v1.13.0

Fix runtime injection in Web Worker.

.hound.yml

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

CHANGELOG.md

@@ -1,3 +1,25 @@
+# 1.13.0
+
+ * Put experimental ES7 features behind a flag `--experimental` and `experimental` option.
+ * Constructor speed performance increase. Thanks [@RReverser](https://github.com/RReverser).
+ * Use `self` instead of `window` in the optional 6to5 runtime. Thanks [@RReverser](https://github.com/RReverser).
+
+# 1.12.26
+
+ * Support computed property destructuring.
+
+# 1.12.25
+
+ * Update `acorn-6to5`, `ast-types`, `es6-shim`, `chokidar`, `estraverse` and `private`.
+
+# 1.12.24
+
+ * Collect references that haven't been declared in scope.
+
+# 1.12.23
+
+ * Fix generator function export hoisting.
+
 # 1.12.22
 
  * Update `fs-readdir-recursive` and `chokidar`.

bin/6to5/index.js

@@ -11,6 +11,7 @@ commander.option("-s, --source-maps", "Save source map alongside the compiled co
 commander.option("-f, --filename [filename]", "Filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]", "stdin");
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
+commander.option("-e, --experimental", "Enable experimental support for proposed ES7 features");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
@@ -87,11 +88,12 @@ if (errors.length) {
 
 exports.opts = {
   sourceMapName: commander.outFile,
+  amdModuleIds:  commander.amdModuleIds,
+  experimental:  commander.experimental,
   blacklist:     commander.blacklist,
   whitelist:     commander.whitelist,
   sourceMap:     commander.sourceMaps || commander.sourceMapsInline,
   comments:      !commander.removeComments,
-  amdModuleIds:   commander.amdModuleIds,
   runtime:       commander.runtime,
   modules:       commander.modules
 };

bin/_6to5-node

@@ -8,10 +8,11 @@ var util      = require("../lib/6to5/util");
 var vm        = require("vm");
 var _         = require("lodash");
 
-commander.option("-e, --eval [script]", "evaluate script");
-commander.option("-p, --print", "evaluate script and print result");
-commander.option("-i, --ignore [regex]", "ignore all files that match this regex when using the require hook");
-commander.option("-x, --extensions [extensions]", "list of extensions to hook into [.es6,.js]", util.list);
+commander.option("-e, --eval [script]", "Evaluate script");
+commander.option("-p, --print", "Evaluate script and print result");
+commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
+commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
+commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
@@ -20,17 +21,11 @@ commander.parse(process.argv);
 
 //
 
-var registerOpts = {};
-
-if (commander.ignore) {
-  registerOpts.ignoreRegex = new RegExp(commander.ignore);
-}
-
-if (commander.extensions && commander.extensions.length) {
-  registerOpts.extensions = commander.extensions;
-}
-
-to5.register(registerOpts);
+to5.register({
+  experimental: commander.experimental,
+  extensions:   commander.extensions,
+  ignore:       commander.ignore
+});
 
 //
 

doc/caveats.md

@@ -5,6 +5,16 @@
 The [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js)
 and an [ES6 polyfill](polyfill.md) are required in order for generators to work.
 
+### Async/Comprehensions
+
+[Experimental support](usage.md#experimental) must be enabled for these proposed
+ES7 features to work.
+
+### Array comprehension/Array destructuring/Spread
+
+An [ES6 polyfill](polyfill.md) is required. More specifically a polyfill for
+`Array.from`.
+
 ## Classes
 
 Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
@@ -31,13 +41,13 @@ class Bar extends Foo {
 }
 ```
 
+## Constructor spread
+
+Constructor spreads do not currently support built-ins. ie.
+`new Array(...items)`.
+
 ## For-of
 
 A polyfill is required for for-of functionality that implements `Symbol` and
 adds `prototype[Symbol.iterator]` behaviour to built-ins. Using the polyfills
 specified in [polyfill](polyfill.md) suffices.
-
-### Array destructuring / Spread
-
-An [ES6 polyfill](polyfill.md) is required for spread and array destructuring.
-More specifically a polyfill for `Array.from`.

doc/features.md

@@ -1,6 +1,6 @@
 # Features
 
-## Array comprehension
+## Array comprehension ([experimental](usage.md#experimental))
 
 ```javascript
 var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
@@ -31,7 +31,7 @@ var bob = {
 };
 ```
 
-## Async functions
+## Async functions ([experimental](usage.md#experimental))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -133,13 +133,31 @@ for (var i of [1, 2, 3]) {
 ## Generators
 
 ```javascript
+function* fibonacci() {
+  var pre = 0, cur = 1;
+  for (;;) {
+    var temp = pre;
+    pre = cur;
+    cur += temp;
+    yield cur;
+  }
+}
 
+for (var n of fibonacci()) {
+  // truncate the sequence at 1000
+  if (n > 1000) break;
+  console.log(n);
+}
 ```
 
-## Generator comprehension
+## Generator comprehension ([experimental](usage.md#experimental))
 
 ```javascript
-
+var nums = [1, 2, 3, 4, 5, 6];
+var multiples = (for (i of nums) if (i % 2) i * i);
+assert.equal(multiples.next().value, 1);
+assert.equal(multiples.next().value, 9);
+assert.equal(multiples.next().value, 25);
 ```
 
 ## Let scoping
@@ -153,7 +171,17 @@ for (let i in arr) {
 ## Modules
 
 ```javascript
+import "foo";
+import foo from "foo";
+import * as foo from "foo";
+import {bar} from "foo";
+import {foo as bar} from "foo";
 
+export { test };
+export var test = 5;
+export function test() {}
+
+export default test;
 ```
 
 ## Numeric literals

doc/index.md

@@ -3,7 +3,7 @@
  - **Readable** - formatting is retained if possible so your generated code is as similar as possible.
  - **Extensible** - with a large range of [plugins](plugins.md) and **browser support**.
  - **Lossless** - **source map support** so you can debug your compiled code with ease.
- - **Compact** - maps directly to the equivalent ES5 with **no runtime**[\*](caveats.md#generators).
+ - **Compact** - maps directly to the equivalent ES5 with **no runtime**[\*](caveats.md).
 
 ## Installation
 
@@ -31,8 +31,8 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
 
 ## [Features](features.md)
 
- - [Array comprehension](features.md#array-comprehension)
- - [Async functions](features.md#async-functions) via [regenerator](https://github.com/facebook/regenerator)
+ - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
+ - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
@@ -40,8 +40,8 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
  - [For-of](features.md#for-of)
- - [Generators](features.md#generators) via [regenerator](https://github.com/facebook/regenerator)
- - [Generator comprehension](features.md#generator-comprehension)
+ - [Generators](features.md#generators)
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)

doc/usage.md

@@ -135,7 +135,11 @@ to5.transformFile("filename.js", options, function (err, result) {
 
   // Output comments in generated output
   // Default: true
-  comments: false
+  comments: false,
+
+  // Enable support for experimental ES7 features
+  // Default: false
+  experimental: true
 }
 ```
 
@@ -181,3 +185,11 @@ require("6to5/register")({
   extensions: [".js", ".es6"]
 });
 ```
+
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
+
+**NOTE:** That these are subject to change as their proposal status progresses.

lib/6to5/file.js

@@ -25,15 +25,16 @@ File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
-    whitespace: true,
-    blacklist:  [],
-    whitelist:  [],
-    sourceMap:  false,
-    comments:   true,
-    filename:   "unknown",
-    modules:    "common",
-    runtime:    false,
-    code:       true
+    experimental: false,
+    whitespace:   true,
+    blacklist:    [],
+    whitelist:    [],
+    sourceMap:    false,
+    comments:     true,
+    filename:     "unknown",
+    modules:      "common",
+    runtime:      false,
+    code:         true
   });
 
   // normalise windows path separators to unix
@@ -147,7 +148,7 @@ File.prototype.parse = function (code) {
 
 File.prototype.transform = function (ast) {
   this.ast = ast;
-  this.scope = new Scope(null, ast.program);
+  this.scope = new Scope(ast.program);
 
   var self = this;
 
@@ -196,6 +197,10 @@ File.prototype.generateUid = function (name, scope) {
   return uid;
 };
 
+File.prototype.generateUidIdentifier = function (name, scope) {
+  return t.identifier(this.generateUid(name, scope));
+};
+
 File.prototype._generateUid = function (name) {
   var uids = this.uids;
   var i = uids[name] || 1;

lib/6to5/register.js

@@ -57,24 +57,25 @@ blacklistTest("unicodeRegex", function () { new RegExp("foo", "u"); });
 
 //
 
-var ignoreRegex = /node_modules/;
+var transformOpts = {};
+var ignoreRegex   = /node_modules/;
 var onlyRegex;
-var whitelist   = [];
-var exts        = {};
-var maps        = {};
-var old         = require.extensions[".js"];
+var whitelist     = [];
+var exts          = {};
+var maps          = {};
+var old           = require.extensions[".js"];
 
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, {
+  var result = to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
     modules:   "commonInterop"
-  });
+  }, transformOpts));
 
   maps[filename] = result.map;
 
@@ -107,6 +108,5 @@ module.exports = function (opts) {
 
   if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 
-  if (opts.blacklist) blacklist = util.arrayify(opts.blacklist);
-  if (opts.whitelist) whitelist = util.arrayify(opts.whitelist);
+  _.extend(transformOpts, opts);
 };

lib/6to5/runtime.js

@@ -8,15 +8,13 @@ module.exports = function (namespace) {
   namespace = t.identifier(t.toIdentifier(namespace || "to5Runtime"));
 
   var body      = [];
-  var container = t.functionExpression(null, [], t.blockStatement(body));
-  var tree      = t.program([t.expressionStatement(t.callExpression(container, []))]);
-
-  body.push(util.template("self-global", true));
+  var container = t.functionExpression(null, [t.identifier("global")], t.blockStatement(body));
+  var tree      = t.program([t.expressionStatement(t.callExpression(container, [util.template("self-global")]))]);
 
   body.push(t.variableDeclaration("var", [
     t.variableDeclarator(
       namespace,
-      t.assignmentExpression("=", t.memberExpression(t.identifier("self"), namespace), t.objectExpression([]))
+      t.assignmentExpression("=", t.memberExpression(t.identifier("global"), namespace), t.objectExpression([]))
     )
   ]));
 

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

@@ -1,5 +1,5 @@
 (function (Constructor, args) {
-  var bindArgs = [null].concat(args);
-  var Factory = Constructor.bind.apply(Constructor, bindArgs);
-  return new Factory;
+  var instance = Object.create(Constructor.prototype);
+  Constructor.apply(instance, args);
+  return instance;
 });

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

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

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

@@ -78,7 +78,7 @@ AMDFormatter.prototype._push = function (node) {
   if (ids[id]) {
     return ids[id];
   } else {
-    return this.ids[id] = t.identifier(this.file.generateUid(id));
+    return this.ids[id] = this.file.generateUidIdentifier(id);
   }
 };
 

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

@@ -22,8 +22,7 @@ CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node,
         })])
       )
     ]));
-    return;
+  } else {
+    CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
   }
-
-  CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
 };

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

@@ -6,11 +6,11 @@ var go = function (getBody, node, file, scope) {
   var thisId;
 
   var getArgumentsId = function () {
-    return argumentsId = argumentsId || t.identifier(file.generateUid("arguments", scope));
+    return argumentsId = argumentsId || file.generateUidIdentifier("arguments", scope);
   };
 
   var getThisId = function () {
-    return thisId = thisId || t.identifier(file.generateUid("this", scope));
+    return thisId = thisId || file.generateUidIdentifier("this", scope);
   };
 
   // traverse the function and find all alias functions so we can alias

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

@@ -1,12 +1,12 @@
 var t = require("../../types");
-var _ = require("lodash");
 
 module.exports = function (ast, file) {
   var body = ast.program.body;
 
-  _.each(file.declarations, function (declar) {
+  for (var i in file.declarations) {
+    var declar = file.declarations[i];
     body.unshift(t.variableDeclaration("var", [
       t.variableDeclarator(declar.uid, declar.node)
     ]));
-  });
+  }
 };

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

@@ -2,16 +2,21 @@ var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
 
-var singleArrayExpression = function (node) {
+var single = function (node) {
   var block = node.blocks[0];
 
   var templateName = "array-expression-comprehension-map";
   if (node.filter) templateName = "array-expression-comprehension-filter";
 
+  var right = block.right;
+  if (!t.isArrayExpression(right)) {
+    right = util.template("array-from", { VALUE: right });
+  }
+
   var result = util.template(templateName, {
     STATEMENT: node.body,
     FILTER:    node.filter,
-    ARRAY:     block.right,
+    ARRAY:     right,
     KEY:       block.left
   });
 
@@ -25,7 +30,7 @@ var singleArrayExpression = function (node) {
 };
 
 var multiple = function (node, file) {
-  var uid = file.generateUid("arr");
+  var uid = file.generateUidIdentifier("arr");
 
   var container = util.template("array-comprehension-container", {
     KEY: uid
@@ -73,8 +78,8 @@ exports._build = function (node, buildBody) {
 exports.ComprehensionExpression = function (node, parent, file) {
   if (node.generator) return;
 
-  if (node.blocks.length === 1 && t.isArrayExpression(node.blocks[0].right)) {
-    return singleArrayExpression(node);
+  if (node.blocks.length === 1) {
+    return single(node);
   } else {
     return multiple(node, file);
   }

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

@@ -36,7 +36,7 @@ function Class(node, file, scope) {
   this.instanceMutatorMap = {};
   this.staticMutatorMap   = {};
   this.hasConstructor     = false;
-  this.className          = node.id || t.identifier(file.generateUid("class", scope));
+  this.className          = node.id || file.generateUidIdentifier("class", scope);
   this.superName          = node.superClass;
 }
 
@@ -58,7 +58,7 @@ Class.prototype.run = function () {
       superClassArgument = superClassCallee = getMemberExpressionObject(superName);
     } else if (!t.isIdentifier(superName)) {
       superClassArgument = superName;
-      superClassCallee   = superName = t.identifier(file.generateUid("ref", this.scope));
+      superClassCallee   = superName = file.generateUidIdentifier("ref", this.scope);
     }
   }
 

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

@@ -27,7 +27,7 @@ var push = function (opts, nodes, elem, parentId) {
 var pushObjectPattern = function (opts, nodes, pattern, parentId) {
   _.each(pattern.properties, function (prop) {
     var pattern2   = prop.value;
-    var patternId2 = t.memberExpression(parentId, prop.key);
+    var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
 
     if (t.isPattern(pattern2)) {
       push(opts, nodes, pattern2, patternId2);
@@ -38,7 +38,7 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
 };
 
 var pushArrayPattern = function (opts, nodes, pattern, parentId) {
-  var _parentId = t.identifier(opts.file.generateUid("ref", opts.scope));
+  var _parentId = opts.file.generateUidIdentifier("ref", opts.scope);
   nodes.push(t.variableDeclaration("var", [
     t.variableDeclarator(_parentId, util.template("array-from", {
       VALUE: parentId
@@ -77,7 +77,7 @@ var pushPattern = function (opts) {
   var scope = opts.scope;
 
   if (!t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = t.identifier(file.generateUid("ref", scope));
+    var key = file.generateUidIdentifier("ref", scope);
 
     nodes.push(t.variableDeclaration("var", [
       t.variableDeclarator(key, parentId)
@@ -97,7 +97,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   var pattern = declar.declarations[0].id;
   if (!t.isPattern(pattern)) return;
 
-  var key = t.identifier(file.generateUid("ref", scope));
+  var key = file.generateUidIdentifier("ref", scope);
   node.left = t.variableDeclaration(declar.kind, [
     t.variableDeclarator(key, null)
   ]);
@@ -125,7 +125,7 @@ exports.Function = function (node, parent, file, scope) {
     if (!t.isPattern(pattern)) return pattern;
 
     hasDestructuring = true;
-    var parentId = t.identifier(file.generateUid("ref", scope));
+    var parentId = file.generateUidIdentifier("ref", scope);
 
     pushPattern({
       kind:    "var",
@@ -155,7 +155,7 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
 
   var nodes = [];
 
-  var ref = t.identifier(file.generateUid("ref", scope));
+  var ref = file.generateUidIdentifier("ref", scope);
   nodes.push(t.variableDeclaration("var", [
     t.variableDeclarator(ref, expr.right)
   ]));

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

@@ -5,7 +5,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   var left = node.left;
   var declar;
 
-  var stepKey   = t.identifier(file.generateUid("step", scope));
+  var stepKey   = file.generateUidIdentifier("step", scope);
   var stepValue = t.memberExpression(stepKey, t.identifier("value"));
 
   if (t.isIdentifier(left)) {
@@ -19,7 +19,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   }
 
   var node2 = util.template("for-of", {
-    ITERATOR_KEY: file.generateUid("iterator", scope),
+    ITERATOR_KEY: file.generateUidIdentifier("iterator", scope),
     STEP_KEY:     stepKey,
     OBJECT:       node.right
   });

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

@@ -18,170 +18,172 @@ var runtimeAsyncMethod = runtimeProperty("async");
 var runtimeWrapMethod  = runtimeProperty("wrap");
 var runtimeMarkMethod  = runtimeProperty("mark");
 
-exports.transform = function transform(node) {
-  return types.visit(node, visitor);
+exports.transform = function transform(node, file) {
+  return types.visit(node, {
+    visitFunction: function (path) {
+      return visitor.call(this, path, file);
+    }
+  });
 };
 
-var visitor = types.PathVisitor.fromMethodsObject({
-  visitFunction: function (path) {
-    // Calling this.traverse(path) first makes for a post-order traversal.
-    this.traverse(path);
+var visitor = function (path, file) {
+  // Calling this.traverse(path) first makes for a post-order traversal.
+  this.traverse(path);
 
-    var node = path.value;
+  var node = path.value;
+  var scope; // we need to actually get the current scope
 
-    if (!node.generator && !node.async) {
+  if (!node.generator && !node.async) {
+    return;
+  }
+
+  node.generator = false;
+
+  if (node.expression) {
+    // Transform expression lambdas into normal functions.
+    node.expression = false;
+    node.body = t.blockStatement([
+      t.returnStatement(node.body)
+    ]);
+  }
+
+  if (node.async) {
+    awaitVisitor.visit(path.get("body"));
+  }
+
+  var outerFnId = node.id || (
+    node.id = file.generateUidIdentifier("callee", scope)
+  );
+
+  var innerFnId = t.identifier(node.id.name + "$");
+  var contextId = file.generateUidIdentifier("context$", scope);
+  var vars = hoist(path);
+
+  var emitter = new Emitter(contextId);
+  emitter.explode(path.get("body"));
+
+  var outerBody = [];
+
+  if (vars && vars.declarations.length > 0) {
+    outerBody.push(vars);
+  }
+
+  var wrapArgs = [
+    emitter.getContextFunction(innerFnId),
+    // Async functions don't care about the outer function because they
+    // don't need it to be marked and don't inherit from its .prototype.
+    node.async ? t.literal(null) : outerFnId,
+    t.thisExpression()
+  ];
+
+  var tryEntryList = emitter.getTryEntryList();
+  if (tryEntryList) {
+    wrapArgs.push(tryEntryList);
+  }
+
+  var wrapCall = t.callExpression(
+    node.async ? runtimeAsyncMethod : runtimeWrapMethod,
+    wrapArgs
+  );
+
+  outerBody.push(t.returnStatement(wrapCall));
+  node.body = t.blockStatement(outerBody);
+
+  if (node.async) {
+    node.async = false;
+    return;
+  }
+
+  if (t.isFunctionDeclaration(node)) {
+    var pp = path.parent;
+
+    while (pp && !(t.isBlockStatement(pp.value) || t.isProgram(pp.value))) {
+      pp = pp.parent;
+    }
+
+    if (!pp) {
       return;
     }
 
-    node.generator = false;
+    // Here we turn the FunctionDeclaration into a named
+    // FunctionExpression that will be assigned to a variable of the
+    // same name at the top of the enclosing block. This is important
+    // for a very subtle reason: named function expressions can refer to
+    // themselves by name without fear that the binding may change due
+    // to code executing outside the function, whereas function
+    // declarations are vulnerable to the following rebinding:
+    //
+    //   function f() { return f }
+    //   var g = f;
+    //   f = "asdf";
+    //   g(); // "asdf"
+    //
+    // One way to prevent the problem illustrated above is to transform
+    // the function declaration thus:
+    //
+    //   var f = function f() { return f };
+    //   var g = f;
+    //   f = "asdf";
+    //   g(); // f
+    //   g()()()()(); // f
+    //
+    // In the code below, we transform generator function declarations
+    // in the following way:
+    //
+    //   gen().next(); // { value: gen, done: true }
+    //   function *gen() {
+    //     return gen;
+    //   }
+    //
+    // becomes something like
+    //
+    //   var gen = runtime.mark(function *gen() {
+    //     return gen;
+    //   });
+    //   gen().next(); // { value: gen, done: true }
+    //
+    // which ensures that the generator body can always reliably refer
+    // to gen by name.
 
-    if (node.expression) {
-      // Transform expression lambdas into normal functions.
-      node.expression = false;
-      node.body = t.blockStatement([
-        t.returnStatement(node.body)
-      ]);
-    }
+    // Remove the FunctionDeclaration so that we can add it back as a
+    // FunctionExpression passed to runtime.mark.
+    path.replace();
 
-    if (node.async) {
-      awaitVisitor.visit(path.get("body"));
-    }
+    // Change the type of the function to be an expression instead of a
+    // declaration. Note that all the other fields are the same.
+    node.type = "FunctionExpression";
 
-    var outerFnId = node.id || (
-      node.id = path.scope.parent.declareTemporary("callee$")
-    );
+    var varDecl = t.variableDeclaration("var", [
+      t.variableDeclarator(
+        node.id,
+        t.callExpression(runtimeMarkMethod, [node])
+      )
+    ]);
 
-    var innerFnId = t.identifier(node.id.name + "$");
-    var contextId = path.scope.declareTemporary("context$");
-    var vars = hoist(path);
+    // Copy any comments preceding the function declaration to the
+    // variable declaration, to avoid weird formatting consequences.
+    t.inheritsComments(varDecl, node);
+    t.removeComments(node);
 
-    var emitter = new Emitter(contextId);
-    emitter.explode(path.get("body"));
+    varDecl._blockHoist = true;
 
-    var outerBody = [];
+    var bodyPath = pp.get("body");
+    var bodyLen = bodyPath.value.length;
 
-    if (vars && vars.declarations.length > 0) {
-      outerBody.push(vars);
-    }
-
-    var wrapArgs = [
-      emitter.getContextFunction(innerFnId),
-      // Async functions don't care about the outer function because they
-      // don't need it to be marked and don't inherit from its .prototype.
-      node.async ? t.literal(null) : outerFnId,
-      t.thisExpression()
-    ];
-
-    var tryEntryList = emitter.getTryEntryList();
-    if (tryEntryList) {
-      wrapArgs.push(tryEntryList);
-    }
-
-    var wrapCall = t.callExpression(
-      node.async ? runtimeAsyncMethod : runtimeWrapMethod,
-      wrapArgs
-    );
-
-    outerBody.push(t.returnStatement(wrapCall));
-    node.body = t.blockStatement(outerBody);
-
-    if (node.async) {
-      node.async = false;
-      return;
-    }
-
-    if (t.isFunctionDeclaration(node)) {
-      var pp = path.parent;
-
-      while (pp && !(t.isBlockStatement(pp.value) || t.isProgram(pp.value))) {
-        pp = pp.parent;
-      }
-
-      if (!pp) {
+    for (var i = 0; i < bodyLen; ++i) {
+      var firstStmtPath = bodyPath.get(i);
+      if (!shouldNotHoistAbove(firstStmtPath)) {
+        firstStmtPath.insertBefore(varDecl);
         return;
       }
-
-      // Here we turn the FunctionDeclaration into a named
-      // FunctionExpression that will be assigned to a variable of the
-      // same name at the top of the enclosing block. This is important
-      // for a very subtle reason: named function expressions can refer to
-      // themselves by name without fear that the binding may change due
-      // to code executing outside the function, whereas function
-      // declarations are vulnerable to the following rebinding:
-      //
-      //   function f() { return f }
-      //   var g = f;
-      //   f = "asdf";
-      //   g(); // "asdf"
-      //
-      // One way to prevent the problem illustrated above is to transform
-      // the function declaration thus:
-      //
-      //   var f = function f() { return f };
-      //   var g = f;
-      //   f = "asdf";
-      //   g(); // f
-      //   g()()()()(); // f
-      //
-      // In the code below, we transform generator function declarations
-      // in the following way:
-      //
-      //   gen().next(); // { value: gen, done: true }
-      //   function *gen() {
-      //     return gen;
-      //   }
-      //
-      // becomes something like
-      //
-      //   var gen = runtime.mark(function *gen() {
-      //     return gen;
-      //   });
-      //   gen().next(); // { value: gen, done: true }
-      //
-      // which ensures that the generator body can always reliably refer
-      // to gen by name.
-
-      // Remove the FunctionDeclaration so that we can add it back as a
-      // FunctionExpression passed to runtime.mark.
-      path.replace();
-
-      // Change the type of the function to be an expression instead of a
-      // declaration. Note that all the other fields are the same.
-      node.type = "FunctionExpression";
-
-      var varDecl = t.variableDeclaration("var", [
-        t.variableDeclarator(
-          node.id,
-          t.callExpression(runtimeMarkMethod, [node])
-        )
-      ]);
-
-      if (node.comments) {
-        // Copy any comments preceding the function declaration to the
-        // variable declaration, to avoid weird formatting consequences.
-        varDecl.comments = node.comments;
-        node.comments = null;
-      }
-
-      var bodyPath = pp.get("body");
-      var bodyLen = bodyPath.value.length;
-
-      for (var i = 0; i < bodyLen; ++i) {
-        var firstStmtPath = bodyPath.get(i);
-        if (!shouldNotHoistAbove(firstStmtPath)) {
-          firstStmtPath.insertBefore(varDecl);
-          return;
-        }
-      }
-
-      bodyPath.push(varDecl);
-
-    } else {
-      t.assertFunctionExpression(node);
-      return t.callExpression(runtimeMarkMethod, [node]);
     }
+
+    bodyPath.push(varDecl);
+  } else {
+    t.assertFunctionExpression(node);
+    return t.callExpression(runtimeMarkMethod, [node]);
   }
-});
+};
 
 function shouldNotHoistAbove(stmtPath) {
   var value = stmtPath.value;

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

@@ -129,7 +129,7 @@ LetScoping.prototype.run = function () {
 
   // build a call and a unique id that we can assign the return value to
   var call = t.callExpression(fn, params);
-  var ret  = t.identifier(this.file.generateUid("ret", this.scope));
+  var ret  = this.file.generateUidIdentifier("ret", this.scope);
 
   var hasYield = traverse.hasType(fn.body, "YieldExpression", t.FUNCTION_TYPES);
   if (hasYield) {
@@ -445,7 +445,7 @@ LetScoping.prototype.buildHas = function (ret, call) {
   if (has.hasBreak || has.hasContinue) {
     // ensure that the parent has a label as we're building a switch and we
     // need to be able to access it
-    var label = forParent.label = forParent.label || t.identifier(this.file.generateUid("loop", this.scope));
+    var label = forParent.label = forParent.label || this.file.generateUidIdentifier("loop", this.scope);
 
     if (has.hasBreak) {
       cases.push(t.switchCase(t.literal("break"), [t.breakStatement(label)]));

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

@@ -22,9 +22,7 @@ exports.TaggedTemplateExpression = function (node, parent, file) {
     t.arrayExpression(raw)
   ]));
 
-  _.each(quasi.expressions, function (expr) {
-    args.push(expr);
-  });
+  args = args.concat(quasi.expressions);
 
   return t.callExpression(node.tag, args);
 };

lib/6to5/traverse/index.js

@@ -55,7 +55,7 @@ function traverse(parent, callbacks, opts) {
 
       //
       var opts2 = { scope: opts.scope, blacklist: opts.blacklist };
-      if (t.isScope(node)) opts2.scope = new Scope(opts.scope, node);
+      if (t.isScope(node)) opts2.scope = new Scope(node, opts.scope);
 
       // enter
       if (callbacks.enter) {
@@ -89,9 +89,10 @@ function traverse(parent, callbacks, opts) {
 
 traverse.removeProperties = function (tree) {
   var clear = function (node) {
+    delete node._scopeReferences;
     delete node.extendedRange;
-    delete node._scopeIds;
     delete node._parent;
+    delete node._scope;
     delete node.tokens;
     delete node.range;
     delete node.start;

lib/6to5/traverse/scope.js

@@ -6,25 +6,30 @@ var _        = require("lodash");
 
 var FOR_KEYS = ["left", "init"];
 
-function Scope(parent, block) {
+/**
+ * This searches the current "scope" and collects all references/declarations
+ * within.
+ *
+ * @param {Node} block
+ * @param {Scope} [parent]
+ */
+
+function Scope(block, parent) {
   this.parent = parent;
   this.block  = block;
 
-  this.info         = this.getInfo();
-  this.declarations = this.info.declarations;
+  this.references = this.getReferences();
 }
 
-Scope.prototype.getInfo = function () {
+Scope.prototype.getReferences = function () {
   var block = this.block;
-  if (block._scope) return block._scope;
+  if (block._scopeReferences) return block._scopeReferences;
 
-  var self = this;
-  var info = block._scope = {
-    declarations: {}
-  };
+  var self       = this;
+  var references = block._scopeReferences = {};
 
   var add = function (node) {
-    self.addDeclaration(node, info.declarations);
+    self.add(node, references);
   };
 
   // ForStatement - left, init
@@ -56,7 +61,7 @@ Scope.prototype.getInfo = function () {
   // Program, Function - var variables
 
   if (t.isProgram(block) || t.isFunction(block)) {
-    traverse(block, function (node) {
+    traverse(block, function (node, parent, scope) {
       if (t.isFor(node)) {
         _.each(FOR_KEYS, function (key) {
           var declar = node[key];
@@ -68,12 +73,16 @@ Scope.prototype.getInfo = function () {
       // declared within are accessible
       if (t.isFunction(node)) return false;
 
+      if (t.isIdentifier(node) && t.isReferenced(node, parent) && !scope.has(node.name)) {
+        add(node);
+      }
+
       // we've ran into a declaration!
       // we'll let the BlockStatement scope deal with `let` declarations
       if (t.isDeclaration(node) && !t.isLet(node)) {
         add(node);
       }
-    });
+    }, { scope: this });
   }
 
   // Function - params, rest
@@ -85,12 +94,12 @@ Scope.prototype.getInfo = function () {
     });
   }
 
-  return info;
+  return references;
 };
 
-Scope.prototype.addDeclaration = function (node, declarations) {
+Scope.prototype.add = function (node, references) {
   if (!node) return;
-  _.merge(declarations || this.declarations, t.getIds(node, true));
+  _.merge(references || this.references, t.getIds(node, true));
 };
 
 Scope.prototype.get = function (id) {
@@ -98,7 +107,7 @@ Scope.prototype.get = function (id) {
 };
 
 Scope.prototype.getOwn = function (id) {
-  return _.has(this.declarations, id) && this.declarations[id];
+  return _.has(this.references, id) && this.references[id];
 };
 
 Scope.prototype.parentGet = function (id) {

lib/6to5/types/index.js

@@ -250,6 +250,11 @@ t.inheritsComments = function (child, parent) {
   return child;
 };
 
+t.removeComments = function (node) {
+  delete node.leadingComments;
+  delete node.trailingComments;
+};
+
 t.inherits = function (child, parent) {
   child.loc   = parent.loc;
   child.end   = parent.end;

lib/6to5/util.js

@@ -65,7 +65,7 @@ exports.getUid = function (parent, file) {
 
   if (t.isIdentifier(node)) id = node.name;
 
-  return t.identifier(file.generateUid(id));
+  return file.generateUidIdentifier(id);
 };
 
 exports.isAbsolute = function (loc) {
@@ -218,7 +218,7 @@ exports.parse = function (opts, code, callback) {
     var ast = acorn.parse(code, {
       allowReturnOutsideFunction: true,
       preserveParens:             true,
-      ecmaVersion:                Infinity,
+      ecmaVersion:                opts.experimental ? 7 : 6,
       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": "1.12.22",
+  "version": "1.13.0",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://github.com/6to5/6to5",
   "repository": {
@@ -35,21 +35,21 @@
     "test": "make test"
   },
   "dependencies": {
-    "ast-types": "~0.6.0",
+    "ast-types": "0.6.5",
     "commander": "2.5.0",
     "fs-readdir-recursive": "0.1.0",
     "lodash": "2.4.1",
     "mkdirp": "0.5.0",
-    "es6-shim": "0.20.2",
+    "es6-shim": "0.20.3",
     "es6-symbol": "0.1.1",
     "regexpu": "0.3.0",
     "source-map": "0.1.40",
-    "chokidar": "0.11.0",
+    "chokidar": "0.11.1",
     "source-map-support": "0.2.8",
     "esutils": "1.1.4",
-    "acorn-6to5": "0.9.1-2",
-    "estraverse": "^1.7.0",
-    "private": "^0.1.6"
+    "acorn-6to5": "0.9.1-3",
+    "estraverse": "1.8.0",
+    "private": "0.1.6"
   },
   "devDependencies": {
     "istanbul": "0.3.2",

test/fixtures/transformation/array-comprehension/options.json

@@ -0,0 +1,3 @@
+{
+  "experimental": true
+}

test/fixtures/transformation/array-comprehension/single-if/actual.js

@@ -0,0 +1 @@
+var arr = [for (i of nums) if (i > 1) i * i];

test/fixtures/transformation/array-comprehension/single-if/expected.js

@@ -0,0 +1,7 @@
+"use strict";
+
+var arr = Array.from(nums).filter(function (i) {
+  return i > 1;
+}).map(function (i) {
+  return i * i;
+});

test/fixtures/transformation/array-comprehension/single/actual.js

@@ -0,0 +1 @@
+var arr = [for (i of nums) i * i];

test/fixtures/transformation/array-comprehension/single/expected.js

@@ -0,0 +1,5 @@
+"use strict";
+
+var arr = Array.from(nums).map(function (i) {
+  return i * i;
+});

test/fixtures/transformation/async/options.json

@@ -1,3 +1,4 @@
 {
-  "asyncExec": true
+  "asyncExec": true,
+  "experimental": true
 }

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

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

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

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

test/fixtures/transformation/generator-comprehension/options.json

@@ -0,0 +1,3 @@
+{
+  "experimental": true
+}

test/fixtures/transformation/react/display-name-variable-declaration/actual.js

@@ -1,5 +1,5 @@
 var Component = React.createClass({
   render: function () {
-  return null;
+    return null;
   }
 });

test/fixtures/transformation/spread/new-expression/expected.js

@@ -1,11 +1,11 @@
 "use strict";
 
 var _applyConstructor = function (Constructor, args) {
-  var bindArgs = [null].concat(args);
+  var instance = Object.create(Constructor.prototype);
 
-  var Factory = Constructor.bind.apply(Constructor, bindArgs);
+  Constructor.apply(instance, args);
 
-  return new Factory();
+  return instance;
 };
 
 _applyConstructor(Numbers, Array.from(nums));

test/generation.js

@@ -26,7 +26,7 @@ _.each(helper.get("generation"), function (testSuite) {
         var expect = task.expect;
         var actual = task.actual;
 
-        var actualAst  = util.parse({ filename: actual.loc }, actual.code);
+        var actualAst  = util.parse({ filename: actual.loc, experimental: true }, actual.code);
         var actualCode = generate(actualAst, null, actual.code).code;
 
         chai.expect(actualCode).to.equal(expect.code, actual.loc + " !== " + expect.loc);

test/util.js

@@ -3,8 +3,6 @@ var util   = require("../lib/6to5/util");
 var t      = require("../lib/6to5/types");
 
 suite("util", function () {
-  test("duplicate mutator map");
-
   test("invalid template", function () {
     assert.throws(function () {
       util.template("invalid template");
@@ -45,6 +43,34 @@ suite("util", function () {
     assert.deepEqual(util.list("foo,bar"), ["foo", "bar"]);
   });
 
+  test("arrayify", function () {
+    assert.deepEqual(util.arrayify(undefined), []);
+    assert.deepEqual(util.arrayify(false), []);
+    assert.deepEqual(util.arrayify(null), []);
+    assert.deepEqual(util.arrayify(""), []);
+    assert.deepEqual(util.arrayify("foo"), ["foo"]);
+    assert.deepEqual(util.arrayify("foo,bar"), ["foo", "bar"]);
+    assert.deepEqual(util.arrayify(["foo", "bar"]), ["foo", "bar"]);
+
+    assert.throws(function () {
+      util.arrayify({});
+    }, /illegal type for arrayify/);
+  });
+
+  test("regexify", function () {
+    assert.deepEqual(util.regexify(undefined), /(?:)/);
+    assert.deepEqual(util.regexify(false), /(?:)/);
+    assert.deepEqual(util.regexify(null), /(?:)/);
+    assert.deepEqual(util.regexify(""), /(?:)/);
+    assert.deepEqual(util.regexify(["foo", "bar"]), /foo|bar/);
+    assert.deepEqual(util.regexify("foobar"), /foobar/);
+    assert.deepEqual(util.regexify(/foobar/), /foobar/);
+
+    assert.throws(function () {
+      util.regexify({});
+    }, /illegal type for regexify/);
+  });
+
   test("getIds");
 
   test("toStatement");