v1.14.17

Only slice arguments when necessary - fixes #239

CHANGELOG.md

@@ -1,3 +1,81 @@
+# 1.14.17
+
+ * Add default initializer to let variables within loop bodies.
+ * Fix excessive `break` replacement inside of switches in let scoping.
+
+# 1.14.16
+
+ * Add object getter memos and this shorthand to playground.
+ * Fix while loops in let scoping.
+ * Upgrade `acorn-6to5`.
+
+# 1.14.14
+
+ * Fix template literals escaping.
+
+# 1.14.13
+
+ * Fix let scoping of `while` loops.
+ * Make class methods enumerable.
+
+# 1.14.12
+
+ * Fix duplicate dynamic expressions in call spread.
+
+# 1.14.10
+
+ * Fix let scoping unneccesary override.
+
+# 1.14.6
+
+ * Avoid ensuring a block on non-array node replacements.
+
+# 1.14.5
+
+ * Upgrade `acorn-6to5`.
+ * Fix JSON recursion error for unknown code generator node types.
+ * Ensure that a statement is a block on block/statement types when replacing them with multiple nodes.
+
+# 1.14.4
+
+ * Merge pretzel maps and method binding.
+
+# 1.14.3
+
+ * Add playground pretzel maps.
+
+# 1.14.2
+
+ * Fix `commonInterop` default export handling.
+ * Fix keyworded property key identifiers being turned into computed property key literals.
+
+# 1.14.1
+
+ * Inherit comments from `ClassDeclaration`.
+
+# 1.14.0
+
+ * Add [playground](https://6to5.github.io/playground.html).
+
+# 1.13.13
+
+ * Fix `--debug` in `bin/6to5-node`. Thanks [@timoxley](https://github.com/timoxley).
+
+# 1.13.12
+
+ * Ignore `XJSEmptyExpression`s in `react` transformer output.
+
+# 1.13.11
+
+ * Fix `util.regexify` on falsy values.
+ * Fix `_aliasFunction` with rest parameters.
+ * Export as `module.exports` instead of `exports.default` if there are no other `ExportDeclaration`s in `commonInterop` module formatter.
+ * Add `system` module formatter. Thanks [@douglasduteil](https://github.com/douglasduteil).
+
+# 1.13.10
+
+ * Add support for `AssignmentExpression` destructuring outside of `ExpressionStatement`.
+
 # 1.13.9
 
  * Fix `VirtualPropertyExpression` visitor keys.

CONTRIBUTING.md

@@ -9,7 +9,6 @@
    * CamelCase all class names
    * camelBack all variable names
  * **Spacing**
-   * 80 character line max
    * Spaces after all keywords
    * Spaces before all left curly braces
  * **Comments**

Makefile

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

bin/6to5-node

@@ -14,18 +14,19 @@ process.argv.slice(2).forEach(function(arg){
   switch (flag) {
     case "-d":
       args.unshift("--debug");
-      args.push("--no-timeouts");
       break;
+
     case "debug":
     case "--debug":
     case "--debug-brk":
       args.unshift(arg);
-      args.push("--no-timeouts");
       break;
+
     case "-gc":
     case "--expose-gc":
       args.unshift("--expose-gc");
       break;
+
     case "--gc-global":
     case "--harmony":
     case "--harmony-proxies":
@@ -37,16 +38,20 @@ process.argv.slice(2).forEach(function(arg){
     case "--trace-deprecation":
       args.unshift(arg);
       break;
+
     default:
-      if (0 == arg.indexOf("--trace")) args.unshift(arg);
-      else args.push(arg);
+      if (arg.indexOf("--trace") === 0) {
+        args.unshift(arg);
+      } else {
+        args.push(arg);
+      }
       break;
   }
 });
 
 var proc = spawn(process.argv[0], args, { stdio: "inherit" });
 proc.on("exit", function (code, signal) {
-  process.on("exit", function (){
+  process.on("exit", function () {
     if (signal) {
       process.kill(process.pid, signal);
     } else {

bin/6to5/index.js

@@ -12,6 +12,7 @@ commander.option("-f, --filename [filename]", "Filename to use when reading from
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
 commander.option("-e, --experimental", "Enable experimental support for proposed ES7 features");
+commander.option("-p, --playground", "Enable playground support");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
@@ -90,6 +91,7 @@ exports.opts = {
   sourceMapName: commander.outFile,
   amdModuleIds:  commander.amdModuleIds,
   experimental:  commander.experimental,
+  playground:    commander.playground,
   blacklist:     commander.blacklist,
   whitelist:     commander.whitelist,
   sourceMap:     commander.sourceMaps || commander.sourceMapsInline,

bin/_6to5-node

@@ -13,6 +13,7 @@ commander.option("-p, --print", "Evaluate script and print result");
 commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
 commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
 commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
+commander.option("-g, --playground", "Enable playground support");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
@@ -31,6 +32,7 @@ to5.register({
 
 var _eval = function (code, filename) {
   code = to5.transform(code, {
+    modules: "commonInterop",
     filename: filename,
     blacklist: ["useStrict"],
     experimental: commander.experimental

doc/browser.md

@@ -30,7 +30,9 @@ test.test();
 You can build a browser version of the compiler by running the following in the
 6to5 directory:
 
-    $ make build
+```sh
+$ make build
+```
 
 This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
@@ -38,7 +40,9 @@ This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
 To test 6to5 in your browser run:
 
-    $ make test-browser
+```sh
+$ make test-browser
+```
 
 And open `test/browser.html` in your browser if it doesn't open automatically.
 

doc/differences.md

@@ -17,7 +17,7 @@ var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, a
 is generated to the following with 6to5:
 
 ```javascript
-var seattlers = customers.filter(function (c) {
+var seattlers = Array.from(customers).filter(function (c) {
   return c.city == "Seattle";
 }).map(function (c) {
   return {
@@ -51,8 +51,7 @@ As you can tell, it's not very pretty, unreadable even. Instead of mapping
 directly to a runtime, like other transpilers, 6to5 maps directly to the
 equivalent ES5.
 
-I'm not saying 6to5 is for everyone or even suited for everything. Traceur is
-better suited if you'd like a full ES6 environment with polyfills and all.
+Sometimes there are little things that 6to5 needs
 
 ## Comparison to other transpilers
 

doc/index.md

@@ -19,12 +19,16 @@ how you want to use it.
 6to5 will simply compile your ES6+ script to ES5 if you pass it as an argument
 to the command-line tool `6to5`:
 
-    $ 6to5 script.js
+```sh
+$ 6to5 script.js
+```
 
 If you have a file written using ES6+ and you just want to run it, `6to5-node`
 has you covered:
 
-    $ 6to5-node script.js
+```sh
+$ 6to5-node script.js
+```
 
 And it doesn't end here! To see all the ways you can use 6to5, check out the
 [Usage](http://6to5.github.io/usage.html) page.

doc/modules.md

@@ -4,7 +4,9 @@
 
 ### CLI
 
-    $ 6to5 --modules common script.js
+```sh
+$ 6to5 --modules common script.js
+```
 
 ### Node
 
@@ -15,8 +17,19 @@ to5.transform('import "foo";', { modules: "common" });
 
 ## Formats
 
+ * [AMD](#amd)
+ * [Common (Default)](#common-default)
+ * [Common Interop](#common-interop)
+ * [Ignore](#ignore)
+ * [System](#system)
+ * [UMD](#umd)
+
 ### Common (Default)
 
+```sh
+$ 6to5 --modules common
+```
+
 **In**
 
 ```javascript
@@ -51,8 +64,79 @@ var test = 5; exports.test = test;
 exports.default = test;
 ```
 
+### Common interop
+
+```sh
+$ 6to5 --modules commonInterop
+```
+
+**In**
+
+```javascript
+import "foo";
+
+import foo from "foo";
+import * as foo from "foo";
+
+import {bar} from "foo";
+import {foo as bar} from "foo";
+
+export {test};
+export var test = 5;
+
+export default test;
+```
+
+**Out**
+
+```javascript
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
+require("foo");
+
+var foo = _interopRequire(require("foo"));
+var foo = require("foo");
+
+var bar = require("foo").bar;
+var bar = require("foo").foo;
+
+exports.test = test;
+var test = exports.test = 5;
+
+exports["default"] = test;
+```
+
+#### module.exports behaviour
+
+If there exist no other non-default `export`s then `default exports` are
+exported as `module.exports` instead of `exports.default`.
+
+**In**
+
+```javascript
+export default function foo() {
+
+}
+```
+
+**Out**
+
+```javascript
+module.exports = foo;
+
+function foo() {
+
+}
+```
+
 ### AMD
 
+```sh
+$ 6to5 --modules amd
+```
+
 **In**
 
 ```javascript
@@ -85,6 +169,10 @@ define("filename", ["exports", "foo"], function (exports, _foo) {})
 
 ### UMD
 
+```sh
+$ 6to5 --modules umd
+```
+
 **In**
 
 ```javascript
@@ -117,6 +205,10 @@ export function bar() {
 
 ### Ignore
 
+```sh
+$ 6to5 --modules ignore
+```
+
 **In**
 
 ```javascript
@@ -135,11 +227,52 @@ function bar() {
 }
 ```
 
+### System
+
+```sh
+$ 6to5 --modules system
+```
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+System.register("bar", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "bar";
+
+  var foo;
+  function bar() {
+    return foo("foobar");
+  }
+  return {
+    setters: [function (m) {
+      foo = m.default;
+    }],
+    execute: function () {
+      _export("bar", bar);
+    }
+  };
+});
+```
+
 ## Custom
 
 You can alternatively specify module names instead of one of the built-in types.
 
-    $ 6to5 --modules custom-module-formatter
+```sh
+$ 6to5 --modules custom-module-formatter
+```
 
 **node_modules/custom-module-formatter/index.js**
 

doc/optional-runtime.md

@@ -18,7 +18,9 @@ Simply use the following option if you're using the [Node API](usage.md#node):
 
 or the following flag if you're using the [CLI](usage.md#cli):
 
-    $ 6to5 --runtime
+```ssh
+$ 6to5 --runtime
+```
 
 Then just include the runtime before your generated code.
 
@@ -26,7 +28,9 @@ Then just include the runtime before your generated code.
 
 You can get the runtime via either:
 
-    $ 6to5-runtime
+```sh
+$ 6to5-runtime
+```
 
 or
 
@@ -45,7 +49,9 @@ argument:
 require("6to5").runtime("myCustomNamespace");
 ```
 
-    $ 6to5-runtime myCustomNamespace
+```sh
+$ 6to5-runtime myCustomNamespace
+```
 
 See [Options - runtime](usage.md#options) for documentation on changing the
 reference in generated code.

doc/playground.md

@@ -0,0 +1,120 @@
+# Playground
+
+Playground is a proving ground for **possible** ES7 proposals.
+
+**NOTE: These features are in no way endorsed by Ecma International and are not a part of ES6. They might become a part of ECMAScript in the future.**
+
+## Usage
+
+    $ 6to5 --playground
+
+```javascript
+to5.transform("code", { playground: true });
+```
+
+**NOTE:** Enabling `playground` also enables [experimental support](usage.md#experimental).
+
+## Features
+
+ * [Memoization operator](#memoization-operator)
+ * [Method binding](#method-binding)
+ * [Object getter memoization](#object-getter-memoization)
+ * [This shorthand](#this-shorthand)
+
+### Memoization assignment operator
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+obj.x; // 2
+
+obj = { x: 1 };
+obj.x ?= 2;
+obj.x; // 1
+
+obj = { x: undefined }
+obj.x ?= 2;
+obj.x; // undefined
+```
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+```
+
+equivalent to:
+
+```javascript
+var obj = {};
+if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
+```
+
+### Method binding
+
+```javascript
+var fn = obj:method;
+var fn = obj:method("foob");
+
+["foo", "bar"].map(:toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(:toFixed(2)); // ["1.12", "23.53", "3.00"]
+```
+
+equivalent to:
+
+```javascript
+var fn = obj.method.bind(obj);
+var fn = obj.method.bind(obj, "foob");
+
+["foo", "bar"].map(function (val) { return val.toUpperCase(); });
+[1.1234, 23.53245, 3].map(function (val) { return val.toFixed(2); });
+```
+
+### Object getter memoization
+
+```javascript
+var foo = {
+  memo bar() {
+    return complex();
+  }
+};
+
+class Foo {
+  memo bar() {
+    return complex();
+  }
+}
+```
+
+equivalent to
+
+```javascript
+var foo = {
+  get bar() {
+    if (this._barRan) return this._bar;
+    this._barRan = true;
+    return this._bar = complex();
+  }
+};
+
+class Foo {
+  get bar() {
+    if (this._barRan) return this._bar;
+    this._barRan = true;
+    return this._bar = complex();
+  }
+}
+```
+
+**NOTE:** Memoised functions will return the result of the **first** execution, regardless of arguments.
+
+### This shorthand
+
+```javascript
+@foo
+```
+
+equivalent to
+
+```javascirpt
+this.foo
+```

doc/plugins.md

@@ -8,9 +8,10 @@
  - [Gobble](https://github.com/gobblejs/gobble-6to5)
  - [Gulp](https://github.com/sindresorhus/gulp-6to5)
  - [Grunt](https://github.com/sindresorhus/grunt-6to5)
+ - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
  - [Jade](https://github.com/Apoxx/jade-6to5)
  - [Jest](https://github.com/6to5/6to5-jest)
- - [JSXHint](https://github.com/STRML/JSXHint) (A wrapper around JSHint to allow linting of JSX files)
+ - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
  - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
  - [Mocha](https://github.com/6to5/6to5-mocha)
  - [Rails](https://github.com/josh/sprockets-es6) or via [browserify-rails](https://github.com/6to5/6to5-rails)

doc/react.md

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

doc/usage.md

@@ -4,47 +4,67 @@
 
 Compile the file `script.js` and output it to stdout.
 
-    $ 6to5 script.js
+```sh
+$ 6to5 script.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js`.
 
-    $ 6to5 script.js --out-file script-compiled.js
+```sh
+$ 6to5 script.js --out-file script-compiled.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js` and save a
 source map to `script-compiled.js.map`.
 
-    $ 6to5 script.js --source-maps --out-file script-compiled.js
+```sh
+$ 6to5 script.js --source-maps --out-file script-compiled.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js` with a source
 map embedded in a comment at the bottom.
 
-    $ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```sh
+$ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```
 
 Compile the entire `src` directory and output it to the `lib` directory.
 
-    $ 6to5 src --out-dir lib
+```sh
+$ 6to5 src --out-dir lib
+```
 
 Compile the entire `src` directory and output it to the one concatenated file.
 
-    $ 6to5 src --out-file script-compiled.js
+```sh
+$ 6to5 src --out-file script-compiled.js
+```
 
 Pipe a file in via stdin and output it to `script-compiled.js`
 
-    $ 6to5 --out-file script-compiled.js < script.js
+```sh
+$ 6to5 --out-file script-compiled.js < script.js
+```
 
 ### Node
 
 Launch a repl.
 
-    $ 6to5-node
+```sh
+$ 6to5-node
+```
 
 Evaluate code.
 
-    $ 6to5-node -e "class Test { }"
+```sh
+$ 6to5-node -e "class Test { }"
+```
 
 Compile and run `test.js`.
 
-    $ 6to5-node test
+```sh
+$ 6to5-node test
+```
 
 ## Node
 

lib/6to5/file.js

@@ -10,9 +10,7 @@ var t         = require("./types");
 var _         = require("lodash");
 
 function File(opts) {
-  this.opts            = File.normaliseOptions(opts);
-  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
-
+  this.opts = File.normaliseOptions(opts);
   this.uids = {};
   this.ast  = {};
 }
@@ -24,8 +22,9 @@ File.declarations = [
   "tagged-template-literal",
   "interop-require",
   "to-array",
-  "arguments-to-array",
-  "object-spread"
+  "object-spread",
+  "has-own",
+  "slice"
 ];
 
 File.normaliseOptions = function (opts) {
@@ -33,6 +32,7 @@ File.normaliseOptions = function (opts) {
 
   _.defaults(opts, {
     experimental: false,
+    playground:   false,
     whitespace:   true,
     blacklist:    [],
     whitelist:    [],
@@ -41,7 +41,8 @@ File.normaliseOptions = function (opts) {
     filename:     "unknown",
     modules:      "common",
     runtime:      false,
-    code:         true
+    code:         true,
+    ast:          true
   });
 
   // normalise windows path separators to unix
@@ -71,6 +72,10 @@ File.normaliseOptions = function (opts) {
     opts.runtime = "to5Runtime";
   }
 
+  if (opts.playground) {
+    opts.experimental = true;
+  }
+
   transform._ensureTransformerNames("blacklist", opts.blacklist);
   transform._ensureTransformerNames("whitelist", opts.whitelist);
 
@@ -80,14 +85,11 @@ File.normaliseOptions = function (opts) {
 File.prototype.toArray = function (node) {
   if (t.isArrayExpression(node)) {
     return node;
+  } else if (t.isIdentifier(node) && node.name === "arguments") {
+    return t.callExpression(t.memberExpression(this.addDeclaration("slice"), t.identifier("call")), [node]);
+  } else {
+    return t.callExpression(this.addDeclaration("to-array"), [node]);
   }
-
-  var templateName = "to-array";
-  if (t.isIdentifier(node) && node.name === "arguments") {
-    templateName = "arguments-to-array";
-  }
-
-  return t.callExpression(this.addDeclaration(templateName), [node]);
 };
 
 File.prototype.getModuleFormatter = function (type) {
@@ -137,7 +139,11 @@ File.prototype.addDeclaration = function (name) {
   }
 
   var uid = this.generateUidIdentifier(name);
-  this.scope.push(name, uid, ref);
+  this.scope.push({
+    key: name,
+    id: uid,
+    init: ref
+  });
   return uid;
 };
 
@@ -168,6 +174,7 @@ File.prototype.parse = function (code) {
 File.prototype.transform = function (ast) {
   this.ast = ast;
   this.scope = new Scope(ast.program);
+  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
 
   var self = this;
 
@@ -180,15 +187,18 @@ File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;
 
-  if (!opts.code) {
-    return {
-      code: "",
-      map:  null,
-      ast:  ast
-    };
-  }
+  var result = {
+    code: "",
+    map: null,
+    ast: null
+  };
 
-  var result = generate(ast, opts, this.code);
+  if (opts.ast) result.ast = ast;
+  if (!opts.code) return result;
+
+  var _result = generate(ast, opts, this.code);
+  result.code = _result.code;
+  result.map  = _result.map;
 
   if (this.shebang) {
     // add back shebang
@@ -199,8 +209,6 @@ File.prototype.generate = function () {
     result.code += "\n" + util.sourceMapToComment(result.map);
   }
 
-  result.ast = result;
-
   return result;
 };
 

lib/6to5/generation/generator.js

@@ -53,6 +53,7 @@ CodeGenerator.generators = {
   comprehensions:   require("./generators/comprehensions"),
   expressions:      require("./generators/expressions"),
   statements:       require("./generators/statements"),
+  playground:       require("./generators/playground"),
   classes:          require("./generators/classes"),
   methods:          require("./generators/methods"),
   modules:          require("./generators/modules"),
@@ -160,7 +161,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     this.printTrailingComments(node, parent);
   } else {
-    throw new ReferenceError("unknown node " + node.type + " " + JSON.stringify(node));
+    throw new ReferenceError("unknown node " + node.type);
   }
 };
 

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

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

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

@@ -28,7 +28,13 @@ exports.before = {
 };
 
 exports.after = {
-  nodes: {},
+  nodes: {
+    AssignmentExpression: function (node) {
+      if (t.isFunction(node.right)) {
+        return 1;
+      }
+    }
+  },
 
   list: {
     VariableDeclaration: function (node) {

lib/6to5/patch.js

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

lib/6to5/register.js

@@ -3,6 +3,7 @@ require("./polyfill");
 var sourceMapSupport = require("source-map-support");
 var util             = require("./util");
 var to5              = require("./index");
+var fs               = require("fs");
 var _                = require("lodash");
 
 sourceMapSupport.install({
@@ -61,22 +62,42 @@ var transformOpts = {};
 var ignoreRegex   = /node_modules/;
 var onlyRegex;
 var whitelist     = [];
+var cache;
 var exts          = {};
 var maps          = {};
 var old           = require.extensions[".js"];
 
+var mtime = function (filename) {
+  return +fs.statSync(filename).mtime;
+};
+
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, _.extend({
+  var result;
+
+  if (cache) {
+    var cached = cache[filename];
+    if (cached && cached.mtime === mtime(filename)) {
+      result = cached;
+    }
+  }
+
+  result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
-    modules:   "commonInterop"
+    modules:   "commonInterop",
+    ast:       false
   }, transformOpts));
 
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
+
   maps[filename] = result.map;
 
   m._compile(result.code, filename);
@@ -108,5 +129,8 @@ module.exports = function (opts) {
 
   if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 
+  if (opts.cache) cache = opts.cache;
+  if (opts.cache === false) cache = null;
+
   _.extend(transformOpts, opts);
 };

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

@@ -1,7 +0,0 @@
-(function (args) {
-  var target = new Array(args.length);
-  for (var i = 0; i< args.length; i++) {
-    target[i] = args[i];
-  }
-  return target;
-})

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

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

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

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

lib/6to5/templates/register.js

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

lib/6to5/templates/slice.js

@@ -0,0 +1 @@
+Array.prototype.slice;

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

@@ -41,34 +41,11 @@ AMDFormatter.prototype.transform = function (ast) {
 };
 
 AMDFormatter.prototype.getModuleName = function () {
-  var opts = this.file.opts;
-  var filenameRelative = opts.filenameRelative;
-  var moduleName = "";
-
-  if (!opts.amdModuleIds) {
+  if (this.file.opts.amdModuleIds) {
+    return CommonJSFormatter.prototype.getModuleName.apply(this, arguments);
+  } else {
     return null;
   }
-
-  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;
 };
 
 AMDFormatter.prototype._push = function (node) {

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

@@ -3,9 +3,16 @@ module.exports = CommonJSInteropFormatter;
 var CommonJSFormatter = require("./common");
 var util              = require("../../util");
 var t                 = require("../../types");
+var _                 = require("lodash");
 
 function CommonJSInteropFormatter(file) {
-  this.file = 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);
@@ -26,3 +33,24 @@ CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node,
     CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
   }
 };
+
+CommonJSInteropFormatter.prototype.export = function (node, nodes) {
+  if (node.default && !this.has) {
+    var declar = node.declaration;
+
+    // module.exports = VALUE;
+    var assign = util.template("exports-default-module", {
+      VALUE: this._pushStatement(declar, nodes)
+    }, true);
+
+    // hoist to the top if this default is a function
+    nodes.push(this._hoistExport(declar, assign));
+    return;
+  }
+
+  CommonJSFormatter.prototype.export.apply(this, arguments);
+};
+
+CommonJSInteropFormatter.prototype.exportSpecifier = function () {
+  CommonJSFormatter.prototype.exportSpecifier.apply(this, arguments);
+};

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

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

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

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

lib/6to5/transformation/transform.js

@@ -22,12 +22,18 @@ 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")
 };
 
 _.each({
+  // plyground
+  methodBinding:             require("./transformers/playground-method-binding"),
+  memoizationOperator:       require("./transformers/playground-memoization-operator"),
+  objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),
+
   modules:                   require("./transformers/es6-modules"),
   propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
   arrayComprehension:        require("./transformers/es7-array-comprehension"),
@@ -35,7 +41,6 @@ _.each({
   arrowFunctions:            require("./transformers/es6-arrow-functions"),
   classes:                   require("./transformers/es6-classes"),
 
-  _propertyLiterals:         require("./transformers/_property-literals"),
   computedPropertyNames:     require("./transformers/es6-computed-property-names"),
 
   objectSpread:              require("./transformers/es7-object-spread"),
@@ -62,7 +67,8 @@ _.each({
 
   useStrict:                 require("./transformers/use-strict"),
 
-  _memberExpressionKeywords: require("./transformers/_member-expression-keywords"),
+  _propertyLiterals:         require("./transformers/_property-literals"),
+  _memberExpressioLiterals:  require("./transformers/_member-expression-literals"),
   _moduleFormatter:          require("./transformers/_module-formatter")
 }, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);

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

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

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

@@ -3,9 +3,21 @@ var _ = require("lodash");
 
 exports.BlockStatement =
 exports.Program = function (node) {
+  var kinds = {};
+
   _.each(node._declarations, function (declar) {
-    node.body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(declar.id, declar.init)
-    ]));
+    var kind = declar.kind || "var";
+    var declarNode = t.variableDeclarator(declar.id, declar.init);
+
+    if (!declar.init) {
+      kinds[kind] = kinds[kind] || [];
+      kinds[kind].push(declarNode);
+    } else {
+      node.body.unshift(t.variableDeclaration(kind, [declarNode]));
+    }
+  });
+
+  _.each(kinds, function (declars, kind) {
+    node.body.unshift(t.variableDeclaration(kind, declars));
   });
 };

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

@@ -1,10 +0,0 @@
-var esutils = require("esutils");
-var t = require("../../types");
-
-exports.MemberExpression = function (node) {
-  var prop = node.property;
-  if (t.isIdentifier(prop) && esutils.keyword.isKeywordES6(prop.name, true)) {
-    node.property = t.literal(prop.name);
-    node.computed = true;
-  }
-};

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

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

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

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

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

@@ -4,9 +4,13 @@ var t        = require("../../types");
 var _        = require("lodash");
 
 exports.ClassDeclaration = function (node, parent, file, scope) {
-  return t.variableDeclaration("let", [
-    t.variableDeclarator(node.id, new Class(node, file, scope).run())
+  var built = new Class(node, file, scope).run();
+
+  var declar = t.variableDeclaration("let", [
+    t.variableDeclarator(node.id, built)
   ]);
+  t.inheritsComments(declar, node);
+  return declar;
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
@@ -158,17 +162,22 @@ Class.prototype.buildBody = function () {
 Class.prototype.pushMethod = function (node) {
   var methodName = node.key;
 
-  var mutatorMap = this.instanceMutatorMap;
-  if (node.static) mutatorMap = this.staticMutatorMap;
-
   var kind = node.kind;
 
   if (kind === "") {
-    kind = "value";
-    util.pushMutatorMap(mutatorMap, methodName, "writable", t.identifier("true"));
-  }
+    // method
 
-  util.pushMutatorMap(mutatorMap, methodName, kind, node);
+    var className = this.className;
+    if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
+    methodName = t.memberExpression(className, methodName, node.computed);
+
+    this.body.push(t.expressionStatement(t.assignmentExpression("=", methodName, node.value)));
+  } else {
+    // mutator
+    var mutatorMap = this.instanceMutatorMap;
+    if (node.static) mutatorMap = this.staticMutatorMap;
+    util.pushMutatorMap(mutatorMap, methodName, kind, node);
+  }
 };
 
 /**

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

@@ -11,7 +11,7 @@ exports.Function = function (node, parent, file, scope) {
     return t.getIds(param);
   });
 
-  var closure = false;
+  var iife = false;
 
   _.each(node.defaults, function (def, i) {
     if (!def) return;
@@ -29,7 +29,7 @@ exports.Function = function (node, parent, file, scope) {
         }
 
         if (scope.has(node.name)) {
-          closure = true;
+          iife = true;
         }
       };
 
@@ -40,7 +40,7 @@ exports.Function = function (node, parent, file, scope) {
     // we're accessing a variable that's already defined within this function
     var has = scope.get(param.name);
     if (has && !_.contains(node.params, has)) {
-      closure = true;
+      iife = true;
     }
   });
 
@@ -55,7 +55,7 @@ exports.Function = function (node, parent, file, scope) {
     }, true));
   });
 
-  if (closure) {
+  if (iife) {
     var container = t.functionExpression(null, [], node.body, node.generator);
     container._aliasFunction = true;
 

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

@@ -1,11 +1,16 @@
+// TODO: Clean up
+
 var t = require("../../types");
 var _ = require("lodash");
 
-var buildVariableAssign = function (kind, id, init) {
-  if (kind === false) {
+var buildVariableAssign = function (opts, id, init) {
+  var op = opts.operator;
+  if (t.isMemberExpression(id)) op = "=";
+
+  if (op) {
     return t.expressionStatement(t.assignmentExpression("=", id, init));
   } else {
-    return t.variableDeclaration(kind, [
+    return t.variableDeclaration(opts.kind, [
       t.variableDeclarator(id, init)
     ]);
   }
@@ -16,10 +21,8 @@ var push = function (opts, nodes, elem, parentId) {
     pushObjectPattern(opts, nodes, elem, parentId);
   } else if (t.isArrayPattern(elem)) {
     pushArrayPattern(opts, nodes, elem, parentId);
-  } else if (t.isMemberExpression(elem)) {
-    nodes.push(buildVariableAssign(false, elem, parentId));
   } else {
-    nodes.push(buildVariableAssign(opts.kind, elem, parentId));
+    nodes.push(buildVariableAssign(opts, elem, parentId));
   }
 };
 
@@ -41,7 +44,7 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
         keys = t.arrayExpression(keys);
 
         var value = t.callExpression(opts.file.addDeclaration("object-spread"), [parentId, keys]);
-        nodes.push(buildVariableAssign(opts.kind, prop.argument, value));
+        nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
       var pattern2   = prop.value;
       var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
@@ -49,7 +52,7 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
       if (t.isPattern(pattern2)) {
         push(opts, nodes, pattern2, patternId2);
       } else {
-        nodes.push(buildVariableAssign(opts.kind, pattern2, patternId2));
+        nodes.push(buildVariableAssign(opts, pattern2, patternId2));
       }
     }
   });
@@ -175,7 +178,7 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
   ]));
 
   push({
-    kind: false,
+    operator: expr.operator,
     file: file,
     scope: scope
   }, nodes, expr.left, ref);
@@ -183,10 +186,29 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
   return nodes;
 };
 
-exports.AssignmentExpression = function (node, parent, file) {
+exports.AssignmentExpression = function (node, parent, file, scope) {
   if (parent.type === "ExpressionStatement") return;
   if (!t.isPattern(node.left)) return;
-  throw file.errorWithNode(node, "AssignmentExpression destructuring outside of a ExpressionStatement is forbidden due to current 6to5 limitations");
+
+  var tempName = file.generateUid("temp", scope);
+  var ref = t.identifier(tempName);
+  scope.push({
+    key: tempName,
+    id: ref
+  });
+
+  var nodes = [];
+  nodes.push(t.assignmentExpression("=", ref, node.right));
+
+  push({
+    operator: node.operator,
+    file: file,
+    scope: scope
+  }, nodes, node.left, ref);
+
+  nodes.push(ref);
+
+  return t.toSequenceExpression(nodes, scope);
 };
 
 exports.VariableDeclaration = function (node, parent, file, scope) {
@@ -206,17 +228,18 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   _.each(node.declarations, function (declar) {
     var patternId = declar.init;
     var pattern   = declar.id;
+    var opts = {
+      kind:    node.kind,
+      nodes:   nodes,
+      pattern: pattern,
+      id:      patternId,
+      file:    file,
+      scope:   scope
+    };
     if (t.isPattern(pattern) && patternId) {
-      pushPattern({
-        kind:    node.kind,
-        nodes:   nodes,
-        pattern: pattern,
-        id:      patternId,
-        file:    file,
-        scope:   scope
-      });
+      pushPattern(opts);
     } else {
-      nodes.push(buildVariableAssign(node.kind, declar.id, declar.init));
+      nodes.push(buildVariableAssign(opts, declar.id, declar.init));
     }
   });
 
@@ -238,4 +261,3 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
 
   return nodes;
 };
-

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

@@ -56,7 +56,7 @@ var visitor = function (path, file) {
   );
 
   var innerFnId = t.identifier(node.id.name + "$");
-  var contextId = file.generateUidIdentifier("context$", scope);
+  var contextId = file.generateUidIdentifier("context", scope);
   var vars = hoist(path);
 
   var emitter = new Emitter(contextId);

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

@@ -27,7 +27,7 @@ exports.VariableDeclaration = function (node) {
   isLet(node);
 };
 
-exports.For = function (node, parent, file, scope) {
+exports.Loop = function (node, parent, file, scope) {
   var init = node.left || node.init;
   if (isLet(init)) {
     t.ensureBlock(node);
@@ -49,7 +49,7 @@ exports.For = function (node, parent, file, scope) {
 };
 
 exports.BlockStatement = function (block, parent, file, scope) {
-  if (!t.isFor(parent)) {
+  if (!t.isLoop(parent)) {
     var letScoping = new LetScoping(false, block, parent, file, scope);
     letScoping.run();
   }
@@ -58,19 +58,19 @@ exports.BlockStatement = function (block, parent, file, scope) {
 /**
  * Description
  *
- * @param {Boolean|Node} forParent
+ * @param {Boolean|Node} loopParent
  * @param {Node} block
  * @param {Node} parent
  * @param {File} file
  * @param {Scope} scope
  */
 
-function LetScoping(forParent, block, parent, file, scope) {
-  this.forParent = forParent;
-  this.parent    = parent;
-  this.scope     = scope;
-  this.block     = block;
-  this.file      = file;
+function LetScoping(loopParent, block, parent, file, scope) {
+  this.loopParent = loopParent;
+  this.parent     = parent;
+  this.scope      = scope;
+  this.block      = block;
+  this.file       = file;
 
   this.letReferences = {};
   this.body          = [];
@@ -91,6 +91,9 @@ LetScoping.prototype.run = function () {
   // remap all let references that exist in upper scopes to their uid
   this.remap();
 
+  // add default initializer to let variables in loop bodys
+  this.initialiseLoopLets();
+
   // this is a block within a `Function` so we can safely leave it be
   if (t.isFunction(this.parent)) return this.noClosure();
 
@@ -106,7 +109,7 @@ LetScoping.prototype.run = function () {
 
   // if we're inside of a for loop then we search to see if there are any
   // `break`s, `continue`s, `return`s etc
-  this.has = this.checkFor();
+  this.has = this.checkLoop();
 
   // hoist var references to retain scope
   this.hoistVarDeclarations();
@@ -172,11 +175,11 @@ LetScoping.prototype.remap = function () {
     traverse(node, replace);
   };
 
-  var forParent = this.forParent;
-  if (forParent) {
-    traverseReplace(forParent.right, forParent);
-    traverseReplace(forParent.test, forParent);
-    traverseReplace(forParent.update, forParent);
+  var loopParent = this.loopParent;
+  if (loopParent) {
+    traverseReplace(loopParent.right, loopParent);
+    traverseReplace(loopParent.test, loopParent);
+    traverseReplace(loopParent.update, loopParent);
   }
 
   traverse(block, replace);
@@ -244,6 +247,30 @@ LetScoping.prototype.getInfo = function () {
   return opts;
 };
 
+/**
+ * Any let variable declared within a loop body need to have an initializer or
+ * else they'll be hoisted and subsequent iterations of the loop will have a
+ * previous state. This function adds a default initializer of `undefined` to
+ * those variables.
+ */
+
+LetScoping.prototype.initialiseLoopLets = function () {
+  var loopParent = this.loopParent;
+  if (!loopParent) return;
+
+  traverse(this.block, function (node) {
+    if (t.isFunction(node) || t.isLoop(node)) {
+      return false;
+    }
+
+    if (isLet(node)) {
+      _.each(node.declarations, function (declar) {
+        declar.init = declar.init || t.identifier("undefined");
+      });
+    }
+  });
+};
+
 /**
  * If we're inside of a `For*Statement` then traverse it and check if it has one
  * of the following node types `ReturnStatement`, `BreakStatement`,
@@ -253,24 +280,24 @@ LetScoping.prototype.getInfo = function () {
  * @returns {Object}
  */
 
-LetScoping.prototype.checkFor = function () {
+LetScoping.prototype.checkLoop = function () {
   var has = {
     hasContinue: false,
     hasReturn:   false,
     hasBreak:    false,
   };
 
-  var forParent = this.forParent;
-
-  traverse(this.block, function (node) {
+  traverse(this.block, function (node, parent) {
     var replace;
 
-    if (t.isFunction(node) || t.isFor(node)) {
+    if (t.isFunction(node) || t.isLoop(node)) {
       return false;
     }
 
-    if (forParent && node && !node.label) {
+    if (node && !node.label) {
       if (t.isBreakStatement(node)) {
+        if (t.isSwitchCase(parent)) return;
+
         has.hasBreak = true;
         replace = t.returnStatement(t.literal("break"));
       } else if (t.isContinueStatement(node)) {
@@ -367,7 +394,7 @@ LetScoping.prototype.getLetReferences = function () {
       });
 
       return false;
-    } else if (t.isFor(node)) {
+    } else if (t.isLoop(node)) {
       return false;
     }
   });
@@ -430,7 +457,7 @@ LetScoping.prototype.buildHas = function (ret, call) {
     t.variableDeclarator(ret, call)
   ]));
 
-  var forParent = this.forParent;
+  var loopParent = this.loopParent;
   var retCheck;
   var has = this.has;
   var cases = [];
@@ -445,7 +472,7 @@ LetScoping.prototype.buildHas = function (ret, call) {
   if (has.hasBreak || has.hasContinue) {
     // ensure that the parent has a label as we're building a switch and we
     // need to be able to access it
-    var label = forParent.label = forParent.label || this.file.generateUidIdentifier("loop", this.scope);
+    var label = loopParent.label = loopParent.label || this.file.generateUidIdentifier("loop", this.scope);
 
     if (has.hasBreak) {
       cases.push(t.switchCase(t.literal("break"), [t.breakStatement(label)]));

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

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

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

@@ -1,3 +1,4 @@
 exports.Property = function (node) {
-  if (node.shorthand) node.shorthand = false;
+  if (!node.shorthand) return;
+  node.shorthand = false;
 };

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

@@ -8,13 +8,10 @@ exports.Function = function (node, parent, file) {
 
   t.ensureBlock(node);
 
-  var call = t.callExpression(
-    file.addDeclaration("arguments-to-array"),
-    [t.identifier("arguments")]
-  );
+  var call = file.toArray(t.identifier("arguments"));
 
   if (node.params.length) {
-    call = t.callExpression(t.memberExpression(call, t.identifier("slice")), [t.literal(node.params.length)]);
+    call.arguments.push(t.literal(node.params.length));
   }
 
   call._ignoreAliasFunctions = true;

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

@@ -56,7 +56,7 @@ exports.ArrayExpression = function (node, parent, file) {
   return t.callExpression(t.memberExpression(first, t.identifier("concat")), nodes);
 };
 
-exports.CallExpression = function (node, parent, file) {
+exports.CallExpression = function (node, parent, file, scope) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
@@ -64,7 +64,12 @@ exports.CallExpression = function (node, parent, file) {
 
   node.arguments = [];
 
-  var nodes = build(args, file);
+  var nodes;
+  if (args.length === 1 && args[0].argument.name === 'arguments') {
+    nodes = [args[0].argument];
+  } else {
+    nodes = build(args, file);
+  }
   var first = nodes.shift();
 
   if (nodes.length) {
@@ -74,10 +79,16 @@ exports.CallExpression = function (node, parent, file) {
   }
 
   var callee = node.callee;
+  var temp;
 
   if (t.isMemberExpression(callee)) {
     contextLiteral = callee.object;
 
+    if (t.isDynamic(contextLiteral)) {
+      temp = contextLiteral = scope.generateTemp(file);
+      callee.object = t.assignmentExpression("=", temp, callee.object);
+    }
+
     if (callee.computed) {
       callee.object = t.memberExpression(callee.object, callee.property, true);
       callee.property = t.identifier("apply");

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

@@ -31,7 +31,7 @@ exports.TemplateLiteral = function (node) {
   var nodes = [];
 
   _.each(node.quasis, function (elem) {
-    nodes.push(t.literal(elem.value.raw));
+    nodes.push(t.literal(elem.value.cooked));
 
     var expr = node.expressions.shift();
     if (expr) {

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

@@ -29,10 +29,8 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
   // we need to return `node.right`
   if (!t.isExpressionStatement(parent)) {
     // `node.right` isn't a simple identifier so we need to reference it
-    if (!t.isIdentifier(value)) {
-      var tempName = file.generateUid("temp");
-      temp = value = t.identifier(tempName);
-      scope.push(tempName, temp);
+    if (t.isDynamic(value)) {
+      temp = value = scope.generateTemp(file);
     }
   }
 
@@ -70,11 +68,9 @@ exports.CallExpression = function (node, parent, file, scope) {
   if (!t.isVirtualPropertyExpression(callee)) return;
 
   var temp;
-  if (!t.isIdentifier(callee.object)) {
+  if (t.isDynamic(callee.object)) {
     // we need to save `callee.object` so we can call it again
-    var tempName = file.generateUid("temp");
-    temp = t.identifier(tempName);
-    scope.push(tempName, temp);
+    temp = scope.generateTemp(file);
   }
 
   var call = util.template("abstract-expression-call", {

lib/6to5/transformation/transformers/playground-memoization-operator.js

@@ -0,0 +1,90 @@
+var t = require("../../types");
+
+var isMemo = function (node) {
+  var is = t.isAssignmentExpression(node) && node.operator === "?=";
+  if (is) t.assertMemberExpression(node.left);
+  return is;
+};
+
+var getPropRef = function (nodes, prop, file, scope) {
+  if (t.isIdentifier(prop)) {
+    return t.literal(prop.name);
+  } else {
+    var temp = file.generateUidIdentifier("propKey", scope);
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(temp, prop)
+    ]));
+    return temp;
+  }
+};
+
+var getObjRef = function (nodes, obj, file, scope) {
+  if (t.isDynamic(obj)) {
+    var temp = file.generateUidIdentifier("obj", scope);
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(temp, obj)
+    ]));
+    return temp;
+  } else {
+    return obj;
+  }
+};
+
+var buildHasOwn = function (obj, prop, file) {
+  return t.unaryExpression(
+    "!",
+    t.callExpression(
+      t.memberExpression(file.addDeclaration("has-own"), t.identifier("call")),
+      [obj, prop]
+    ),
+    true
+  );
+};
+
+var buildAbsoluteRef = function (left, obj, prop) {
+  var computed = left.computed || t.isLiteral(prop);
+  return t.memberExpression(obj, prop, computed);
+};
+
+var buildAssignment = function (expr, obj, prop) {
+  return t.assignmentExpression("=", buildAbsoluteRef(expr.left, obj, prop), expr.right);
+};
+
+exports.ExpressionStatement = function (node, parent, file, scope) {
+  var expr = node.expression;
+  if (!isMemo(expr)) return;
+
+  var nodes = [];
+
+  var left = expr.left;
+  var obj  = getObjRef(nodes, left.object, file, scope);
+  var prop = getPropRef(nodes, left.property, file, scope);
+
+  nodes.push(t.ifStatement(
+    buildHasOwn(obj, prop, file),
+    t.expressionStatement(buildAssignment(expr, obj, prop))
+  ));
+
+  return nodes;
+};
+
+exports.AssignmentExpression = function (node, parent, file, scope) {
+  if (t.isExpressionStatement(parent)) return;
+  if (!isMemo(node)) return;
+
+  var nodes = [];
+
+  var left = node.left;
+  var obj  = getObjRef(nodes, left.object, file, scope);
+  var prop = getPropRef(nodes, left.property, file, scope);
+
+  nodes.push(t.logicalExpression(
+    "&&",
+    buildHasOwn(obj, prop, file),
+    buildAssignment(node, obj, prop)
+  ));
+
+  nodes.push(buildAbsoluteRef(left, obj, prop));
+
+  return t.toSequenceExpression(nodes, scope);
+};

lib/6to5/transformation/transformers/playground-method-binding.js

@@ -0,0 +1,48 @@
+var t = require("../../types");
+var _ = require("lodash");
+
+exports.BindMemberExpression = function (node, parent, file, scope) {
+  var object = node.object;
+  var prop   = node.property;
+
+  var temp;
+  if (t.isDynamic(object)) {
+    temp = object = scope.generateTemp(file);
+  }
+
+  var call = t.callExpression(
+    t.memberExpression(t.memberExpression(object, prop), t.identifier("bind")),
+    [object].concat(node.arguments)
+  );
+
+  if (temp) {
+    return t.sequenceExpression([
+      t.assignmentExpression("=", temp, node.object),
+      call
+    ]);
+  } else {
+    return call;
+  }
+};
+
+exports.BindFunctionExpression = function (node, parent, file, scope) {
+  var buildCall = function (args) {
+    var param = file.generateUidIdentifier("val", scope);
+    return t.functionExpression(null, [param], t.blockStatement([
+      t.returnStatement(t.callExpression(t.memberExpression(param, node.callee), args))
+    ]));
+  };
+
+  if (_.find(node.arguments, t.isDynamic)) {
+    var temp = scope.generateTemp(file, "args");
+
+    return t.sequenceExpression([
+      t.assignmentExpression("=", temp, t.arrayExpression(node.arguments)),
+      buildCall(node.arguments.map(function (node, i) {
+        return t.memberExpression(temp, t.literal(i), true);
+      }))
+    ]);
+  } else {
+    return buildCall(node.arguments);
+  }
+};

lib/6to5/transformation/transformers/playground-object-getter-memoization.js

@@ -0,0 +1,37 @@
+var traverse = require("../../traverse");
+var t        = require("../../types");
+
+exports.Property =
+exports.MethodDefinition = function (node, parent, file, scope) {
+  if (node.kind !== "memo") return;
+  node.kind = "get";
+
+  var value = node.value;
+  t.ensureBlock(value);
+
+  var body  = value.body.body;
+  var key   = node.key;
+
+  if (t.isIdentifier(key) && !node.computed) {
+    key = "_" + key.name;
+  } else {
+    key = file.generateUid("memo", scope);
+  }
+
+  var memoId = t.memberExpression(t.thisExpression(), t.identifier(key));
+  var doneId = t.memberExpression(t.thisExpression(), t.identifier(key + "Done"));
+
+  traverse(value, function (node) {
+    if (t.isFunction(node)) return;
+
+    if (t.isReturnStatement(node) && node.argument) {
+      node.argument = t.assignmentExpression("=", memoId, node.argument);
+    }
+  });
+
+  // this._barDone = true;
+  body.unshift(t.expressionStatement(t.assignmentExpression("=", doneId, t.literal(true))));
+
+  // if (this._barDone) return this._bar;
+  body.unshift(t.ifStatement(doneId, t.returnStatement(memoId)));
+};

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

@@ -132,6 +132,8 @@ exports.XJSElement = {
           }
         });
 
+        return;
+      } else if (t.isXJSEmptyExpression(child)) {
         return;
       }
 

lib/6to5/traverse/index.js

@@ -50,6 +50,10 @@ function traverse(parent, callbacks, opts) {
         if (result != null) {
           updated = true;
           node = obj[key] = result;
+
+          if (_.isArray(result) && _.contains(t.STATEMENT_OR_BLOCK_KEYS, key) && !t.isBlockStatement(obj)) {
+            t.ensureBlock(obj, key);
+          }
         }
       };
 

lib/6to5/traverse/scope.js

@@ -21,15 +21,28 @@ function Scope(block, parent) {
   this.references = this.getReferences();
 }
 
+Scope.add = function (node, references) {
+  if (!node) return;
+  _.defaults(references, t.getIds(node, true));
+};
+
+Scope.prototype.generateTemp = function (file, name) {
+    var id = file.generateUidIdentifier(name || "temp", this);
+    this.push({
+      key: id.name,
+      id: id
+    });
+    return id;
+};
+
 Scope.prototype.getReferences = function () {
   var block = this.block;
   if (block._scopeReferences) return block._scopeReferences;
 
-  var self       = this;
   var references = block._scopeReferences = {};
 
   var add = function (node) {
-    self.add(node, references);
+    Scope.add(node, references);
   };
 
   // ForStatement - left, init
@@ -97,7 +110,7 @@ Scope.prototype.getReferences = function () {
   return references;
 };
 
-Scope.prototype.push = function (name, id, init) {
+Scope.prototype.push = function (opts) {
   var block = this.block;
 
   if (t.isFor(block) || t.isCatchClause(block) || t.isFunction(block)) {
@@ -107,18 +120,18 @@ Scope.prototype.push = function (name, id, init) {
 
   if (t.isBlockStatement(block) || t.isProgram(block)) {
     block._declarations = block._declarations || {};
-    block._declarations[name] = {
-      id: id,
-      init: init
+    block._declarations[opts.key] = {
+      kind: opts.kind,
+      id: opts.id,
+      init: opts.init
     };
   } else {
-    throw new Error("wtf");
+    throw new TypeError("cannot add a declaration here in node type " + block.type);
   }
 };
 
-Scope.prototype.add = function (node, references) {
-  if (!node) return;
-  _.merge(references || this.references, t.getIds(node, true));
+Scope.prototype.add = function (node) {
+  Scope.add(node, this.references);
 };
 
 Scope.prototype.get = function (id) {

lib/6to5/types/alias-keys.json

@@ -3,13 +3,13 @@
   "BreakStatement":      ["Statement"],
   "ContinueStatement":   ["Statement"],
   "DebuggerStatement":   ["Statement"],
-  "DoWhileStatement":    ["Statement"],
+  "DoWhileStatement":    ["Statement", "Loop", "While"],
   "IfStatement":         ["Statement"],
   "ReturnStatement":     ["Statement"],
   "SwitchStatement":     ["Statement"],
   "ThrowStatement":      ["Statement"],
   "TryStatement":        ["Statement"],
-  "WhileStatement":      ["Statement"],
+  "WhileStatement":      ["Statement", "Loop", "While"],
   "WithStatement":       ["Statement"],
   "EmptyStatement":      ["Statement"],
   "LabeledStatement":    ["Statement"],
@@ -35,9 +35,9 @@
   "ClassDeclaration": ["Statement", "Declaration", "Class"],
   "ClassExpression":  ["Class"],
 
-  "ForOfStatement": ["Statement", "For", "Scope"],
-  "ForInStatement": ["Statement", "For", "Scope"],
-  "ForStatement":   ["Statement", "For", "Scope"],
+  "ForOfStatement": ["Statement", "For", "Scope", "Loop"],
+  "ForInStatement": ["Statement", "For", "Scope", "Loop"],
+  "ForStatement":   ["Statement", "For", "Scope", "Loop"],
 
   "ObjectPattern": ["Pattern"],
   "ArrayPattern":  ["Pattern"],

lib/6to5/types/builder-keys.json

@@ -11,6 +11,7 @@
   "Identifier":              ["name"],
   "IfStatement":             ["test", "consequent", "alternate"],
   "Literal":                 ["value"],
+  "LogicalExpression":       ["operator", "left", "right"],
   "MemberExpression":        ["object", "property", "computed"],
   "NewExpression":           ["callee", "arguments"],
   "ObjectExpression":        ["properties"],

lib/6to5/types/index.js

@@ -1,4 +1,5 @@
-var _ = require("lodash");
+var esutils = require("esutils");
+var _       = require("lodash");
 
 var t = exports;
 
@@ -11,6 +12,8 @@ var addAssert = function (type, is) {
   };
 };
 
+t.STATEMENT_OR_BLOCK_KEYS = ["consequent", "body"];
+
 //
 
 t.VISITOR_KEYS = require("./visitor-keys");
@@ -71,6 +74,31 @@ addAssert("Expression", t.isExpression);
 
 //
 
+t.toSequenceExpression = function (nodes, scope) {
+  var exprs = [];
+
+  _.each(nodes, function (node) {
+    if (t.isExpression(node)) {
+      exprs.push(node);
+    } if (t.isExpressionStatement(node)) {
+      exprs.push(node.expression);
+    } else if (t.isVariableDeclaration(node)) {
+      _.each(node.declarations, function (declar) {
+        scope.push({
+          kind: node.kind,
+          key: declar.id.name,
+          id: declar.id
+        });
+        exprs.push(t.assignmentExpression("=", declar.id, declar.init));
+      });
+    }
+  });
+
+  return t.sequenceExpression(exprs);
+};
+
+//
+
 t.shallowEqual = function (actual, expected) {
   var same = true;
 
@@ -87,6 +115,18 @@ t.shallowEqual = function (actual, expected) {
 
 //
 
+t.isDynamic = function (node) {
+  if (t.isParenthesizedExpression(node) || t.isExpressionStatement(node)) {
+    return t.isDynamic(node.expression);
+  } else if (t.isIdentifier(node) || t.isLiteral(node) || t.isThisExpression(node)) {
+    return false;
+  } else if (t.isMemberExpression(node)) {
+    return t.isDynamic(node.object) || t.isDynamic(node.property);
+  } else {
+    return true;
+  }
+};
+
 t.isReferenced = function (node, parent) {
   // we're a property key so we aren't referenced
   if (t.isProperty(parent) && parent.key === node) return false;
@@ -122,11 +162,16 @@ t.toIdentifier = function (name) {
     return c ? c.toUpperCase() : "";
   });
 
-  return name;
+  return name || '_';
 };
 
-t.ensureBlock = function (node) {
-  node.body = t.toBlock(node.body, node);
+t.isValidIdentifier = function (name) {
+  return _.isString(name) && esutils.keyword.isIdentifierName(name) && !esutils.keyword.isKeywordES6(name, true);
+};
+
+t.ensureBlock = function (node, key) {
+  key = key || "body";
+  node[key] = t.toBlock(node[key], node);
 };
 
 t.toStatement = function (node, ignore) {

lib/6to5/types/visitor-keys.json

@@ -5,6 +5,7 @@
   "AssignmentExpression":      ["left", "right"],
   "AwaitExpression":           ["argument"],
   "BinaryExpression":          ["left", "right"],
+  "BindMemberExpression":      ["object", "property", "arguments"],
   "BlockStatement":            ["body"],
   "BreakStatement":            ["label"],
   "CallExpression":            ["callee", "arguments"],
@@ -43,6 +44,7 @@
   "ObjectExpression":          ["properties"],
   "ObjectPattern":             ["properties"],
   "ParenthesizedExpression":   ["expression"],
+  "BindFunctionExpression":    ["callee", "arguments"],
   "Program":                   ["body"],
   "Property":                  ["key", "value"],
   "ReturnStatement":           ["argument"],

lib/6to5/util.js

@@ -38,9 +38,9 @@ exports.list = function (val) {
 };
 
 exports.regexify = function (val) {
-  if (!val) return new RegExp;
+  if (!val) return new RegExp(/.^/);
   if (_.isArray(val)) val = val.join("|");
-  if (_.isString(val)) return new RegExp(val || "");
+  if (_.isString(val)) return new RegExp(val);
   if (_.isRegExp(val)) return val;
   throw new TypeError("illegal type for regexify");
 };
@@ -219,6 +219,7 @@ exports.parse = function (opts, code, callback) {
       allowReturnOutsideFunction: true,
       preserveParens:             true,
       ecmaVersion:                opts.experimental ? 7 : 6,
+      playground:                 opts.playground,
       strictMode:                 true,
       onComment:                  comments,
       locations:                  true,

package.json

@@ -1,7 +1,7 @@
 {
   "name": "6to5",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "1.13.9",
+  "version": "1.14.17",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://github.com/6to5/6to5",
   "repository": {
@@ -35,30 +35,31 @@
     "test": "make test"
   },
   "dependencies": {
+    "acorn-6to5": "0.9.1-12",
     "ast-types": "0.6.5",
+    "chokidar": "0.11.1",
     "commander": "2.5.0",
+    "es6-shim": "0.21.0",
+    "es6-symbol": "0.1.1",
+    "estraverse": "1.8.0",
+    "esutils": "1.1.6",
     "fs-readdir-recursive": "0.1.0",
     "lodash": "2.4.1",
     "mkdirp": "0.5.0",
-    "es6-shim": "0.21.0",
-    "es6-symbol": "0.1.1",
+    "private": "0.1.6",
     "regexpu": "0.3.0",
     "source-map": "0.1.40",
-    "chokidar": "0.11.1",
-    "source-map-support": "0.2.8",
-    "esutils": "1.1.6",
-    "acorn-6to5": "0.9.1-7",
-    "estraverse": "1.8.0",
-    "private": "0.1.6"
+    "source-map-support": "0.2.8"
   },
   "devDependencies": {
-    "istanbul": "0.3.2",
-    "matcha": "0.6.0",
-    "mocha": "2.0.1",
-    "uglify-js": "2.4.15",
     "browserify": "6.3.2",
-    "rimraf": "2.2.8",
+    "chai": "^1.9.2",
+    "istanbul": "0.3.2",
     "jshint": "2.5.10",
-    "chai": "^1.9.2"
+    "jshint-stylish": "^1.0.0",
+    "matcha": "0.6.0",
+    "mocha": "1.21.4",
+    "rimraf": "2.2.8",
+    "uglify-js": "2.4.15"
   }
 }

test/fixtures/bin/6to5/stdin --filename/stderr.txt

@@ -1 +1 @@
-SyntaxError: test.js: Unexpected character '@'
+SyntaxError: test.js: Unexpected character '#'

test/fixtures/bin/6to5/stdin --filename/stdin.txt

@@ -1,3 +1,3 @@
 arr.map(x => {
-  $@!
+  $#!
 });

test/fixtures/transformation/.es6-modules-system/exports-default/actual.js

@@ -0,0 +1,8 @@
+export default 42;
+export default {};
+export default [];
+export default foo;
+export default function () {}
+export default class {}
+export default function foo () {}
+export default class Foo {}

test/fixtures/transformation/.es6-modules-system/exports-default/expected.js

@@ -0,0 +1,32 @@
+System.register("actual", [], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  function _anonymous() {}
+  var _anonymous2;
+
+  function foo() {}
+  var Foo;
+
+  return {
+    setters: [],
+    execute: function () {
+      _export("default", 42);
+
+      _export("default", {});
+
+      _export("default", []);
+
+      _export("default", foo);
+
+      _export("default", _anonymous);
+
+      _export("default", _anonymous2 = function _anonymous2() {});
+
+      _export("default", foo);
+
+      _export("default", Foo = function Foo() {});
+    }
+  };
+});

test/fixtures/transformation/.es6-modules-system/exports-from/actual.js

@@ -0,0 +1,6 @@
+export * from "foo";
+export {foo} from "foo";
+export {foo, bar} from "foo";
+export {foo as bar} from "foo";
+export {foo as default} from "foo";
+export {foo as default, bar} from "foo";

test/fixtures/transformation/.es6-modules-system/exports-from/expected.js

@@ -0,0 +1,34 @@
+System.register("actual", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var _localExports = ['foo', 'bar', 'default'];
+
+  return {
+    setters: [
+    function(m) {
+      _export("foo", m.foo);
+
+      _export("foo", m.foo);
+
+      _export("bar", m.bar);
+
+      _export("bar", m.foo);
+
+      _export("default", m.foo);
+
+      _export("default", m.foo);
+
+      _export("bar", m.bar);
+
+      for (var p in m) {
+        if (_localExports.indexOf(i) == -1)
+          _export(p, m[p]);
+      }
+    }
+    ],
+    execute: function () {
+    }
+  };
+});

test/fixtures/transformation/.es6-modules-system/exports-named/actual.js

@@ -0,0 +1,5 @@
+export {foo};
+export {foo, bar};
+export {foo as bar};
+export {foo as default};
+export {foo as default, bar};

test/fixtures/transformation/.es6-modules-system/exports-named/expected.js

@@ -0,0 +1,26 @@
+System.register("actual", [], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  return {
+    setters: [
+    function(m) {
+      _export("foo", m.foo);
+
+      _export("foo", m.foo);
+
+      _export("bar", m.bar);
+
+      _export("bar", m.foo);
+
+      _export("default", m.foo);
+
+      _export("default", m.foo);
+
+      _export("bar", m.bar);
+    }],
+    execute: function () {
+    }
+  };
+});

test/fixtures/transformation/.es6-modules-system/exports-variable/actual.js

@@ -0,0 +1,8 @@
+export var foo = 1;
+export var foo2 = function () {};
+export var foo3;
+export let foo4 = 2;
+export let foo5;
+export const foo6 = 3;
+export function foo7 () {}
+export class foo8 {}

test/fixtures/transformation/.es6-modules-system/exports-variable/expected.js

@@ -0,0 +1,37 @@
+System.register("actual", [], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var foo;
+  var foo2;
+  var foo3;
+  var foo4;
+  var foo5;
+  var foo6;
+  function foo7() {}
+  _export("foo7", foo7);
+
+  var foo8;
+
+  return {
+    setters: [],
+    execute: function () {
+      _export("foo", foo = 1);
+
+      _export("foo2", foo2 = function () {});
+
+      _export("foo3", foo3);
+
+      _export("foo4", foo4 = 2);
+
+      _export("foo5", foo5);
+
+      _export("foo6", foo6 = 3);
+
+      _export("foo7", foo7);
+
+      _export("foo8", foo8 = function foo8() {});
+    }
+  };
+});

test/fixtures/transformation/.es6-modules-system/hoist-function-exports/actual.js

@@ -0,0 +1,11 @@
+import { isEven } from "./evens";
+
+export function nextOdd(n) {
+  return isEven(n) ? n + 1 : n + 2;
+}
+
+export var isOdd = (function (isEven) {
+  return function (n) {
+    return !isEven(n);
+  };
+})(isEven);

test/fixtures/transformation/.es6-modules-system/hoist-function-exports/expected.js

@@ -0,0 +1,25 @@
+System.register("actual", ["./evens"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var isEven;
+  function nextOdd(n) {
+    return isEven(n) ? n + 1 : n + 2;
+  }
+  _export("nextOdd", nextOdd);
+
+  var isOdd;
+  return {
+    setters: [function (m) {
+      isEven = m.isEven;
+    }],
+    execute: function () {
+      _export("isOdd", isOdd = (function (isEven) {
+        return function (n) {
+          return !isEven(n);
+        };
+      })(isEven));
+    }
+  };
+});

test/fixtures/transformation/.es6-modules-system/imports-default/actual.js

@@ -0,0 +1,2 @@
+import foo from "foo";
+import {default as foo} from "foo";

test/fixtures/transformation/.es6-modules-system/imports-default/expected.js

@@ -0,0 +1,14 @@
+System.register("actual", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var foo;
+  return {
+    setters: [function (m) {
+      foo = m.default;
+      foo = m.default;
+    }],
+    execute: function () {}
+  };
+});

test/fixtures/transformation/.es6-modules-system/imports-glob/actual.js

@@ -0,0 +1 @@
+import * as foo from "foo";

test/fixtures/transformation/.es6-modules-system/imports-glob/expected.js

@@ -0,0 +1,13 @@
+System.register("actual", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var foo;
+  return {
+    setters: [function (m) {
+      foo = m;
+    }],
+    execute: function () {}
+  };
+});

test/fixtures/transformation/.es6-modules-system/imports-mixing/actual.js

@@ -0,0 +1 @@
+import foo, {baz as xyz} from "foo";

test/fixtures/transformation/.es6-modules-system/imports-mixing/expected.js

@@ -0,0 +1,14 @@
+System.register("actual", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var foo, xyz;
+  return {
+    setters: [function (m) {
+      foo = m.default;
+      xyz = m.baz;
+    }],
+    execute: function () {}
+  };
+});

test/fixtures/transformation/.es6-modules-system/imports-named/actual.js

@@ -0,0 +1,4 @@
+import {bar} from "foo";
+import {bar, baz} from "foo";
+import {bar as baz} from "foo";
+import {bar as baz, xyz} from "foo";

test/fixtures/transformation/.es6-modules-system/imports-named/expected.js

@@ -0,0 +1,18 @@
+System.register("actual", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var bar, baz, xyz;
+  return {
+    setters: [function (m) {
+      bar = m.bar;
+      bar = m.bar;
+      baz = m.baz;
+      baz = m.bar;
+      baz = m.bar;
+      xyz = m.xyz;
+    }],
+    execute: function () {}
+  };
+});

test/fixtures/transformation/.es6-modules-system/imports/actual.js

@@ -0,0 +1,3 @@
+import "foo";
+import "foo-bar";
+import "./directory/foo-bar";

test/fixtures/transformation/.es6-modules-system/imports/expected.js

@@ -0,0 +1,10 @@
+System.register("actual", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  return {
+    setters: [null, null, null],
+    execute: function () {}
+  };
+});

test/fixtures/transformation/.es6-modules-system/options.json

@@ -0,0 +1,3 @@
+{
+  "modules": "system"
+}

test/fixtures/transformation/.es6-modules-system/overview/actual.js

@@ -0,0 +1,12 @@
+import "foo";
+import "foo-bar";
+import "./directory/foo-bar";
+import foo from "foo";
+import * as foo from "foo";
+import {bar} from "foo";
+import {foo as bar} from "foo";
+
+export {test};
+export var test = 5;
+
+export default test;

test/fixtures/transformation/.es6-modules-system/overview/expected.js

@@ -0,0 +1,24 @@
+System.register("actual", ["foo", "foo-bar", "./directory/foo-bar"], function (_export) {
+  "use strict";
+
+  var __moduleName = "actual";
+
+  var foo, bar;
+  var test;
+
+  return {
+    setters: [function (m) {
+      foo = m.default;
+      foo = m;
+      bar = m.bar;
+      bar = m.foo;
+    }, null, null],
+    execute: function () {
+      _export("test", test);
+
+      _export("test", test = 5);
+
+      _export("default", test);
+    }
+  };
+});

test/fixtures/transformation/api/blacklist/actual.js

@@ -1,5 +1,5 @@
 class Test {
   constructor() {
-  arr.map(x => x * x);
+    arr.map(x => x * x);
   }
 }

test/fixtures/transformation/errors/syntax/actual.js

@@ -1,3 +1,3 @@
 arr.map(function () {
-  return $@!@#;
+  return $#!;
 });

test/fixtures/transformation/errors/syntax/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected character '@'"
+  "throws": "Unexpected character '#'"
 }

test/fixtures/transformation/es6-classes/accessing-super-class/expected.js

@@ -1,19 +1,6 @@
 "use strict";
 
-var _argumentsToArray = function (args) {
-  var target = new Array(args.length);
-  for (var i = 0; i < args.length; i++) {
-    target[i] = args[i];
-  }
-
-  return target;
-};
-
-var _classProps = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
+var _slice = Array.prototype.slice;
 var _extends = function (child, parent) {
   child.prototype = Object.create(parent.prototype, {
     constructor: {
@@ -33,34 +20,26 @@ var Test = (function (Foo) {
     Foo.prototype.test.call(this);
     foob(Foo);
 
-    Foo.call.apply(Foo, [this].concat(_argumentsToArray(arguments)));
-    Foo.call.apply(Foo, [this, "test"].concat(_argumentsToArray(arguments)));
+    Foo.call.apply(Foo, [this].concat(_slice.call(arguments)));
+    Foo.call.apply(Foo, [this, "test"].concat(_slice.call(arguments)));
 
-    Foo.prototype.test.call.apply(Foo.prototype, [this].concat(_argumentsToArray(arguments)));
-    Foo.prototype.test.call.apply(Foo.prototype, [this, "test"].concat(_argumentsToArray(arguments)));
+    Foo.prototype.test.call.apply(Foo.prototype, [this].concat(_slice.call(arguments)));
+    Foo.prototype.test.call.apply(Foo.prototype, [this, "test"].concat(_slice.call(arguments)));
   };
 
   _extends(Test, Foo);
 
-  _classProps(Test, {
-    foo: {
-      writable: true,
-      value: function () {
-        Foo.foo.call(this);
-        Foo.foo.call.apply(Foo.foo, [this].concat(_argumentsToArray(arguments)));
-        Foo.foo.call.apply(Foo.foo, [this, "test"].concat(_argumentsToArray(arguments)));
-      }
-    }
-  }, {
-    test: {
-      writable: true,
-      value: function () {
-        Foo.prototype.test.call(this);
-        Foo.prototype.test.call.apply(Foo.prototype.test, [this].concat(_argumentsToArray(arguments)));
-        Foo.prototype.test.call.apply(Foo.prototype.test, [this, "test"].concat(_argumentsToArray(arguments)));
-      }
-    }
-  });
+  Test.prototype.test = function () {
+    Foo.prototype.test.call(this);
+    Foo.prototype.test.call.apply(Foo.prototype.test, [this].concat(_slice.call(arguments)));
+    Foo.prototype.test.call.apply(Foo.prototype.test, [this, "test"].concat(_slice.call(arguments)));
+  };
+
+  Test.foo = function () {
+    Foo.foo.call(this);
+    Foo.foo.call.apply(Foo.foo, [this].concat(_slice.call(arguments)));
+    Foo.foo.call.apply(Foo.foo, [this, "test"].concat(_slice.call(arguments)));
+  };
 
   return Test;
 })(Foo);

test/fixtures/transformation/es6-classes/calling-super-properties/expected.js

@@ -1,10 +1,5 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
 var _extends = function (child, parent) {
   child.prototype = Object.create(parent.prototype, {
     constructor: {
@@ -25,14 +20,9 @@ var Test = (function (Foo) {
 
   _extends(Test, Foo);
 
-  _classProps(Test, {
-    test: {
-      writable: true,
-      value: function () {
-        return Foo.wow.call(this);
-      }
-    }
-  });
+  Test.test = function () {
+    return Foo.wow.call(this);
+  };
 
   return Test;
 })(Foo);

test/fixtures/transformation/es6-classes/instance-method/expected.js

@@ -1,21 +1,11 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
 var Test = (function () {
   var Test = function Test() {};
 
-  _classProps(Test, null, {
-    test: {
-      writable: true,
-      value: function () {
-        return 5 + 5;
-      }
-    }
-  });
+  Test.prototype.test = function () {
+    return 5 + 5;
+  };
 
   return Test;
 })();

test/fixtures/transformation/es6-classes/statement/expected.js

@@ -1,10 +1,5 @@
 "use strict";
 
-var _classProps = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
 var BaseView = function BaseView() {
   this.autoRender = true;
 };
@@ -16,14 +11,9 @@ var BaseView = function () {
 var BaseView = (function () {
   var _class2 = function () {};
 
-  _classProps(_class2, null, {
-    foo: {
-      writable: true,
-      value: function () {
-        this.autoRender = true;
-      }
-    }
-  });
+  _class2.prototype.foo = function () {
+    this.autoRender = true;
+  };
 
   return _class2;
 })();

test/fixtures/transformation/es6-classes/static/expected.js

@@ -8,11 +8,9 @@ var _classProps = function (child, staticProps, instanceProps) {
 var A = (function () {
   var A = function A() {};
 
+  A.a = function () {};
+
   _classProps(A, {
-    a: {
-      writable: true,
-      value: function () {}
-    },
     b: {
       get: function () {},
       set: function (b) {}

test/fixtures/transformation/es6-computed-property-names/method/actual.js

@@ -1,5 +1,5 @@
 var obj = {
   [foobar]() {
-  return "foobar";
+    return "foobar";
   }
 };

test/fixtures/transformation/es6-computed-property-names/method/expected.js

@@ -4,5 +4,6 @@ var obj = (function (_obj) {
   _obj[foobar] = function () {
     return "foobar";
   };
+
   return _obj;
 })({});

test/fixtures/transformation/es6-destructuring/assignment-expression-statement-only/actual.js

@@ -1 +0,0 @@
-console.log([x] = [1]);

test/fixtures/transformation/es6-destructuring/assignment-expression-statement-only/options.json

@@ -1,3 +0,0 @@
-{
-  "throws": "AssignmentExpression destructuring outside of a ExpressionStatement is forbidden due to current 6to5 limitations"
-}

test/fixtures/transformation/es6-destructuring/assignment-expression/expected.js

@@ -0,0 +1,8 @@
+"use strict";
+
+var _temp, _ref;
+var _toArray = function (arr) {
+  return Array.isArray(arr) ? arr : Array.from(arr);
+};
+
+console.log((_temp = [123], _ref = _toArray(_temp), x = _ref[0], _temp));

test/fixtures/transformation/es6-destructuring/assignment-expression/options.json

@@ -1,3 +0,0 @@
-{
-  "throws": "AssignmentExpression destructuring outside of a ExpressionStatement is forbidden due to current 6to5 limitations"
-}

test/fixtures/transformation/es6-let-scoping/loop-initializer-default/actual.js

@@ -0,0 +1,11 @@
+while (value) {
+  let foo;
+
+  if (bar) {
+    foo = [];
+  }
+
+  if (foo) {
+    doIt();
+  }
+}