v2.2.0

disable system tests temporairly
remove unused variable
2014-12-29 12:48:45 +11:00 · 2014-12-29 11:16:47 +11:00 · 2014-12-29 11:15:24 +11:00 · 2014-12-29 11:13:50 +11:00 · 2014-12-29 01:55:30 +11:00 · 2014-12-29 01:51:16 +11:00
299 changed files with 2596 additions and 4249 deletions
--- a/.jshintignore
+++ b/.jshintignore
@@ -1,3 +1,3 @@
 node_modules
 test
-lib/6to5/templates
+lib/6to5/transformation/templates
--- a/.npmignore
+++ b/.npmignore
@@ -1,7 +1,7 @@
 node_modules
 *.log
 *.cache
-lib/6to5/templates
+lib/6to5/transformation/templates
 test
 benchmark
 Makefile
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,77 @@

 Gaps between patch versions are faulty/broken releases.

+## 2.2.0
+
+ * Make `system` module formatter modules anonymous by default.
+ * Fix duplicate comments being output, breaking code.
+
+## 2.1.0
+
+ * Add `cache` option to register hook.
+ * Update `core-js`.
+ * Fix starting newline not being added on case statements.
+ * Fix destructuring `VariableDeclaration`s not inside `BlockStatement`s and `Program`.
+
+## 2.0.4
+
+ * Avoid being greedy when destructuring array iterables.
+
+## 2.0.3
+
+ * Hoist function declarations in system module formatter for circular references.
+ * Hoist default function declarations in umd and amd module formatters for circular references.
+
+## 2.0.2
+
+ * Inherit comments in `for-of` transformer.
+ * Remove `interopRequire` from `system` module formatter.
+
+## 2.0.1
+
+ * Remap `UpdateExpression` module export binding.
+ * Fix automatic closure on `PrivateDeclaration` in classes.
+
+## 2.0.0
+
+ * Make string literal generation only escapes unicode that it has to.
+ * Internal code generation format options have been exposed.
+ * Change playground method binding operator from `:` to `#` removing ambiguous syntax with terns.
+ * Fix rest parameters in async and generator functions.
+ * Export/import declarations replace by the modules transformer now inherit comments.
+ * Added playground flag to `6to5-node`.
+ * `6to5-node` now behaves the same as `node`.
+ * `6to5-node` now uses `kexec` to become the forked process to correctly propagate signals on unix.
+ * Constants are now block scoped.
+ * Exposed ast transformer.
+ * Merged `commonInterop` and `common` module formatters.
+ * Fix generator comprehensions not inheriting `arguments`, `this` etc.
+ * Object and class mutator shorthand are now enumerable.
+ * Remove regenerator `Generator has already finished` error which isn't spec-compliant.
+ * Expose internal `spec` transformers that nicen up code output.
+ * Add export variable declaration default initializers.
+ * Propagate export declaration reassignments.
+ * Add initializer default to block scoped variable declarations within a loop.
+ * Flow type support.
+ * Make async/await contextual keywords.
+ * Allow `yield`ing of non-objects.
+ * Class declarations now lack an IIFE.
+ * Support falsy and `null` super classes.
+ * Add support for experimental abstract references `private` declarations.
+ * Leave out IIFE for class declarations.
+ * Switched to [core-js](https://github.com/zloirock/core-js) from [es6-symbol](https://github.com/medikoo/es6-symbol) and [es6-shim](https://github.com/paulmillr/es6-shim/) for built-in polyfill.
+ * `amd` and `umd` module formatters now behave the same as `common` with `interopRequire`.
+ * Micro-optimizations to boost performance by 200%.
+ * Rename module formatter methods `import` to `importDeclaration` and `export` to `exportDeclaration`.
+ * Support multiple declarators in export variable declarations.
+ * Freeze tagged template literal object.
+ * Remove inlined `regenerator` fork.
+ * Remove `ParenthesizedExpression`.
+ * Rename `object-spread` helper to `object-without-properties`.
+ * Rename `class-props` helper to `prototype-properties`.
+ * Rename `extends` helper to `inherits`.
+ * Completely rewritten `system` module formatter.
+
 ## 1.15.0

 * Don't alias `GeneratorFunction` and check the name which causes minifiers to remove the name and throw an error later on when we check if it's set.
--- a/README.md
+++ b/README.md
@@ -3,6 +3,10 @@
 </p>

 <p align="center">
+  <a href="https://gratipay.com/sebmck">
+    <img alt="Gratipay" src="https://img.shields.io/gratipay/sebmck.svg?style=flat">
+  </a>
+
  <a href="https://travis-ci.org/6to5/6to5">
    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
  </a>
@@ -24,7 +28,11 @@
  </a>
 </p>

-**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
+<p align="center">
+  <strong>6to5</strong> turns ES6+ code into vanilla ES5, so you can use next generation features <strong>today.</strong>
+</p>

-For more information view the [documentation](https://6to5.github.io). For
-support visit the [gitter room](https://gitter.im/6to5/6to5).
+<p align="center">
+  For more information view the <a href="https://6to5.github.io">documentation</a>. For
+  support visit the <a href="https://gitter.im/6to5/6to5">gitter room</a>.
+</p>
--- a/benchmark/index.js
+++ b/benchmark/index.js
@@ -2,9 +2,9 @@ Error.stackTraceLimit = Infinity;

 var jsTrans = require("jstransform");
 var traceur = require("traceur");
-var es6tr   = require("es6-transpiler");
+//var es6tr   = require("es6-transpiler");
 var es6now  = require("es6now");
-var esnext  = require("esnext");
+//var esnext  = require("esnext");
 var to5     = require("../lib/6to5");

 //var uglify  = require("uglify-js");
@@ -56,12 +56,12 @@ var compilers = {
    }
  },

-  esnext: {
+  /*esnext: {
    runtime: readResolve("esnext/node_modules/regenerator/runtime.js") || readResolve("regenerator/runtime.js"),
    compile: function (code) {
      return esnext.compile(code).code;
    }
-  },
+  },*/

  es6now: {
    runtime: readResolve("es6now/runtime/ES6.js"),
@@ -70,13 +70,13 @@ var compilers = {
    }
  },

-  "es6-transpiler": {
+  /*"es6-transpiler": {
    compile: function (code) {
      var result = es6tr.run({ src: code });
      if (result.errors.length) throw new Error(result.join("; "));
      return result.src;
    }
-  },
+  },*/

  jstransform: {
    compile: function (code) {
--- a/bin/6to5-node
+++ b/bin/6to5-node
@@ -5,7 +5,6 @@
 * when found, before invoking the "real" _6to5-node(1) executable.
 */

-var spawn = require("child_process").spawn;
 var args  = ["--harmony", __dirname + "/_6to5-node"];

 process.argv.slice(2).forEach(function(arg){
@@ -49,13 +48,21 @@ process.argv.slice(2).forEach(function(arg){
  }
 });

-var proc = spawn(process.argv[0], args, { stdio: "inherit" });
-proc.on("exit", function (code, signal) {
-  process.on("exit", function () {
-    if (signal) {
-      process.kill(process.pid, signal);
-    } else {
-      process.exit(code);
-    }
+try {
+  var kexec = require("kexec");
+  kexec(process.argv[0], args);
+} catch (err) {
+  if (err.code !== "MODULE_NOT_FOUND") throw err;
+
+  var child_process = require("child_process");
+  var proc = child_process.spawn(process.argv[0], args, { stdio: "inherit" });
+  proc.on("exit", function (code, signal) {
+    process.on("exit", function () {
+      if (signal) {
+        process.kill(process.pid, signal);
+      } else {
+        process.exit(code);
+      }
+    })
  });
-});
+}
--- a/bin/6to5-runtime
+++ b/bin/6to5-runtime
@@ -1,4 +1,4 @@
 #!/usr/bin/env node

-var runtime = require("../lib/6to5/runtime");
+var runtime = require("../lib/6to5/runtime-generator");
 console.log(runtime(process.argv[2]));
--- a/bin/6to5/file.js
+++ b/bin/6to5/file.js
@@ -113,16 +113,14 @@ module.exports = function (commander, filenames) {
    walk();

    if (commander.watch) {
-      var watcher = chokidar.watch(filenames, {
+      chokidar.watch(filenames, {
        persistent: true,
        ignoreInitial: true
-      });
-
-      _.each(["add", "change", "unlink"], function (type) {
-        watcher.on(type, function (filename) {
+      }).on("all", function (type, filename) {
+        if (type === "add" || type === "change" || type === "unlink" ) {
          console.log(type, filename);
          walk();
-        });
+        }
      });
    }
  };
--- a/bin/6to5/index.js
+++ b/bin/6to5/index.js
@@ -20,7 +20,8 @@ commander.option("-b, --blacklist [blacklist]", "Blacklist of transformers to NO
 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.option("-a, --amd-module-ids", "Insert module id in AMD modules", false); // todo: remove in 3.0.0
+commander.option("-m, --module-ids", "Insert module id in modules", false);

 commander.on("--help", function(){
  var outKeys = function (title, obj) {
@@ -89,9 +90,9 @@ if (errors.length) {

 exports.opts = {
  sourceMapName: commander.outFile,
-  amdModuleIds:  commander.amdModuleIds,
  experimental:  commander.experimental,
  playground:    commander.playground,
+  moduleIds:     commander.amdModuleIds || commander.moduleIds,
  blacklist:     commander.blacklist,
  whitelist:     commander.whitelist,
  sourceMap:     commander.sourceMaps || commander.sourceMapsInline,
--- a/bin/_6to5-node
+++ b/bin/_6to5-node
@@ -1,12 +1,14 @@
 #!/usr/bin/env node

-var commander = require("commander");
-var path      = require("path");
-var repl      = require("repl");
-var to5       = require("../lib/6to5");
-var util      = require("../lib/6to5/util");
-var vm        = require("vm");
-var _         = require("lodash");
+var roadrunner = require("roadrunner");
+var commander  = require("commander");
+var Module     = require("module");
+var path       = require("path");
+var repl       = require("repl");
+var to5        = require("../lib/6to5");
+var util       = require("../lib/6to5/util");
+var vm         = require("vm");
+var _          = require("lodash");

 commander.option("-e, --eval [script]", "Evaluate script");
 commander.option("-p, --print", "Evaluate script and print result");
@@ -14,28 +16,33 @@ commander.option("-i, --ignore [regex]", "Ignore all files that match this regex
 commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
 commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
 commander.option("-g, --playground", "Enable playground support");
+commander.option("-c, --cache", "Cache compiled files and require paths");

 var pkg = require("../package.json");
 commander.version(pkg.version);
 commander.usage("[options] [ -e script | script.js ] [arguments]");
 commander.parse(process.argv);

+if (commander.cache) roadrunner.load();
+
 //

 to5.register({
  experimental: commander.experimental,
  extensions:   commander.extensions,
-  ignore:       commander.ignore
+  playground:   commander.playground,
+  ignore:       commander.ignore,
+  cache:        commander.cache && roadrunner.get("6to5")
 });

 //

 var _eval = function (code, filename) {
  code = to5.transform(code, {
-    modules: "commonInterop",
    filename: filename,
    blacklist: ["useStrict"],
-    experimental: commander.experimental
+    experimental: commander.experimental,
+    playground: commander.playground
  }).code;
  return vm.runInThisContext(code, filename);
 };
@@ -44,21 +51,34 @@ if (commander.eval) {
  var result = _eval(commander.eval, "eval");
  if (commander.print) console.log(result);
 } else {
-  var filenames = commander.args;
+  if (commander.args.length) {
+    // slice all arguments up to the first filename since they're 6to5 args that we handle
+    var args = process.argv.slice(2);

-  if (filenames.length) {
-    _.each(filenames, function (filename) {
-      if (!util.isAbsolute(filename)) {
-        filename = path.join(process.cwd(), filename);
+    var i = 0;
+    _.each(args, function (arg, i2) {
+      if (arg[0] !== "-") {
+        i = i2;
+        return false;
      }
-
-      require(require.resolve(filename));
    });
+    args = args.slice(i);
+
+    // make the filename absolute
+    var filename = args[0]
+    if (!util.isAbsolute(filename)) args[0] = path.join(process.cwd(), filename);
+
+    // add back on node and concat the sliced args
+    process.argv = ["node"].concat(args);
+
+    Module.runMain();
  } else {
    replStart();
  }
 }

+if (commander.cache) roadrunner.save();
+
 function replStart() {
  repl.start({
    prompt: "> ",
--- a/doc/caveats.md
+++ b/doc/caveats.md
@@ -2,22 +2,31 @@

 In order for certain features to work they require certain polyfills. You can
 satisfy **all** 6to5 feature requirements by using the included
-[polyfill](polyfill.md). You may alternatively selectively include what you need:
+[polyfill](polyfill.md).

-| Feature                     | Requirements                                                                                                                 |
-| --------------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
-| Abstract References         | [experimental](usage.md#experimental), `Symbol`                                                                              |
-| Array destructuring         | `Array.isArray`, `Array.from`                                                                                                |
-| Async functions, Generators | [experimental](usage.md#experimental), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
-| Comprehensions              | [experimental](usage.md#experimental), `Array.isArray`, `Array.from`                                                         |
-| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                       |
-| Object spread/rest          | [experimental](usage.md#experimental), `Object.assign`                                                                       |
-| Spread                      | `Array.isArray`, `Array.from`                                                                                                |
+You may alternatively selectively include what you need:

-## Classes
+| Feature                     | Requirements                                                                                                           |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | [experimental](experimental.md), `Symbol`                                                                              |
+| Array destructuring         | `Array.isArray`, `Array.from`                                                                                          |
+| Async functions, Generators | [experimental](experimental.md), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
+| Comprehensions              | [experimental](experimental.md), `Array.isArray`, `Array.from`                                                         |
+| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                 |
+| Object spread/rest          | [experimental](experimental.md), `Object.assign`                                                                       |
+| Spread                      | `Array.isArray`, `Array.from`                                                                                          |

-Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
-limitations in ES5 implementations.
+## ES5
+
+Since 6to5 assumes that your code will be ran in an ES5 environment it uses ES5
+functions. So if you're using an environment that has limited or no support for
+ES5 such as lower versions of IE then using the
+[es5-shim](https://github.com/es-shims/es5-shim) along with the
+[6to5 polyfill](polyfill.md) will add support for these methods.
+
+## Internet Explorer
+
+### Classes (9 and below)

 If you're inheriting from a class then static properties are inherited from it
 via [\_\_proto\_\_](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto),
@@ -39,3 +48,12 @@ class Bar extends Foo {
  }
 }
 ```
+
+## Getters/setters (8 and below)
+
+In IE8 `Object.defineProperty` can only be used on DOM objects. This is
+unfortunate as it's required to set getters and setters. Due to this if
+you plan on supporting IE8 or below then the user of getters and setters
+isn't recommended.
+
+Reference: [MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty#Internet_Explorer_8_specific_notes).
--- a/doc/differences.md
+++ b/doc/differences.md
@@ -1,6 +1,8 @@
 # Differences

-## Philosophy
+There are three main points that separate 6to5 from all other transpilers.
+
+### Readable code

 The fundamental concept behind 6to5 is that the generated code must be close as
 possible to the original, retaining all the same formatting and readability.
@@ -51,7 +53,27 @@ As you can tell, it's not very pretty, unreadable even. Instead of mapping
 directly to a runtime, like other transpilers, 6to5 maps directly to the
 equivalent ES5.

-Sometimes there are little things that 6to5 needs
+Sometimes there are little inline functions that 6to5 needs. These are
+placed at the top of your file much like coffee-script does. If these
+are bother you then you can use the [optional runtime](optional-runtime.md).
+We promise that these inline functions will never be significant and will
+always be used as little as possible.
+
+### Static analysis
+
+6to5 uses a lot of static analysis to simplify code as much as possible.
+Not many other transpilers do this, and those that do don't do it nearly
+as much as 6to5. This process is pretty intensive but it leads to higher
+quality code.
+
+### Spec compliancy
+
+6to5 prides itself on
+[spec compliancy](https://kangax.github.io/compat-table/es6/). We have
+excellent support for edgecases, something that many other transpilers
+suffer from, including Traceur. When you use 6to5 you can be confident
+that when you turn it off and use your code in a full ES6 environment
+**it'll just work**.

 ## Comparison to other transpilers

@@ -62,40 +84,44 @@ Sometimes there are little things that 6to5 needs
 | Source maps                  | ✓    | ✓       | ✓              | ✓      |        | ✓           |
 | No compiler global pollution | ✓    |         | ✓              | ✓      |        | ✓           |
 | Optional runtime             | ✓    |         | ✓              |        |        | ✓           |
-| Browser support              | ✓    | ✓       |                | ✓      |        |             |
+| Browser compiler             | ✓    | ✓       |                | ✓      |        |             |

 ### Language Support

-|                              | 6to5  | Traceur | es6-transpiler | esnext | es6now | jstransform |
-| ---------------------------- | ----- | ------- | -------------- | ------ | ------ | ----------- |
-| Abstract references          | ✓     |         |                |        |        |             |
-| Array comprehension          | ✓     | ✓       | ✓              |        |        |             |
-| Arrow functions              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Async functions              | ✓     | ✓       |                | ✓      |        |             |
-| Classes                      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Computed property names      | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Constants                    | ✓     | ✓       | ✓              |        |        |             |
-| Default parameters           | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Destructuring                | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Exponentiation operator      | ✓     | ✓       |                |        |        |             |
-| For-of                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Generators                   | ✓     | ✓       |                | ✓      |        |             |
-| Generator comprehension      | ✓     | ✓       |                |        |        |             |
-| Let scoping                  | ✓     | ✓       | ✓              |        |        |             |
-| Modules                      | ✓     | ✓       |                |        | ✓      |             |
-| Object rest/spread           | ✓     |         |                |        |        | ✓           |
-| Property method assignment   | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Property name shorthand      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Rest parameters              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Spread                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Template literals            | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Unicode regex                | ✓     | ✓       | ✓              |        |        |             |
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓    |         |                |        |        |             |
+| Array comprehension          | ✓    | ✓       | ✓              |        |        |             |
+| Arrow functions              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Async functions              | ✓    | ✓       |                | ✓      |        |             |
+| Async generator functions    | ✓    | ✓       |                |        |        |             |
+| Classes                      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Computed property names      | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Constants                    | ✓    | ✓       | ✓              |        |        |             |
+| Default parameters           | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Destructuring                | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓    | ✓       |                |        |        |             |
+| Flow types                   | ✓    |         |                |        |        | ✓           |
+| For-of                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Generators                   | ✓    | ✓       |                | ✓      |        |             |
+| Generator comprehension      | ✓    | ✓       |                |        |        |             |
+| JSX                          | ✓    |         |                |        |        |             |
+| Let scoping                  | ✓    | ✓       | ✓              |        |        |             |
+| Modules                      | ✓    | ✓       |                |        | ✓      |             |
+| Object rest/spread           | ✓    |         |                |        |        | ✓           |
+| Property method assignment   | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Property name shorthand      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Rest parameters              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| React                        | ✓    |         |                |        |        |             |
+| Spread                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Template literals            | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Unicode regex                | ✓    | ✓       | ✓              |        |        |             |

 ### [Traceur](https://github.com/google/traceur-compiler)

 Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
 While this can be trimmed down by selectively building the runtime, it's an
-unneccesary step when a large runtime can be eliminated entirely.
+unnecessary step when a large runtime can be eliminated entirely.

 ### [es6now](https://github.com/zenparsing/es6now)

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

-## Abstract references ([experimental](usage.md#experimental)) ([spec](https://github.com/zenparsing/es-abstract-refs))
+## Abstract references ([experimental](experimental.md)) ([spec](https://github.com/zenparsing/es-abstract-refs))

 ```javascript
 foo::bar;
@@ -8,7 +8,7 @@ foo::bar = baz;
 delete foo::bar;
 ```

-## Array comprehensions ([experimental](usage.md#experimental))
+## Array comprehensions ([experimental](experimental.md))

 ```javascript
 var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
@@ -39,7 +39,7 @@ var bob = {
 };
 ```

-## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
+## Async functions ([experimental](experimental.md)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))

 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -49,6 +49,12 @@ async function chainAnimationsAsync(elem, animations) {
 }
 ```

+## Async generator functions ([experimental](experimental.md)) ([spec](https://github.com/jhusain/asyncgenerator))
+
+```javascript
+
+```
+
 ## Classes

 ```javascript
@@ -130,7 +136,7 @@ var [a] = [];
 a === undefined;
 ```

-## Exponentiation operator ([experimental](usage.md#experimental)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+## Exponentiation operator ([experimental](experimental.md)) ([spec](https://github.com/rwaldron/exponentiation-operator))

 ```javascript
 var a = 2;
@@ -167,7 +173,7 @@ for (var n of fibonacci()) {
 }
 ```

-## Generator comprehensions ([experimental](usage.md#experimental))
+## Generator comprehensions ([experimental](experimental.md))

 ```javascript
 var nums = [1, 2, 3, 4, 5, 6];
@@ -208,7 +214,7 @@ export default test;
 0o767 === 503; // true
 ```

-## Object spread/rest ([experimental](usage.md#experimental)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
+## Object spread/rest ([experimental](experimental.md)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))

 ```javascript
 var n = { x, y, ...z };
--- a/doc/index.md
+++ b/doc/index.md
@@ -35,23 +35,24 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the

 ## [Features](features.md)

- - [Abstract references](features.md#abstract-references) ([experimental](usage.md#experimental))
- - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
- - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
+ - [Abstract references](features.md#abstract-references) ([experimental](experimental.md))
+ - [Array comprehension](features.md#array-comprehension) ([experimental](experimental.md))
+ - [Async functions](features.md#async-functions) ([experimental](experimental.md))
+ - [Async generator functions](features.md#async-generator-functions) ([experimental](experimental.md))
 - [Arrow functions](features.md#arrow-functions)
 - [Classes](features.md#classes)
 - [Computed property names](features.md#computed-property-names)
 - [Constants](features.md#constants)
 - [Default parameters](features.md#default-parameters)
 - [Destructuring](features.md#destructuring)
- - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](usage.md#experimental))
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](experimental.md))
 - [For-of](features.md#for-of)
 - [Generators](features.md#generators)
- - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](experimental.md))
 - [Let scoping](features.md#let-scoping)
 - [Modules](features.md#modules)
 - [Numeric literals](features.md#numeric-literals)
- - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](usage.md#experimental))
+ - [Object Rest/Spread](features.md#object-rest-spread) ([experimental](experimental.md))
 - [Property method assignment](features.md#property-method-assignment)
 - [Property name shorthand](features.md#property-name-shorthand)
 - [React/JSX](react.md)
--- a/doc/modules.md
+++ b/doc/modules.md
@@ -19,12 +19,11 @@ to5.transform('import "foo";', { modules: "common" });

 * [AMD](#amd)
 * [Common (Default)](#common-default)
- * [Common Interop](#common-interop)
 * [Ignore](#ignore)
 * [System](#system)
 * [UMD](#umd)

-### Common (Default)
+### Common

 ```sh
 $ 6to5 --modules common
@@ -33,6 +32,11 @@ $ 6to5 --modules common
 **In**

 ```javascript
+export default test;
+
+export {test};
+export var test = 5;
+
 import "foo";

 import foo from "foo";
@@ -40,95 +44,30 @@ import * as foo from "foo";

 import {bar} from "foo";
 import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
 ```

 **Out**

 ```javascript
-require("foo");
+"use strict";

-var foo = require("foo").default;
-var foo = require("foo");
-
-var bar = require("foo").bar;
-var bar = require("foo").foo;
-
-exports.test = test;
-var test = 5; exports.test = test;
-
-exports.default = test;
-```
-
-### Common interop
-
-```sh
-$ 6to5 --modules commonInterop
-```
-
-**In**
-
-```javascript
-import "foo";
-
-import foo from "foo";
-import * as foo from "foo";
-
-import {bar} from "foo";
-import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
-```
-
-**Out**
-
-```javascript
 var _interopRequire = function (obj) {
  return obj && (obj["default"] || obj);
 };

-require("foo");
-
-var foo = _interopRequire(require("foo"));
-var foo = require("foo");
-
-var bar = require("foo").bar;
-var bar = require("foo").foo;
+exports = module.exports = test;

 exports.test = test;
 var test = exports.test = 5;

-exports["default"] = test;
-```
+require("foo");

-#### module.exports behaviour
+var foo = _interopRequire(require("foo"));

-If there exist no other non-default `export`s then `default exports` are
-exported as `module.exports` instead of `exports.default`.
+var foo = require("foo");

-**In**
-
-```javascript
-export default function foo() {
-
-}
-```
-
-**Out**
-
-```javascript
-module.exports = foo;
-
-function foo() {
-
-}
+var bar = require("foo").bar;
+var bar = require("foo").foo;
 ```

 ### AMD
@@ -151,9 +90,14 @@ export function bar() {

 ```javascript
 define(["exports", "foo"], function (exports, _foo) {
-  exports.bar = bar;
+  "use strict";

-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);

  function bar() {
    return foo("foobar");
@@ -192,10 +136,15 @@ export function bar() {
  } else if (typeof exports !== "undefined") {
    factory(exports, require("foo"));
  }
-})(function (exports) {
-  exports.bar = bar;
+})(function (exports, _foo) {
+  "use strict";

-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);

  function bar() {
    return foo("foobar");
@@ -288,7 +237,7 @@ ModuleFormatter.prototype.transform = function (ast) {
  // feel free to modify this however
 };

-ModuleFormatter.prototype.import = function (node, nodes) {
+ModuleFormatter.prototype.importDeclaration = function (node, nodes) {
  // node is an ImportDeclaration
 };

@@ -297,7 +246,7 @@ ModuleFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
  // node is an ImportDeclaration
 };

-ModuleFormatter.prototype.export = function (node, nodes) {
+ModuleFormatter.prototype.exportDeclaration = function (node, nodes) {
  // node is an ExportDeclaration
 };

--- a/doc/playground.md
+++ b/doc/playground.md
@@ -12,7 +12,7 @@ Playground is a proving ground for **possible** ES7 proposals.
 to5.transform("code", { playground: true });
 ```

-**NOTE:** Enabling `playground` also enables [experimental support](usage.md#experimental).
+**NOTE:** Enabling `playground` also enables [experimental support](experimental.md).

 ## Features

@@ -52,11 +52,11 @@ if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
 ### Method binding

 ```javascript
-var fn = obj:method;
-var fn = obj:method("foob");
+var fn = obj#method;
+var fn = obj#method("foob");

-["foo", "bar"].map(:toUpperCase); // ["FOO", "BAR"]
-[1.1234, 23.53245, 3].map(:toFixed(2)); // ["1.12", "23.53", "3.00"]
+["foo", "bar"].map(#toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(#toFixed(2)); // ["1.12", "23.53", "3.00"]
 ```

 equivalent to:
--- a/doc/plugins.md
+++ b/doc/plugins.md
@@ -1,18 +1,33 @@
 # Plugins

- - [Broccoli](https://github.com/very-geek/broccoli-6to5-transpiler)
- - [Browserify](https://github.com/6to5/6to5-browserify)
- - [Brunch](https://github.com/es128/6to5-brunch)
- - [Duo](https://github.com/bdo-labs/duo6to5)
- - [Connect](https://github.com/6to5/6to5-connect)
- - [Gobble](https://github.com/gobblejs/gobble-6to5)
- - [Gulp](https://github.com/sindresorhus/gulp-6to5)
- - [Grunt](https://github.com/sindresorhus/grunt-6to5)
+## Build systems
+
+ - [Broccoli](https://github.com/6to5/broccoli-6to5-transpiler)
+ - [Browserify](https://github.com/6to5/6to5ify)
+ - [Brunch](https://github.com/6to5/6to5-brunch)
+ - [Duo](https://github.com/6to5/duo6to5)
+ - [Gobble](https://github.com/6to5/gobble-6to5)
+ - [Gulp](https://github.com/6to5/gulp-6to5)
+ - [Grunt](https://github.com/6to5/grunt-6to5)
+ - [Sprockets](https://github.com/josh/sprockets-es6) or via [Browserify](https://github.com/6to5/6to5-rails)
+ - [webpack](https://github.com/6to5/6to5-loader)
+
+## Integrations
+
 - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
- - [Jade](https://github.com/Apoxx/jade-6to5)
- - [Jest](https://github.com/6to5/6to5-jest)
 - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
- - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
+
+## Bridges
+
+ - [Ruby](https://github.com/6to5/6to5-ruby)
+
+## Testing
+
+ - [Jest](https://github.com/6to5/6to5-jest)
+ - [Karma](https://github.com/6to5/karma-6to5-preprocessor)
 - [Mocha](https://github.com/6to5/6to5-mocha)
- - [Rails](https://github.com/josh/sprockets-es6) or via [browserify-rails](https://github.com/6to5/6to5-rails)
- - [webpack](https://github.com/Couto/6to5-loader)
+
+## Misc
+
+ - [Connect](https://github.com/6to5/6to5-connect)
+ - [Jade](https://github.com/6to5/jade-6to5)
--- a/doc/polyfill.md
+++ b/doc/polyfill.md
@@ -1,16 +1,15 @@
 # Polyfill

-6to5 includes a polyfill that includes the
-[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and the
-[es6-shim](https://github.com/paulmillr/es6-shim) and
-[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
+6to5 includes a polyfill that includes a custom
+[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and
+[core.js](https://github.com/zloirock/core-js).

 This will emulate a full ES6 environment. This polyfill is automatically loaded
-when using [6to5-node](usage.md#node).
+when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).

 ## Usage

-### Node
+### Node/Browserify

 You need to include the polyfill require at the top the **entry point** to your
 application.
@@ -19,9 +18,17 @@ application.
 require("6to5/polyfill");
 ```

+Fortunately, this is automatically loaded when using:
+
+```javascript
+require("6to5/register");
+```
+
 ### Browser

 Available from the `browser-polyfill.js` file within the 6to5 directory of an
 npm release. This needs to be included **before** all your compiled 6to5 code.
 You can either prepend it to your compiled code or include it in a `<script>`
 before it.
+
+**NOTE:** Do not `require` this via browserify etc, use `6to5/polyfill`.
--- a/doc/usage.md
+++ b/doc/usage.md
@@ -95,6 +95,15 @@ to5.transformFile("filename.js", options, function (err, result) {
 });
 ```

+### to5.transform.fromAst(ast, [code], [opts])
+
+```javascript
+var result = to5.transform.fromAst(ast, "var a = 2;", opts);
+result.code;
+result.map;
+result.ast;
+```
+
 #### Options

 ```javascript
@@ -143,23 +152,57 @@ to5.transformFile("filename.js", options, function (err, result) {
  // Default: `sourceRoot` option.
  moduleRoot: "my-app",

-  // If truthy, insert an explicit id for each defined AMD module.
-  // By default, AMD modules are anonymous.
+  // If truthy, insert an explicit id for each defined AMD/System module.
+  // By default, AMD/System modules are anonymous.
  // Default: false
-  amdModuleIds: true,
+  moduleIds: true,

  // Optionally replace all 6to5 helper declarations with a referenece to this
  // variable. If set to `true` then the default namespace is used "to5Runtime".
  // Default: false
  runtime: true,

-  // Output comments in generated output
-  // Default: true
-  comments: false,
-
  // Enable support for experimental ES7 features
  // Default: false
-  experimental: true
+  experimental: true,
+
+  // Set this to `false` if you don't want the transformed AST in the returned
+  // result
+  // Default: true
+  ast: true,
+
+  // Set this to `false` if you don't want the transformed code in the returned
+  // result
+  // Default: true
+  code: true,
+
+  format: {
+    // Output comments in generated output
+    // Default: true
+    comments: true,
+
+    // Do not include superfluous whitespace characters and line terminators
+    // Default: false
+    compact: false,
+
+    indent: {
+      // Preserve parentheses in new expressions that have no arguments
+      // Default: true
+      parentheses: true,
+
+      // Adjust the indentation of multiline comments to keep asterisks vertically aligned
+      // Default: true
+      adjustMultilineComment: true,
+
+      // Indent string
+      // Default: "  "
+      style: "  ",
+
+      // Base indent level
+      // Default: 0
+      base: 0
+    }
+  }
 }
 ```

@@ -167,7 +210,10 @@ to5.transformFile("filename.js", options, function (err, result) {

 All subsequent files required by node with the extensions `.es6` and `.js` will
 be transformed by 6to5. The polyfill specified in [Polyfill](polyfill.md) is
-also required.
+also required; but this is automatically loaded when using:
+
+Source maps are automatically configured so if any errors a thrown then line
+number info is mapped and you'll get the correct source location.

 ```javascript
 require("6to5/register");
@@ -184,6 +230,8 @@ require("6to5/register")({
 });
 ```

+**NOTE:** Using 6to5-node or `require("6to5/register")`, 6to5 will check what features are available in the current environment and blacklists them if they're supported.
+
 #### Options

 ```javascript
@@ -202,15 +250,10 @@ require("6to5/register")({

  // This will remove the currently hooked extensions of .es6 and .js so you'll
  // have to add them back if you want them to be used again.
-  extensions: [".js", ".es6"]
+  extensions: [".js", ".es6"],
+
+  // Enables `roadrunner` cache that will save to a `.roadrunner.json` file in your cwd
+  // Do not check this into git as it's user-specific
+  cache: true
 });
 ```
-
-## 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**.
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -16,13 +16,14 @@ function File(opts) {
 }

 File.declarations = [
-  "extends",
-  "class-props",
+  "inherits",
+  "prototype-properties",
  "apply-constructor",
  "tagged-template-literal",
  "interop-require",
  "to-array",
-  "object-spread",
+  "sliced-to-array",
+  "object-without-properties",
  "has-own",
  "slice"
 ];
@@ -34,6 +35,7 @@ File.normaliseOptions = function (opts) {
    experimental: false,
    playground:   false,
    whitespace:   true,
+    moduleIds:    opts.amdModuleIds || false,
    blacklist:    [],
    whitelist:    [],
    sourceMap:    false,
@@ -82,13 +84,19 @@ File.normaliseOptions = function (opts) {
  return opts;
 };

-File.prototype.toArray = function (node) {
+File.prototype.toArray = function (node, i) {
  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]);
+    var declarationName = "to-array";
+    var args = [node];
+    if (i) {
+      args.push(t.literal(i));
+      declarationName = "sliced-to-array";
+    }
+    return t.callExpression(this.addDeclaration(declarationName), args);
  }
 };

@@ -101,7 +109,7 @@ File.prototype.getModuleFormatter = function (type) {
  }

  if (!ModuleFormatter) {
-    throw new ReferenceError("unknown module formatter type " + type);
+    throw new ReferenceError("Unknown module formatter type " + JSON.stringify(type));
  }

  return new ModuleFormatter(this);
@@ -156,14 +164,16 @@ File.prototype.errorWithNode = function (node, msg, Error) {
  return err;
 };

-File.prototype.parse = function (code) {
+File.prototype.addCode = function (code) {
  code = (code || "") + "";
+  this.code = code;
+  return this.parseShebang(code);
+};

+File.prototype.parse = function (code) {
  var self = this;

-  this.code = code;
-
-  code = this.parseShebang(code);
+  code = this.addCode(code);

  return util.parse(this.opts, code, function (tree) {
    self.transform(tree);
--- a/lib/6to5/generation/buffer.js
+++ b/lib/6to5/generation/buffer.js
@@ -35,7 +35,7 @@ Buffer.prototype.dedent = function () {
 };

 Buffer.prototype.semicolon = function () {
-  if (this.format.semicolons) this.push(";");
+  this.push(";");
 };

 Buffer.prototype.ensureSemicolon = function () {
@@ -66,9 +66,7 @@ Buffer.prototype.removeLast = function (cha) {
 };

 Buffer.prototype.newline = function (i, removeLast) {
-  if (!this.buf) return;
  if (this.format.compact) return;
-  if (this.endsWith("{\n")) return;

  if (_.isBoolean(i)) {
    removeLast = i;
@@ -76,6 +74,7 @@ Buffer.prototype.newline = function (i, removeLast) {
  }

  if (_.isNumber(i)) {
+    if (this.endsWith("{\n")) i--;
    if (this.endsWith(util.repeat(i, "\n"))) return;

    var self = this;
@@ -88,7 +87,10 @@ Buffer.prototype.newline = function (i, removeLast) {
  if (removeLast && this.isLast("\n")) this.removeLast("\n");

  this.removeLast(" ");
+
+  // remove whitespace if last character was a newline
  this.buf = this.buf.replace(/\n +$/, "\n");
+
  this._push("\n");
 };

--- a/lib/6to5/generation/generator.js
+++ b/lib/6to5/generation/generator.js
@@ -37,7 +37,6 @@ _.each(Buffer.prototype, function (fn, key) {
 CodeGenerator.normaliseOptions = function (opts) {
  return _.merge({
    parentheses: true,
-    semicolons: true,
    comments: opts.comments == null || opts.comments,
    compact: false,
    indent: {
@@ -58,6 +57,7 @@ CodeGenerator.generators = {
  methods:          require("./generators/methods"),
  modules:          require("./generators/modules"),
  types:            require("./generators/types"),
+  flow:             require("./generators/flow"),
  base:             require("./generators/base"),
  jsx:              require("./generators/jsx")
 };
@@ -71,6 +71,12 @@ CodeGenerator.prototype.generate = function () {

  this.print(ast);

+  var comments = [];
+  _.each(ast.comments, function (comment) {
+    if (!comment._displayed) comments.push(comment);
+  });
+  this._printComments(comments);
+
  return {
    map:  this.map.get(),
    code: this.buffer.get()
@@ -132,6 +138,9 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
      var needs = n.needsWhitespaceAfter;
      if (leading) needs = n.needsWhitespaceBefore;
      lines += needs(node, parent);
+
+      // generated nodes can't add starting file whitespace
+      if (!self.buffer.get()) lines = 0;
    }

    self.newline(lines);
@@ -147,7 +156,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {

    // only compute if this node needs parens if our parent has been changed
    // since acorn would've wrapped us in a ParanthesizedExpression
-    var needsParens = parent !== node._parent && n.needsParens(node, parent);
+    var needsParens = n.needsParens(node, parent);
    if (needsParens) this.push("(");

    this[node.type](node, this.buildPrint(node), parent);
@@ -259,6 +268,14 @@ CodeGenerator.prototype._printComments = function (comments) {
  var self = this;

  _.each(comments, function (comment) {
+    // find the original comment in the ast and set it as displayed
+    _.each(self.ast.comments, function (origComment) {
+      if (origComment.start === comment.start) {
+        origComment._displayed = true;
+        return false;
+      }
+    });
+
    // whitespace before
    self.newline(self.whitespace.getNewlinesBefore(comment));

--- a/lib/6to5/generation/generators/expressions.js
+++ b/lib/6to5/generation/generators/expressions.js
@@ -18,12 +18,6 @@ exports.UnaryExpression = function (node, print) {
  print(node.argument);
 };

-exports.ParenthesizedExpression = function (node, print) {
-  this.push("(");
-  print(node.expression);
-  this.push(")");
-};
-
 exports.UpdateExpression = function (node, print) {
  if (node.prefix) {
    this.push(node.operator);
@@ -98,8 +92,11 @@ exports.AssignmentExpression = function (node, print) {
  print(node.right);
 };

+var SCIENTIFIC_NOTATION = /e/i;
+
 exports.MemberExpression = function (node, print) {
-  print(node.object);
+  var obj = node.object;
+  print(obj);

  if (node.computed) {
    this.push("[");
@@ -107,7 +104,7 @@ exports.MemberExpression = function (node, print) {
    this.push("]");
  } else {
    // 5..toFixed(2);
-    if (t.isLiteral(node.object) && util.isInteger(node.object.value)) {
+    if (t.isLiteral(obj) && util.isInteger(obj.value) && !SCIENTIFIC_NOTATION.test(obj.value.toString())) {
      this.push(".");
    }

--- a/lib/6to5/generation/generators/flow.js
+++ b/lib/6to5/generation/generators/flow.js
@@ -0,0 +1,3 @@
+exports.ClassProperty = function () {
+  throw new Error("not implemented");
+};
--- a/lib/6to5/generation/generators/modules.js
+++ b/lib/6to5/generation/generators/modules.js
@@ -1,7 +1,14 @@
 var t = require("../../types");
 var _ = require("lodash");

-exports.ImportSpecifier =
+exports.ImportSpecifier = function (node, print) {
+  if (node.id && node.id.name === "default") {
+    print(node.name);
+  } else {
+    return exports.ExportSpecifier.apply(this, arguments);
+  }
+};
+
 exports.ExportSpecifier = function (node, print) {
  print(node.id);
  if (node.name) {
@@ -62,7 +69,9 @@ exports.ImportDeclaration = function (node, print) {
        self.push(", ");
      }

-      if (!spec.default && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
+      var isDefault = spec.id && spec.id.name === "default";
+
+      if (!isDefault && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
        foundImportSpecifier = true;
        self.push("{ ");
      }
--- a/lib/6to5/generation/generators/statements.js
+++ b/lib/6to5/generation/generators/statements.js
@@ -146,7 +146,7 @@ exports.SwitchCase = function (node, print) {
    this.push("default:");
  }

-  this.space();
+  this.newline();
  print.sequence(node.consequent, { indent: true });
 };

@@ -164,6 +164,12 @@ exports.VariableDeclaration = function (node, print, parent) {
  }
 };

+exports.PrivateDeclaration = function (node, print) {
+  this.push("private ");
+  print.join(node.declarations, { separator: ", " });
+  this.semicolon();
+};
+
 exports.VariableDeclarator = function (node, print) {
  if (node.init) {
    print(node.id);
--- a/lib/6to5/generation/generators/types.js
+++ b/lib/6to5/generation/generators/types.js
@@ -84,8 +84,8 @@ exports.Literal = function (node) {
  if (type === "string") {
    val = JSON.stringify(val);

-    // escape unicode characters
-    val = val.replace(/[\u007f-\uffff]/g, function (c) {
+    // escape illegal js but valid json unicode characters
+    val = val.replace(/[\u000A\u000D\u2028\u2029]/g, function (c) {
      return "\\u" + ("0000" + c.charCodeAt(0).toString(16)).slice(-4);
    });

--- a/lib/6to5/generation/node/parentheses.js
+++ b/lib/6to5/generation/node/parentheses.js
@@ -92,13 +92,6 @@ exports.YieldExpression = function (node, parent) {
         t.isYieldExpression(parent);
 };

-exports.Literal = function (node, parent) {
-  // (1).valueOf()
-  if (_.isNumber(node.value) && t.isMemberExpression(parent) && parent.object === node) {
-    return true;
-  }
-};
-
 exports.ClassExpression = function (node, parent) {
  return t.isExpressionStatement(parent);
 };
--- a/lib/6to5/generation/whitespace.js
+++ b/lib/6to5/generation/whitespace.js
@@ -38,7 +38,11 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
    }
  });

-  return this.getNewlinesBetween(startToken, endToken);
+  if (endToken.type.type === "eof") {
+    return 1;
+  } else {
+    return this.getNewlinesBetween(startToken, endToken);
+  }
 };

 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {
--- a/lib/6to5/index.js
+++ b/lib/6to5/index.js
@@ -3,7 +3,11 @@ var util      = require("./util");
 var fs        = require("fs");
 var _         = require("lodash");

-exports.runtime = require("./runtime");
+exports.Transformer = require("./transformation/transformer");
+
+exports.types = require("./types");
+
+exports.runtime = require("./runtime-generator");

 exports.register = function (opts) {
  var register = require("./register");
--- a/lib/6to5/patch.js
+++ b/lib/6to5/patch.js
@@ -1,22 +1,17 @@
 var t = require("./types");
 var _ = require("lodash");

+// estraverse
+
+var estraverse = require("estraverse");
+_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+
+// regenerator/recast/ast-types
+
 var types = require("ast-types");
 var def   = types.Type.def;
 var or    = types.Type.or;

-// Program wrapper
-def("File")
-  .bases("Node")
-  .build("program")
-  .field("program", def("Program"));
-
-// Non-standard Acorn type
-def("ParenthesizedExpression")
-  .bases("Expression")
-  .build("expression")
-  .field("expression", def("Expression"));
-
 // Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
  .bases("Specifier")
@@ -30,6 +25,11 @@ def("VirtualPropertyExpression")
  .field("object", def("Expression"))
  .field("property", or(def("Identifier"), def("Expression")));

+def("PrivateDeclaration")
+  .bases("Declaration")
+  .build("declarations")
+  .field("declarations", [def("Identifier")]);
+
 // Playground
 def("BindMemberExpression")
  .bases("Expression")
@@ -45,6 +45,3 @@ def("BindFunctionExpression")
  .field("arguments", [def("Expression")]);

 types.finalize();
-
-var estraverse = require("estraverse");
-_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
--- a/lib/6to5/polyfill.js
+++ b/lib/6to5/polyfill.js
@@ -1,37 +1,2 @@
-/* jshint newcap: false */
-
-var ensureSymbol = function (key) {
-  Symbol[key] = Symbol[key] || Symbol();
-};
-
-var ensureProto = function (Constructor, key, val) {
-  var proto = Constructor.prototype;
-  proto[key] = proto[key] || val;
-};
-
-//
-
-if (typeof Symbol === "undefined") {
-  require("es6-symbol/implement");
-}
-
-require("es6-shim");
-require("./transformation/transformers/es6-generators/runtime");
-
-// Abstract references
-
-ensureSymbol("referenceGet");
-ensureSymbol("referenceSet");
-ensureSymbol("referenceDelete");
-
-ensureProto(Function, Symbol.referenceGet, function () { return this; });
-
-ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
-ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
-ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
-
-if (global.WeakMap) {
-  ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
-  ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
-  ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);
-}
+require("core-js/shim");
+require("regenerator/runtime");
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -1,6 +1,7 @@
 require("./polyfill");

 var sourceMapSupport = require("source-map-support");
+var roadrunner       = require("roadrunner");
 var util             = require("./util");
 var to5              = require("./index");
 var fs               = require("fs");
@@ -38,15 +39,22 @@ var blacklistTest = function (transformer, code) {
 };

 blacklistTest("arrayComprehension", "var foo = [for (foo of bar) foo * foo];");
-//blacklistTest("generatorComprehension", "");
+blacklistTest("generatorComprehension", "var foo = (for (foo of bar) foo * foo)");
 blacklistTest("arrowFunctions", "var foo = x => x * x;");
 blacklistTest("classes", "class Foo {}");
 blacklistTest("computedPropertyNames", "var foo = { [foo]: bar };");
-//blacklistTest("constants", "const foo = 0;");
+blacklistTest("constants", function () {
+  try {
+    new Function("const foo = 'foo';\nfoo = 'wow';");
+  } catch (err) {
+    return; // constants are supported
+  }
+  throw new SyntaxError;
+});
 blacklistTest("defaultParamaters", "var foo = function (bar = 0) {};");
 blacklistTest("destructuring", "var { x, y } = { x: 0, y: 0 };");
 blacklistTest("forOf", "for (var foo of bar) {}");
-blacklistTest("generators", "function* foo() {}");
+blacklistTest("generators", "function* foo() {}\nasync function bar() {}"); // generators/async functions delegated to same transformer
 blacklistTest("letScoping", "let foo = 0;");
 blacklistTest("modules", 'import foo from "from";');
 blacklistTest("propertyMethodAssignment", "{ get foo() {} }");
@@ -89,7 +97,6 @@ var loader = function (m, filename) {
    whitelist: whitelist,
    blacklist: blacklist,
    sourceMap: true,
-    modules:   "commonInterop",
    ast:       false
  }, transformOpts));

@@ -131,6 +138,11 @@ module.exports = function (opts) {

  if (opts.cache) cache = opts.cache;
  if (opts.cache === false) cache = null;
+  if (opts.cache === true) {
+    roadrunner.load();
+    roadrunner.setup();
+    cache = roadrunner.get("6to5");
+  }

  _.extend(transformOpts, opts);
 };
--- a/lib/6to5/runtime-generator.js
+++ b/lib/6to5/runtime-generator.js
--- a/lib/6to5/templates/class-super-constructor-call.js
+++ b/lib/6to5/templates/class-super-constructor-call.js
@@ -1,2 +0,0 @@
-SUPER_NAME.apply(this, arguments);
-
--- a/lib/6to5/templates/class.js
+++ b/lib/6to5/templates/class.js
@@ -1,7 +0,0 @@
-(function () {
-  var CLASS_NAME = function () {
-
-  };
-
-  return CLASS_NAME;
-})()
--- a/lib/6to5/templates/exports-assign-key.js
+++ b/lib/6to5/templates/exports-assign-key.js
@@ -1 +0,0 @@
-exports.VARIABLE_NAME = OBJECT.KEY;
--- a/lib/6to5/templates/exports-default.js
+++ b/lib/6to5/templates/exports-default.js
@@ -1 +0,0 @@
-exports.default = VALUE;
--- a/lib/6to5/templates/register.js
+++ b/lib/6to5/templates/register.js
@@ -1 +0,0 @@
-System.register(MODULE_NAME, MODULE_DEPENDENCIES, MODULE_BODY);
--- a/lib/6to5/templates/tagged-template-literal.js
+++ b/lib/6to5/templates/tagged-template-literal.js
@@ -1,4 +0,0 @@
-(function (strings, raw) {
-  return Object.defineProperties(strings, { raw: { value: raw } });
-});
-
--- a/lib/6to5/transformation/modules/_default.js
+++ b/lib/6to5/transformation/modules/_default.js
@@ -0,0 +1,204 @@
+module.exports = DefaultFormatter;
+
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+function DefaultFormatter(file) {
+  this.file = file;
+
+  this.localExports = this.getLocalExports();
+  this.remapAssignments();
+}
+
+DefaultFormatter.prototype.getLocalExports = function () {
+  var localExports = {};
+
+  traverse(this.file.ast, {
+    enter: function (node) {
+      var declar = node && node.declaration;
+      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
+        _.extend(localExports, t.getIds(declar, true));
+      }
+    }
+  });
+
+  return localExports;
+};
+
+DefaultFormatter.prototype.remapExportAssignment = function (node) {
+  return t.assignmentExpression(
+    "=",
+    node.left,
+    t.assignmentExpression(
+      node.operator,
+      t.memberExpression(t.identifier("exports"), node.left),
+      node.right
+    )
+  );
+};
+
+DefaultFormatter.prototype.remapAssignments = function () {
+  var localExports = this.localExports;
+  var self = this;
+
+  var isLocalReference = function (node, scope) {
+    var name = node.name;
+    return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
+  };
+
+  traverse(this.file.ast, {
+    enter: function (node, parent, scope) {
+      if (t.isUpdateExpression(node) && isLocalReference(node.argument, scope)) {
+        this.stop();
+
+        // expand to long file assignment expression
+        var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
+
+        // remap this assignment expression
+        var remapped = self.remapExportAssignment(assign);
+
+        // we don't need to change the result
+        if (t.isExpressionStatement(parent) || node.prefix) {
+          return remapped;
+        }
+
+        var nodes = [];
+        nodes.push(remapped);
+
+        var operator;
+        if (node.operator === "--") {
+          operator = "+";
+        } else { // "++"
+          operator = "-";
+        }
+        nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
+
+        return t.sequenceExpression(nodes);
+      }
+
+      if (t.isAssignmentExpression(node) && isLocalReference(node.left, scope)) {
+        this.stop();
+        return self.remapExportAssignment(node);
+      }
+    }
+  });
+};
+
+DefaultFormatter.prototype.getModuleName = function () {
+  var opts = this.file.opts;
+  var filenameRelative = opts.filenameRelative;
+  var moduleName = "";
+
+  if (opts.moduleRoot) {
+    moduleName = opts.moduleRoot + "/";
+  }
+
+  if (!opts.filenameRelative) {
+    return moduleName + opts.filename.replace(/^\//, "");
+  }
+
+  if (opts.sourceRoot) {
+    // remove sourceRoot from filename
+    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
+    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
+  }
+
+  // remove extension
+  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+
+  moduleName += filenameRelative;
+
+  return moduleName;
+};
+
+DefaultFormatter.prototype._pushStatement = function (ref, nodes) {
+  if (t.isClass(ref) || t.isFunction(ref)) {
+    if (ref.id) {
+      nodes.push(t.toStatement(ref));
+      ref = ref.id;
+    }
+  }
+
+  return ref;
+};
+
+DefaultFormatter.prototype._hoistExport = function (declar, assign) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = true;
+  }
+
+  return assign;
+};
+
+DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
+  var inherits = false;
+  if (node.specifiers.length === 1) inherits = node;
+
+  if (node.source) {
+    if (t.isExportBatchSpecifier(specifier)) {
+      // export * from "foo";
+      nodes.push(this._exportsWildcard(getRef()));
+    } else {
+      // export { foo } from "test";
+      nodes.push(this._exportsAssign(
+        t.getSpecifierName(specifier),
+        t.memberExpression(getRef(), specifier.id)
+      ));
+    }
+  } else {
+    // export { foo };
+    nodes.push(this._exportsAssign(t.getSpecifierName(specifier), specifier.id));
+  }
+};
+
+DefaultFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  return util.template("exports-wildcard", {
+    OBJECT: objectIdentifier
+  }, true);
+};
+
+DefaultFormatter.prototype._exportsAssign = function (id, init) {
+  return util.template("exports-assign", {
+    VALUE: init,
+    KEY:   id
+  }, true);
+};
+
+DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
+  var declar = node.declaration;
+
+  var id = declar.id;
+
+  if (node.default) {
+    id = t.identifier("default");
+  }
+
+  var assign;
+
+  if (t.isVariableDeclaration(declar)) {
+    for (var i in declar.declarations) {
+      var decl = declar.declarations[i];
+
+      decl.init = this._exportsAssign(decl.id, decl.init).expression;
+
+      var newDeclar = t.variableDeclaration(declar.kind, [decl]);
+      if (i === "0") t.inherits(newDeclar, declar);
+      nodes.push(newDeclar);
+    }
+  } else {
+    var ref = declar;
+
+    if (t.isFunctionDeclaration(declar) || t.isClassDeclaration(declar)) {
+      ref = declar.id;
+      nodes.push(declar);
+    }
+
+    assign = this._exportsAssign(id, ref);
+
+    nodes.push(assign);
+
+    this._hoistExport(declar, assign);
+  }
+};
--- a/lib/6to5/transformation/modules/amd.js
+++ b/lib/6to5/transformation/modules/amd.js
@@ -1,16 +1,28 @@
 module.exports = AMDFormatter;

-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
+var DefaultFormatter = require("./_default");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");

-function AMDFormatter(file) {
-  this.file = file;
+function AMDFormatter() {
+  DefaultFormatter.apply(this, arguments);
  this.ids  = {};
 }

-util.inherits(AMDFormatter, CommonJSFormatter);
+util.inherits(AMDFormatter, DefaultFormatter);
+
+AMDFormatter.prototype.buildDependencyLiterals = function () {
+  var names = [];
+  for (var name in this.ids) {
+    names.push(t.literal(name));
+  }
+  return names;
+};
+
+/**
+ * Wrap the entire body in a `define` wrapper.
+ */

 AMDFormatter.prototype.transform = function (ast) {
  var program = ast.program;
@@ -18,10 +30,7 @@ AMDFormatter.prototype.transform = function (ast) {

  // build an array of module names

-  var names = [t.literal("exports")];
-  _.each(this.ids, function (id, name) {
-    names.push(t.literal(name));
-  });
+  var names = [t.literal("exports")].concat(this.buildDependencyLiterals());
  names = t.arrayExpression(names);

  // build up define container
@@ -40,9 +49,14 @@ AMDFormatter.prototype.transform = function (ast) {
  program.body = [t.expressionStatement(call)];
 };

+/**
+ * Get the AMD module name that we'll prepend to the wrapper
+ * to define this module
+ */
+
 AMDFormatter.prototype.getModuleName = function () {
-  if (this.file.opts.amdModuleIds) {
-    return CommonJSFormatter.prototype.getModuleName.apply(this, arguments);
+  if (this.file.opts.moduleIds) {
+    return DefaultFormatter.prototype.getModuleName.apply(this, arguments);
  } else {
    return null;
  }
@@ -59,27 +73,22 @@ AMDFormatter.prototype._push = function (node) {
  }
 };

-AMDFormatter.prototype.import = function (node) {
+AMDFormatter.prototype.importDeclaration = function (node) {
  this._push(node);
 };

 AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
  var key = t.getSpecifierName(specifier);
-  var id  = specifier.id;
-
-  // import foo from "foo";
-  if (specifier.default) {
-    id = t.identifier("default");
-  }
-
-  var ref;
+  var ref = this._push(node);

  if (t.isImportBatchSpecifier(specifier)) {
    // import * as bar from "foo";
-    ref = this._push(node);
-  } else {
+  } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
    // import foo from "foo";
-    ref = t.memberExpression(this._push(node), id, false);
+    ref = t.callExpression(this.file.addDeclaration("interop-require"), [ref]);
+  } else {
+    // import {foo} from "foo";
+    ref = t.memberExpression(ref, specifier.id, false);
  }

  nodes.push(t.variableDeclaration("var", [
--- a/lib/6to5/transformation/modules/common-interop.js
+++ b/lib/6to5/transformation/modules/common-interop.js
@@ -1,56 +0,0 @@
-module.exports = CommonJSInteropFormatter;
-
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
-
-function CommonJSInteropFormatter(file) {
-  CommonJSFormatter.apply(this, arguments);
-
-  var has = false;
-  _.each(file.ast.program.body, function (node) {
-    if (t.isExportDeclaration(node) && !node.default) has = true;
-  });
-  this.has = has;
-}
-
-util.inherits(CommonJSInteropFormatter, CommonJSFormatter);
-
-CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  // import foo from "foo";
-   if (specifier.default) {
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(variableName,
-        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
-          MODULE_NAME: node.source.raw
-        })])
-      )
-    ]));
-  } else {
-    CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
-  }
-};
-
-CommonJSInteropFormatter.prototype.export = function (node, nodes) {
-  if (node.default && !this.has) {
-    var declar = node.declaration;
-
-    // module.exports = VALUE;
-    var assign = util.template("exports-default-module", {
-      VALUE: this._pushStatement(declar, nodes)
-    }, true);
-
-    // hoist to the top if this default is a function
-    nodes.push(this._hoistExport(declar, assign));
-    return;
-  }
-
-  CommonJSFormatter.prototype.export.apply(this, arguments);
-};
-
-CommonJSInteropFormatter.prototype.exportSpecifier = function () {
-  CommonJSFormatter.prototype.exportSpecifier.apply(this, arguments);
-};
--- a/lib/6to5/transformation/modules/common.js
+++ b/lib/6to5/transformation/modules/common.js
@@ -1,161 +1,77 @@
 module.exports = CommonJSFormatter;

-var util = require("../../util");
-var t    = require("../../types");
+var DefaultFormatter = require("./_default");
+var traverse         = require("../../traverse");
+var util             = require("../../util");
+var t                = require("../../types");

 function CommonJSFormatter(file) {
-  this.file = file;
+  DefaultFormatter.apply(this, arguments);
+
+  var hasNonDefaultExports = false;
+  traverse(file.ast, {
+    enter: function (node) {
+      if (t.isExportDeclaration(node) && !node.default) hasNonDefaultExports = true;
+    }
+  });
+  this.hasNonDefaultExports = hasNonDefaultExports;
 }

-CommonJSFormatter.prototype.getModuleName = function () {
-  var opts = this.file.opts;
-  var filenameRelative = opts.filenameRelative;
-  var moduleName = "";
-
-  if (opts.moduleRoot) {
-    moduleName = opts.moduleRoot + "/";
-  }
-
-  if (!opts.filenameRelative) {
-    return moduleName + opts.filename.replace(/^\//, "");
-  }
-
-  if (opts.sourceRoot) {
-    // remove sourceRoot from filename
-    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
-    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
-  }
-
-  // remove extension
-  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
-
-  moduleName += filenameRelative;
-
-  return moduleName;
-};
-
-CommonJSFormatter.prototype.import = function (node, nodes) {
-  // import "foo";
-  nodes.push(util.template("require", {
-    //inherits: node,
-
-    MODULE_NAME: node.source.raw
-  }, true));
-};
+util.inherits(CommonJSFormatter, DefaultFormatter);

 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
  var variableName = t.getSpecifierName(specifier);

  // import foo from "foo";
-  if (specifier.default) {
-    specifier.id = t.identifier("default");
+  if (t.isSpecifierDefault(specifier)) {
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(variableName,
+        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
+          MODULE_NAME: node.source
+        })])
+      )
+    ]));
+  } else {
+    // import foo from "foo";
+
+    var templateName = "require-assign";
+
+    // import * as bar from "foo";
+    if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
+
+    nodes.push(util.template(templateName, {
+      VARIABLE_NAME: variableName,
+      MODULE_NAME:   node.source,
+      KEY:           specifier.id
+    }));
  }
-
-  var templateName = "require-assign";
-
-  // import * as bar from "foo";
-  if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
-
-  nodes.push(util.template(templateName, {
-    //inherits: node.specifiers.length === 1 && node,
-
-    VARIABLE_NAME: variableName,
-    MODULE_NAME:   node.source.raw,
-    KEY:           specifier.id
-  }));
 };

-CommonJSFormatter.prototype._hoistExport = function (declar, assign) {
-  if (t.isFunctionDeclaration(declar)) {
-    assign._blockHoist = true;
-  }
-
-  return assign;
+CommonJSFormatter.prototype.importDeclaration = function (node, nodes) {
+  // import "foo";
+  nodes.push(util.template("require", {
+    MODULE_NAME: node.source
+  }, true));
 };

-CommonJSFormatter.prototype._pushStatement = function (ref, nodes) {
-  if (t.isClass(ref) || t.isFunction(ref)) {
-    if (ref.id) {
-      nodes.push(t.toStatement(ref));
-      ref = ref.id;
-    }
-  }
-  return ref;
-};
-
-CommonJSFormatter.prototype.export = function (node, nodes) {
-  var declar = node.declaration;
-
+CommonJSFormatter.prototype.exportDeclaration = function (node, nodes) {
  if (node.default) {
-    nodes.push(util.template("exports-default", {
-      //inherits: node,
+    var declar = node.declaration;

+    // module.exports = VALUE;
+    var templateName = "exports-default-module";
+
+    // exports = module.exports = VALUE;
+    if (this.hasNonDefaultExports) templateName = "exports-default-module-override";
+
+    var assign = util.template(templateName, {
      VALUE: this._pushStatement(declar, nodes)
-    }, true));
+    }, true);
+
+    // hoist to the top if this default is a function
+    nodes.push(this._hoistExport(declar, assign));
  } else {
-    var assign;
-
-    if (t.isVariableDeclaration(declar)) {
-      var decl = declar.declarations[0];
-
-      if (decl.init) {
-        decl.init = util.template("exports-assign", {
-          //inherits: node,
-
-          VALUE: decl.init,
-          KEY:   decl.id
-        });
-      }
-
-      nodes.push(declar);
-    } else {
-      assign = util.template("exports-assign", {
-        //inherits: node,
-
-        VALUE: declar.id,
-        KEY:   declar.id
-      }, true);
-
-      nodes.push(t.toStatement(declar));
-      nodes.push(assign);
-
-      this._hoistExport(declar, assign);
-    }
-  }
-};
-
-CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  var inherits = false;
-  if (node.specifiers.length === 1) inherits = node;
-
-  if (node.source) {
-    if (t.isExportBatchSpecifier(specifier)) {
-      // export * from "foo";
-      nodes.push(util.template("exports-wildcard", {
-        //inherits: inherits,
-
-        OBJECT: getRef()
-      }, true));
-    } else {
-      // export { foo } from "test";
-      nodes.push(util.template("exports-assign-key", {
-        //inherits: inherits,
-
-        VARIABLE_NAME: variableName.name,
-        OBJECT:        getRef(),
-        KEY:           specifier.id
-      }, true));
-    }
-  } else {
-    // export { foo };
-    nodes.push(util.template("exports-assign", {
-      //inherits: inherits,
-
-      VALUE: specifier.id,
-      KEY:   variableName
-    }, true));
+    DefaultFormatter.prototype.exportDeclaration.apply(this, arguments);
  }
 };

--- a/lib/6to5/transformation/modules/ignore.js
+++ b/lib/6to5/transformation/modules/ignore.js
@@ -6,19 +6,13 @@ function IgnoreFormatter() {

 }

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

+IgnoreFormatter.prototype.importDeclaration =
+IgnoreFormatter.prototype.importSpecifier =
 IgnoreFormatter.prototype.exportSpecifier = function () {

 };
--- a/lib/6to5/transformation/modules/system.js
+++ b/lib/6to5/transformation/modules/system.js
@@ -1,202 +1,102 @@
 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);
+var AMDFormatter = require("./amd");
+var traverse     = require("../../traverse");
+var util         = require("../../util");
+var t            = require("../../types");
+var _            = require("lodash");

 function SystemFormatter(file) {
-  this.exportedStatements = [];
-  this.importedModule     = {};
+  this.exportIdentifier  = file.generateUidIdentifier("export");
+  this.noInteropRequire = true;

-  this.exportIdentifier   = file.generateUidIdentifier("export");
-  this.file               = file;
+  AMDFormatter.apply(this, arguments);
 }

+util.inherits(SystemFormatter, AMDFormatter);
+
+SystemFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  var leftIdentifier = t.identifier("i");
+  var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
+
+  var left = t.variableDeclaration("var", [
+    t.variableDeclarator(leftIdentifier)
+  ]);
+
+  var right = objectIdentifier;
+
+  var block = t.blockStatement([
+    this.buildExportCall(leftIdentifier, valIdentifier)
+  ]);
+
+  return t.forInStatement(left, right, block);
+};
+
+SystemFormatter.prototype._exportsAssign = function (id, init) {
+  return this.buildExportCall(t.literal(id.name), init, true);
+};
+
+SystemFormatter.prototype.remapExportAssignment = function (node) {
+  return this.buildExportCall(t.literal(node.left.name), node);
+};
+
+SystemFormatter.prototype.buildExportCall = function (id, init, isStatement) {
+  var call = t.callExpression(this.exportIdentifier, [id, init]);
+  if (isStatement) {
+    return t.expressionStatement(call);
+  } else {
+    return call;
+  }
+};
+
+SystemFormatter.prototype.buildRunnerSetters = function () {
+  return t.arrayExpression(_.map(this.ids, function (uid) {
+    var moduleIdentifier = t.identifier("m");
+
+    return t.functionExpression(null, [moduleIdentifier], t.blockStatement([
+      t.assignmentExpression("=", uid, moduleIdentifier)
+    ]));
+  }));
+};
+
 SystemFormatter.prototype.transform = function (ast) {
  var program = ast.program;
-  var body    = program.body;

-  // extract the module name
-  var moduleName = this.file.opts.filename
-    .replace(/^.*\//, "").replace(/\..*$/, "");
+  var moduleName = this.getModuleName();
+  var moduleNameLiteral = t.literal(moduleName);

-  // build an array of module names
-  var dependencies = Object.keys(this.importedModule).map(t.literal);
+  var runner = util.template("system", {
+    MODULE_NAME: moduleNameLiteral,
+    MODULE_DEPENDENCIES: t.arrayExpression(this.buildDependencyLiterals()),
+    EXPORT_IDENTIFIER: this.exportIdentifier,
+    SETTERS: this.buildRunnerSetters(),
+    EXECUTE: t.functionExpression(null, [], t.blockStatement(program.body))
+  }, true);

-  // generate the __moduleName variable
-  var moduleNameVariableNode = t.variableDeclaration("var", [
-    t.variableDeclarator(
-      t.identifier("__moduleName"),
-      t.literal(moduleName)
-    )
-  ]);
-  body.splice(1, 0, moduleNameVariableNode);
+  var handlerBody = runner.expression.arguments[2].body.body;
+  if (!moduleName) runner.expression.arguments.shift();

-  // generate an array of import variables
+  var returnStatement = handlerBody.pop();

-  var declaredSetters = _(this.importedModule)
-    .map()
-    .flatten()
-    .pluck("variableName")
-    .pluck("name")
-    .uniq()
-    .map(t.identifier)
-    .map(function (name) {
-      return t.variableDeclarator(name);
-    })
-    .value();
+  // hoist up function declarations for circular references
+  traverse(program, {
+    enter: function (node) {
+      if (t.isFunction(node)) this.stop();

-  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);
+      if (t.isFunctionDeclaration(node) || node._blockHoist) {
+        handlerBody.push(node);
+        this.remove();
      }
-
-      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);
+  if (!_.isEmpty(this.ids)) {
+    handlerBody.push(t.variableDeclaration("var", _.map(this.ids, function (uid) {
+      return t.variableDeclarator(uid);
+    })));
  }

-  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);
-  }
+  handlerBody.push(returnStatement);
+
+  program.body = [runner];
 };
--- a/lib/6to5/transformation/modules/umd.js
+++ b/lib/6to5/transformation/modules/umd.js
@@ -18,9 +18,9 @@ UMDFormatter.prototype.transform = function (ast) {
  // build an array of module names

  var names = [];
-  _.each(this.ids, function (id, name) {
+  for (var name in this.ids) {
    names.push(t.literal(name));
-  });
+  }

  // factory

--- a/lib/6to5/transformation/templates/abstract-expression-call.js
+++ b/lib/6to5/transformation/templates/abstract-expression-call.js
--- a/lib/6to5/transformation/templates/abstract-expression-delete.js
+++ b/lib/6to5/transformation/templates/abstract-expression-delete.js
--- a/lib/6to5/transformation/templates/abstract-expression-get.js
+++ b/lib/6to5/transformation/templates/abstract-expression-get.js
--- a/lib/6to5/transformation/templates/abstract-expression-set.js
+++ b/lib/6to5/transformation/templates/abstract-expression-set.js
--- a/lib/6to5/transformation/templates/apply-constructor.js
+++ b/lib/6to5/transformation/templates/apply-constructor.js
--- a/lib/6to5/transformation/templates/array-comprehension-container.js
+++ b/lib/6to5/transformation/templates/array-comprehension-container.js
--- a/lib/6to5/transformation/templates/array-comprehension-for-each.js
+++ b/lib/6to5/transformation/templates/array-comprehension-for-each.js
--- a/lib/6to5/transformation/templates/array-expression-comprehension-filter.js
+++ b/lib/6to5/transformation/templates/array-expression-comprehension-filter.js
--- a/lib/6to5/transformation/templates/array-expression-comprehension-map.js
+++ b/lib/6to5/transformation/templates/array-expression-comprehension-map.js
--- a/lib/6to5/transformation/templates/array-from.js
+++ b/lib/6to5/transformation/templates/array-from.js
--- a/lib/6to5/transformation/templates/array-push.js
+++ b/lib/6to5/transformation/templates/array-push.js
--- a/lib/6to5/transformation/templates/call.js
+++ b/lib/6to5/transformation/templates/call.js
--- a/lib/6to5/transformation/templates/class-super-constructor-call.js
+++ b/lib/6to5/transformation/templates/class-super-constructor-call.js
@@ -0,0 +1,3 @@
+if (SUPER_NAME) {
+  SUPER_NAME.apply(this, arguments);
+}
--- a/lib/6to5/transformation/templates/exports-assign.js
+++ b/lib/6to5/transformation/templates/exports-assign.js
--- a/lib/6to5/transformation/templates/exports-default-module-override.js
+++ b/lib/6to5/transformation/templates/exports-default-module-override.js
@@ -0,0 +1 @@
+exports = module.exports = VALUE;
--- a/lib/6to5/transformation/templates/exports-default-module.js
+++ b/lib/6to5/transformation/templates/exports-default-module.js
--- a/lib/6to5/transformation/templates/exports-wildcard.js
+++ b/lib/6to5/transformation/templates/exports-wildcard.js
--- a/lib/6to5/transformation/templates/for-of.js
+++ b/lib/6to5/transformation/templates/for-of.js
--- a/lib/6to5/transformation/templates/function-return-obj.js
+++ b/lib/6to5/transformation/templates/function-return-obj.js
--- a/lib/6to5/transformation/templates/has-own.js
+++ b/lib/6to5/transformation/templates/has-own.js
--- a/lib/6to5/transformation/templates/if-undefined-set-to.js
+++ b/lib/6to5/transformation/templates/if-undefined-set-to.js
--- a/lib/6to5/transformation/templates/inherits.js
+++ b/lib/6to5/transformation/templates/inherits.js
@@ -1,5 +1,5 @@
 (function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+  child.prototype = Object.create(parent && parent.prototype, {
    constructor: {
      value: child,
      enumerable: false,
@@ -7,5 +7,5 @@
      configurable: true
    }
  });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 })
--- a/lib/6to5/transformation/templates/interop-require.js
+++ b/lib/6to5/transformation/templates/interop-require.js
--- a/lib/6to5/transformation/templates/let-scoping-return.js
+++ b/lib/6to5/transformation/templates/let-scoping-return.js
--- a/lib/6to5/transformation/templates/object-define-properties-closure.js
+++ b/lib/6to5/transformation/templates/object-define-properties-closure.js
--- a/lib/6to5/transformation/templates/object-define-properties.js
+++ b/lib/6to5/transformation/templates/object-define-properties.js
--- a/lib/6to5/transformation/templates/object-without-properties.js
+++ b/lib/6to5/transformation/templates/object-without-properties.js
--- a/lib/6to5/transformation/templates/prototype-identifier.js
+++ b/lib/6to5/transformation/templates/prototype-identifier.js
--- a/lib/6to5/transformation/templates/prototype-properties.js
+++ b/lib/6to5/transformation/templates/prototype-properties.js
--- a/lib/6to5/transformation/templates/require-assign-key.js
+++ b/lib/6to5/transformation/templates/require-assign-key.js
--- a/lib/6to5/transformation/templates/require-assign.js
+++ b/lib/6to5/transformation/templates/require-assign.js
--- a/lib/6to5/transformation/templates/require.js
+++ b/lib/6to5/transformation/templates/require.js
--- a/lib/6to5/transformation/templates/self-global.js
+++ b/lib/6to5/transformation/templates/self-global.js
--- a/lib/6to5/transformation/templates/slice.js
+++ b/lib/6to5/transformation/templates/slice.js
--- a/lib/6to5/transformation/templates/sliced-to-array.js
+++ b/lib/6to5/transformation/templates/sliced-to-array.js
@@ -0,0 +1,12 @@
+(function (arr, i) {
+  if (Array.isArray(arr)) {
+    return arr;
+  } else {
+    var _arr = [];
+    for (var _iterator = arr[Symbol.iterator](), _step; !(_step = _iterator.next()).done;) {
+      _arr.push(_step.value);
+      if (i && _arr.length === i) break;
+    }
+    return _arr;
+  }
+});
--- a/lib/6to5/transformation/templates/system.js
+++ b/lib/6to5/transformation/templates/system.js
@@ -0,0 +1,6 @@
+System.register(MODULE_NAME, MODULE_DEPENDENCIES, function (EXPORT_IDENTIFIER) {
+  return {
+    setters: SETTERS,
+    execute: EXECUTE
+  };
+});
--- a/lib/6to5/transformation/templates/tagged-template-literal.js
+++ b/lib/6to5/transformation/templates/tagged-template-literal.js
@@ -0,0 +1,6 @@
+(function (strings, raw) {
+  return Object.freeze(Object.defineProperties(strings, {
+      raw: { value: Object.freeze(raw) }
+  }));
+});
+
--- a/lib/6to5/transformation/templates/to-array.js
+++ b/lib/6to5/transformation/templates/to-array.js
--- a/lib/6to5/transformation/templates/umd-runner-body.js
+++ b/lib/6to5/transformation/templates/umd-runner-body.js
--- a/lib/6to5/transformation/transform.js
+++ b/lib/6to5/transformation/transform.js
@@ -2,6 +2,7 @@ module.exports = transform;

 var Transformer = require("./transformer");
 var File        = require("../file");
+var util        = require("../util");
 var _           = require("lodash");

 function transform(code, opts) {
@@ -9,31 +10,46 @@ function transform(code, opts) {
  return file.parse(code);
 }

+transform.fromAst = function (ast, code, opts) {
+  ast = util.normaliseAst(ast);
+
+  var file = new File(opts);
+  file.addCode(code);
+  file.transform(ast);
+  return file.generate();
+};
+
 transform._ensureTransformerNames = function (type, keys) {
-  _.each(keys, function (key) {
+  for (var i in keys) {
+    var key = keys[i];
    if (!_.has(transform.transformers, key)) {
      throw new ReferenceError("unknown transformer " + key + " specified in " + type);
    }
-  });
+  }
 };

 transform.transformers = {};

 transform.moduleFormatters = {
-  common:        require("./modules/common"),
-  commonInterop: require("./modules/common-interop"),
-  system:        require("./modules/system"),
-  ignore:        require("./modules/ignore"),
-  amd:           require("./modules/amd"),
-  umd:           require("./modules/umd")
+  common: require("./modules/common"),
+  system: require("./modules/system"),
+  ignore: require("./modules/ignore"),
+  amd:    require("./modules/amd"),
+  umd:    require("./modules/umd")
 };

 _.each({
-  // plyground
+  // spec
+  specBlockHoistFunctions:   require("./transformers/spec-block-hoist-functions"),
+  specNoForInOfAssignment:   require("./transformers/spec-no-for-in-of-assignment"),
+  specNoDuplicateProperties: require("./transformers/spec-no-duplicate-properties"),
+
+  // playground
  methodBinding:             require("./transformers/playground-method-binding"),
  memoizationOperator:       require("./transformers/playground-memoization-operator"),
  objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),

+  react:                     require("./transformers/react"),
  modules:                   require("./transformers/es6-modules"),
  propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
  arrayComprehension:        require("./transformers/es7-array-comprehension"),
@@ -48,28 +64,30 @@ _.each({
  spread:                    require("./transformers/es6-spread"),
  templateLiterals:          require("./transformers/es6-template-literals"),
  propertyMethodAssignment:  require("./transformers/es5-property-method-assignment"),
-  defaultParameters:         require("./transformers/es6-default-parameters"),
-  restParameters:            require("./transformers/es6-rest-parameters"),
  destructuring:             require("./transformers/es6-destructuring"),
+  defaultParameters:         require("./transformers/es6-default-parameters"),
  forOf:                     require("./transformers/es6-for-of"),
  unicodeRegex:              require("./transformers/es6-unicode-regex"),
  abstractReferences:        require("./transformers/es7-abstract-references"),
-  react:                     require("./transformers/react"),

  constants:                 require("./transformers/es6-constants"),
  letScoping:                require("./transformers/es6-let-scoping"),

-  generators:                require("./transformers/es6-generators"),
-
  _blockHoist:               require("./transformers/_block-hoist"),
+
+  generators:                require("./transformers/es6-generators"),
+  restParameters:            require("./transformers/es6-rest-parameters"),
+
  _declarations:             require("./transformers/_declarations"),
+
+  // wrap up
  _aliasFunctions:           require("./transformers/_alias-functions"),
-
  useStrict:                 require("./transformers/use-strict"),
+  _moduleFormatter:          require("./transformers/_module-formatter"),

-  _propertyLiterals:         require("./transformers/_property-literals"),
-  _memberExpressioLiterals:  require("./transformers/_member-expression-literals"),
-  _moduleFormatter:          require("./transformers/_module-formatter")
+  // spec
+  specPropertyLiterals:         require("./transformers/spec-property-literals"),
+  specMemberExpressionLiterals: require("./transformers/spec-member-expression-literals")
 }, function (transformer, key) {
  transform.transformers[key] = new Transformer(key, transformer);
 });
--- a/lib/6to5/transformation/transformer.js
+++ b/lib/6to5/transformation/transformer.js
@@ -4,8 +4,9 @@ var traverse = require("../traverse");
 var t        = require("../types");
 var _        = require("lodash");

-function Transformer(key, transformer) {
+function Transformer(key, transformer, opts) {
  this.transformer = Transformer.normalise(transformer);
+  this.opts        = opts || {};
  this.key         = key;
 }

@@ -18,37 +19,38 @@ Transformer.normalise = function (transformer) {
    if (type[0] === "_") return;
    if (_.isFunction(fns)) fns = { enter: fns };
    transformer[type] = fns;
+
+    var aliases = t.FLIPPED_ALIAS_KEYS[type];
+    if (aliases) {
+      _.each(aliases, function (alias) {
+        transformer[alias] = fns;
+      });
+    }
  });

  return transformer;
 };

+Transformer.prototype.astRun = function (file, key) {
+  var transformer = this.transformer;
+  var ast         = file.ast;
+
+  if (transformer.ast && transformer.ast[key]) {
+    transformer.ast[key](ast, file);
+  }
+};
+
 Transformer.prototype.transform = function (file) {
  if (!this.canRun(file)) return;

  var transformer = this.transformer;
  var ast         = file.ast;

-  var astRun = function (key) {
-    if (transformer.ast && transformer.ast[key]) {
-      transformer.ast[key](ast, file);
-    }
-  };
-
-  astRun("enter");
+  this.astRun(file, "enter");

  var build = function (exit) {
    return function (node, parent, scope) {
-      // add any node type aliases that exist
-      var types = [node.type].concat(t.ALIAS_KEYS[node.type] || []);
-
-      var fns = transformer.all;
-
-      _.each(types, function (type) {
-        fns = transformer[type] || fns;
-      });
-
-      // this transformer cannot deal with this node type
+      var fns = transformer[node.type];
      if (!fns) return;

      var fn = fns.enter;
@@ -64,20 +66,19 @@ Transformer.prototype.transform = function (file) {
    exit:  build(true)
  });

-  astRun("exit");
+  this.astRun(file, "exit");
 };

 Transformer.prototype.canRun = function (file) {
  var opts = file.opts;
  var key  = this.key;
+  if (key[0] === "_") return true;

  var blacklist = opts.blacklist;
  if (blacklist.length && _.contains(blacklist, key)) return false;

-  if (key[0] !== "_") {
-    var whitelist = opts.whitelist;
-    if (whitelist.length && !_.contains(whitelist, key)) return false;
-  }
+  var whitelist = opts.whitelist;
+  if (whitelist.length && !_.contains(whitelist, key)) return false;

  return true;
 };
--- a/lib/6to5/transformation/transformers/_alias-functions.js
+++ b/lib/6to5/transformation/transformers/_alias-functions.js
@@ -15,38 +15,42 @@ var go = function (getBody, node, file, scope) {

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

  var body;
--- a/lib/6to5/transformation/transformers/_declarations.js
+++ b/lib/6to5/transformation/transformers/_declarations.js
@@ -1,12 +1,14 @@
 var t = require("../../types");
-var _ = require("lodash");

 exports.BlockStatement =
 exports.Program = function (node) {
  var kinds = {};
+  var kind;

-  _.each(node._declarations, function (declar) {
-    var kind = declar.kind || "var";
+  for (var i in node._declarations) {
+    var declar = node._declarations[i];
+
+    kind = declar.kind || "var";
    var declarNode = t.variableDeclarator(declar.id, declar.init);

    if (!declar.init) {
@@ -15,9 +17,9 @@ exports.Program = function (node) {
    } else {
      node.body.unshift(t.variableDeclaration(kind, [declarNode]));
    }
-  });
+  }

-  _.each(kinds, function (declars, kind) {
-    node.body.unshift(t.variableDeclaration(kind, declars));
-  });
+  for (kind in kinds) {
+    node.body.unshift(t.variableDeclaration(kind, kinds[kind]));
+  }
 };
--- a/lib/6to5/transformation/transformers/es5-property-method-assignment.js
+++ b/lib/6to5/transformation/transformers/es5-property-method-assignment.js
@@ -1,5 +1,4 @@
 var util = require("../../util");
-var _    = require("lodash");

 exports.Property = function (node) {
  if (node.method) node.method = false;
@@ -7,9 +6,11 @@ exports.Property = function (node) {

 exports.ObjectExpression = function (node, parent, file) {
  var mutatorMap = {};
+  var hasAny = false;

  node.properties = node.properties.filter(function (prop) {
    if (prop.kind === "get" || prop.kind === "set") {
+      hasAny = true;
      util.pushMutatorMap(mutatorMap, prop.key, prop.kind, prop.value);
      return false;
    } else {
@@ -17,7 +18,7 @@ exports.ObjectExpression = function (node, parent, file) {
    }
  });

-  if (_.isEmpty(mutatorMap)) return;
+  if (!hasAny) return;

  var objId = util.getUid(parent, file);

--- a/lib/6to5/transformation/transformers/es6-arrow-functions.js
+++ b/lib/6to5/transformation/transformers/es6-arrow-functions.js
@@ -3,7 +3,7 @@ var t = require("../../types");
 exports.ArrowFunctionExpression = function (node) {
  t.ensureBlock(node);

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

--- a/lib/6to5/transformation/transformers/es6-classes.js
+++ b/lib/6to5/transformation/transformers/es6-classes.js
@@ -1,27 +1,38 @@
 var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
-var _        = require("lodash");

 exports.ClassDeclaration = function (node, parent, file, scope) {
-  var built = new Class(node, file, scope).run();
+  var closure = true;
+  if (t.isProgram(parent) || t.isBlockStatement(parent)) {
+    closure = false;
+  }

-  var declar = t.variableDeclaration("let", [
-    t.variableDeclarator(node.id, built)
-  ]);
-  t.inheritsComments(declar, node);
-  return declar;
+  var factory = new Class(node, file, scope, closure);
+  var newNode = factory.run();
+  if (factory.closure) {
+    if (closure) {
+      // declaration in an expression context...
+      // export default class Foo {}
+      scope.push({
+        kind: "var",
+        key: node.id.key,
+        id: node.id
+      });
+      return t.assignmentExpression("=", node.id, newNode);
+    } else {
+      // likely has a PrivateDeclaration etc
+      return t.variableDeclaration("let", [
+        t.variableDeclarator(node.id, newNode)
+      ]);
+    }
+  } else {
+    return newNode;
+  }
 };

 exports.ClassExpression = function (node, parent, file, scope) {
-  return new Class(node, file, scope).run();
-};
-
-var getMemberExpressionObject = function (node) {
-  while (t.isMemberExpression(node)) {
-    node = node.object;
-  }
-  return node;
+  return new Class(node, file, scope, true).run();
 };

 /**
@@ -30,12 +41,17 @@ var getMemberExpressionObject = function (node) {
 * @param {Node} node
 * @param {File} file
 * @param {Scope} scope
+ * @param {Boolean} closure
 */

-function Class(node, file, scope) {
-  this.scope = scope;
-  this.node  = node;
-  this.file  = file;
+function Class(node, file, scope, closure) {
+  this.closure = closure;
+  this.scope   = scope;
+  this.node    = node;
+  this.file    = file;
+
+  this.hasInstanceMutators = false;
+  this.hasStaticMutators   = false;

  this.instanceMutatorMap = {};
  this.staticMutatorMap   = {};
@@ -51,50 +67,61 @@ function Class(node, file, scope) {
 */

 Class.prototype.run = function () {
-  var superClassArgument = this.superName;
-  var superClassCallee   = this.superName;
-  var superName          = this.superName;
-  var className          = this.className;
-  var file               = this.file;
+  var superName = this.superName;
+  var className = this.className;
+  var file      = this.file;

-  if (superName) {
-    if (t.isMemberExpression(superName)) {
-      superClassArgument = superClassCallee = getMemberExpressionObject(superName);
-    } else if (!t.isIdentifier(superName)) {
-      superClassArgument = superName;
-      superClassCallee   = superName = file.generateUidIdentifier("ref", this.scope);
-    }
+  //
+
+  var body = this.body = [];
+
+  var constructor = t.functionExpression(null, [], t.blockStatement([]));
+  if (this.node.id) constructor.id = className;
+  this.constructor = constructor;
+
+  body.push(t.variableDeclaration("let", [
+    t.variableDeclarator(className, constructor)
+  ]));
+
+  //
+
+  if (superName && t.isDynamic(superName)) {
+    // so we're only evaluating it once
+    var superRefName = "super";
+    if (className) superRefName = className.name + "Super";
+
+    var superRef = file.generateUidIdentifier(superRefName, this.scope);
+    body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(superRef, superName)
+    ]));
+    superName = superRef;
  }

  this.superName = superName;

-  var container = util.template("class", {
-    CLASS_NAME: className
-  });
-
-  var block       = container.callee.expression.body;
-  var body        = this.body = block.body;
-  var constructor = this.constructor = body[0].declarations[0].init;
-
-  if (this.node.id) constructor.id = className;
-
-  var returnStatement = body.pop();
+  //

  if (superName) {
-    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("extends"), [className, superName])));
-
-    container.arguments.push(superClassArgument);
-    container.callee.expression.params.push(superClassCallee);
+    body.push(t.expressionStatement(t.callExpression(file.addDeclaration("inherits"), [className, superName])));
  }

  this.buildBody();

-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    return constructor;
+  t.inheritsComments(body[0], this.node);
+
+  if (this.closure) {
+    if (body.length === 1) {
+      // only a constructor so no need for a closure container
+      return constructor;
+    } else {
+      body.push(t.returnStatement(className));
+      return t.callExpression(
+        t.functionExpression(null, [], t.blockStatement(body)),
+        []
+      );
+    }
  } else {
-    body.push(returnStatement);
-    return container;
+    return body;
  }
 };

@@ -110,15 +137,21 @@ Class.prototype.buildBody = function () {
  var body        = this.body;
  var self        = this;

-  _.each(classBody, function (node) {
-    self.replaceInstanceSuperReferences(node);
+  for (var i in classBody) {
+    var node = classBody[i];
+    if (t.isMethodDefinition(node)) {
+      self.replaceInstanceSuperReferences(node);

-    if (node.key.name === "constructor") {
-      self.pushConstructor(node);
-    } else {
-      self.pushMethod(node);
+      if (node.key.name === "constructor") {
+        self.pushConstructor(node);
+      } else {
+        self.pushMethod(node);
+      }
+    } else if (t.isPrivateDeclaration(node)) {
+      self.closure = true;
+      body.unshift(node);
    }
-  });
+  }

  if (!this.hasConstructor && superName) {
    constructor.body.body.push(util.template("class-super-constructor-call", {
@@ -129,7 +162,7 @@ Class.prototype.buildBody = function () {
  var instanceProps;
  var staticProps;

-  if (!_.isEmpty(this.instanceMutatorMap)) {
+  if (this.hasInstanceMutators) {
    var protoId = util.template("prototype-identifier", {
      CLASS_NAME: className
    });
@@ -137,7 +170,7 @@ Class.prototype.buildBody = function () {
    instanceProps = util.buildDefineProperties(this.instanceMutatorMap, protoId);
  }

-  if (!_.isEmpty(this.staticMutatorMap)) {
+  if (this.hasStaticMutators) {
    staticProps = util.buildDefineProperties(this.staticMutatorMap, className);
  }

@@ -148,7 +181,7 @@ Class.prototype.buildBody = function () {
    if (instanceProps) args.push(instanceProps);

    body.push(t.expressionStatement(
-      t.callExpression(this.file.addDeclaration("class-props"), args)
+      t.callExpression(this.file.addDeclaration("prototype-properties"), args)
    ));
  }
 };
@@ -171,11 +204,18 @@ Class.prototype.pushMethod = function (node) {
    if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
    methodName = t.memberExpression(className, methodName, node.computed);

-    this.body.push(t.expressionStatement(t.assignmentExpression("=", methodName, node.value)));
+    var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
+    t.inheritsComments(expr, node);
+    this.body.push(expr);
  } else {
    // mutator
    var mutatorMap = this.instanceMutatorMap;
-    if (node.static) mutatorMap = this.staticMutatorMap;
+    if (node.static) {
+      this.hasStaticMutators = true;
+      mutatorMap = this.staticMutatorMap;
+    } else {
+      this.hasInstanceMutators = true;
+    }
    util.pushMutatorMap(mutatorMap, methodName, kind, node);
  }
 };
@@ -232,17 +272,19 @@ Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
  var method = methodNode.value;
  var self = this;

-  traverse(method, function (node, parent) {
-    if (t.isIdentifier(node, { name: "super" })) {
-      return self.superIdentifier(methodNode, node, parent);
-    } else if (t.isCallExpression(node)) {
-      var callee = node.callee;
-      if (!t.isMemberExpression(callee)) return;
-      if (callee.object.name !== "super") return;
+  traverse(method, {
+    enter: function (node, parent) {
+      if (t.isIdentifier(node, { name: "super" })) {
+        return self.superIdentifier(methodNode, node, parent);
+      } else if (t.isCallExpression(node)) {
+        var callee = node.callee;
+        if (!t.isMemberExpression(callee)) return;
+        if (callee.object.name !== "super") return;

-      // super.test(); -> ClassName.prototype.MethodName.call(this);
-      callee.property = t.memberExpression(callee.property, t.identifier("call"));
-      node.arguments.unshift(t.thisExpression());
+        // super.test(); -> ClassName.prototype.MethodName.call(this);
+        callee.property = t.memberExpression(callee.property, t.identifier("call"));
+        node.arguments.unshift(t.thisExpression());
+      }
    }
  });
 };
@@ -262,6 +304,7 @@ Class.prototype.pushConstructor = function (method) {
  var fn        = method.value;

  this.hasConstructor = true;
+
  t.inherits(construct, fn);
  t.inheritsComments(construct, method);

--- a/lib/6to5/transformation/transformers/es6-computed-property-names.js
+++ b/lib/6to5/transformation/transformers/es6-computed-property-names.js
@@ -1,6 +1,5 @@
 var util = require("../../util");
 var t    = require("../../types");
-var _    = require("lodash");

 exports.ObjectExpression = function (node, parent, file) {
  var hasComputed = false;
@@ -26,12 +25,13 @@ exports.ObjectExpression = function (node, parent, file) {
    OBJECT: node
  });

-  var containerCallee = container.callee.expression;
+  var containerCallee = container.callee;
  var containerBody = containerCallee.body.body;

  containerCallee._aliasFunction = true;

-  _.each(computed, function (prop) {
+  for (var i in computed) {
+    var prop = computed[i];
    containerBody.unshift(
      t.expressionStatement(
        t.assignmentExpression(
@@ -41,7 +41,7 @@ exports.ObjectExpression = function (node, parent, file) {
        )
      )
    );
-  });
+  }

  return container;
 };
--- a/lib/6to5/transformation/transformers/es6-constants.js
+++ b/lib/6to5/transformation/transformers/es6-constants.js
@@ -7,48 +7,76 @@ exports.BlockStatement =
 exports.ForInStatement =
 exports.ForOfStatement =
 exports.ForStatement = function (node, parent, file) {
+  var hasConstants = false;
  var constants = {};

-  var check = function (parent, names) {
-    _.each(names, function (nameNode, name) {
-      if (!_.has(constants, name)) return;
-      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) return;
+  /**
+   * Check the results of `util.getIds` as `names` generated from a
+   * node against it's parent.
+   */
+
+  var check = function (parent, names, scope) {
+    for (var name in names) {
+      var nameNode = names[name];
+      if (!_.has(constants, name)) continue;
+      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) continue;
+
+      if (scope) {
+        var defined = scope.get(name);
+        if (defined && defined === nameNode) continue;
+      }

      throw file.errorWithNode(nameNode, name + " is read-only");
-    });
+    }
  };

  var getIds = function (node) {
    return t.getIds(node, true, ["MemberExpression"]);
  };

+  /**
+   * Collect all constants in this scope.
+   */
+
  _.each(node.body, function (child, parent) {
-    if (child && t.isVariableDeclaration(child, { kind: "const" })) {
-      _.each(child.declarations, function (declar) {
-        _.each(getIds(declar), function (nameNode, name) {
+    if (t.isExportDeclaration(child)) {
+      child = child.declaration;
+    }
+
+    if (t.isVariableDeclaration(child, { kind: "const" })) {
+      for (var i in child.declarations) {
+        var declar = child.declarations[i];
+
+        var ids = getIds(declar);
+        for (var name in ids) {
+          var nameNode = ids[name];
+
          var names = {};
          names[name] = nameNode;
          check(parent, names);

          constants[name] = parent;
-        });
+          hasConstants = true;
+        }

        declar._ignoreConstant = true;
-      });
+      }

      child._ignoreConstant = true;
      child.kind = "let";
    }
  });

-  if (_.isEmpty(constants)) return;
+  if (!hasConstants) return;

-  traverse(node, function (child, parent) {
-    if (child._ignoreConstant) return;
-    if (t.isVariableDeclaration(child)) return;
+  traverse(node, {
+    enter: function (child, parent, scope) {
+      if (child._ignoreConstant) return;
+      if (t.isVariableDeclaration(child)) return;

-    if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-      check(parent, getIds(child));
+      if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
+        check(parent, getIds(child), scope);
+      }
    }
  });
 };
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -12,9 +12,12 @@ exports.Function = function (node, parent, file, scope) {
  });

  var iife = false;
+  var i;
+  var def;

-  _.each(node.defaults, function (def, i) {
-    if (!def) return;
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;

    var param = node.params[i];

@@ -24,7 +27,7 @@ exports.Function = function (node, parent, file, scope) {
      var check = function (node, parent) {
        if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;

-        if (_.contains(ids, node.name)) {
+        if (ids.indexOf(node.name) >= 0) {
          throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
        }

@@ -34,26 +37,27 @@ exports.Function = function (node, parent, file, scope) {
      };

      check(def, node);
-      traverse(def, check);
+      traverse(def, { enter: check });
    });

    // we're accessing a variable that's already defined within this function
    var has = scope.get(param.name);
-    if (has && !_.contains(node.params, has)) {
+    if (has && node.params.indexOf(has) < 0) {
      iife = true;
    }
-  });
+  }

  var body = [];

-  _.each(node.defaults, function (def, i) {
-    if (!def) return;
+  for (i in node.defaults) {
+    def = node.defaults[i];
+    if (!def) continue;

    body.push(util.template("if-undefined-set-to", {
      VARIABLE: node.params[i],
      DEFAULT:  def
    }, true));
-  });
+  }

  if (iife) {
    var container = t.functionExpression(null, [], node.body, node.generator);
--- a/lib/6to5/transformation/transformers/es6-destructuring.js
+++ b/lib/6to5/transformation/transformers/es6-destructuring.js
@@ -1,7 +1,6 @@
 // TODO: Clean up

 var t = require("../../types");
-var _ = require("lodash");

 var buildVariableAssign = function (opts, id, init) {
  var op = opts.operator;
@@ -27,23 +26,26 @@ var push = function (opts, nodes, elem, parentId) {
 };

 var pushObjectPattern = function (opts, nodes, pattern, parentId) {
-  _.each(pattern.properties, function (prop, i) {
+  for (var i in pattern.properties) {
+    var prop = pattern.properties[i];
    if (t.isSpreadProperty(prop)) {
        // get all the keys that appear in this object before the current spread
        var keys = [];
-        _.each(pattern.properties, function (prop2, i2) {
-          if (i2 >= i) return false;
-          if (t.isSpreadProperty(prop2)) return;
+        for (var i2 in pattern.properties) {
+          var prop2 = pattern.properties[i2];
+
+          if (i2 >= i) break;
+          if (t.isSpreadProperty(prop2)) continue;

          var key = prop2.key;
          if (t.isIdentifier(key)) {
            key = t.literal(prop2.key.name);
          }
          keys.push(key);
-        });
+        }
        keys = t.arrayExpression(keys);

-        var value = t.callExpression(opts.file.addDeclaration("object-spread"), [parentId, keys]);
+        var value = t.callExpression(opts.file.addDeclaration("object-without-properties"), [parentId, keys]);
        nodes.push(buildVariableAssign(opts, prop.argument, value));
    } else {
      var pattern2   = prop.value;
@@ -55,25 +57,42 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
        nodes.push(buildVariableAssign(opts, pattern2, patternId2));
      }
    }
-  });
+  }
 };

 var pushArrayPattern = function (opts, nodes, pattern, parentId) {
+  if (!pattern.elements) return;
+
+  var i;
+
+  var hasSpreadElement = false;
+  for (i in pattern.elements) {
+    if (t.isSpreadElement(pattern.elements[i])) {
+      hasSpreadElement = true;
+      break;
+    }
+  }
+
+  var toArray = opts.file.toArray(parentId, !hasSpreadElement && pattern.elements.length);
+
  var _parentId = opts.file.generateUidIdentifier("ref", opts.scope);
  nodes.push(t.variableDeclaration("var", [
-    t.variableDeclarator(_parentId, opts.file.toArray(parentId))
+    t.variableDeclarator(_parentId, toArray)
  ]));
  parentId = _parentId;

-  _.each(pattern.elements, function (elem, i) {
-    if (!elem) return;
+  for (i in pattern.elements) {
+    var elem = pattern.elements[i];
+    if (!elem) continue;
+
+    i = +i;

    var newPatternId;

    if (t.isSpreadElement(elem)) {
      newPatternId = opts.file.toArray(parentId);

-      if (+i > 0) {
+      if (i > 0) {
        newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
      }

@@ -83,7 +102,7 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
    }

    push(opts, nodes, elem, newPatternId);
-  });
+  }
 };

 var pushPattern = function (opts) {
@@ -215,17 +234,22 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
  if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;

  var nodes = [];
+  var i;
+  var declar;

  var hasPattern = false;
-  _.each(node.declarations, function (declar) {
+  for (i in node.declarations) {
+    declar = node.declarations[i];
    if (t.isPattern(declar.id)) {
      hasPattern = true;
-      return false;
+      break;
    }
-  });
+  }
  if (!hasPattern) return;

-  _.each(node.declarations, function (declar) {
+  for (i in node.declarations) {
+    declar = node.declarations[i];
+
    var patternId = declar.init;
    var pattern   = declar.id;
    var opts = {
@@ -241,12 +265,13 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
    } else {
      nodes.push(buildVariableAssign(opts, declar.id, declar.init));
    }
-  });
+  }

  if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
-    var declar;
+    declar = null;

-    _.each(nodes, function (node) {
+    for (i in nodes) {
+      node = nodes[i];
      declar = declar || t.variableDeclaration(node.kind, []);

      if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
@@ -254,7 +279,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
      }

      declar.declarations = declar.declarations.concat(node.declarations);
-    });
+    }

    return declar;
  }
--- a/lib/6to5/transformation/transformers/es6-for-of.js
+++ b/lib/6to5/transformation/transformers/es6-for-of.js
@@ -24,6 +24,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
    OBJECT:       node.right
  });

+  t.inheritsComments(node2, node);
  t.ensureBlock(node);

  var block = node2.body;
--- a/lib/6to5/transformation/transformers/es6-generators.js
+++ b/lib/6to5/transformation/transformers/es6-generators.js
@@ -0,0 +1 @@
+module.exports = require("regenerator").transform;
--- a/Show More
+++ b/Show More
				`@@ -1 +0,0 @@`
				`System.register(MODULE_NAME, MODULE_DEPENDENCIES, MODULE_BODY);`
				`@@ -0,0 +1 @@`
				`module.exports = require("regenerator").transform;`