | `Array.isArray`, `Array.from`                                                                                                |
+| Async functions, Generators | [experimental](usage.md#experimental), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
+| Comprehensions              | [experimental](usage.md#experimental), `Array.isArray`, `Array.from`                                                         |
+| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                       |
+| Object spread/rest          | [experimental](usage.md#experimental), `Object.assign`                                                                       |
+| Spread                      | `Array.isArray`, `Array.from`                                                                                                |
+
 ## Classes
 
 Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
@@ -25,19 +39,3 @@ class Bar extends Foo {
   }
 }
 ```
-
-## For-of
-
-A polyfill is required for for-of functionality that implements `Symbol` and
-adds `prototype[Symbol.iterator]` behaviour to built-ins. Using the polyfills
-specified in [polyfill](polyfill.md) suffices.
-
-## 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`.

doc/differences.md

@@ -56,37 +56,47 @@ better suited if you'd like a full ES6 environment with polyfills and all.
 
 ## Comparison to other transpilers
 
-|                              | 6to5 | Traceur | esnext | es6now | es6-transpiler | jstransform |
-| ---------------------------- | ---- | ------- | ------ | ------ | -------------- | ----------- |
-| No runtime                   | ✓    |         |        |        | ✓              | ✓           |
-| Source maps                  | ✓    | ✓       | ✓      |        | ✓              | ✓           |
-| No compiler global pollution | ✓    |         | ✓      |        | ✓              | ✓           |
-| 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 support              | ✓    | ✓       |                | ✓      |        |             |
+
+### Language Support
+
+|                              | 6to5  | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ----- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓     |         |                |        |        |             |
+| Array comprehension          | ✓     | ✓       | ✓              |        |        |             |
+| Arrow functions              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Async functions              | ✓     | ✓       |                | ✓      |        |             |
+| Classes                      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Computed property names      | ✓     | ✓       | ✓              | ✓      | ✓      |             |
+| Constants                    | ✓     | ✓       | ✓              |        |        |             |
+| Default parameters           | ✓     | ✓       | ✓              | ✓      | ✓      |             |
+| Destructuring                | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓     | ✓       |                |        |        |             |
+| For-of                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
+| Generators                   | ✓     | ✓       |                | ✓      |        |             |
+| Generator comprehension      | ✓     | ✓       |                |        |        |             |
+| Let scoping                  | ✓     | ✓       | ✓              |        |        |             |
+| Modules                      | ✓     | ✓       |                |        | ✓      |             |
+| Object rest/spread           | ✓     |         |                |        |        | ✓           |
+| Property method assignment   | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Property name shorthand      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Rest parameters              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Spread                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
+| Template literals            | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Unicode regex                | ✓     | ✓       | ✓              |        |        |             |
 
 ### [Traceur](https://github.com/google/traceur-compiler)
 
 Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
 While this can be trimmed down by selectively building the runtime, it's an
-unneccesary step when a runtime can be eliminated entirely.
+unneccesary step when a large runtime can be eliminated entirely.
 
 ### [es6now](https://github.com/zenparsing/es6now)
 

doc/features.md

@@ -1,12 +1,45 @@
 # Features
 
-## Array comprehension
+## Abstract references ([experimental](usage.md#experimental)) ([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](usage.md#experimental))
+
+```javascript
+var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
+```
+
+## Arrow functions
+
+```javascript
+// Expression bodies
+var odds = evens.map(v => v + 1);
+var nums = evens.map((v, i) => v + i);
+
+// Statement bodies
+nums.forEach(v => {
+  if (v % 5 === 0)
+    fives.push(v);
+});
+
+// Lexical this
+var bob = {
+  _name: "Bob",
+  _friends: [],
+  printFriends() {
+    this._friends.forEach(f => {
+      console.log(this._name + " knows " + f);
+    });
+  }
+};
+```
+
+## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -16,31 +49,27 @@ async function chainAnimationsAsync(elem, animations) {
 }
 ```
 
-## Arrow functions
-
-```javascript
-arr.map(x => x * x);
-```
-
-## Let scoping
-
-```javascript
-for (let i in arr) {
-  let v = arr[i];
-}
-```
-
 ## Classes
 
 ```javascript
-class Foo extends Bar {
-  constructor() { }
+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 +99,44 @@ 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](usage.md#experimental)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+
+```javascript
+var a = 2;
+a **= 2;
+
+var squared = 2 ** 2;
 ```
 
 ## For-of
@@ -93,16 +150,55 @@ 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](usage.md#experimental))
 
 ```javascript
+var nums = [1, 2, 3, 4, 5, 6];
+var multiples = (for (i of nums) if (i % 2) i * i);
+assert.equal(multiples.next().value, 1);
+assert.equal(multiples.next().value, 9);
+assert.equal(multiples.next().value, 25);
+```
+
+## Let scoping
+
+```javascript
+for (let i in arr) {
+  let v = arr[i];
+}
 ```
 
 ## Modules
 
 ```javascript
+import "foo";
+import foo from "foo";
+import * as foo from "foo";
+import {bar} from "foo";
+import {foo as bar} from "foo";
+
+export { test };
+export var test = 5;
+export function test() {}
+
+export default test;
 ```
 
 ## Numeric literals
@@ -112,6 +208,13 @@ for (var i of [1, 2, 3]) {
 0o767 === 503; // true
 ```
 
+## Object spread/rest ([experimental](usage.md#experimental)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
+
+```javascript
+var n = { x, y, ...z };
+var { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
+```
+
 ## Property method assignment
 
 ```javascript
@@ -141,23 +244,21 @@ 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 +268,6 @@ 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 +11,47 @@ 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](usage.md#experimental))
+ - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
+ - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
  - [Constants](features.md#constants)
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](usage.md#experimental))
  - [For-of](features.md#for-of)
- - [Generators](features.md#generators) via [regenerator](https://github.com/facebook/regenerator)
- - [Generator comprehension](features.md#generator-comprehension)
+ - [Generators](features.md#generators)
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)
+ - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](usage.md#experimental))
  - [Property method assignment](features.md#property-method-assignment)
  - [Property name shorthand](features.md#property-name-shorthand)
  - [React/JSX](react.md)

doc/modules.md

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

doc/optional-runtime.md

@@ -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 +1,68 @@
+# Playground
+
+Playground is a proving ground for **possible** ES7 proposals.
+
+**NOTE: These features are in no way endorsed by Ecma International and are not a part of ES6. They might become a part of ECMAScript in the future.**
+
+## Usage
+
+    $ 6to5 --playground
+
+```javascript
+to5.transform("code", { playground: true });
+```
+
+**NOTE:** Enabling `playground` also enables [experimental support](usage.md#experimental).
+
+## Features
+
+ * [Memoization operator](#memoization-operator)
+ * [Method binding](#method-binding)
+
+### Memoization assignment operator
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+obj.x; // 2
+
+obj = { x: 1 };
+obj.x ?= 2;
+obj.x; // 1
+
+obj = { x: undefined }
+obj.x ?= 2;
+obj.x; // undefined
+```
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+```
+
+equivalent to:
+
+```javascript
+var obj = {};
+if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
+```
+
+### Method binding
+
+```javascript
+var fn = obj:method;
+var fn = obj:method("foob");
+
+["foo", "bar"].map(:toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(:toFixed(2)); // ["1.12", "23.53", "3.00"]
+```
+
+equivalent to:
+
+```javascript
+var fn = obj.method.bind(obj);
+var fn = obj.method.bind(obj, "foob");
+
+["foo", "bar"].map(function (val) { return val.toUpperCase(); });
+[1.1234, 23.53245, 3].map(function (val) { return val.toFixed(2); });
+```

doc/plugins.md

@@ -5,11 +5,14 @@
  - [Brunch](https://github.com/es128/6to5-brunch)
  - [Duo](https://github.com/bdo-labs/duo6to5)
  - [Connect](https://github.com/6to5/6to5-connect)
+ - [Gobble](https://github.com/gobblejs/gobble-6to5)
  - [Gulp](https://github.com/sindresorhus/gulp-6to5)
  - [Grunt](https://github.com/sindresorhus/grunt-6to5)
+ - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
  - [Jade](https://github.com/Apoxx/jade-6to5)
  - [Jest](https://github.com/6to5/6to5-jest)
+ - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
  - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
  - [Mocha](https://github.com/6to5/6to5-mocha)
- - [Rails](https://github.com/6to5/6to5-rails)
+ - [Rails](https://github.com/josh/sprockets-es6) or via [browserify-rails](https://github.com/6to5/6to5-rails)
  - [webpack](https://github.com/Couto/6to5-loader)

doc/polyfill.md

@@ -5,13 +5,23 @@
 [es6-shim](https://github.com/paulmillr/es6-shim) and
 [es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
 
-## Node
+This will emulate a full ES6 environment. This polyfill is automatically loaded
+when using [6to5-node](usage.md#node).
+
+## Usage
+
+### Node
+
+You need to include the polyfill require at the top the **entry point** to your
+application.
 
 ```javascript
 require("6to5/polyfill");
 ```
 
-## Browser
+### 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.

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

@@ -4,62 +4,94 @@
 
 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;
 });
 ```
 
@@ -71,6 +103,10 @@ 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 +127,39 @@ 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,
+
+  // Output comments in generated output
+  // Default: true
+  comments: false,
+
+  // Enable support for experimental ES7 features
+  // Default: false
+  experimental: true
 }
 ```
 
@@ -147,3 +205,12 @@ require("6to5/register")({
   extensions: [".js", ".es6"]
 });
 ```
+
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
+
+**WARNING:** These proposals are subject to change so use with
+**extreme caution**.

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 = [
+  "extends",
+  "class-props",
+  "apply-constructor",
+  "tagged-template-literal",
+  "interop-require",
+  "to-array",
+  "object-spread",
+  "has-own",
+  "slice"
+];
 
 File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
-    whitespace: true,
-    blacklist:  [],
-    whitelist:  [],
-    sourceMap:  false,
-    filename:   "unknown",
-    modules:    "common",
-    runtime:    false,
-    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);
@@ -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;
 };
 
@@ -130,7 +173,8 @@ 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 +187,18 @@ 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 +209,6 @@ File.prototype.generate = function () {
     result.code += "\n" + util.sourceMapToComment(result.map);
   }
 
-  result.ast = result;
-
   return result;
 };
 
@@ -179,6 +224,10 @@ 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/generator.js

@@ -35,21 +35,17 @@ _.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 = {
@@ -57,6 +53,7 @@ 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"),
@@ -164,11 +161,13 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     this.printTrailingComments(node, parent);
   } else {
-    throw new ReferenceError("unknown node " + node.type + " " + JSON.stringify(node));
+    throw new ReferenceError("unknown node " + node.type);
   }
 };
 
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
+  if (!nodes || !nodes.length) return;
+
   opts = opts || {};
 
   var self = this;

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);
@@ -105,6 +106,11 @@ exports.MemberExpression = function (node, print) {
     print(node.property);
     this.push("]");
   } else {
+    // 5..toFixed(2);
+    if (t.isLiteral(node.object) && util.isInteger(node.object.value)) {
+      this.push(".");
+    }
+
     this.push(".");
     print(node.property);
   }

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

@@ -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

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

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

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

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

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

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

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

lib/6to5/generation/node/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/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;

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

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

lib/6to5/index.js

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

lib/6to5/patch.js

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

lib/6to5/polyfill.js

@@ -1,6 +1,37 @@
+/* jshint newcap: false */
+
+var ensureSymbol = function (key) {
+  Symbol[key] = Symbol[key] || Symbol();
+};
+
+var ensureProto = function (Constructor, key, val) {
+  var proto = Constructor.prototype;
+  proto[key] = proto[key] || val;
+};
+
+//
+
 if (typeof Symbol === "undefined") {
   require("es6-symbol/implement");
 }
 
 require("es6-shim");
-require("regenerator-6to5/runtime");
+require("./transformation/transformers/es6-generators/runtime");
+
+// Abstract references
+
+ensureSymbol("referenceGet");
+ensureSymbol("referenceSet");
+ensureSymbol("referenceDelete");
+
+ensureProto(Function, Symbol.referenceGet, function () { return this; });
+
+ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
+ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
+ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
+
+if (global.WeakMap) {
+  ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
+  ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
+  ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);
+}

lib/6to5/register.js

@@ -1,7 +1,9 @@
 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 +58,45 @@ 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,
+    modules:   "commonInterop",
+    ast:       false
+  }, transformOpts));
+
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
 
   maps[filename] = result.map;
 
@@ -100,11 +124,13 @@ 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/exports-default-module.js

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

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

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

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

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

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

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

lib/6to5/templates/register.js

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

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

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

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

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

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

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

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

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

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

@@ -0,0 +1,56 @@
+module.exports = CommonJSInteropFormatter;
+
+var CommonJSFormatter = require("./common");
+var util              = require("../../util");
+var t                 = require("../../types");
+var _                 = require("lodash");
+
+function CommonJSInteropFormatter(file) {
+  CommonJSFormatter.apply(this, arguments);
+
+  var has = false;
+  _.each(file.ast.program.body, function (node) {
+    if (t.isExportDeclaration(node) && !node.default) has = true;
+  });
+  this.has = has;
+}
+
+util.inherits(CommonJSInteropFormatter, CommonJSFormatter);
+
+CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
+  var variableName = t.getSpecifierName(specifier);
+
+  // import foo from "foo";
+   if (specifier.default) {
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(variableName,
+        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
+          MODULE_NAME: node.source.raw
+        })])
+      )
+    ]));
+  } else {
+    CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
+  }
+};
+
+CommonJSInteropFormatter.prototype.export = function (node, nodes) {
+  if (node.default && !this.has) {
+    var declar = node.declaration;
+
+    // module.exports = VALUE;
+    var assign = util.template("exports-default-module", {
+      VALUE: this._pushStatement(declar, nodes)
+    }, true);
+
+    // hoist to the top if this default is a function
+    nodes.push(this._hoistExport(declar, assign));
+    return;
+  }
+
+  CommonJSFormatter.prototype.export.apply(this, arguments);
+};
+
+CommonJSInteropFormatter.prototype.exportSpecifier = function () {
+  CommonJSFormatter.prototype.exportSpecifier.apply(this, arguments);
+};

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

@@ -7,6 +7,33 @@ function CommonJSFormatter(file) {
   this.file = file;
 }
 
+CommonJSFormatter.prototype.getModuleName = function () {
+  var opts = this.file.opts;
+  var filenameRelative = opts.filenameRelative;
+  var moduleName = "";
+
+  if (opts.moduleRoot) {
+    moduleName = opts.moduleRoot + "/";
+  }
+
+  if (!opts.filenameRelative) {
+    return moduleName + opts.filename.replace(/^\//, "");
+  }
+
+  if (opts.sourceRoot) {
+    // remove sourceRoot from filename
+    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
+    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
+  }
+
+  // remove extension
+  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+
+  moduleName += filenameRelative;
+
+  return moduleName;
+};
+
 CommonJSFormatter.prototype.import = function (node, nodes) {
   // import "foo";
   nodes.push(util.template("require", {
@@ -38,23 +65,32 @@ CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes)
   }));
 };
 
+CommonJSFormatter.prototype._hoistExport = function (declar, assign) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = true;
+  }
+
+  return assign;
+};
+
+CommonJSFormatter.prototype._pushStatement = function (ref, nodes) {
+  if (t.isClass(ref) || t.isFunction(ref)) {
+    if (ref.id) {
+      nodes.push(t.toStatement(ref));
+      ref = ref.id;
+    }
+  }
+  return ref;
+};
+
 CommonJSFormatter.prototype.export = function (node, nodes) {
   var declar = node.declaration;
 
   if (node.default) {
-    var ref = declar;
-
-    if (t.isClass(ref) || t.isFunction(ref)) {
-      if (ref.id) {
-        nodes.push(t.toStatement(ref));
-        ref = ref.id;
-      }
-    }
-
     nodes.push(util.template("exports-default", {
       //inherits: node,
 
-      VALUE: ref
+      VALUE: this._pushStatement(declar, nodes)
     }, true));
   } else {
     var assign;
@@ -83,9 +119,7 @@ CommonJSFormatter.prototype.export = function (node, nodes) {
       nodes.push(t.toStatement(declar));
       nodes.push(assign);
 
-      if (t.isFunctionDeclaration(declar)) {
-        assign._blockHoist = true;
-      }
+      this._hoistExport(declar, assign);
     }
   }
 };
@@ -126,7 +160,7 @@ CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node
 };
 
 CommonJSFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  return this._exportSpecifier(function () {
+  this._exportSpecifier(function () {
     return t.callExpression(t.identifier("require"), [node.source]);
   }, specifier, node, nodes);
 };

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

@@ -0,0 +1,202 @@
+module.exports = SystemFormatter;
+
+var util = require("../../util");
+var t    = require("../../types");
+var _    = require("lodash");
+
+var SETTER_MODULE_NAMESPACE = t.identifier("m");
+var DEFAULT_IDENTIFIER      = t.identifier("default");
+var NULL_SETTER             = t.literal(null);
+
+function SystemFormatter(file) {
+  this.exportedStatements = [];
+  this.importedModule     = {};
+
+  this.exportIdentifier   = file.generateUidIdentifier("export");
+  this.file               = file;
+}
+
+SystemFormatter.prototype.transform = function (ast) {
+  var program = ast.program;
+  var body    = program.body;
+
+  // extract the module name
+  var moduleName = this.file.opts.filename
+    .replace(/^.*\//, "").replace(/\..*$/, "");
+
+  // build an array of module names
+  var dependencies = Object.keys(this.importedModule).map(t.literal);
+
+  // generate the __moduleName variable
+  var moduleNameVariableNode = t.variableDeclaration("var", [
+    t.variableDeclarator(
+      t.identifier("__moduleName"),
+      t.literal(moduleName)
+    )
+  ]);
+  body.splice(1, 0, moduleNameVariableNode);
+
+  // generate an array of import variables
+
+  var declaredSetters = _(this.importedModule)
+    .map()
+    .flatten()
+    .pluck("variableName")
+    .pluck("name")
+    .uniq()
+    .map(t.identifier)
+    .map(function (name) {
+      return t.variableDeclarator(name);
+    })
+    .value();
+
+  if (declaredSetters.length) {
+    body.splice(2, 0, t.variableDeclaration("var", declaredSetters));
+  }
+
+  // generate the execute function expression
+  var executeFunctionExpression = t.functionExpression(
+    null, [], t.blockStatement(this.exportedStatements)
+  );
+
+  // generate the execute function expression
+  var settersArrayExpression = t.arrayExpression(this._buildSetters());
+
+  // generate the return statement
+  var moduleReturnStatement = t.returnStatement(t.objectExpression([
+    t.property("init", t.identifier("setters"), settersArrayExpression),
+    t.property("init", t.identifier("execute"), executeFunctionExpression)
+  ]));
+  body.push(moduleReturnStatement);
+
+  // runner
+  var runner = util.template("register", {
+    MODULE_NAME: t.literal(moduleName),
+    MODULE_DEPENDENCIES: t.arrayExpression(dependencies),
+    MODULE_BODY: t.functionExpression(
+      null,
+      [this.exportIdentifier],
+      t.blockStatement(body)
+    )
+  });
+
+  program.body = [t.expressionStatement(runner)];
+};
+
+SystemFormatter.prototype._buildSetters = function () {
+  // generate setters array expression elements
+  return _.map(this.importedModule, function (specs) {
+    if (!specs.length) {
+      return NULL_SETTER;
+    }
+
+    var expressionStatements = _.map(specs, function (spec) {
+      var right = SETTER_MODULE_NAMESPACE;
+      if (!spec.isBatch) {
+        right = t.memberExpression(right, spec.key);
+      }
+
+      return t.expressionStatement(
+        t.assignmentExpression("=", spec.variableName, right
+        )
+      );
+    });
+
+    return t.functionExpression(
+      null, [SETTER_MODULE_NAMESPACE], t.blockStatement(expressionStatements)
+    );
+  });
+};
+
+SystemFormatter.prototype.import = function (node) {
+  var MODULE_NAME = node.source.value;
+  this.importedModule[MODULE_NAME] = this.importedModule[MODULE_NAME] || [];
+};
+
+SystemFormatter.prototype.importSpecifier = function (specifier, node) {
+  var variableName = t.getSpecifierName(specifier);
+
+  // import foo from "foo";
+  if (specifier.default) {
+    specifier.id = DEFAULT_IDENTIFIER;
+  }
+
+  var MODULE_NAME = node.source.value;
+
+  this.importedModule[MODULE_NAME] = this.importedModule[MODULE_NAME] || [];
+
+  this.importedModule[MODULE_NAME].push({
+    variableName: variableName,
+    isBatch:      specifier.type === "ImportBatchSpecifier",
+    key:          specifier.id
+  });
+};
+
+SystemFormatter.prototype._export = function (name, identifier) {
+  this.exportedStatements.push(t.expressionStatement(
+    t.callExpression(this.exportIdentifier, [t.literal(name), identifier])
+  ));
+};
+
+SystemFormatter.prototype.export = function (node, nodes) {
+  var declar = node.declaration;
+  var variableName, identifier;
+
+  if (node.default) {
+    // export default foo
+    variableName = DEFAULT_IDENTIFIER.name;
+    if (t.isClass(declar) || t.isFunction(declar)) {
+      if (!declar.id) {
+        declar.id = this.file.generateUidIdentifier("anonymous");
+      }
+
+      nodes.push(t.toStatement(declar));
+      declar = declar.id;
+    }
+
+    identifier = declar;
+  } else if (t.isVariableDeclaration(declar)) {
+    // export var foo
+    variableName = declar.declarations[0].id.name;
+    identifier = declar.declarations[0].id;
+
+    nodes.push(declar);
+  } else {
+    // export function foo () {}
+    variableName = declar.id.name;
+    identifier = declar.id;
+
+    nodes.push(declar);
+  }
+
+  this._export(variableName, identifier);
+};
+
+SystemFormatter.prototype.exportSpecifier = function (specifier, node) {
+  var variableName = t.getSpecifierName(specifier);
+
+  if (node.source) {
+    if (t.isExportBatchSpecifier(specifier)) {
+      // export * from "foo";
+      var exportIdentifier = t.identifier("exports");
+      this.exportedStatements.push(
+        t.variableDeclaration("var", [
+          t.variableDeclarator(exportIdentifier, this.exportIdentifier)
+        ])
+      );
+
+      this.exportedStatements.push(util.template("exports-wildcard", {
+        OBJECT: t.identifier(node.source.value)
+      }, true));
+    } else {
+      // export { foo } from "test";
+      this._export(variableName.name, t.memberExpression(
+        t.identifier(node.source.value),
+        specifier.id
+      ));
+    }
+  } else {
+    // export { foo };
+    this._export(variableName.name, specifier.id);
+  }
+};

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

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

lib/6to5/transformation/transform.js

@@ -20,44 +20,55 @@ transform._ensureTransformerNames = function (type, keys) {
 transform.transformers = {};
 
 transform.moduleFormatters = {
-  common: require("./modules/common"),
-  ignore: require("./modules/ignore"),
-  amd:    require("./modules/amd"),
-  umd:    require("./modules/umd")
+  common:        require("./modules/common"),
+  commonInterop: require("./modules/common-interop"),
+  system:        require("./modules/system"),
+  ignore:        require("./modules/ignore"),
+  amd:           require("./modules/amd"),
+  umd:           require("./modules/umd")
 };
 
 _.each({
-  modules:                  require("./transformers/modules"),
-  propertyNameShorthand:    require("./transformers/property-name-shorthand"),
-  constants:                require("./transformers/constants"),
-  arrayComprehension:       require("./transformers/array-comprehension"),
-  generatorComprehension:   require("./transformers/generator-comprehension"),
-  arrowFunctions:           require("./transformers/arrow-functions"),
-  classes:                  require("./transformers/classes"),
+  modules:                   require("./transformers/es6-modules"),
+  propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
+  arrayComprehension:        require("./transformers/es7-array-comprehension"),
+  generatorComprehension:    require("./transformers/es7-generator-comprehension"),
+  arrowFunctions:            require("./transformers/es6-arrow-functions"),
+  classes:                   require("./transformers/es6-classes"),
 
-  _propertyLiterals:        require("./transformers/_property-literals"),
-  computedPropertyNames:    require("./transformers/computed-property-names"),
+  computedPropertyNames:     require("./transformers/es6-computed-property-names"),
 
-  spread:                   require("./transformers/spread"),
-  templateLiterals:         require("./transformers/template-literals"),
-  propertyMethodAssignment: require("./transformers/property-method-assignment"),
-  defaultParameters:        require("./transformers/default-parameters"),
-  restParameters:           require("./transformers/rest-parameters"),
-  destructuring:            require("./transformers/destructuring"),
-  letScoping:               require("./transformers/let-scoping"),
-  forOf:                    require("./transformers/for-of"),
-  unicodeRegex:             require("./transformers/unicode-regex"),
+  objectSpread:              require("./transformers/es7-object-spread"),
+  exponentiationOperator:    require("./transformers/es7-exponentiation-operator"),
+  spread:                    require("./transformers/es6-spread"),
+  templateLiterals:          require("./transformers/es6-template-literals"),
+  propertyMethodAssignment:  require("./transformers/es5-property-method-assignment"),
+  defaultParameters:         require("./transformers/es6-default-parameters"),
+  restParameters:            require("./transformers/es6-rest-parameters"),
+  destructuring:             require("./transformers/es6-destructuring"),
+  forOf:                     require("./transformers/es6-for-of"),
+  unicodeRegex:              require("./transformers/es6-unicode-regex"),
+  abstractReferences:        require("./transformers/es7-abstract-references"),
+  react:                     require("./transformers/react"),
 
-  react:                    require("./transformers/react"),
+  constants:                 require("./transformers/es6-constants"),
+  letScoping:                require("./transformers/es6-let-scoping"),
 
-  _aliasFunctions:          require("./transformers/_alias-functions"),
-  _blockHoist:              require("./transformers/_block-hoist"),
-  _declarations:            require("./transformers/_declarations"),
+  generators:                require("./transformers/es6-generators"),
 
-  generators:               require("./transformers/generators"),
-  useStrict:                require("./transformers/use-strict"),
+  // plyground
+  methodBinding:             require("./transformers/playground-method-binding"),
+  memoizationOperator:       require("./transformers/playground-memoization-operator"),
 
-  _moduleFormatter:         require("./transformers/_module-formatter")
+  _blockHoist:               require("./transformers/_block-hoist"),
+  _declarations:             require("./transformers/_declarations"),
+  _aliasFunctions:           require("./transformers/_alias-functions"),
+
+  useStrict:                 require("./transformers/use-strict"),
+
+  _propertyLiterals:         require("./transformers/_property-literals"),
+  _memberExpressioLiterals:  require("./transformers/_member-expression-literals"),
+  _moduleFormatter:          require("./transformers/_module-formatter")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });

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

@@ -6,11 +6,11 @@ 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
@@ -31,7 +31,7 @@ var go = function (getBody, node, file, scope) {
         return false;
       }
 
-      if (node._ignoreAliasFunctions) return;
+      if (node._ignoreAliasFunctions) return false;
 
       var getId;
 

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

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

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

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

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

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

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

@@ -4,9 +4,13 @@ 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 built = new Class(node, file, scope).run();
+
+  var declar = t.variableDeclaration("let", [
+    t.variableDeclarator(node.id, built)
   ]);
+  t.inheritsComments(declar, node);
+  return declar;
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
@@ -36,7 +40,7 @@ function Class(node, file, scope) {
   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;
 }
 
@@ -58,7 +62,7 @@ Class.prototype.run = function () {
       superClassArgument = superClassCallee = getMemberExpressionObject(superName);
     } else if (!t.isIdentifier(superName)) {
       superClassArgument = superName;
-      superClassCallee   = superName = t.identifier(file.generateUid("ref", this.scope));
+      superClassCallee   = superName = file.generateUidIdentifier("ref", this.scope);
     }
   }
 
@@ -254,6 +258,7 @@ Class.prototype.pushConstructor = function (method) {
 
   this.hasConstructor = true;
   t.inherits(construct, fn);
+  t.inheritsComments(construct, method);
 
   construct.defaults = fn.defaults;
   construct.params   = fn.params;

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

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

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

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

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

@@ -1,60 +1,92 @@
+// TODO: Clean up
+
 var t = require("../../types");
 var _ = require("lodash");
 
-var buildVariableAssign = function (kind, id, init) {
-  if (kind === false) {
+var buildVariableAssign = function (opts, id, init) {
+  var op = opts.operator;
+  if (t.isMemberExpression(id)) op = "=";
+
+  if (op) {
     return t.expressionStatement(t.assignmentExpression("=", id, init));
   } else {
-    return t.variableDeclaration(kind, [
+    return t.variableDeclaration(opts.kind, [
       t.variableDeclarator(id, init)
     ]);
   }
 };
 
-var push = function (kind, nodes, elem, parentId) {
+var push = function (opts, nodes, elem, parentId) {
   if (t.isObjectPattern(elem)) {
-    pushObjectPattern(kind, nodes, elem, parentId);
+    pushObjectPattern(opts, nodes, elem, parentId);
   } else if (t.isArrayPattern(elem)) {
-    pushArrayPattern(kind, nodes, elem, parentId);
-  } else if (t.isMemberExpression(elem)) {
-    nodes.push(buildVariableAssign(false, elem, parentId));
+    pushArrayPattern(opts, nodes, elem, parentId);
   } else {
-    nodes.push(buildVariableAssign(kind, elem, parentId));
+    nodes.push(buildVariableAssign(opts, elem, parentId));
   }
 };
 
-var pushObjectPattern = function (kind, nodes, pattern, parentId) {
-  _.each(pattern.properties, function (prop) {
-    var pattern2   = prop.value;
-    var patternId2 = t.memberExpression(parentId, prop.key);
+var pushObjectPattern = function (opts, nodes, pattern, parentId) {
+  _.each(pattern.properties, function (prop, i) {
+    if (t.isSpreadProperty(prop)) {
+        // get all the keys that appear in this object before the current spread
+        var keys = [];
+        _.each(pattern.properties, function (prop2, i2) {
+          if (i2 >= i) return false;
+          if (t.isSpreadProperty(prop2)) return;
 
-    if (t.isPattern(pattern2)) {
-      push(kind, nodes, pattern2, patternId2);
+          var key = prop2.key;
+          if (t.isIdentifier(key)) {
+            key = t.literal(prop2.key.name);
+          }
+          keys.push(key);
+        });
+        keys = t.arrayExpression(keys);
+
+        var value = t.callExpression(opts.file.addDeclaration("object-spread"), [parentId, keys]);
+        nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
-      nodes.push(buildVariableAssign(kind, pattern2, patternId2));
+      var pattern2   = prop.value;
+      var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
+
+      if (t.isPattern(pattern2)) {
+        push(opts, nodes, pattern2, patternId2);
+      } else {
+        nodes.push(buildVariableAssign(opts, pattern2, patternId2));
+      }
     }
   });
 };
 
-var pushArrayPattern = function (kind, nodes, pattern, parentId) {
+var pushArrayPattern = function (opts, nodes, pattern, parentId) {
+  var _parentId = opts.file.generateUidIdentifier("ref", opts.scope);
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(_parentId, opts.file.toArray(parentId))
+  ]));
+  parentId = _parentId;
+
   _.each(pattern.elements, function (elem, i) {
     if (!elem) return;
 
     var newPatternId;
 
     if (t.isSpreadElement(elem)) {
-      newPatternId = t.callExpression(t.memberExpression(parentId, t.identifier("slice")), [t.literal(i)]);
+      newPatternId = opts.file.toArray(parentId);
+
+      if (+i > 0) {
+        newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
+      }
+
       elem = elem.argument;
     } else {
       newPatternId = t.memberExpression(parentId, t.literal(i), true);
     }
 
-    push(kind, nodes, elem, newPatternId);
+    push(opts, nodes, elem, newPatternId);
   });
 };
 
 var pushPattern = function (opts) {
-  var kind = opts.kind;
   var nodes = opts.nodes;
   var pattern = opts.pattern;
   var parentId = opts.id;
@@ -62,7 +94,7 @@ var pushPattern = function (opts) {
   var scope = opts.scope;
 
   if (!t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = t.identifier(file.generateUid("ref", scope));
+    var key = file.generateUidIdentifier("ref", scope);
 
     nodes.push(t.variableDeclaration("var", [
       t.variableDeclarator(key, parentId)
@@ -71,7 +103,7 @@ var pushPattern = function (opts) {
     parentId = key;
   }
 
-  push(kind, nodes, pattern, parentId);
+  push(opts, nodes, pattern, parentId);
 };
 
 exports.ForInStatement =
@@ -82,14 +114,18 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   var pattern = declar.declarations[0].id;
   if (!t.isPattern(pattern)) return;
 
-  var key = t.identifier(file.generateUid("ref", scope));
+  var key = file.generateUidIdentifier("ref", scope);
   node.left = t.variableDeclaration(declar.kind, [
     t.variableDeclarator(key, null)
   ]);
 
   var nodes = [];
 
-  push(declar.kind, nodes, pattern, key);
+  push({
+    kind: declar.kind,
+    file: file,
+    scope: scope
+  }, nodes, pattern, key);
 
   t.ensureBlock(node);
 
@@ -106,7 +142,7 @@ exports.Function = function (node, parent, file, scope) {
     if (!t.isPattern(pattern)) return pattern;
 
     hasDestructuring = true;
-    var parentId = t.identifier(file.generateUid("ref", scope));
+    var parentId = file.generateUidIdentifier("ref", scope);
 
     pushPattern({
       kind:    "var",
@@ -136,16 +172,45 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
 
   var nodes = [];
 
-  var ref = t.identifier(file.generateUid("ref", scope));
+  var ref = file.generateUidIdentifier("ref", scope);
   nodes.push(t.variableDeclaration("var", [
     t.variableDeclarator(ref, expr.right)
   ]));
 
-  push(false, nodes, expr.left, ref);
+  push({
+    operator: expr.operator,
+    file: file,
+    scope: scope
+  }, nodes, expr.left, ref);
 
   return nodes;
 };
 
+exports.AssignmentExpression = function (node, parent, file, scope) {
+  if (parent.type === "ExpressionStatement") return;
+  if (!t.isPattern(node.left)) return;
+
+  var tempName = file.generateUid("temp", scope);
+  var ref = t.identifier(tempName);
+  scope.push({
+    key: tempName,
+    id: ref
+  });
+
+  var nodes = [];
+  nodes.push(t.assignmentExpression("=", ref, node.right));
+
+  push({
+    operator: node.operator,
+    file: file,
+    scope: scope
+  }, nodes, node.left, ref);
+
+  nodes.push(ref);
+
+  return t.toSequenceExpression(nodes, scope);
+};
+
 exports.VariableDeclaration = function (node, parent, file, scope) {
   if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
 
@@ -163,17 +228,18 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   _.each(node.declarations, function (declar) {
     var patternId = declar.init;
     var pattern   = declar.id;
+    var opts = {
+      kind:    node.kind,
+      nodes:   nodes,
+      pattern: pattern,
+      id:      patternId,
+      file:    file,
+      scope:   scope
+    };
     if (t.isPattern(pattern) && patternId) {
-      pushPattern({
-        kind:    node.kind,
-        nodes:   nodes,
-        pattern: pattern,
-        id:      patternId,
-        file:    file,
-        scope:   scope
-      });
+      pushPattern(opts);
     } else {
-      nodes.push(buildVariableAssign(node.kind, declar.id, declar.init));
+      nodes.push(buildVariableAssign(opts, declar.id, declar.init));
     }
   });
 
@@ -195,4 +261,3 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
 
   return nodes;
 };
-

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

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

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

@@ -0,0 +1,204 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var assert = require("assert");
+var loc    = require("../util").loc;
+var t      = require("../../../../types");
+
+exports.ParenthesizedExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(this.explodeExpression(path.get("expression")));
+};
+
+exports.MemberExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.memberExpression(
+    this.explodeExpression(path.get("object")),
+    expr.computed ? explodeViaTempVar(null, path.get("property")) : expr.property,
+    expr.computed
+  ));
+};
+
+exports.CallExpression = function (expr, path, explodeViaTempVar, finish) {
+  var oldCalleePath = path.get("callee");
+  var newCallee = this.explodeExpression(oldCalleePath);
+
+  // If the callee was not previously a MemberExpression, then the
+  // CallExpression was "unqualified," meaning its `this` object should
+  // be the global object. If the exploded expression has become a
+  // MemberExpression, then we need to force it to be unqualified by
+  // using the (0, object.property)(...) trick; otherwise, it will
+  // receive the object of the MemberExpression as its `this` object.
+  if (!t.isMemberExpression(oldCalleePath.node) && t.isMemberExpression(newCallee)) {
+    newCallee = t.sequenceExpression([
+      t.literal(0),
+      newCallee
+    ]);
+  }
+
+  return finish(t.callExpression(
+    newCallee,
+    path.get("arguments").map(function (argPath) {
+      return explodeViaTempVar(null, argPath);
+    })
+  ));
+};
+
+exports.NewExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.newExpression(
+    explodeViaTempVar(null, path.get("callee")),
+    path.get("arguments").map(function (argPath) {
+      return explodeViaTempVar(null, argPath);
+    })
+  ));
+};
+
+exports.ObjectExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.objectExpression(
+    path.get("properties").map(function (propPath) {
+      return t.property(
+        propPath.value.kind,
+        propPath.value.key,
+        explodeViaTempVar(null, propPath.get("value"))
+      );
+    })
+  ));
+};
+
+exports.ArrayExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.arrayExpression(
+    path.get("elements").map(function (elemPath) {
+      return explodeViaTempVar(null, elemPath);
+    })
+  ));
+};
+
+exports.SequenceExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
+  var lastIndex = expr.expressions.length - 1;
+  var self = this;
+  var result;
+
+  path.get("expressions").each(function (exprPath) {
+    if (exprPath.name === lastIndex) {
+      result = self.explodeExpression(exprPath, ignoreResult);
+    } else {
+      self.explodeExpression(exprPath, true);
+    }
+  });
+
+  return result;
+};
+
+exports.LogicalExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
+  var after = loc();
+  var result;
+
+  if (!ignoreResult) {
+    result = this.makeTempVar();
+  }
+
+  var left = explodeViaTempVar(result, path.get("left"));
+
+  if (expr.operator === "&&") {
+    this.jumpIfNot(left, after);
+  } else {
+    assert.strictEqual(expr.operator, "||");
+    this.jumpIf(left, after);
+  }
+
+  explodeViaTempVar(result, path.get("right"), ignoreResult);
+
+  this.mark(after);
+
+  return result;
+};
+
+exports.ConditionalExpression = function (expr, path, explodeViaTempVar, finish, ignoreResult) {
+  var elseLoc = loc();
+  var after = loc();
+  var test = this.explodeExpression(path.get("test"));
+  var result;
+
+  this.jumpIfNot(test, elseLoc);
+
+  if (!ignoreResult) {
+    result = this.makeTempVar();
+  }
+
+  explodeViaTempVar(result, path.get("consequent"), ignoreResult);
+  this.jump(after);
+
+  this.mark(elseLoc);
+  explodeViaTempVar(result, path.get("alternate"), ignoreResult);
+
+  this.mark(after);
+
+  return result;
+};
+
+exports.UnaryExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.unaryExpression(
+    expr.operator,
+    // Can't (and don't need to) break up the syntax of the argument.
+    // Think about delete a[b].
+    this.explodeExpression(path.get("argument")),
+    !!expr.prefix
+  ));
+};
+
+exports.BinaryExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.binaryExpression(
+    expr.operator,
+    explodeViaTempVar(null, path.get("left")),
+    explodeViaTempVar(null, path.get("right"))
+  ));
+};
+
+exports.AssignmentExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.assignmentExpression(
+    expr.operator,
+    this.explodeExpression(path.get("left")),
+    this.explodeExpression(path.get("right"))
+  ));
+};
+
+exports.UpdateExpression = function (expr, path, explodeViaTempVar, finish) {
+  return finish(t.updateExpression(
+    expr.operator,
+    this.explodeExpression(path.get("argument")),
+    expr.prefix
+  ));
+};
+
+exports.YieldExpression = function (expr, path) {
+  var after = loc();
+  var arg = expr.argument && this.explodeExpression(path.get("argument"));
+  var result;
+
+  if (arg && expr.delegate) {
+    result = this.makeTempVar();
+
+    this.emit(t.returnStatement(t.callExpression(
+      this.contextProperty("delegateYield"), [
+        arg,
+        t.literal(result.property.name),
+        after
+      ]
+    )));
+
+    this.mark(after);
+
+    return result;
+  }
+
+  this.emitAssign(this.contextProperty("next"), after);
+  this.emit(t.returnStatement(arg || null));
+  this.mark(after);
+
+  return this.contextProperty("sent");
+};

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

@@ -0,0 +1,334 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var assert = require("assert");
+var types  = require("ast-types");
+var leap   = require("../leap");
+var util   = require("../util");
+var t      = require("../../../../types");
+
+var runtimeKeysMethod = util.runtimeProperty("keys");
+var loc               = util.loc;
+
+exports.ExpressionStatement = function (path) {
+  this.explodeExpression(path.get("expression"), true);
+};
+
+exports.LabeledStatement = function (path, stmt) {
+  this.explodeStatement(path.get("body"), stmt.label);
+};
+
+exports.WhileStatement = function (path, stmt, labelId) {
+  var before = loc();
+  var after = loc();
+
+  this.mark(before);
+  this.jumpIfNot(this.explodeExpression(path.get("test")), after);
+  this.leapManager.withEntry(
+    new leap.LoopEntry(after, before, labelId),
+    function () { this.explodeStatement(path.get("body")); }
+  );
+  this.jump(before);
+  this.mark(after);
+};
+
+exports.DoWhileStatement = function (path, stmt, labelId) {
+  var first = loc();
+  var test = loc();
+  var after = loc();
+
+  this.mark(first);
+  this.leapManager.withEntry(
+    new leap.LoopEntry(after, test, labelId),
+    function () { this.explode(path.get("body")); }
+  );
+  this.mark(test);
+  this.jumpIf(this.explodeExpression(path.get("test")), first);
+  this.mark(after);
+};
+
+exports.ForStatement = function (path, stmt, labelId) {
+  var head = loc();
+  var update = loc();
+  var after = loc();
+
+  if (stmt.init) {
+    // We pass true here to indicate that if stmt.init is an expression
+    // then we do not care about its result.
+    this.explode(path.get("init"), true);
+  }
+
+  this.mark(head);
+
+  if (stmt.test) {
+    this.jumpIfNot(this.explodeExpression(path.get("test")), after);
+  } else {
+    // No test means continue unconditionally.
+  }
+
+  this.leapManager.withEntry(
+    new leap.LoopEntry(after, update, labelId),
+    function () { this.explodeStatement(path.get("body")); }
+  );
+
+  this.mark(update);
+
+  if (stmt.update) {
+    // We pass true here to indicate that if stmt.update is an
+    // expression then we do not care about its result.
+    this.explode(path.get("update"), true);
+  }
+
+  this.jump(head);
+
+  this.mark(after);
+};
+
+exports.ForInStatement = function (path, stmt, labelId) {
+  t.assertIdentifier(stmt.left);
+
+  var head = loc();
+  var after = loc();
+
+  var keyIterNextFn = this.makeTempVar();
+  this.emitAssign(
+    keyIterNextFn,
+    t.callExpression(
+      runtimeKeysMethod,
+      [this.explodeExpression(path.get("right"))]
+    )
+  );
+
+  this.mark(head);
+
+  var keyInfoTmpVar = this.makeTempVar();
+  this.jumpIf(
+    t.memberExpression(
+      t.assignmentExpression(
+        "=",
+        keyInfoTmpVar,
+        t.callExpression(keyIterNextFn, [])
+      ),
+      t.identifier("done"),
+      false
+    ),
+    after
+  );
+
+  this.emitAssign(
+    stmt.left,
+    t.memberExpression(
+      keyInfoTmpVar,
+      t.identifier("value"),
+      false
+    )
+  );
+
+  this.leapManager.withEntry(
+    new leap.LoopEntry(after, head, labelId),
+    function () { this.explodeStatement(path.get("body")); }
+  );
+
+  this.jump(head);
+
+  this.mark(after);
+};
+
+exports.BreakStatement = function (path, stmt) {
+  this.emitAbruptCompletion({
+    type: "break",
+    target: this.leapManager.getBreakLoc(stmt.label)
+  });
+};
+
+exports.ContinueStatement = function (path, stmt) {
+  this.emitAbruptCompletion({
+    type: "continue",
+    target: this.leapManager.getContinueLoc(stmt.label)
+  });
+};
+
+exports.SwitchStatement = function (path, stmt) {
+  // Always save the discriminant into a temporary variable in case the
+  // test expressions overwrite values like context.sent.
+  var disc = this.emitAssign(
+    this.makeTempVar(),
+    this.explodeExpression(path.get("discriminant"))
+  );
+
+  var after = loc();
+  var defaultLoc = loc();
+  var condition = defaultLoc;
+  var caseLocs = [];
+  var self = this;
+
+  // If there are no cases, .cases might be undefined.
+  var cases = stmt.cases || [];
+
+  for (var i = cases.length - 1; i >= 0; --i) {
+    var c = cases[i];
+    t.assertSwitchCase(c);
+
+    if (c.test) {
+      condition = t.conditionalExpression(
+        t.binaryExpression("===", disc, c.test),
+        caseLocs[i] = loc(),
+        condition
+      );
+    } else {
+      caseLocs[i] = defaultLoc;
+    }
+  }
+
+  this.jump(this.explodeExpression(
+    new types.NodePath(condition, path, "discriminant")
+  ));
+
+  this.leapManager.withEntry(
+    new leap.SwitchEntry(after),
+    function () {
+      path.get("cases").each(function (casePath) {
+        var i = casePath.name;
+
+        self.mark(caseLocs[i]);
+
+        casePath.get("consequent").each(
+          self.explodeStatement,
+          self
+        );
+      });
+    }
+  );
+
+  this.mark(after);
+  if (defaultLoc.value === -1) {
+    this.mark(defaultLoc);
+    assert.strictEqual(after.value, defaultLoc.value);
+  }
+};
+
+exports.IfStatement = function (path, stmt) {
+  var elseLoc = stmt.alternate && loc();
+  var after = loc();
+
+  this.jumpIfNot(
+    this.explodeExpression(path.get("test")),
+    elseLoc || after
+  );
+
+  this.explodeStatement(path.get("consequent"));
+
+  if (elseLoc) {
+    this.jump(after);
+    this.mark(elseLoc);
+    this.explodeStatement(path.get("alternate"));
+  }
+
+  this.mark(after);
+};
+
+exports.ReturnStatement = function (path) {
+  this.emitAbruptCompletion({
+    type: "return",
+    value: this.explodeExpression(path.get("argument"))
+  });
+};
+
+exports.TryStatement = function (path, stmt) {
+  var after = loc();
+  var self = this;
+
+  var handler = stmt.handler;
+  if (!handler && stmt.handlers) {
+    handler = stmt.handlers[0] || null;
+  }
+
+  var catchLoc = handler && loc();
+  var catchEntry = catchLoc && new leap.CatchEntry(
+    catchLoc,
+    handler.param
+  );
+
+  var finallyLoc = stmt.finalizer && loc();
+  var finallyEntry = finallyLoc && new leap.FinallyEntry(finallyLoc);
+
+  var tryEntry = new leap.TryEntry(
+    this.getUnmarkedCurrentLoc(),
+    catchEntry,
+    finallyEntry
+  );
+
+  this.tryEntries.push(tryEntry);
+  this.updateContextPrevLoc(tryEntry.firstLoc);
+
+  this.leapManager.withEntry(tryEntry, function () {
+    this.explodeStatement(path.get("block"));
+
+    if (catchLoc) {
+      if (finallyLoc) {
+        // If we have both a catch block and a finally block, then
+        // because we emit the catch block first, we need to jump over
+        // it to the finally block.
+        this.jump(finallyLoc);
+
+      } else {
+        // If there is no finally block, then we need to jump over the
+        // catch block to the fall-through location.
+        this.jump(after);
+      }
+
+      this.updateContextPrevLoc(self.mark(catchLoc));
+
+      var bodyPath = path.get("handler", "body");
+      var safeParam = this.makeTempVar();
+      this.clearPendingException(tryEntry.firstLoc, safeParam);
+
+      var catchScope = bodyPath.scope;
+      var catchParamName = handler.param.name;
+      t.assertCatchClause(catchScope.node);
+      assert.strictEqual(catchScope.lookup(catchParamName), catchScope);
+
+      types.visit(bodyPath, {
+        visitIdentifier: function (path) {
+          if (path.value.name === catchParamName &&
+              path.scope.lookup(catchParamName) === catchScope) {
+            return safeParam;
+          }
+          this.traverse(path);
+        }
+      });
+
+      this.leapManager.withEntry(catchEntry, function () {
+        this.explodeStatement(bodyPath);
+      });
+    }
+
+    if (finallyLoc) {
+      this.updateContextPrevLoc(this.mark(finallyLoc));
+
+      this.leapManager.withEntry(finallyEntry, function () {
+        this.explodeStatement(path.get("finalizer"));
+      });
+
+      this.emit(t.callExpression(
+        this.contextProperty("finish"),
+        [finallyEntry.firstLoc]
+      ));
+    }
+  });
+
+  this.mark(after);
+};
+
+exports.ThrowStatement = function (path) {
+  this.emit(t.throwStatement(
+    this.explodeExpression(path.get("argument"))
+  ));
+};

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

@@ -0,0 +1,611 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+exports.Emitter = Emitter;
+
+var explodeExpressions = require("./explode-expressions");
+var explodeStatements  = require("./explode-statements");
+var assert             = require("assert");
+var types              = require("ast-types");
+var leap               = require("../leap");
+var meta               = require("../meta");
+var util               = require("../util");
+var t                  = require("../../../../types");
+var _                  = require("lodash");
+
+var loc = util.loc;
+var n   = types.namedTypes;
+
+function Emitter(contextId) {
+  assert.ok(this instanceof Emitter);
+  t.assertIdentifier(contextId);
+
+  // In order to make sure the context object does not collide with
+  // anything in the local scope, we might have to rename it, so we
+  // refer to it symbolically instead of just assuming that it will be
+  // called "context".
+  this.contextId = contextId;
+
+  // An append-only list of Statements that grows each time this.emit is
+  // called.
+  this.listing = [];
+
+  // A sparse array whose keys correspond to locations in this.listing
+  // that have been marked as branch/jump targets.
+  this.marked = [true];
+
+  // The last location will be marked when this.getDispatchLoop is
+  // called.
+  this.finalLoc = loc();
+
+  // A list of all leap.TryEntry statements emitted.
+  this.tryEntries = [];
+
+  // Each time we evaluate the body of a loop, we tell this.leapManager
+  // to enter a nested loop context that determines the meaning of break
+  // and continue statements therein.
+  this.leapManager = new leap.LeapManager(this);
+}
+
+// Sets the exact value of the given location to the offset of the next
+// Statement emitted.
+Emitter.prototype.mark = function (loc) {
+  t.assertLiteral(loc);
+  var index = this.listing.length;
+  if (loc.value === -1) {
+    loc.value = index;
+  } else {
+    // Locations can be marked redundantly, but their values cannot change
+    // once set the first time.
+    assert.strictEqual(loc.value, index);
+  }
+  this.marked[index] = true;
+  return loc;
+};
+
+Emitter.prototype.emit = function (node) {
+  if (t.isExpression(node)) node = t.expressionStatement(node);
+  t.assertStatement(node);
+  this.listing.push(node);
+};
+
+// Shorthand for emitting assignment statements. This will come in handy
+// for assignments to temporary variables.
+Emitter.prototype.emitAssign = function (lhs, rhs) {
+  this.emit(this.assign(lhs, rhs));
+  return lhs;
+};
+
+// Shorthand for an assignment statement.
+Emitter.prototype.assign = function (lhs, rhs) {
+  return t.expressionStatement(
+    t.assignmentExpression("=", lhs, rhs));
+};
+
+// Convenience function for generating expressions like context.next,
+// context.sent, and context.rval.
+Emitter.prototype.contextProperty = function (name, computed) {
+  return t.memberExpression(
+    this.contextId,
+    computed ? t.literal(name) : t.identifier(name),
+    !!computed
+  );
+};
+
+var volatileContextPropertyNames = {
+  prev: true,
+  next: true,
+  sent: true,
+  rval: true
+};
+
+// A "volatile" context property is a MemberExpression like context.sent
+// that should probably be stored in a temporary variable when there's a
+// possibility the property will get overwritten.
+Emitter.prototype.isVolatileContextProperty = function (expr) {
+  if (t.isMemberExpression(expr)) {
+    if (expr.computed) {
+      // If it's a computed property such as context[couldBeAnything],
+      // assume the worst in terms of volatility.
+      return true;
+    }
+
+    if (t.isIdentifier(expr.object) &&
+        t.isIdentifier(expr.property) &&
+        expr.object.name === this.contextId.name &&
+        _.has(volatileContextPropertyNames, expr.property.name)) {
+      return true;
+    }
+  }
+
+  return false;
+};
+
+// Shorthand for setting context.rval and jumping to `context.stop()`.
+Emitter.prototype.stop = function (rval) {
+  if (rval) {
+    this.setReturnValue(rval);
+  }
+
+  this.jump(this.finalLoc);
+};
+
+Emitter.prototype.setReturnValue = function (valuePath) {
+  t.assertExpression(valuePath.value);
+
+  this.emitAssign(
+    this.contextProperty("rval"),
+    this.explodeExpression(valuePath)
+  );
+};
+
+Emitter.prototype.clearPendingException = function (tryLoc, assignee) {
+  t.assertLiteral(tryLoc);
+
+  var catchCall = t.callExpression(
+    this.contextProperty("catch", true),
+    [tryLoc]
+  );
+
+  if (assignee) {
+    this.emitAssign(assignee, catchCall);
+  } else {
+    this.emit(catchCall);
+  }
+};
+
+// Emits code for an unconditional jump to the given location, even if the
+// exact value of the location is not yet known.
+Emitter.prototype.jump = function (toLoc) {
+  this.emitAssign(this.contextProperty("next"), toLoc);
+  this.emit(t.breakStatement());
+};
+
+// Conditional jump.
+Emitter.prototype.jumpIf = function (test, toLoc) {
+  t.assertExpression(test);
+  t.assertLiteral(toLoc);
+
+  this.emit(t.ifStatement(
+    test,
+    t.blockStatement([
+      this.assign(this.contextProperty("next"), toLoc),
+      t.breakStatement()
+    ])
+  ));
+};
+
+// Conditional jump, with the condition negated.
+Emitter.prototype.jumpIfNot = function (test, toLoc) {
+  t.assertExpression(test);
+  t.assertLiteral(toLoc);
+
+  var negatedTest;
+  if (t.isUnaryExpression(test) && test.operator === "!") {
+    // Avoid double negation.
+    negatedTest = test.argument;
+  } else {
+    negatedTest = t.unaryExpression("!", test);
+  }
+
+  this.emit(t.ifStatement(
+    negatedTest,
+    t.blockStatement([
+      this.assign(this.contextProperty("next"), toLoc),
+      t.breakStatement()
+    ])
+  ));
+};
+
+// Returns a unique MemberExpression that can be used to store and
+// retrieve temporary values. Since the object of the member expression is
+// the context object, which is presumed to coexist peacefully with all
+// other local variables, and since we just increment `nextTempId`
+// monotonically, uniqueness is assured.
+var nextTempId = 0;
+Emitter.prototype.makeTempVar = function () {
+  return this.contextProperty("t" + nextTempId++);
+};
+
+Emitter.prototype.getContextFunction = function (id) {
+  var node = t.functionExpression(
+    id || null,
+    [this.contextId],
+    t.blockStatement([this.getDispatchLoop()]),
+    false, // Not a generator anymore!
+    false // Nor an expression.
+  );
+  node._aliasFunction = true;
+  return node;
+};
+
+// Turns this.listing into a loop of the form
+//
+//   while (1) switch (context.next) {
+//   case 0:
+//   ...
+//   case n:
+//     return context.stop();
+//   }
+//
+// Each marked location in this.listing will correspond to one generated
+// case statement.
+Emitter.prototype.getDispatchLoop = function () {
+  var self = this;
+  var cases = [];
+  var current;
+
+  // If we encounter a break, continue, or return statement in a switch
+  // case, we can skip the rest of the statements until the next case.
+  var alreadyEnded = false;
+
+  self.listing.forEach(function (stmt, i) {
+    if (self.marked.hasOwnProperty(i)) {
+      cases.push(t.switchCase(t.literal(i), current = []));
+      alreadyEnded = false;
+    }
+
+    if (!alreadyEnded) {
+      current.push(stmt);
+      if (isSwitchCaseEnder(stmt))
+        alreadyEnded = true;
+    }
+  });
+
+  // Now that we know how many statements there will be in this.listing,
+  // we can finally resolve this.finalLoc.value.
+  this.finalLoc.value = this.listing.length;
+
+  cases.push(
+    t.switchCase(this.finalLoc, [
+      // Intentionally fall through to the "end" case...
+    ]),
+
+    // So that the runtime can jump to the final location without having
+    // to know its offset, we provide the "end" case as a synonym.
+    t.switchCase(t.literal("end"), [
+      // This will check/clear both context.thrown and context.rval.
+      t.returnStatement(
+        t.callExpression(this.contextProperty("stop"), [])
+      )
+    ])
+  );
+
+  return t.whileStatement(
+    t.literal(true),
+    t.switchStatement(
+      t.assignmentExpression(
+        "=",
+        this.contextProperty("prev"),
+        this.contextProperty("next")
+      ),
+      cases
+    )
+  );
+};
+
+// See comment above re: alreadyEnded.
+function isSwitchCaseEnder(stmt) {
+  return t.isBreakStatement(stmt) ||
+         t.isContinueStatement(stmt) ||
+         t.isReturnStatement(stmt) ||
+         t.isThrowStatement(stmt);
+}
+
+Emitter.prototype.getTryEntryList = function () {
+  if (this.tryEntries.length === 0) {
+    // To avoid adding a needless [] to the majority of runtime.wrap
+    // argument lists, force the caller to handle this case specially.
+    return null;
+  }
+
+  var lastLocValue = 0;
+
+  return t.arrayExpression(
+    this.tryEntries.map(function (tryEntry) {
+      var thisLocValue = tryEntry.firstLoc.value;
+      assert.ok(thisLocValue >= lastLocValue, "try entries out of order");
+      lastLocValue = thisLocValue;
+
+      var ce = tryEntry.catchEntry;
+      var fe = tryEntry.finallyEntry;
+
+      var triple = [
+        tryEntry.firstLoc,
+        // The null here makes a hole in the array.
+        ce ? ce.firstLoc : null
+      ];
+
+      if (fe) {
+        triple[2] = fe.firstLoc;
+      }
+
+      return t.arrayExpression(triple);
+    })
+  );
+};
+
+// All side effects must be realized in order.
+
+// If any subexpression harbors a leap, all subexpressions must be
+// neutered of side effects.
+
+// No destructive modification of AST nodes.
+
+Emitter.prototype.explode = function (path, ignoreResult) {
+  assert.ok(path instanceof types.NodePath);
+
+  var node = path.value;
+  var self = this;
+
+  n.Node.check(node);
+
+  if (t.isStatement(node))
+    return self.explodeStatement(path);
+
+  if (t.isExpression(node))
+    return self.explodeExpression(path, ignoreResult);
+
+  if (t.isDeclaration(node))
+    throw getDeclError(node);
+
+  switch (node.type) {
+  case "Program":
+    return path.get("body").map(self.explodeStatement, self);
+
+  case "VariableDeclarator":
+    throw getDeclError(node);
+
+  // These node types should be handled by their parent nodes
+  // (ObjectExpression, SwitchStatement, and TryStatement, respectively).
+  case "Property":
+  case "SwitchCase":
+  case "CatchClause":
+    throw new Error(node.type + " nodes should be handled by their parents");
+
+  default:
+    throw new Error("unknown Node of type " + JSON.stringify(node.type));
+  }
+};
+
+function getDeclError(node) {
+  return new Error(
+    "all declarations should have been transformed into " +
+    "assignments before the Exploder began its work: " +
+    JSON.stringify(node));
+}
+
+Emitter.prototype.explodeStatement = function (path, labelId) {
+  assert.ok(path instanceof types.NodePath);
+
+  var stmt = path.value;
+  var self = this;
+
+  t.assertStatement(stmt);
+
+  if (labelId) {
+    t.assertIdentifier(labelId);
+  } else {
+    labelId = null;
+  }
+
+  // Explode BlockStatement nodes even if they do not contain a yield,
+  // because we don't want or need the curly braces.
+  if (t.isBlockStatement(stmt)) {
+    return path.get("body").each(
+      self.explodeStatement,
+      self
+    );
+  }
+
+  if (!meta.containsLeap(stmt)) {
+    // Technically we should be able to avoid emitting the statement
+    // altogether if !meta.hasSideEffects(stmt), but that leads to
+    // confusing generated code (for instance, `while (true) {}` just
+    // disappears) and is probably a more appropriate job for a dedicated
+    // dead code elimination pass.
+    self.emit(stmt);
+    return;
+  }
+
+  var fn = explodeStatements[stmt.type];
+  if (fn) {
+    fn.call(this, path, stmt, labelId);
+  } else {
+    throw new Error("unknown Statement of type " + JSON.stringify(stmt.type));
+  }
+};
+
+Emitter.prototype.emitAbruptCompletion = function (record) {
+  if (!isValidCompletion(record)) {
+    assert.ok(
+      false,
+      "invalid completion record: " + JSON.stringify(record)
+    );
+  }
+
+  assert.notStrictEqual(
+    record.type, "normal",
+    "normal completions are not abrupt"
+  );
+
+  var abruptArgs = [t.literal(record.type)];
+
+  if (record.type === "break" || record.type === "continue") {
+    t.assertLiteral(record.target);
+    abruptArgs[1] = record.target;
+  } else if (record.type === "return" || record.type === "throw") {
+    if (record.value) {
+      t.assertExpression(record.value);
+      abruptArgs[1] = record.value;
+    }
+  }
+
+  this.emit(
+    t.returnStatement(
+      t.callExpression(
+        this.contextProperty("abrupt"),
+        abruptArgs
+      )
+    )
+  );
+};
+
+function isValidCompletion(record) {
+  var type = record.type;
+
+  if (type === "normal") {
+    return !_.has(record, "target");
+  }
+
+  if (type === "break" || type === "continue") {
+    return !_.has(record, "value") && t.isLiteral(record.target);
+  }
+
+  if (type === "return" || type === "throw") {
+    return _.has(record, "value") && !_.has(record, "target");
+  }
+
+  return false;
+}
+
+// Not all offsets into emitter.listing are potential jump targets. For
+// example, execution typically falls into the beginning of a try block
+// without jumping directly there. This method returns the current offset
+// without marking it, so that a switch case will not necessarily be
+// generated for this offset (I say "not necessarily" because the same
+// location might end up being marked in the process of emitting other
+// statements). There's no logical harm in marking such locations as jump
+// targets, but minimizing the number of switch cases keeps the generated
+// code shorter.
+Emitter.prototype.getUnmarkedCurrentLoc = function () {
+  return t.literal(this.listing.length);
+};
+
+// The context.prev property takes the value of context.next whenever we
+// evaluate the switch statement discriminant, which is generally good
+// enough for tracking the last location we jumped to, but sometimes
+// context.prev needs to be more precise, such as when we fall
+// successfully out of a try block and into a finally block without
+// jumping. This method exists to update context.prev to the freshest
+// available location. If we were implementing a full interpreter, we
+// would know the location of the current instruction with complete
+// precision at all times, but we don't have that luxury here, as it would
+// be costly and verbose to set context.prev before every statement.
+Emitter.prototype.updateContextPrevLoc = function (loc) {
+  if (loc) {
+    t.assertLiteral(loc);
+
+    if (loc.value === -1) {
+      // If an uninitialized location literal was passed in, set its value
+      // to the current this.listing.length.
+      loc.value = this.listing.length;
+    } else {
+      // Otherwise assert that the location matches the current offset.
+      assert.strictEqual(loc.value, this.listing.length);
+    }
+
+  } else {
+    loc = this.getUnmarkedCurrentLoc();
+  }
+
+  // Make sure context.prev is up to date in case we fell into this try
+  // statement without jumping to it. TODO Consider avoiding this
+  // assignment when we know control must have jumped here.
+  this.emitAssign(this.contextProperty("prev"), loc);
+};
+
+Emitter.prototype.explodeExpression = function (path, ignoreResult) {
+  assert.ok(path instanceof types.NodePath);
+
+  var expr = path.value;
+  if (expr) {
+    t.assertExpression(expr);
+  } else {
+    return expr;
+  }
+
+  var self = this;
+
+  function finish(expr) {
+    t.assertExpression(expr);
+    if (ignoreResult) {
+      self.emit(expr);
+    } else {
+      return expr;
+    }
+  }
+
+  // If the expression does not contain a leap, then we either emit the
+  // expression as a standalone statement or return it whole.
+  if (!meta.containsLeap(expr)) {
+    return finish(expr);
+  }
+
+  // If any child contains a leap (such as a yield or labeled continue or
+  // break statement), then any sibling subexpressions will almost
+  // certainly have to be exploded in order to maintain the order of their
+  // side effects relative to the leaping child(ren).
+  var hasLeapingChildren = meta.containsLeap.onlyChildren(expr);
+
+  // In order to save the rest of explodeExpression from a combinatorial
+  // trainwreck of special cases, explodeViaTempVar is responsible for
+  // deciding when a subexpression needs to be "exploded," which is my
+  // very technical term for emitting the subexpression as an assignment
+  // to a temporary variable and the substituting the temporary variable
+  // for the original subexpression. Think of exploded view diagrams, not
+  // Michael Bay movies. The point of exploding subexpressions is to
+  // control the precise order in which the generated code realizes the
+  // side effects of those subexpressions.
+  function explodeViaTempVar(tempVar, childPath, ignoreChildResult) {
+    assert.ok(childPath instanceof types.NodePath);
+
+    assert.ok(
+      !ignoreChildResult || !tempVar,
+      "Ignoring the result of a child expression but forcing it to " +
+        "be assigned to a temporary variable?"
+    );
+
+    var result = self.explodeExpression(childPath, ignoreChildResult);
+
+    if (ignoreChildResult) {
+      // Side effects already emitted above.
+
+    } else if (tempVar || (hasLeapingChildren &&
+                           (self.isVolatileContextProperty(result) ||
+                            meta.hasSideEffects(result)))) {
+      // If tempVar was provided, then the result will always be assigned
+      // to it, even if the result does not otherwise need to be assigned
+      // to a temporary variable.  When no tempVar is provided, we have
+      // the flexibility to decide whether a temporary variable is really
+      // necessary.  In general, temporary assignment is required only
+      // when some other child contains a leap and the child in question
+      // is a context property like $ctx.sent that might get overwritten
+      // or an expression with side effects that need to occur in proper
+      // sequence relative to the leap.
+      result = self.emitAssign(
+        tempVar || self.makeTempVar(),
+        result
+      );
+    }
+    return result;
+  }
+
+  // If ignoreResult is true, then we must take full responsibility for
+  // emitting the expression with all its side effects, and we should not
+  // return a result.
+
+  var fn = explodeExpressions[expr.type];
+  if (fn) {
+    return fn.call(this, expr, path, explodeViaTempVar, finish, ignoreResult);
+  } else {
+    throw new Error("unknown Expression of type " + JSON.stringify(expr.type));
+  }
+};

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

@@ -0,0 +1,151 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.githut.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var assert = require("assert");
+var types  = require("ast-types");
+var t      = require("../../../types");
+var _      = require("lodash");
+
+// The hoist function takes a FunctionExpression or FunctionDeclaration
+// and replaces any Declaration nodes in its body with assignments, then
+// returns a VariableDeclaration containing just the names of the removed
+// declarations.
+exports.hoist = function (funPath) {
+  assert.ok(funPath instanceof types.NodePath);
+  t.assertFunction(funPath.value);
+
+  var vars = {};
+
+  function varDeclToExpr(vdec, includeIdentifiers) {
+    t.assertVariableDeclaration(vdec);
+    var exprs = [];
+
+    vdec.declarations.forEach(function (dec) {
+      vars[dec.id.name] = dec.id;
+
+      if (dec.init) {
+        exprs.push(t.assignmentExpression(
+          "=", dec.id, dec.init
+        ));
+      } else if (includeIdentifiers) {
+        exprs.push(dec.id);
+      }
+    });
+
+    if (exprs.length === 0)
+      return null;
+
+    if (exprs.length === 1)
+      return exprs[0];
+
+    return t.sequenceExpression(exprs);
+  }
+
+  types.visit(funPath.get("body"), {
+    visitVariableDeclaration: function (path) {
+      var expr = varDeclToExpr(path.value, false);
+      if (expr === null) {
+        path.replace();
+      } else {
+        // We don't need to traverse this expression any further because
+        // there can't be any new declarations inside an expression.
+        return t.expressionStatement(expr);
+      }
+
+      // Since the original node has been either removed or replaced,
+      // avoid traversing it any further.
+      return false;
+    },
+
+    visitForStatement: function (path) {
+      var init = path.value.init;
+      if (t.isVariableDeclaration(init)) {
+        path.get("init").replace(varDeclToExpr(init, false));
+      }
+      this.traverse(path);
+    },
+
+    visitForInStatement: function (path) {
+      var left = path.value.left;
+      if (t.isVariableDeclaration(left)) {
+        path.get("left").replace(varDeclToExpr(left, true));
+      }
+      this.traverse(path);
+    },
+
+    visitFunctionDeclaration: function (path) {
+      var node = path.value;
+      vars[node.id.name] = node.id;
+
+      var assignment = t.expressionStatement(
+        t.assignmentExpression(
+          "=",
+          node.id,
+          t.functionExpression(
+            node.id,
+            node.params,
+            node.body,
+            node.generator,
+            node.expression
+          )
+        )
+      );
+
+      if (t.isBlockStatement(path.parent.node)) {
+        // Insert the assignment form before the first statement in the
+        // enclosing block.
+        path.parent.get("body").unshift(assignment);
+
+        // Remove the function declaration now that we've inserted the
+        // equivalent assignment form at the beginning of the block.
+        path.replace();
+
+      } else {
+        // If the parent node is not a block statement, then we can just
+        // replace the declaration with the equivalent assignment form
+        // without worrying about hoisting it.
+        path.replace(assignment);
+      }
+
+      // Don't hoist variables out of inner functions.
+      return false;
+    },
+
+    visitFunctionExpression: function () {
+      // Don't descend into nested function expressions.
+      return false;
+    }
+  });
+
+  var paramNames = {};
+  funPath.get("params").each(function (paramPath) {
+    var param = paramPath.value;
+    if (t.isIdentifier(param)) {
+      paramNames[param.name] = param;
+    } else {
+      // Variables declared by destructuring parameter patterns will be
+      // harmlessly re-declared.
+    }
+  });
+
+  var declarations = [];
+
+  Object.keys(vars).forEach(function (name) {
+    if (!_.has(paramNames, name)) {
+      declarations.push(t.variableDeclarator(vars[name], null));
+    }
+  });
+
+  if (declarations.length === 0) {
+    return null; // Be sure to handle this case!
+  }
+
+  return t.variableDeclaration("var", declarations);
+};

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

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

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

@@ -0,0 +1,163 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+exports.FunctionEntry = FunctionEntry;
+exports.FinallyEntry  = FinallyEntry;
+exports.SwitchEntry   = SwitchEntry;
+exports.LeapManager   = LeapManager;
+exports.CatchEntry    = CatchEntry;
+exports.LoopEntry     = LoopEntry;
+exports.TryEntry      = TryEntry;
+
+var assert = require("assert");
+var util   = require("util");
+var t      = require("../../../types");
+
+var inherits = util.inherits;
+
+function Entry() {
+  assert.ok(this instanceof Entry);
+}
+
+function FunctionEntry(returnLoc) {
+  Entry.call(this);
+
+  t.assertLiteral(returnLoc);
+
+  this.returnLoc = returnLoc;
+}
+
+inherits(FunctionEntry, Entry);
+
+function LoopEntry(breakLoc, continueLoc, label) {
+  Entry.call(this);
+
+  t.assertLiteral(breakLoc);
+  t.assertLiteral(continueLoc);
+
+  if (label) {
+    t.assertIdentifier(label);
+  } else {
+    label = null;
+  }
+
+  this.breakLoc = breakLoc;
+  this.continueLoc = continueLoc;
+  this.label = label;
+}
+
+inherits(LoopEntry, Entry);
+
+function SwitchEntry(breakLoc) {
+  Entry.call(this);
+
+  t.assertLiteral(breakLoc);
+
+  this.breakLoc = breakLoc;
+}
+
+inherits(SwitchEntry, Entry);
+
+function TryEntry(firstLoc, catchEntry, finallyEntry) {
+  Entry.call(this);
+
+  t.assertLiteral(firstLoc);
+
+  if (catchEntry) {
+    assert.ok(catchEntry instanceof CatchEntry);
+  } else {
+    catchEntry = null;
+  }
+
+  if (finallyEntry) {
+    assert.ok(finallyEntry instanceof FinallyEntry);
+  } else {
+    finallyEntry = null;
+  }
+
+  // Have to have one or the other (or both).
+  assert.ok(catchEntry || finallyEntry);
+
+  this.firstLoc = firstLoc;
+  this.catchEntry = catchEntry;
+  this.finallyEntry = finallyEntry;
+}
+
+inherits(TryEntry, Entry);
+
+function CatchEntry(firstLoc, paramId) {
+  Entry.call(this);
+
+  t.assertLiteral(firstLoc);
+  t.assertIdentifier(paramId);
+
+  this.firstLoc = firstLoc;
+  this.paramId = paramId;
+}
+
+inherits(CatchEntry, Entry);
+
+function FinallyEntry(firstLoc) {
+  Entry.call(this);
+
+  t.assertLiteral(firstLoc);
+
+  this.firstLoc = firstLoc;
+}
+
+inherits(FinallyEntry, Entry);
+
+function LeapManager(emitter) {
+  assert.ok(this instanceof LeapManager);
+
+  var Emitter = require("./emit").Emitter;
+  assert.ok(emitter instanceof Emitter);
+
+  this.emitter = emitter;
+  this.entryStack = [new FunctionEntry(emitter.finalLoc)];
+}
+
+LeapManager.prototype.withEntry = function (entry, callback) {
+  assert.ok(entry instanceof Entry);
+  this.entryStack.push(entry);
+  try {
+    callback.call(this.emitter);
+  } finally {
+    var popped = this.entryStack.pop();
+    assert.strictEqual(popped, entry);
+  }
+};
+
+LeapManager.prototype._findLeapLocation = function (property, label) {
+  for (var i = this.entryStack.length - 1; i >= 0; --i) {
+    var entry = this.entryStack[i];
+    var loc = entry[property];
+    if (loc) {
+      if (label) {
+        if (entry.label &&
+            entry.label.name === label.name) {
+          return loc;
+        }
+      } else {
+        return loc;
+      }
+    }
+  }
+
+  return null;
+};
+
+LeapManager.prototype.getBreakLoc = function (label) {
+  return this._findLeapLocation("breakLoc", label);
+};
+
+LeapManager.prototype.getContinueLoc = function (label) {
+  return this._findLeapLocation("continueLoc", label);
+};

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

@@ -0,0 +1,98 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var assert = require("assert");
+var types  = require("ast-types");
+var m      = require("private").makeAccessor();
+var _      = require("lodash");
+
+var isArray = types.builtInTypes.array;
+var n       = types.namedTypes;
+
+function makePredicate(propertyName, knownTypes) {
+  function onlyChildren(node) {
+    n.Node.check(node);
+
+    // Assume no side effects until we find out otherwise.
+    var result = false;
+
+    function check(child) {
+      if (result) {
+        // Do nothing.
+      } else if (isArray.check(child)) {
+        child.some(check);
+      } else if (n.Node.check(child)) {
+        assert.strictEqual(result, false);
+        result = predicate(child);
+      }
+      return result;
+    }
+
+    types.eachField(node, function (name, child) {
+      check(child);
+    });
+
+    return result;
+  }
+
+  function predicate(node) {
+    n.Node.check(node);
+
+    var meta = m(node);
+    if (_.has(meta, propertyName)) return meta[propertyName];
+
+    // Certain types are "opaque," which means they have no side
+    // effects or leaps and we don't care about their subexpressions.
+    if (_.has(opaqueTypes, node.type)) return meta[propertyName] = false;
+
+    if (_.has(knownTypes, node.type)) return meta[propertyName] = true;
+
+    return meta[propertyName] = onlyChildren(node);
+  }
+
+  predicate.onlyChildren = onlyChildren;
+
+  return predicate;
+}
+
+var opaqueTypes = {
+  FunctionExpression: true
+};
+
+// These types potentially have side effects regardless of what side
+// effects their subexpressions have.
+var sideEffectTypes = {
+  CallExpression: true, // Anything could happen!
+  ForInStatement: true, // Modifies the key variable.
+  UnaryExpression: true, // Think delete.
+  BinaryExpression: true, // Might invoke .toString() or .valueOf().
+  AssignmentExpression: true, // Side-effecting by definition.
+  UpdateExpression: true, // Updates are essentially assignments.
+  NewExpression: true // Similar to CallExpression.
+};
+
+// These types are the direct cause of all leaps in control flow.
+var leapTypes = {
+  YieldExpression: true,
+  BreakStatement: true,
+  ContinueStatement: true,
+  ReturnStatement: true,
+  ThrowStatement: true
+};
+
+// All leap types are also side effect types.
+for (var type in leapTypes) {
+  if (_.has(leapTypes, type)) {
+    sideEffectTypes[type] = leapTypes[type];
+  }
+}
+
+exports.hasSideEffects = makePredicate("hasSideEffects", sideEffectTypes);
+exports.containsLeap = makePredicate("containsLeap", leapTypes);

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

@@ -0,0 +1,454 @@
+/**
+* Copyright (c) 2014, Facebook, Inc.
+* All rights reserved.
+*
+* This source code is licensed under the BSD-style license found in the
+* https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+* additional grant of patent rights can be found in the PATENTS file in
+* the same directory.
+*/
+
+var iteratorSymbol = typeof Symbol === "function" && Symbol.iterator || "@@iterator";
+var runtime = global.regeneratorRuntime = exports;
+var hasOwn = Object.prototype.hasOwnProperty;
+
+var wrap = runtime.wrap = function wrap(innerFn, outerFn, self, tryList) {
+  return new Generator(innerFn, outerFn, self || null, tryList || []);
+};
+
+var GenStateSuspendedStart = "suspendedStart";
+var GenStateSuspendedYield = "suspendedYield";
+var GenStateExecuting = "executing";
+var GenStateCompleted = "completed";
+
+// Returning this object from the innerFn has the same effect as
+// breaking out of the dispatch switch statement.
+var ContinueSentinel = {};
+
+// Dummy constructor that we use as the .constructor property for
+// functions that return Generator objects.
+var GF = function GeneratorFunction() {};
+var GFp = function GeneratorFunctionPrototype() {};
+var Gp = GFp.prototype = Generator.prototype;
+(GFp.constructor = GF).prototype =
+  Gp.constructor = GFp;
+
+// Ensure isGeneratorFunction works when Function#name not supported.
+var GFName = "GeneratorFunction";
+if (GF.name !== GFName) GF.name = GFName;
+if (GF.name !== GFName) throw new Error(GFName + " renamed?");
+
+runtime.isGeneratorFunction = function (genFun) {
+  var ctor = genFun && genFun.constructor;
+  return ctor ? GF.name === ctor.name : false;
+};
+
+runtime.mark = function (genFun) {
+  genFun.__proto__ = GFp;
+  genFun.prototype = Object.create(Gp);
+  return genFun;
+};
+
+runtime.async = function (innerFn, outerFn, self, tryList) {
+  return new Promise(function (resolve, reject) {
+    var generator = wrap(innerFn, outerFn, self, tryList);
+    var callNext = step.bind(generator.next);
+    var callThrow = step.bind(generator["throw"]);
+
+    function step(arg) {
+      var info;
+      var value;
+
+      try {
+        info = this(arg);
+        value = info.value;
+      } catch (error) {
+        return reject(error);
+      }
+
+      if (info.done) {
+        resolve(value);
+      } else {
+        Promise.resolve(value).then(callNext, callThrow);
+      }
+    }
+
+    callNext();
+  });
+};
+
+function Generator(innerFn, outerFn, self, tryList) {
+  var generator = outerFn ? Object.create(outerFn.prototype) : this;
+  var context = new Context(tryList);
+  var state = GenStateSuspendedStart;
+
+  function invoke(method, arg) {
+    if (state === GenStateExecuting) {
+      throw new Error("Generator is already running");
+    }
+
+    if (state === GenStateCompleted) {
+      throw new Error("Generator has already finished");
+    }
+
+    while (true) {
+      var delegate = context.delegate;
+      var info;
+
+      if (delegate) {
+        try {
+          info = delegate.iterator[method](arg);
+
+          // Delegate generator ran and handled its own exceptions so
+          // regardless of what the method was, we continue as if it is
+          // "next" with an undefined arg.
+          method = "next";
+          arg = undefined;
+
+        } catch (uncaught) {
+          context.delegate = null;
+
+          // Like returning generator.throw(uncaught), but without the
+          // overhead of an extra function call.
+          method = "throw";
+          arg = uncaught;
+
+          continue;
+        }
+
+        if (info.done) {
+          context[delegate.resultName] = info.value;
+          context.next = delegate.nextLoc;
+        } else {
+          state = GenStateSuspendedYield;
+          return info;
+        }
+
+        context.delegate = null;
+      }
+
+      if (method === "next") {
+        if (state === GenStateSuspendedStart &&
+            typeof arg !== "undefined") {
+          // https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorresume
+          throw new TypeError(
+            "attempt to send " + JSON.stringify(arg) + " to newborn generator"
+          );
+        }
+
+        if (state === GenStateSuspendedYield) {
+          context.sent = arg;
+        } else {
+          delete context.sent;
+        }
+
+      } else if (method === "throw") {
+        if (state === GenStateSuspendedStart) {
+          state = GenStateCompleted;
+          throw arg;
+        }
+
+        if (context.dispatchException(arg)) {
+          // If the dispatched exception was caught by a catch block,
+          // then let that catch block handle the exception normally.
+          method = "next";
+          arg = undefined;
+        }
+
+      } else if (method === "return") {
+        context.abrupt("return", arg);
+      }
+
+      state = GenStateExecuting;
+
+      try {
+        var value = innerFn.call(self, context);
+
+        // If an exception is thrown from innerFn, we leave state ===
+        // GenStateExecuting and loop back for another invocation.
+        state = context.done ? GenStateCompleted : GenStateSuspendedYield;
+
+        info = {
+          value: value,
+          done: context.done
+        };
+
+        if (value === ContinueSentinel) {
+          if (context.delegate && method === "next") {
+            // Deliberately forget the last sent value so that we don't
+            // accidentally pass it on to the delegate.
+            arg = undefined;
+          }
+        } else {
+          return info;
+        }
+
+      } catch (thrown) {
+        state = GenStateCompleted;
+
+        if (method === "next") {
+          context.dispatchException(thrown);
+        } else {
+          arg = thrown;
+        }
+      }
+    }
+  }
+
+  generator.next = invoke.bind(generator, "next");
+  generator["throw"] = invoke.bind(generator, "throw");
+  generator["return"] = invoke.bind(generator, "return");
+
+  return generator;
+}
+
+Gp[iteratorSymbol] = function () {
+  return this;
+};
+
+Gp.toString = function () {
+  return "[object Generator]";
+};
+
+function pushTryEntry(triple) {
+  var entry = { tryLoc: triple[0] };
+
+  if (1 in triple) {
+    entry.catchLoc = triple[1];
+  }
+
+  if (2 in triple) {
+    entry.finallyLoc = triple[2];
+  }
+
+  this.tryEntries.push(entry);
+}
+
+function resetTryEntry(entry, i) {
+  var record = entry.completion || {};
+  record.type = i === 0 ? "normal" : "return";
+  delete record.arg;
+  entry.completion = record;
+}
+
+function Context(tryList) {
+  // The root entry object (effectively a try statement without a catch
+  // or a finally block) gives us a place to store values thrown from
+  // locations where there is no enclosing try statement.
+  this.tryEntries = [{ tryLoc: "root" }];
+  tryList.forEach(pushTryEntry, this);
+  this.reset();
+}
+
+runtime.keys = function (object) {
+  var keys = [];
+  for (var key in object) {
+    keys.push(key);
+  }
+  keys.reverse();
+
+  // Rather than returning an object with a next method, we keep
+  // things simple and return the next function itself.
+  return function next() {
+    while (keys.length) {
+      var key = keys.pop();
+      if (key in object) {
+        next.value = key;
+        next.done = false;
+        return next;
+      }
+    }
+
+    // To avoid creating an additional object, we just hang the .value
+    // and .done properties off the next function object itself. This
+    // also ensures that the minifier will not anonymize the function.
+    next.done = true;
+    return next;
+  };
+};
+
+function values(iterable) {
+  var iterator = iterable;
+  if (iteratorSymbol in iterable) {
+    iterator = iterable[iteratorSymbol]();
+  } else if (!isNaN(iterable.length)) {
+    var i = -1;
+    iterator = function next() {
+      while (++i < iterable.length) {
+        if (i in iterable) {
+          next.value = iterable[i];
+          next.done = false;
+          return next;
+        }
+      }
+      next.done = true;
+      return next;
+    };
+    iterator.next = iterator;
+  }
+  return iterator;
+}
+runtime.values = values;
+
+Context.prototype = {
+  constructor: Context,
+
+  reset: function () {
+    this.prev = 0;
+    this.next = 0;
+    this.sent = undefined;
+    this.done = false;
+    this.delegate = null;
+
+    this.tryEntries.forEach(resetTryEntry);
+
+    // Pre-initialize at least 20 temporary variables to enable hidden
+    // class optimizations for simple generators.
+    for (var tempIndex = 0, tempName;
+         hasOwn.call(this, tempName = "t" + tempIndex) || tempIndex < 20;
+         ++tempIndex) {
+      this[tempName] = null;
+    }
+  },
+
+  stop: function () {
+    this.done = true;
+
+    var rootEntry = this.tryEntries[0];
+    var rootRecord = rootEntry.completion;
+    if (rootRecord.type === "throw") {
+      throw rootRecord.arg;
+    }
+
+    return this.rval;
+  },
+
+  dispatchException: function (exception) {
+    if (this.done) {
+      throw exception;
+    }
+
+    var context = this;
+    function handle(loc, caught) {
+      record.type = "throw";
+      record.arg = exception;
+      context.next = loc;
+      return !!caught;
+    }
+
+    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
+      var entry = this.tryEntries[i];
+      var record = entry.completion;
+
+      if (entry.tryLoc === "root") {
+        // Exception thrown outside of any try block that could handle
+        // it, so set the completion value of the entire function to
+        // throw the exception.
+        return handle("end");
+      }
+
+      if (entry.tryLoc <= this.prev) {
+        var hasCatch = hasOwn.call(entry, "catchLoc");
+        var hasFinally = hasOwn.call(entry, "finallyLoc");
+
+        if (hasCatch && hasFinally) {
+          if (this.prev < entry.catchLoc) {
+            return handle(entry.catchLoc, true);
+          } else if (this.prev < entry.finallyLoc) {
+            return handle(entry.finallyLoc);
+          }
+
+        } else if (hasCatch) {
+          if (this.prev < entry.catchLoc) {
+            return handle(entry.catchLoc, true);
+          }
+
+        } else if (hasFinally) {
+          if (this.prev < entry.finallyLoc) {
+            return handle(entry.finallyLoc);
+          }
+
+        } else {
+          throw new Error("try statement without catch or finally");
+        }
+      }
+    }
+  },
+
+  _findFinallyEntry: function (finallyLoc) {
+    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
+      var entry = this.tryEntries[i];
+      if (entry.tryLoc <= this.prev &&
+          hasOwn.call(entry, "finallyLoc") && (
+            entry.finallyLoc === finallyLoc ||
+            this.prev < entry.finallyLoc)) {
+        return entry;
+      }
+    }
+  },
+
+  abrupt: function (type, arg) {
+    var entry = this._findFinallyEntry();
+    var record = entry ? entry.completion : {};
+
+    record.type = type;
+    record.arg = arg;
+
+    if (entry) {
+      this.next = entry.finallyLoc;
+    } else {
+      this.complete(record);
+    }
+
+    return ContinueSentinel;
+  },
+
+  complete: function (record) {
+    if (record.type === "throw") {
+      throw record.arg;
+    }
+
+    if (record.type === "break" || record.type === "continue") {
+      this.next = record.arg;
+    } else if (record.type === "return") {
+      this.rval = record.arg;
+      this.next = "end";
+    }
+
+    return ContinueSentinel;
+  },
+
+  finish: function (finallyLoc) {
+    var entry = this._findFinallyEntry(finallyLoc);
+    return this.complete(entry.completion);
+  },
+
+  "catch": function (tryLoc) {
+    for (var i = this.tryEntries.length - 1; i >= 0; --i) {
+      var entry = this.tryEntries[i];
+      if (entry.tryLoc === tryLoc) {
+        var record = entry.completion;
+        var thrown;
+        if (record.type === "throw") {
+          thrown = record.arg;
+          resetTryEntry(entry, i);
+        }
+        return thrown;
+      }
+    }
+
+    // The context.catch method must only be called with a location
+    // argument that corresponds to a known catch block.
+    throw new Error("illegal catch attempt");
+  },
+
+  delegateYield: function (iterable, resultName, nextLoc) {
+    this.delegate = {
+      iterator: values(iterable),
+      resultName: resultName,
+      nextLoc: nextLoc
+    };
+
+    return ContinueSentinel;
+  }
+};

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

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var t = require("../../../types");
+
+exports.runtimeProperty = function (name) {
+  return t.memberExpression(
+    t.identifier("regeneratorRuntime"),
+    t.identifier(name)
+  );
+};
+
+// Offsets into this.listing that could be used as targets for branches or
+// jumps are represented as numeric Literal nodes. This representation has
+// the amazingly convenient benefit of allowing the exact value of the
+// location to be determined at any time, even after generating code that
+// refers to the location.
+
+exports.loc = function () {
+  return t.literal(-1);
+};

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

@@ -0,0 +1,221 @@
+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.githut.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+var runtimeProperty = require("./util").runtimeProperty;
+var Emitter         = require("./emit").Emitter;
+var hoist           = require("./hoist").hoist;
+var types           = require("ast-types");
+var t               = require("../../../types");
+
+var runtimeAsyncMethod = runtimeProperty("async");
+var runtimeWrapMethod  = runtimeProperty("wrap");
+var runtimeMarkMethod  = runtimeProperty("mark");
+
+exports.transform = function transform(node, file) {
+  return types.visit(node, {
+    visitFunction: function (path) {
+      return visitor.call(this, path, file);
+    }
+  });
+};
+
+var visitor = function (path, file) {
+  // Calling this.traverse(path) first makes for a post-order traversal.
+  this.traverse(path);
+
+  var node = path.value;
+  var scope; // we need to actually get the current scope
+
+  if (!node.generator && !node.async) {
+    return;
+  }
+
+  node.generator = false;
+
+  if (node.expression) {
+    // Transform expression lambdas into normal functions.
+    node.expression = false;
+    node.body = t.blockStatement([
+      t.returnStatement(node.body)
+    ]);
+  }
+
+  if (node.async) {
+    awaitVisitor.visit(path.get("body"));
+  }
+
+  var outerFnId = node.id || (
+    node.id = file.generateUidIdentifier("callee", scope)
+  );
+
+  var innerFnId = t.identifier(node.id.name + "$");
+  var contextId = file.generateUidIdentifier("context", scope);
+  var vars = hoist(path);
+
+  var emitter = new Emitter(contextId);
+  emitter.explode(path.get("body"));
+
+  var outerBody = [];
+
+  if (vars && vars.declarations.length > 0) {
+    outerBody.push(vars);
+  }
+
+  var wrapArgs = [
+    emitter.getContextFunction(innerFnId),
+    // Async functions don't care about the outer function because they
+    // don't need it to be marked and don't inherit from its .prototype.
+    node.async ? t.literal(null) : outerFnId,
+    t.thisExpression()
+  ];
+
+  var tryEntryList = emitter.getTryEntryList();
+  if (tryEntryList) {
+    wrapArgs.push(tryEntryList);
+  }
+
+  var wrapCall = t.callExpression(
+    node.async ? runtimeAsyncMethod : runtimeWrapMethod,
+    wrapArgs
+  );
+
+  outerBody.push(t.returnStatement(wrapCall));
+  node.body = t.blockStatement(outerBody);
+
+  if (node.async) {
+    node.async = false;
+    return;
+  }
+
+  if (t.isFunctionDeclaration(node)) {
+    var pp = path.parent;
+
+    while (pp && !(t.isBlockStatement(pp.value) || t.isProgram(pp.value))) {
+      pp = pp.parent;
+    }
+
+    if (!pp) {
+      return;
+    }
+
+    // Here we turn the FunctionDeclaration into a named
+    // FunctionExpression that will be assigned to a variable of the
+    // same name at the top of the enclosing block. This is important
+    // for a very subtle reason: named function expressions can refer to
+    // themselves by name without fear that the binding may change due
+    // to code executing outside the function, whereas function
+    // declarations are vulnerable to the following rebinding:
+    //
+    //   function f() { return f }
+    //   var g = f;
+    //   f = "asdf";
+    //   g(); // "asdf"
+    //
+    // One way to prevent the problem illustrated above is to transform
+    // the function declaration thus:
+    //
+    //   var f = function f() { return f };
+    //   var g = f;
+    //   f = "asdf";
+    //   g(); // f
+    //   g()()()()(); // f
+    //
+    // In the code below, we transform generator function declarations
+    // in the following way:
+    //
+    //   gen().next(); // { value: gen, done: true }
+    //   function *gen() {
+    //     return gen;
+    //   }
+    //
+    // becomes something like
+    //
+    //   var gen = runtime.mark(function *gen() {
+    //     return gen;
+    //   });
+    //   gen().next(); // { value: gen, done: true }
+    //
+    // which ensures that the generator body can always reliably refer
+    // to gen by name.
+
+    // Remove the FunctionDeclaration so that we can add it back as a
+    // FunctionExpression passed to runtime.mark.
+    path.replace();
+
+    // Change the type of the function to be an expression instead of a
+    // declaration. Note that all the other fields are the same.
+    node.type = "FunctionExpression";
+
+    var varDecl = t.variableDeclaration("var", [
+      t.variableDeclarator(
+        node.id,
+        t.callExpression(runtimeMarkMethod, [node])
+      )
+    ]);
+
+    // Copy any comments preceding the function declaration to the
+    // variable declaration, to avoid weird formatting consequences.
+    t.inheritsComments(varDecl, node);
+    t.removeComments(node);
+
+    varDecl._blockHoist = true;
+
+    var bodyPath = pp.get("body");
+    var bodyLen = bodyPath.value.length;
+
+    for (var i = 0; i < bodyLen; ++i) {
+      var firstStmtPath = bodyPath.get(i);
+      if (!shouldNotHoistAbove(firstStmtPath)) {
+        firstStmtPath.insertBefore(varDecl);
+        return;
+      }
+    }
+
+    bodyPath.push(varDecl);
+  } else {
+    t.assertFunctionExpression(node);
+    return t.callExpression(runtimeMarkMethod, [node]);
+  }
+};
+
+function shouldNotHoistAbove(stmtPath) {
+  var value = stmtPath.value;
+  t.assertStatement(value);
+
+  // If the first statement is a "use strict" declaration, make sure to
+  // insert hoisted declarations afterwards.
+  if (t.isExpressionStatement(value) &&
+      t.isLiteral(value.expression) &&
+      value.expression.value === "use strict") {
+    return true;
+  }
+
+  if (t.isVariableDeclaration(value)) {
+    for (var i = 0; i < value.declarations.length; ++i) {
+      var decl = value.declarations[i];
+      if (t.isCallExpression(decl.init) && types.astNodesAreEquivalent(decl.init.callee, runtimeMarkMethod)) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+var awaitVisitor = types.PathVisitor.fromMethodsObject({
+  visitFunction: function () {
+    return false; // Don't descend into nested function scopes.
+  },
+
+  visitAwaitExpression: function (path) {
+    // Convert await expressions to yield expressions.
+    return t.yieldExpression(path.value.argument, false);
+  }
+});

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

@@ -74,7 +74,6 @@ function LetScoping(forParent, block, parent, file, scope) {
 
   this.letReferences = {};
   this.body          = [];
-  this.info          = this.getInfo();
 }
 
 /**
@@ -87,8 +86,13 @@ 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();
@@ -125,31 +129,57 @@ 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 () {
-  var replacements = this.info.duplicates;
-  var declarators  = this.info.declarators;
-  var block        = this.block;
+  standardiseLets(this.info.declarators);
+};
 
-  standardiseLets(declarators);
+/**
+ * Traverse through block and replace all references that exist in a higher
+ * scope to their uids.
+ */
+
+LetScoping.prototype.remap = function () {
+  var replacements = this.info.duplicates;
+  var block        = this.block;
 
   if (_.isEmpty(replacements)) return;
 
-  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, replace);
+  };
+
+  var forParent = this.forParent;
+  if (forParent) {
+    traverseReplace(forParent.right, forParent);
+    traverseReplace(forParent.test, forParent);
+    traverseReplace(forParent.update, forParent);
+  }
+
+  traverse(block, replace);
 };
 
 /**
@@ -181,10 +211,23 @@ LetScoping.prototype.getInfo = function () {
     keys:        []
   };
 
+  var duplicates = function (id, key) {
+    var has = scope.parentGet(key);
+
+    if (has && has !== id) {
+      // there's a variable with this exact name in an upper scope so we need
+      // to generate a new name
+      opts.duplicates[key] = id.name = file.generateUid(key, scope);
+    }
+  };
+
   _.each(opts.declarators, function (declar) {
     opts.declarators.push(declar);
 
-    var keys = t.getIds(declar);
+    var keys = t.getIds(declar, true);
+    _.each(keys, duplicates);
+    keys = _.keys(keys);
+
     opts.outsideKeys = opts.outsideKeys.concat(keys);
     opts.keys = opts.keys.concat(keys);
   });
@@ -193,14 +236,7 @@ LetScoping.prototype.getInfo = function () {
     if (!isLet(declar)) return;
 
     _.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);
     });
   });
@@ -211,7 +247,8 @@ LetScoping.prototype.getInfo = function () {
 /**
  * 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.
+ * `ContinueStatement` and replace it with a return value that we can track
+ * later on.
  *
  * @returns {Object}
  */
@@ -223,35 +260,41 @@ LetScoping.prototype.checkFor = function () {
     hasBreak:    false,
   };
 
-  if (this.forParent) {
-    traverse(this.block, function (node) {
-      var replace;
+  var forParent = this.forParent;
 
-      if (t.isFunction(node) || t.isFor(node)) {
-        return false;
-      } else if (t.isBreakStatement(node) && !node.label) {
+  traverse(this.block, function (node) {
+    var replace;
+
+    if (t.isFunction(node) || t.isFor(node)) {
+      return false;
+    }
+
+    if (forParent && node && !node.label) {
+      if (t.isBreakStatement(node)) {
         has.hasBreak = true;
         replace = t.returnStatement(t.literal("break"));
-      } else if (t.isContinueStatement(node) && !node.label) {
+      } else if (t.isContinueStatement(node)) {
         has.hasContinue = true;
         replace = t.returnStatement(t.literal("continue"));
-      } else if (t.isReturnStatement(node)) {
-        has.hasReturn = true;
-        replace = t.returnStatement(t.objectExpression([
-          t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
-        ]));
       }
+    }
 
-      if (replace) return t.inherits(replace, node);
-    });
-  }
+    if (t.isReturnStatement(node)) {
+      has.hasReturn = true;
+      replace = t.returnStatement(t.objectExpression([
+        t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
+      ]));
+    }
+
+    if (replace) return t.inherits(replace, node);
+  });
 
   return has;
 };
 
 /**
  * Hoist all var declarations in this block to before it so they retain scope
- * once we wrap everything is in a closure.
+ * once we wrap everything in a closure.
  */
 
 LetScoping.prototype.hoistVarDeclarations = function () {
@@ -340,7 +383,7 @@ 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);
   })));
@@ -402,7 +445,7 @@ 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 = forParent.label = forParent.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

@@ -5,10 +5,10 @@ exports.ImportDeclaration = function (node, parent, file) {
 
   if (node.specifiers.length) {
     _.each(node.specifiers, function (specifier) {
-      file.moduleFormatter.importSpecifier(specifier, node, nodes);
+      file.moduleFormatter.importSpecifier(specifier, node, nodes, parent);
     });
   } else {
-    file.moduleFormatter.import(node, nodes);
+    file.moduleFormatter.import(node, nodes, parent);
   }
 
   return nodes;
@@ -18,10 +18,10 @@ exports.ExportDeclaration = function (node, parent, file) {
   var nodes = [];
 
   if (node.declaration) {
-    file.moduleFormatter.export(node, nodes);
+    file.moduleFormatter.export(node, nodes, parent);
   } else {
     _.each(node.specifiers, function (specifier) {
-      file.moduleFormatter.exportSpecifier(specifier, node, nodes);
+      file.moduleFormatter.exportSpecifier(specifier, node, nodes, parent);
     });
   }
 

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

@@ -0,0 +1,4 @@
+exports.Property = function (node) {
+  if (!node.shorthand) return;
+  node.shorthand = false;
+};

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

@@ -1,15 +1,8 @@
 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) {
@@ -23,7 +16,7 @@ var hasSpread = function (nodes) {
   return has;
 };
 
-var build = function (props) {
+var build = function (props, file) {
   var nodes = [];
 
   var _props = [];
@@ -37,7 +30,7 @@ var build = function (props) {
   _.each(props, function (prop) {
     if (t.isSpreadElement(prop)) {
       push();
-      nodes.push(getSpreadLiteral(prop));
+      nodes.push(getSpreadLiteral(prop, file));
     } else {
       _props.push(prop);
     }
@@ -48,19 +41,22 @@ var build = function (props) {
   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 +64,12 @@ 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 +79,16 @@ 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 +107,7 @@ 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) {

lib/6to5/transformation/transformers/es6-template-literals.js

@@ -5,19 +5,25 @@ var buildBinaryExpression = function (left, right) {
   return t.binaryExpression("+", left, right);
 };
 
-exports.TaggedTemplateExpression = function (node) {
+exports.TaggedTemplateExpression = function (node, parent, file) {
   var args = [];
   var quasi = node.quasi;
 
-  var strings = quasi.quasis.map(function (elem) {
-    return t.literal(elem.value.raw);
-  });
-  args.push(t.arrayExpression(strings));
+  var strings = [];
+  var raw = [];
 
-  _.each(quasi.expressions, function (expr) {
-    args.push(expr);
+  _.each(quasi.quasis, function (elem) {
+    strings.push(t.literal(elem.value.cooked));
+    raw.push(t.literal(elem.value.raw));
   });
 
+  args.push(t.callExpression(file.addDeclaration("tagged-template-literal"), [
+    t.arrayExpression(strings),
+    t.arrayExpression(raw)
+  ]));
+
+  args = args.concat(quasi.expressions);
+
   return t.callExpression(node.tag, args);
 };
 

lib/6to5/transformation/transformers/es7-abstract-references.js

@@ -0,0 +1,98 @@
+// https://github.com/zenparsing/es-abstract-refs
+
+var util = require("../../util");
+var t    = require("../../types");
+
+var container = function (parent, call, ret) {
+  if (t.isExpressionStatement(parent)) {
+    // we don't need to worry about return values
+    return call;
+  } else {
+    var exprs = [];
+    if (t.isSequenceExpression(call)) {
+      exprs = call.expressions;
+    } else {
+      exprs.push(call);
+    }
+    exprs.push(ret);
+    return t.sequenceExpression(exprs);
+  }
+};
+
+exports.AssignmentExpression = function (node, parent, file, scope) {
+  var left = node.left;
+  if (!t.isVirtualPropertyExpression(left)) return;
+
+  var value = node.right;
+  var temp;
+
+  // we need to return `node.right`
+  if (!t.isExpressionStatement(parent)) {
+    // `node.right` isn't a simple identifier so we need to reference it
+    if (t.isDynamic(value)) {
+      temp = value = scope.generateTemp(file);
+    }
+  }
+
+  var call = util.template("abstract-expression-set", {
+    PROPERTY: left.property,
+    OBJECT:   left.object,
+    VALUE:    value
+  });
+
+  if (temp) {
+    call = t.sequenceExpression([
+      t.assignmentExpression("=", temp, node.right),
+      call
+    ]);
+  }
+
+  return container(parent, call, value);
+};
+
+exports.UnaryExpression = function (node, parent) {
+  var arg = node.argument;
+  if (!t.isVirtualPropertyExpression(arg)) return;
+  if (node.operator !== "delete") return;
+
+  var call = util.template("abstract-expression-delete", {
+    PROPERTY: arg.property,
+    OBJECT:   arg.object
+  });
+
+  return container(parent, call, t.literal(true));
+};
+
+exports.CallExpression = function (node, parent, file, scope) {
+  var callee = node.callee;
+  if (!t.isVirtualPropertyExpression(callee)) return;
+
+  var temp;
+  if (t.isDynamic(callee.object)) {
+    // we need to save `callee.object` so we can call it again
+    temp = scope.generateTemp(file);
+  }
+
+  var call = util.template("abstract-expression-call", {
+    PROPERTY: callee.property,
+    OBJECT:   temp || callee.object
+  });
+
+  call.arguments = call.arguments.concat(node.arguments);
+
+  if (temp) {
+    return t.sequenceExpression([
+      t.assignmentExpression("=", temp, callee.object),
+      call
+    ]);
+  } else {
+    return call;
+  }
+};
+
+exports.VirtualPropertyExpression = function (node) {
+  return util.template("abstract-expression-get", {
+    PROPERTY: node.property,
+    OBJECT:   node.object
+  });
+};

lib/6to5/transformation/transformers/es7-array-comprehension.js

@@ -2,7 +2,7 @@ var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
 
-var singleArrayExpression = function (node) {
+var single = function (node, file) {
   var block = node.blocks[0];
 
   var templateName = "array-expression-comprehension-map";
@@ -11,7 +11,7 @@ var singleArrayExpression = function (node) {
   var result = util.template(templateName, {
     STATEMENT: node.body,
     FILTER:    node.filter,
-    ARRAY:     block.right,
+    ARRAY:     file.toArray(block.right),
     KEY:       block.left
   });
 
@@ -25,7 +25,7 @@ var singleArrayExpression = function (node) {
 };
 
 var multiple = function (node, file) {
-  var uid = file.generateUid("arr");
+  var uid = file.generateUidIdentifier("arr");
 
   var container = util.template("array-comprehension-container", {
     KEY: uid
@@ -73,8 +73,8 @@ exports._build = function (node, buildBody) {
 exports.ComprehensionExpression = function (node, parent, file) {
   if (node.generator) return;
 
-  if (node.blocks.length === 1 && t.isArrayExpression(node.blocks[0].right)) {
-    return singleArrayExpression(node);
+  if (node.blocks.length === 1) {
+    return single(node, file);
   } else {
     return multiple(node, file);
   }

lib/6to5/transformation/transformers/es7-exponentiation-operator.js

@@ -0,0 +1,16 @@
+// https://github.com/rwaldron/exponentiation-operator
+
+var t = require("../../types");
+var pow = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
+
+exports.AssignmentExpression = function (node) {
+  if (node.operator !== "**=") return;
+  node.operator = "=";
+  node.right = t.callExpression(pow, [node.left, node.right]);
+};
+
+exports.BinaryExpression = function (node) {
+  if (node.operator !== "**") return;
+
+  return t.callExpression(pow, [node.left, node.right]);
+};

lib/6to5/transformation/transformers/es7-generator-comprehension.js

@@ -1,4 +1,4 @@
-var arrayComprehension = require("./array-comprehension");
+var arrayComprehension = require("./es7-array-comprehension");
 var t                  = require("../../types");
 
 exports.ComprehensionExpression = function (node) {

lib/6to5/transformation/transformers/es7-object-spread.js

@@ -0,0 +1,41 @@
+// https://github.com/sebmarkbage/ecmascript-rest-spread
+
+var t = require("../../types");
+var _ = require("lodash");
+
+exports.ObjectExpression = function (node) {
+  var hasSpread = false;
+  _.each(node.properties, function (prop) {
+    if (t.isSpreadProperty(prop)) {
+      hasSpread = true;
+      return false;
+    }
+  });
+  if (!hasSpread) return;
+
+  var args = [];
+  var props = [];
+
+  var push = function () {
+    if (!props.length) return;
+    args.push(t.objectExpression(props));
+    props = [];
+  };
+
+  _.each(node.properties, function (prop) {
+    if (t.isSpreadProperty(prop)) {
+      push();
+      args.push(prop.argument);
+    } else {
+      props.push(prop);
+    }
+  });
+
+  push();
+
+  if (!t.isObjectExpression(args[0])) {
+    args.unshift(t.objectExpression([]));
+  }
+
+  return t.callExpression(t.memberExpression(t.identifier("Object"), t.identifier("assign")), args);
+};