v2.12.4

Rm unused dependencies (pass lint)

.travis.yml

@@ -1,3 +1,4 @@
+sudo: false
 language: node_js
 node_js:
   - "0.10"

CHANGELOG.md

@@ -11,6 +11,20 @@
 
 _Note: Gaps between patch versions are faulty/broken releases._
 
+## 2.12.4
+
+ * **Polish**
+  * Rest parameters now allocate the array before populating.
+ * **Internal**
+  * `for...in` loops have been changed to optimised `for` loops - better performance and no enumeration of protoype keys.
+  * Parts of the code generator have now been optimised thanks to [gaearon](https://github.com/gaearon).
+
+## 2.12.3
+
+ * **Spec Compliancy**
+  * Optional `typeof` transformer checks for `undefined` before passing it to the helper.
+  * Class methods are now named.
+
 ## 2.12.2
 
  * **Internal**

CONTRIBUTING.md

@@ -1,6 +1,20 @@
 # Contributing
 
-Before contributing, please read the [code of conduct](https://github.com/6to5/6to5/blob/master/CODE_OF_CONDUCT.md).
+Contributions are always welcome, no matter how large or small. Before contributing, please read the [code of conduct](https://github.com/6to5/6to5/blob/master/CODE_OF_CONDUCT.md).
+
+## Developing
+
+#### Workflow
+
+* Fork the repository
+* Clone your fork and change directory to it (`git clone git@github.com:yourUserName/6to5.git && cd 6to5`)
+* Install the project dependencies (`make bootstrap`)
+* Link your forked clone (`npm link`)
+* Develop your changes ensuring you're fetching updates from upstream often
+* Ensure the test are passing (`make test`)
+* Create new pull request explaining your proposed change or reference an issue in your commit message
+
+#### Code Standards
 
  * **General**
    * No ES6 syntax features or methods, exclusively ES5.

bin/6to5/dir.js

@@ -1,9 +1,9 @@
-var chokidar = require("chokidar");
-var mkdirp   = require("mkdirp");
-var path     = require("path");
-var util     = require("./util");
-var fs       = require("fs");
-var _        = require("lodash");
+var outputFileSync = require("output-file-sync");
+var chokidar       = require("chokidar");
+var path           = require("path");
+var util           = require("./util");
+var fs             = require("fs");
+var _              = require("lodash");
 
 module.exports = function (commander, filenames, opts) {
   if (commander.sourceMapsInline) {
@@ -15,16 +15,13 @@ module.exports = function (commander, filenames, opts) {
 
     var data = util.compile(src, { sourceMapName: dest });
 
-    var up = path.normalize(dest + "/..");
-    mkdirp.sync(up);
-
     if (commander.sourceMaps) {
       var mapLoc = dest + ".map";
       data.code = util.addSourceMappingUrl(data.code, mapLoc);
-      fs.writeFileSync(mapLoc, JSON.stringify(data.map));
+      outputFileSync(mapLoc, JSON.stringify(data.map));
     }
 
-    fs.writeFileSync(dest, data.code);
+    outputFileSync(dest, data.code);
 
     console.log(src + " -> " + dest);
   };

bin/_6to5-node

@@ -96,8 +96,8 @@ function replEval(code, context, filename, callback) {
   var result;
 
   try {
-    if (/^\((.*?)\n\)$/.test(code)) {
-      code = code.slice(1, -2); // remove "(" and "\n)"
+    if (code[0] === "(" && code[code.length - 1] === ")") {
+      code = code.slice(1, -1); // remove "(" and ")"
     }
 
     result = _eval(code, filename);

lib/6to5/generation/buffer.js

@@ -67,32 +67,57 @@ Buffer.prototype.removeLast = function (cha) {
 
 Buffer.prototype.newline = function (i, removeLast) {
   if (this.format.compact) return;
-
-  if (_.isBoolean(i)) {
-    removeLast = i;
-    i = null;
-  }
+  removeLast = removeLast || false;
 
   if (_.isNumber(i)) {
     if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
-    for (var j = 0; j < i; j++) {
-      this.newline(null, removeLast);
+    while (i--) {
+      this._newline(removeLast);
     }
     return;
   }
 
+  if (_.isBoolean(i)) {
+    removeLast = i;
+  }
+
+  this._newline(removeLast);
+};
+
+Buffer.prototype._newline = function (removeLast) {
   if (removeLast && this.isLast("\n")) this.removeLast("\n");
 
   this.removeLast(" ");
 
   // remove whitespace if last character was a newline
-  this.buf = this.buf.replace(/\n +$/, "\n");
-
+  this._removeSpacesAfterLastNewline();
   this._push("\n");
 };
 
+/**
+ * If buffer ends with a newline and some spaces after it, trim those spaces.
+ */
+Buffer.prototype._removeSpacesAfterLastNewline = function () {
+  var lastNewlineIndex = this.buf.lastIndexOf('\n');
+  if (lastNewlineIndex === -1)
+    return;
+
+  var index = this.buf.length - 1;
+  while (index > lastNewlineIndex) {
+    if (this.buf[index] !== ' ') {
+      break;
+    }
+
+    index--;
+  }
+
+  if (index === lastNewlineIndex) {
+    this.buf = this.buf.substring(0, index + 1);
+  }
+};
+
 Buffer.prototype.push = function (str, noIndent) {
   if (this._indent && !noIndent && str !== "\n") {
     // we have an indent level and we aren't pushing a newline

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

@@ -169,7 +169,7 @@ exports.VariableDeclaration = function (node, print, parent) {
 
   var inits = 0;
   var noInits = 0;
-  for (var i in node.declarations) {
+  for (var i = 0; i < node.declarations.length; i++) {
     if (node.declarations[i].init) {
       inits++;
     } else {

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

@@ -13,7 +13,7 @@ var find = function (obj, node, parent) {
   for (var i = 0; i < types.length; i++) {
     var type = types[i];
 
-    if (t["is" + type](node)) {
+    if (t.is(type, node)) {
       var fn = obj[type];
       result = fn(node, parent);
       if (result != null) break;
@@ -28,13 +28,11 @@ function Node(node, parent) {
   this.node   = node;
 }
 
-Node.prototype.isUserWhitespacable = function () {
-  return t.isUserWhitespacable(this.node);
+Node.isUserWhitespacable = function (node) {
+  return t.isUserWhitespacable(node);
 };
 
-Node.prototype.needsWhitespace = function (type) {
-  var parent = this.parent;
-  var node   = this.node;
+Node.needsWhitespace = function (node, parent, type) {
   if (!node) return 0;
 
   if (t.isExpressionStatement(node)) {
@@ -51,18 +49,15 @@ Node.prototype.needsWhitespace = function (type) {
   return lines || 0;
 };
 
-Node.prototype.needsWhitespaceBefore = function () {
-  return this.needsWhitespace("before");
+Node.needsWhitespaceBefore = function (node, parent) {
+  return Node.needsWhitespace(node, parent, "before");
 };
 
-Node.prototype.needsWhitespaceAfter = function () {
-  return this.needsWhitespace("after");
+Node.needsWhitespaceAfter = function (node, parent) {
+  return Node.needsWhitespace(node, parent, "after");
 };
 
-Node.prototype.needsParens = function () {
-  var parent = this.parent;
-  var node   = this.node;
-
+Node.needsParens = function (node, parent) {
   if (!parent) return false;
 
   if (t.isNewExpression(parent) && parent.callee === node) {
@@ -77,10 +72,7 @@ Node.prototype.needsParens = function () {
   return find(parens, node, parent);
 };
 
-Node.prototype.needsParensNoLineTerminator = function () {
-  var parent = this.parent;
-  var node   = this.node;
-
+Node.needsParensNoLineTerminator = function (node, parent) {
   if (!parent) return false;
 
   // no comments
@@ -100,17 +92,18 @@ Node.prototype.needsParensNoLineTerminator = function () {
   return false;
 };
 
-_.each(Node.prototype, function (fn, key) {
-  Node[key] = function (node, parent) {
-    var n = new Node(node, parent);
-
+_.each(Node, function (fn, key) {
+  Node.prototype[key] = function () {
     // Avoid leaking arguments to prevent deoptimization
-    var skipCount = 2;
-    var args = new Array(arguments.length - skipCount);
+    var args = new Array(arguments.length + 2);
+
+    args[0] = this.node;
+    args[1] = this.parent;
+
     for (var i = 0; i < args.length; i++) {
-      args[i] = arguments[i + 2];
+      args[i + 2] = arguments[i];
     }
 
-    return n[key].apply(n, args);
+    return Node[key].apply(null, args);
   };
 });

lib/6to5/generation/whitespace.js

@@ -1,10 +1,38 @@
 module.exports = Whitespace;
 
-var _ = require("lodash");
+var _    = require("lodash");
+
+/**
+ * Returns `i`th number from `base`, continuing from 0 when `max` is reached.
+ * Useful for shifting `for` loop by a fixed number but going over all items.
+ *
+ * @param {Number} i Current index in the loop
+ * @param {Number} base Start index for which to return 0
+ * @param {Number} max Array length
+ * @returns {Number} shiftedIndex
+ */
+function getLookupIndex(i, base, max) {
+  i += base;
+
+  if (i >= max)
+    i -= max;
+
+  return i;
+}
 
 function Whitespace(tokens, comments) {
   this.tokens = _.sortBy(tokens.concat(comments), "start");
-  this.used   = [];
+  this.used   = {};
+
+  // Profiling this code shows that while generator passes over it, indexes
+  // returned by `getNewlinesBefore` and `getNewlinesAfter` are always increasing.
+
+  // We use this implementation detail for an optimization: instead of always
+  // starting to look from `this.tokens[0]`, we will start `for` loops from the
+  // previous successful match. We will enumerate all tokens—but the common
+  // case will be much faster.
+
+  this._lastFoundIndex = 0;
 }
 
 Whitespace.prototype.getNewlinesBefore = function (node) {
@@ -13,13 +41,17 @@ Whitespace.prototype.getNewlinesBefore = function (node) {
   var tokens = this.tokens;
   var token;
 
-  for (var i = 0; i < tokens.length; i++) {
+  for (var j = 0; j < tokens.length; j++) {
+    // optimize for forward traversal by shifting for loop index
+    var i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
     token = tokens[i];
 
     // this is the token this node starts with
     if (node.start === token.start) {
       startToken = tokens[i - 1];
       endToken = token;
+
+      this._lastFoundIndex = i;
       break;
     }
   }
@@ -33,13 +65,17 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
   var tokens = this.tokens;
   var token;
 
-  for (var i = 0; i < tokens.length; i++) {
+  for (var j = 0; j < tokens.length; j++) {
+    // optimize for forward traversal by shifting for loop index
+    var i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
     token = tokens[i];
 
     // this is the token this node ends with
     if (node.end === token.end) {
       startToken = token;
       endToken = tokens[i + 1];
+
+      this._lastFoundIndex = i;
       break;
     }
   }
@@ -60,15 +96,14 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {
   var start = startToken ? startToken.loc.end.line : 1;
   var end   = endToken.loc.start.line;
-
   var lines = 0;
 
   for (var line = start; line < end; line++) {
-    if (!_.contains(this.used, line)) {
-      this.used.push(line);
+    if (typeof this.used[line] === 'undefined') {
+      this.used[line] = true;
       lines++;
     }
   }
 
   return lines;
-};
+};

lib/6to5/register.js

@@ -21,51 +21,6 @@ sourceMapSupport.install({
   }
 });
 
-//
-
-var blacklist  = [];
-
-var blacklistTest = function (transformer, code) {
-  try {
-    if (_.isFunction(code)) {
-      code();
-    } else {
-      new Function(code);
-    }
-    blacklist.push(transformer);
-  } catch (err) {
-    if (err.name !== "SyntaxError") throw err;
-  }
-};
-
-blacklistTest("arrayComprehension", "var foo = [for (foo of bar) foo * foo];");
-blacklistTest("generatorComprehension", "var foo = (for (foo of bar) foo * foo)");
-blacklistTest("arrowFunctions", "var foo = x => x * x;");
-blacklistTest("classes", "class Foo {}");
-blacklistTest("computedPropertyNames", "var foo = { [foo]: bar };");
-blacklistTest("constants", function () {
-  try {
-    new Function("const foo = 'foo';\nfoo = 'wow';");
-  } catch (err) {
-    return; // constants are supported
-  }
-  throw new SyntaxError;
-});
-blacklistTest("defaultParamaters", "var foo = function (bar = 0) {};");
-blacklistTest("destructuring", "var { x, y } = { x: 0, y: 0 };");
-blacklistTest("forOf", "for (var foo of bar) {}");
-blacklistTest("generators", "function* foo() {}\nasync function bar() {}"); // generators/async functions delegated to same transformer
-blacklistTest("letScoping", "let foo = 0;");
-blacklistTest("modules", 'import foo from "from";');
-blacklistTest("propertyMethodAssignment", "{ get foo() {} }");
-blacklistTest("propertyNameShorthand", "var foo = { x, y };");
-blacklistTest("restParameters", "function foo(...bar) {}");
-blacklistTest("spread", "foo(...bar);");
-blacklistTest("templateLiterals", "var foo = `foo`;");
-blacklistTest("unicodeRegex", function () { new RegExp("foo", "u"); });
-
-//
-
 var transformOpts = {};
 var ignoreRegex   = /node_modules/;
 var onlyRegex;
@@ -95,7 +50,6 @@ var loader = function (m, filename) {
 
   result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
-    blacklist: blacklist,
     sourceMap: true,
     ast:       false
   }, transformOpts));

lib/6to5/transformation/helpers/build-comprehension.js

@@ -0,0 +1,23 @@
+var t = require("../../types");
+
+module.exports = function build(node, buildBody) {
+  var self = node.blocks.shift();
+  if (!self) return;
+
+  var child = build(node, buildBody);
+  if (!child) {
+    // last item
+    child = buildBody();
+
+    // add a filter as this is our final stop
+    if (node.filter) {
+      child = t.ifStatement(node.filter, t.blockStatement([child]));
+    }
+  }
+
+  return t.forOfStatement(
+    t.variableDeclaration("let", [t.variableDeclarator(self.left)]),
+    self.right,
+    t.blockStatement([child])
+  );
+};

lib/6to5/transformation/helpers/name-method.js

@@ -0,0 +1,43 @@
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+
+module.exports = function (node, file, scope) {
+  var key = t.toComputedKey(node, node.key);
+  if (!t.isLiteral(key)) return node; // we can't set a function id with this
+
+  var id = t.toIdentifier(key.value);
+  key = t.identifier(id);
+
+  var selfReference = false;
+  var outerDeclar = scope.get(id, true);
+
+  traverse(node, {
+    enter: function (node, parent, scope) {
+      // check if this node is an identifier that matches the same as our function id
+      if (!t.isIdentifier(node, { name: id })) return;
+
+      // check if this node is the one referenced
+      if (!t.isReferenced(node, parent)) return;
+
+      // check that we don't have a local variable declared as that removes the need
+      // for the wrapper
+      var localDeclar = scope.get(id, true);
+      if (localDeclar !== outerDeclar) return;
+
+      selfReference = true;
+      this.stop();
+    }
+  }, scope);
+
+  if (selfReference) {
+    node.value = util.template("property-method-assignment-wrapper", {
+      FUNCTION: node.value,
+      FUNCTION_ID: key,
+      FUNCTION_KEY: file.generateUidIdentifier(id, scope),
+      WRAPPER_KEY: file.generateUidIdentifier(id + "Wrapper", scope)
+    });
+  } else {
+    node.value.id = key;
+  }
+};

lib/6to5/transformation/helpers/remap-async-to-generator.js

@@ -0,0 +1,29 @@
+var traverse = require("../../traverse");
+var t        = require("../../types");
+
+module.exports = function (node, callId) {
+  node.async = false;
+  node.generator = true;
+
+  traverse(node, {
+    enter: function (node) {
+      if (t.isFunction(node)) this.skip();
+
+      if (t.isAwaitExpression(node)) {
+        node.type = "YieldExpression";
+      }
+    }
+  });
+
+  var call = t.callExpression(callId, [node]);
+
+  if (t.isFunctionDeclaration(node)) {
+    var declar = t.variableDeclaration("var", [
+      t.variableDeclarator(node.id, call)
+    ]);
+    declar._blockHoist = true;
+    return declar;
+  } else {
+    return call;
+  }
+};

lib/6to5/transformation/helpers/use-strict.js

@@ -0,0 +1,19 @@
+var t = require("../../types");
+
+exports.has = function (node) {
+  var first = node.body[0];
+  return t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" });
+};
+
+exports.wrap = function (node, callback) {
+  var useStrictNode;
+  if (exports.has(node)) {
+    useStrictNode = node.body.shift();
+  }
+
+  callback();
+
+  if (useStrictNode) {
+    node.body.unshift(useStrictNode);
+  }
+};

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

@@ -244,13 +244,13 @@ DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
   var assign;
 
   if (t.isVariableDeclaration(declar)) {
-    for (var i in declar.declarations) {
+    for (var i = 0; i < declar.declarations.length; i++) {
       var decl = declar.declarations[i];
 
       decl.init = this._exportsAssign(decl.id, decl.init, node).expression;
 
       var newDeclar = t.variableDeclaration(declar.kind, [decl]);
-      if (i === "0") t.inherits(newDeclar, declar);
+      if (i === 0) t.inherits(newDeclar, declar);
       nodes.push(newDeclar);
     }
   } else {

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

@@ -1,7 +1,7 @@
 module.exports = SystemFormatter;
 
 var AMDFormatter = require("./amd");
-var useStrict    = require("../transformers/use-strict");
+var useStrict    = require("../helpers/use-strict");
 var traverse     = require("../../traverse");
 var util         = require("../../util");
 var t            = require("../../types");
@@ -171,7 +171,7 @@ SystemFormatter.prototype.transform = function (ast) {
 
   handlerBody.push(returnStatement);
 
-  if (useStrict._has(block)) {
+  if (useStrict.has(block)) {
     handlerBody.unshift(block.body.shift());
   }
 

lib/6to5/transformation/templates/rest.js

@@ -1,3 +1,3 @@
-for (var KEY = START; KEY < ARGUMENTS.length; KEY++) {
+for (var LEN = ARGUMENTS.length, ARRAY = Array(ARRAY_LEN), KEY = START; KEY < LEN; KEY++) {
   ARRAY[ARRAY_KEY] = ARGUMENTS[KEY];
 }

lib/6to5/transformation/transform.js

@@ -20,7 +20,7 @@ transform.fromAst = function (ast, code, opts) {
 };
 
 transform._ensureTransformerNames = function (type, keys) {
-  for (var i in keys) {
+  for (var i = 0; i < keys.length; i++) {
     var key = keys[i];
     if (!_.has(transform.transformers, key)) {
       throw new ReferenceError("unknown transformer " + key + " specified in " + type);

lib/6to5/transformation/transformer.js

@@ -65,7 +65,7 @@ Transformer.prototype.transform = function (file) {
       if (exit) fn = fns.exit;
       if (!fn) return;
 
-      return fn(node, parent, file, scope);
+      return fn.call(this, node, parent, file, scope);
     };
   };
 

lib/6to5/transformation/transformers/_block-hoist.js

@@ -1,4 +1,4 @@
-var useStrict = require("./use-strict");
+var useStrict = require("../helpers/use-strict");
 var _         = require("lodash");
 
 // Priority:
@@ -12,13 +12,13 @@ exports.BlockStatement =
 exports.Program = {
   exit: function (node) {
     var hasChange = false;
-    for (var i in node.body) {
+    for (var i = 0; i < node.body.length; i++) {
       var bodyNode = node.body[i];
       if (bodyNode && bodyNode._blockHoist != null) hasChange = true;
     }
     if (!hasChange) return;
 
-    useStrict._wrap(node, function () {
+    useStrict.wrap(node, function () {
       var nodePriorities = _.groupBy(node.body, function (bodyNode) {
         var priority = bodyNode._blockHoist;
         if (priority == null) priority = 1;

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

@@ -1,14 +1,16 @@
-var useStrict = require("./use-strict");
+var useStrict = require("../helpers/use-strict");
 var t         = require("../../types");
 
 exports.secondPass = true;
 
 exports.BlockStatement =
 exports.Program = function (node) {
+  if (!node._declarations) return;
+
   var kinds = {};
   var kind;
 
-  useStrict._wrap(node, function () {
+  useStrict.wrap(node, function () {
     for (var i in node._declarations) {
       var declar = node._declarations[i];
 

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

@@ -1,12 +1,25 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
+var nameMethod = require("../helpers/name-method");
+var traverse   = require("../../traverse");
+var util       = require("../../util");
+var t          = require("../../types");
 
 exports.ClassDeclaration = function (node, parent, file, scope) {
   return new Class(node, file, scope, true).run();
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
+  if (!node.id) {
+    if (t.isProperty(parent) && parent.value === node && !parent.computed && t.isIdentifier(parent.key)) {
+      // var o = { foo: class {} };
+      node.id = parent.key;
+    }
+
+    if (t.isVariableDeclarator(parent) && t.isIdentifier(parent.id)) {
+      // var foo = class {};
+      node.id = parent.id;
+    }
+  }
+
   return new Class(node, file, scope, false).run();
 };
 
@@ -119,10 +132,10 @@ Class.prototype.buildBody = function () {
   var classBody   = this.node.body.body;
   var body        = this.body;
 
-  for (var i in classBody) {
+  for (var i = 0; i < classBody.length; i++) {
     var node = classBody[i];
     if (t.isMethodDefinition(node)) {
-      this.replaceInstanceSuperReferences(node);
+      this.replaceSuperReferences(node);
 
       if (node.key.name === "constructor") {
         this.pushConstructor(node);
@@ -179,15 +192,10 @@ Class.prototype.pushMethod = function (node) {
   var methodName = node.key;
 
   var kind = node.kind;
-  var mutatorMap = this.instanceMutatorMap;
-  if (node.static) {
-    this.hasStaticMutators = true;
-    mutatorMap = this.staticMutatorMap;
-  } else {
-    this.hasInstanceMutators = true;
-  }
 
   if (kind === "") {
+    nameMethod(node, this.file, this.scope);
+
     if (this.isLoose) {
       // use assignments instead of define properties for loose classes
 
@@ -204,6 +212,14 @@ Class.prototype.pushMethod = function (node) {
     kind = "value";
   }
 
+  var mutatorMap = this.instanceMutatorMap;
+  if (node.static) {
+    this.hasStaticMutators = true;
+    mutatorMap = this.staticMutatorMap;
+  } else {
+    this.hasInstanceMutators = true;
+  }
+
   util.pushMutatorMap(mutatorMap, methodName, kind, node.computed, node);
 };
 
@@ -284,7 +300,7 @@ Class.prototype.looseSuperProperty = function (methodNode, id, parent) {
  * @param {Node} methodNode MethodDefinition
  */
 
-Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
+Class.prototype.replaceSuperReferences = function (methodNode) {
   var method = methodNode.value;
   var self   = this;
 
@@ -307,6 +323,11 @@ Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
           return this.skip();
         }
 
+        if (t.isProperty(node, { method: true }) || t.isMethodDefinition(node)) {
+          // break on object methods
+          return this.skip();
+        }
+
         var getThisReference = function () {
           if (topLevel) {
             // top level so `this` is the instance

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

@@ -3,7 +3,7 @@ var t = require("../../types");
 exports.ObjectExpression = function (node, parent, file, scope) {
   var hasComputed = false;
 
-  for (var i in node.properties) {
+  for (var i = 0; i < node.properties.length; i++) {
     hasComputed = t.isProperty(node.properties[i], { computed: true, kind: "init" });
     if (hasComputed) break;
   }
@@ -39,7 +39,7 @@ exports.ObjectExpression = function (node, parent, file, scope) {
 };
 
 var loose = function (node, body, objId) {
-  for (var i in node.properties) {
+  for (var i = 0; i < node.properties.length; i++) {
     var prop = node.properties[i];
 
     body.push(t.expressionStatement(
@@ -58,7 +58,7 @@ var spec = function (node, body, objId, initProps, file) {
 
   // normalise key
 
-  for (var i in props) {
+  for (var i = 0; i < props.length; i++) {
     prop = props[i];
     if (prop.kind !== "init") continue;
 
@@ -73,7 +73,7 @@ var spec = function (node, body, objId, initProps, file) {
 
   var broken = false;
 
-  for (i in props) {
+  for (i = 0; i < props.length; i++) {
     prop = props[i];
 
     if (prop.computed) {
@@ -89,7 +89,7 @@ var spec = function (node, body, objId, initProps, file) {
   // add a simple assignment for all Symbol member expressions due to symbol polyfill limitations
   // otherwise use Object.defineProperty
 
-  for (i in props) {
+  for (i = 0; i < props.length; i++) {
     prop = props[i];
     if (!prop) continue;
 

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

@@ -44,7 +44,7 @@ exports.ForStatement = function (node, parent, file) {
     }
 
     if (t.isVariableDeclaration(child, { kind: "const" })) {
-      for (var i in child.declarations) {
+      for (var i = 0; i < child.declarations.length; i++) {
         var declar = child.declarations[i];
 
         var ids = getIds(declar);

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

@@ -11,7 +11,6 @@ exports.Function = function (node, parent, file, scope) {
   });
 
   var iife = false;
-  var i;
   var def;
 
   var checkTDZ = function (ids) {
@@ -31,7 +30,7 @@ exports.Function = function (node, parent, file, scope) {
     traverse(def, { enter: check });
   };
 
-  for (i in node.defaults) {
+  for (var i = 0; i < node.defaults.length; i++) {
     def = node.defaults[i];
     if (!def) continue;
 
@@ -40,8 +39,8 @@ exports.Function = function (node, parent, file, scope) {
     // temporal dead zone check - here we prevent accessing of params that
     // are to the right - ie. uninitialized parameters
     var rightIds = ids.slice(i);
-    for (i in rightIds) {
-      checkTDZ(rightIds[i]);
+    for (var i2 = 0; i2 < rightIds.length; i2++) {
+      checkTDZ(rightIds[i2]);
     }
 
     // we're accessing a variable that's already defined within this function
@@ -58,7 +57,7 @@ exports.Function = function (node, parent, file, scope) {
 
   var lastNonDefaultParam = 0;
 
-  for (i in node.defaults) {
+  for (i = 0; i < node.defaults.length; i++) {
     def = node.defaults[i];
     if (!def) {
       lastNonDefaultParam = +i + 1;

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

@@ -46,12 +46,12 @@ var pushAssignmentPattern = function (opts, nodes, pattern, parentId) {
 };
 
 var pushObjectPattern = function (opts, nodes, pattern, parentId) {
-  for (var i in pattern.properties) {
+  for (var i = 0; i < pattern.properties.length; i++) {
     var prop = pattern.properties[i];
     if (t.isSpreadProperty(prop)) {
         // get all the keys that appear in this object before the current spread
         var keys = [];
-        for (var i2 in pattern.properties) {
+        for (var i2 = 0; i2 < pattern.properties.length; i2++) {
           var prop2 = pattern.properties[i2];
 
           if (i2 >= i) break;
@@ -88,7 +88,7 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
   var i;
 
   var hasSpreadElement = false;
-  for (i in pattern.elements) {
+  for (i = 0; i < pattern.elements.length; i++) {
     if (t.isSpreadElement(pattern.elements[i])) {
       hasSpreadElement = true;
       break;
@@ -103,7 +103,7 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
   ]));
   parentId = _parentId;
 
-  for (i in pattern.elements) {
+  for (i = 0; i < pattern.elements.length; i++) {
     var elem = pattern.elements[i];
     if (!elem) continue;
 
@@ -278,7 +278,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   var declar;
 
   var hasPattern = false;
-  for (i in node.declarations) {
+  for (i = 0; i < node.declarations.length; i++) {
     declar = node.declarations[i];
     if (t.isPattern(declar.id)) {
       hasPattern = true;
@@ -287,7 +287,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   }
   if (!hasPattern) return;
 
-  for (i in node.declarations) {
+  for (i = 0; i < node.declarations.length; i++) {
     declar = node.declarations[i];
 
     var patternId = declar.init;
@@ -317,7 +317,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
     declar = null;
 
-    for (i in nodes) {
+    for (i = 0; i < nodes.length; i++) {
       node = nodes[i];
       declar = declar || t.variableDeclaration(node.kind, []);
 

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

@@ -25,7 +25,7 @@ var isVar = function (node, parent) {
 };
 
 var standardiseLets = function (declars) {
-  for (var i in declars) {
+  for (var i = 0; i < declars.length; i++) {
     delete declars[i]._let;
   }
 };
@@ -231,10 +231,9 @@ LetScoping.prototype.getInfo = function () {
     }
   };
 
-  var i;
   var declar;
 
-  for (i in opts.declarators) {
+  for (var i in opts.declarators) {
     declar = opts.declarators[i];
     opts.declarators.push(declar);
 
@@ -246,14 +245,16 @@ LetScoping.prototype.getInfo = function () {
     opts.keys = opts.keys.concat(keys);
   }
 
-  for (i in block.body) {
-    declar = block.body[i];
-    if (!isLet(declar, block)) continue;
+  if (block.body) {
+    for (i = 0; i < block.body.length; i++) {
+      declar = block.body[i];
+      if (!isLet(declar, block)) continue;
 
-    var declars = t.getIds(declar, true);
-    for (var key in declars) {
-      duplicates(declars[key], key);
-      opts.keys.push(key);
+      var declars = t.getIds(declar, true);
+      for (var key in declars) {
+        duplicates(declars[key], key);
+        opts.keys.push(key);
+      }
     }
   }
 
@@ -412,7 +413,7 @@ LetScoping.prototype.pushDeclar = function (node) {
 
   var replace = [];
 
-  for (var i in node.declarations) {
+  for (var i = 0; i < node.declarations.length; i++) {
     var declar = node.declarations[i];
     if (!declar.init) continue;
 

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

@@ -10,7 +10,7 @@ exports.ImportDeclaration = function (node, parent, file) {
   var nodes = [];
 
   if (node.specifiers.length) {
-    for (var i in node.specifiers) {
+    for (var i = 0; i < node.specifiers.length; i++) {
       file.moduleFormatter.importSpecifier(node.specifiers[i], node, nodes, parent);
     }
   } else {
@@ -39,7 +39,7 @@ exports.ExportDeclaration = function (node, parent, file) {
 
     file.moduleFormatter.exportDeclaration(node, nodes, parent);
   } else {
-    for (var i in node.specifiers) {
+    for (var i = 0; i < node.specifiers.length; i++) {
       file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, parent);
     }
   }

lib/6to5/transformation/transformers/es6-property-method-assignment.js

@@ -1,49 +1,13 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
+var nameMethod = require("../helpers/name-method");
+var util       = require("../../util");
+var t          = require("../../types");
 
 exports.Property = function (node, parent, file, scope) {
   if (!node.method) return;
 
   node.method = false;
 
-  var key = t.toComputedKey(node, node.key);
-  if (!t.isLiteral(key)) return; // we can't set a function id with this
-
-  var id = t.toIdentifier(key.value);
-  key = t.identifier(id);
-
-  var selfReference = false;
-  var outerDeclar = scope.get(id, true);
-
-  traverse(node, {
-    enter: function (node, parent, scope) {
-      // check if this node is an identifier that matches the same as our function id
-      if (!t.isIdentifier(node, { name: id })) return;
-
-      // check if this node is the one referenced
-      if (!t.isReferenced(node, parent)) return;
-
-      // check that we don't have a local variable declared as that removes the need
-      // for the wrapper
-      var localDeclar = scope.get(id, true);
-      if (localDeclar !== outerDeclar) return;
-
-      selfReference = true;
-      this.stop();
-    }
-  }, scope);
-
-  if (selfReference) {
-    node.value = util.template("property-method-assignment-wrapper", {
-      FUNCTION: node.value,
-      FUNCTION_ID: key,
-      FUNCTION_KEY: file.generateUidIdentifier(id, scope),
-      WRAPPER_KEY: file.generateUidIdentifier(id + "Wrapper", scope)
-    });
-  } else {
-    node.value.id = key;
-  }
+  nameMethod(node, file, scope);
 };
 
 exports.ObjectExpression = function (node) {

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

@@ -10,27 +10,42 @@ exports.Function = function (node, parent, file) {
   t.ensureBlock(node);
 
   var argsId = t.identifier("arguments");
+
+  // otherwise `arguments` will be remapped in arrow functions
   argsId._ignoreAliasFunctions = true;
 
   var start = t.literal(node.params.length);
   var key = file.generateUidIdentifier("key");
+  var len = file.generateUidIdentifier("len");
 
   var arrKey = key;
+  var arrLen = len;
   if (node.params.length) {
-    arrKey = t.binaryExpression("-", arrKey, start);
+    // this method has additional params, so we need to subtract
+    // the index of the current argument position from the
+    // position in the array that we want to populate
+    arrKey = t.binaryExpression("-", key, start);
+
+    // we need to work out the size of the array that we're
+    // going to store all the rest parameters in, if there
+    // are less arguments than params then the array can be
+    // constructed with <1 which will cause an error
+    arrLen = t.conditionalExpression(
+      t.binaryExpression(">", len, start),
+      t.binaryExpression("-", len, start),
+      t.literal(0)
+    );
   }
 
   node.body.body.unshift(
-    t.variableDeclaration("var", [
-      t.variableDeclarator(rest, t.arrayExpression([]))
-    ]),
-
     util.template("rest", {
       ARGUMENTS: argsId,
       ARRAY_KEY: arrKey,
+      ARRAY_LEN: arrLen,
       START: start,
       ARRAY: rest,
-      KEY: key
+      KEY: key,
+      LEN: len,
     })
   );
 };

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

@@ -6,7 +6,7 @@ var getSpreadLiteral = function (spread, file) {
 };
 
 var hasSpread = function (nodes) {
-  for (var i in nodes) {
+  for (var i = 0; i < nodes.length; i++) {
     if (t.isSpreadElement(nodes[i])) {
       return true;
     }
@@ -25,7 +25,7 @@ var build = function (props, file) {
     _props = [];
   };
 
-  for (var i in props) {
+  for (var i = 0; i < props.length; i++) {
     var prop = props[i];
     if (t.isSpreadElement(prop)) {
       push();

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

@@ -11,7 +11,7 @@ exports.TaggedTemplateExpression = function (node, parent, file) {
   var strings = [];
   var raw = [];
 
-  for (var i in quasi.quasis) {
+  for (var i = 0; i < quasi.quasis.length; i++) {
     var elem = quasi.quasis[i];
     strings.push(t.literal(elem.value.cooked));
     raw.push(t.literal(elem.value.raw));
@@ -33,7 +33,7 @@ exports.TemplateLiteral = function (node) {
   var nodes = [];
   var i;
 
-  for (i in node.quasis) {
+  for (i = 0; i < node.quasis.length; i++) {
     var elem = node.quasis[i];
 
     nodes.push(t.literal(elem.value.cooked));
@@ -49,7 +49,7 @@ exports.TemplateLiteral = function (node) {
 
     var root = buildBinaryExpression(nodes.shift(), nodes.shift());
 
-    for (i in nodes) {
+    for (i = 0; i < nodes.length; i++) {
       root = buildBinaryExpression(root, nodes[i]);
     }
 

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

@@ -1,6 +1,7 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
+var buildComprehension = require("../helpers/build-comprehension");
+var traverse           = require("../../traverse");
+var util               = require("../../util");
+var t                  = require("../../types");
 
 exports.experimental = true;
 
@@ -22,7 +23,7 @@ var build = function (node, parent, file, scope) {
 
   var returnStatement = body.pop();
 
-  body.push(exports._build(node, function () {
+  body.push(buildComprehension(node, function () {
     return util.template("array-push", {
       STATEMENT: node.body,
       KEY:       uid
@@ -33,28 +34,6 @@ var build = function (node, parent, file, scope) {
   return container;
 };
 
-exports._build = function (node, buildBody) {
-  var self = node.blocks.shift();
-  if (!self) return;
-
-  var child = exports._build(node, buildBody);
-  if (!child) {
-    // last item
-    child = buildBody();
-
-    // add a filter as this is our final stop
-    if (node.filter) {
-      child = t.ifStatement(node.filter, t.blockStatement([child]));
-    }
-  }
-
-  return t.forOfStatement(
-    t.variableDeclaration("let", [t.variableDeclarator(self.left)]),
-    self.right,
-    t.blockStatement([child])
-  );
-};
-
 exports.ComprehensionExpression = function (node, parent, file, scope) {
   if (node.generator) return;
 

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

@@ -1,4 +1,4 @@
-var arrayComprehension = require("./es7-array-comprehension");
+var buildComprehension = require("../helpers/build-comprehension");
 var t                  = require("../../types");
 
 exports.experimental = true;
@@ -10,7 +10,7 @@ exports.ComprehensionExpression = function (node) {
   var container = t.functionExpression(null, [], t.blockStatement(body), true);
   container._aliasFunction = true;
 
-  body.push(arrayComprehension._build(node, function () {
+  body.push(buildComprehension(node, function () {
     return t.expressionStatement(t.yieldExpression(node.body));
   }));
 

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

@@ -8,7 +8,7 @@ exports.ObjectExpression = function (node, parent, file) {
   var hasSpread = false;
   var i;
   var prop;
-  for (i in node.properties) {
+  for (i = 0; i < node.properties.length; i++) {
     prop = node.properties[i];
     if (t.isSpreadProperty(prop)) {
       hasSpread = true;
@@ -26,7 +26,7 @@ exports.ObjectExpression = function (node, parent, file) {
     props = [];
   };
 
-  for (i in node.properties) {
+  for (i = 0; i < node.properties.length; i++) {
     prop = node.properties[i];
     if (t.isSpreadProperty(prop)) {
       push();

lib/6to5/transformation/transformers/optional-async-to-generator.js

@@ -1,4 +1,5 @@
-var bluebirdCoroutines = require("./optional-bluebird-coroutines");
+var remapAsyncToGenerator = require("../helpers/remap-async-to-generator");
+var bluebirdCoroutines    = require("./optional-bluebird-coroutines");
 
 exports.optional = true;
 
@@ -7,5 +8,5 @@ exports.manipulateOptions = bluebirdCoroutines.manipulateOptions;
 exports.Function = function (node, parent, file) {
   if (!node.async || node.generator) return;
 
-  return bluebirdCoroutines._Function(node, file.addHelper("async-to-generator"));
+  return remapAsyncToGenerator(node, file.addHelper("async-to-generator"));
 };

lib/6to5/transformation/transformers/optional-bluebird-coroutines.js

@@ -1,5 +1,5 @@
-var traverse = require("../../traverse");
-var t        = require("../../types");
+var remapAsyncToGenerator = require("../helpers/remap-async-to-generator");
+var t                     = require("../../types");
 
 exports.manipulateOptions = function (opts) {
   opts.experimental = true;
@@ -8,36 +8,12 @@ exports.manipulateOptions = function (opts) {
 
 exports.optional = true;
 
-exports._Function = function (node, callId) {
-  node.async = false;
-  node.generator = true;
-
-  traverse(node, {
-    enter: function (node) {
-      if (t.isFunction(node)) this.skip();
-
-      if (t.isAwaitExpression(node)) {
-        node.type = "YieldExpression";
-      }
-    }
-  });
-
-  var call = t.callExpression(callId, [node]);
-
-  if (t.isFunctionDeclaration(node)) {
-    var declar = t.variableDeclaration("var", [
-      t.variableDeclarator(node.id, call)
-    ]);
-    declar._blockHoist = true;
-    return declar;
-  } else {
-    return call;
-  }
-};
 
 exports.Function = function (node, parent, file) {
   if (!node.async || node.generator) return;
 
-  var id = file.addImport("bluebird");
-  return exports._Function(node, t.memberExpression(id, t.identifier("coroutine")));
+  return remapAsyncToGenerator(
+    node,
+    t.memberExpression(file.addImport("bluebird"), t.identifier("coroutine"))
+  );
 };

lib/6to5/transformation/transformers/optional-proto-to-assign.js

@@ -44,7 +44,7 @@ exports.ExpressionStatement = function (node, parent, file) {
 exports.ObjectExpression = function (node, parent, file) {
   var proto;
 
-  for (var i in node.properties) {
+  for (var i = 0; i < node.properties.length; i++) {
     var prop = node.properties[i];
 
     if (isProtoKey(prop)) {

lib/6to5/transformation/transformers/optional-typeof-symbol.js

@@ -3,7 +3,19 @@ var t = require("../../types");
 exports.optional = true;
 
 exports.UnaryExpression = function (node, parent, file) {
+  this.skip();
+
   if (node.operator === "typeof") {
-    return t.callExpression(file.addHelper("typeof"), [node.argument]);
+    var call = t.callExpression(file.addHelper("typeof"), [node.argument]);
+    if (t.isIdentifier(node.argument)) {
+      var undefLiteral = t.literal("undefined");
+      return t.conditionalExpression(
+        t.binaryExpression("===", t.unaryExpression("typeof", node.argument), undefLiteral),
+        undefLiteral,
+        call
+      );
+    } else {
+      return call;
+    }
   }
 };

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

@@ -6,9 +6,11 @@ var isMemo = function (node) {
   return is;
 };
 
-var getPropRef = function (nodes, prop, file, scope) {
-  if (t.isIdentifier(prop)) {
-    return t.literal(prop.name);
+var getPropRef = function (nodes, member, file, scope) {
+  var prop = member.property;
+  var key = t.toComputedKey(member, member.property);
+  if (t.isLiteral(key)) {
+    return key;
   } else {
     var temp = scope.generateUidBasedOnNode(prop, file);
     nodes.push(t.variableDeclaration("var", [
@@ -54,7 +56,7 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
 
   var left = expr.left;
   var obj  = getObjRef(nodes, left.object, file, scope);
-  var prop = getPropRef(nodes, left.property, file, scope);
+  var prop = getPropRef(nodes, left, file, scope);
 
   nodes.push(t.ifStatement(
     buildHasOwn(obj, prop, file),
@@ -72,7 +74,7 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
 
   var left = node.left;
   var obj  = getObjRef(nodes, left.object, file, scope);
-  var prop = getPropRef(nodes, left.property, file, scope);
+  var prop = getPropRef(nodes, left, file, scope);
 
   nodes.push(t.logicalExpression(
     "&&",

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

@@ -134,19 +134,18 @@ exports.XJSOpeningElement = {
 exports.XJSElement = {
   exit: function (node) {
     var callExpr = node.openingElement;
-    var i;
 
-    for (i in node.children) {
+    for (var i = 0; i < node.children.length; i++) {
       var child = node.children[i];
 
       if (t.isLiteral(child) && _.isString(child.value)) {
         var lines = child.value.split(/\r\n|\n|\r/);
 
-        for (i in lines) {
-          var line = lines[i];
+        for (var i2 = 0; i2 < lines.length; i2++) {
+          var line = lines[i2];
 
-          var isFirstLine = i === "0";
-          var isLastLine = +i === lines.length - 1;
+          var isFirstLine = i2 === 0;
+          var isLastLine = i2 === lines.length - 1;
 
           // replace rendered whitespace tabs with spaces
           var trimmedLine = line.replace(/\t/g, " ");
@@ -209,7 +208,7 @@ var addDisplayName = function (id, call) {
   var props = first.properties;
   var safe = true;
 
-  for (var i in props) {
+  for (var i = 0; i < props.length; i++) {
     prop = props[i];
     if (t.isIdentifier(prop.key, { name: "displayName" })) {
       safe = false;

lib/6to5/transformation/transformers/use-strict.js

@@ -1,26 +1,9 @@
-var t = require("../../types");
-
-exports._has = function (node) {
-  var first = node.body[0];
-  return t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" });
-};
-
-exports._wrap = function (node, callback) {
-  var useStrictNode;
-  if (exports._has(node)) {
-    useStrictNode = node.body.shift();
-  }
-
-  callback();
-
-  if (useStrictNode) {
-    node.body.unshift(useStrictNode);
-  }
-};
+var useStrict = require("../helpers/use-strict");
+var t         = require("../../types");
 
 exports.ast = {
   exit: function (ast) {
-    if (!exports._has(ast.program)) {
+    if (!useStrict.has(ast.program)) {
       ast.program.body.unshift(t.expressionStatement(t.literal("use strict")));
     }
   }

lib/6to5/types/index.js

@@ -7,14 +7,25 @@ t.NATIVE_TYPE_NAMES = ["Array", "Object", "Number", "Boolean", "Date", "Array",
 
 //
 
-var addAssert = function (type, is) {
+/**
+ * Registers `is[Type]` and `assert[Type]` generated functions for a given `type`.
+ * Pass `skipAliasCheck` to force it to directly compare `node.type` with `type`.
+ *
+ * @param {String} type
+ * @param {Boolean?} skipAliasCheck
+ */
+function registerType(type, skipAliasCheck) {
+  var is = t["is" + type] = function (node, opts) {
+    return t.is(type, node, opts, skipAliasCheck);
+  };
+
   t["assert" + type] = function (node, opts) {
     opts = opts || {};
     if (!is(node, opts)) {
       throw new Error("Expected type " + JSON.stringify(type) + " with option " + JSON.stringify(opts));
     }
   };
-};
+}
 
 t.STATEMENT_OR_BLOCK_KEYS = ["consequent", "body"];
 
@@ -22,14 +33,59 @@ t.STATEMENT_OR_BLOCK_KEYS = ["consequent", "body"];
 
 t.VISITOR_KEYS = require("./visitor-keys");
 
-_.each(t.VISITOR_KEYS, function (keys, type) {
-  var is = t["is" + type] = function (node, opts) {
-    return node && node.type === type && t.shallowEqual(node, opts);
-  };
+t.ALIAS_KEYS = require("./alias-keys");
 
-  addAssert(type, is);
+t.FLIPPED_ALIAS_KEYS = {};
+
+_.each(t.VISITOR_KEYS, function (keys, type) {
+  registerType(type, true);
 });
 
+_.each(t.ALIAS_KEYS, function (aliases, type) {
+  _.each(aliases, function (alias) {
+    var types = t.FLIPPED_ALIAS_KEYS[alias] = t.FLIPPED_ALIAS_KEYS[alias] || [];
+    types.push(type);
+  });
+});
+
+_.each(t.FLIPPED_ALIAS_KEYS, function (types, type) {
+  t[type.toUpperCase() + "_TYPES"] = types;
+  registerType(type, false);
+});
+
+/**
+ * Returns whether `node` is of given `type`.
+ * For better performance, use this instead of `is[Type]` when `type` is unknown.
+ * Optionally, pass `skipAliasCheck` to directly compare `node.type` with `type`.
+ *
+ * @param {String} type
+ * @param {Node} node
+ * @param {Object?} opts
+ * @param {Boolean?} skipAliasCheck
+ * @returns {Boolean} isOfType
+ */
+t.is = function (type, node, opts, skipAliasCheck) {
+  if (!node) return;
+
+  var typeMatches = (type === node.type);
+
+  if (!typeMatches && !skipAliasCheck) {
+    var aliases = t.FLIPPED_ALIAS_KEYS[type];
+
+    if (typeof aliases !== 'undefined')
+      typeMatches = aliases.indexOf(node.type) > -1;
+  }
+
+  if (!typeMatches) {
+    return false;
+  }
+
+  if (typeof opts !== 'undefined')
+    return t.shallowEqual(node, opts);
+
+  return true;
+};
+
 //
 
 t.BUILDER_KEYS = _.defaults(require("./builder-keys"), t.VISITOR_KEYS);
@@ -45,29 +101,6 @@ _.each(t.BUILDER_KEYS, function (keys, type) {
   };
 });
 
-//
-
-t.ALIAS_KEYS = require("./alias-keys");
-
-t.FLIPPED_ALIAS_KEYS = {};
-
-_.each(t.ALIAS_KEYS, function (aliases, type) {
-  _.each(aliases, function (alias) {
-    var types = t.FLIPPED_ALIAS_KEYS[alias] = t.FLIPPED_ALIAS_KEYS[alias] || [];
-    types.push(type);
-  });
-});
-
-_.each(t.FLIPPED_ALIAS_KEYS, function (types, type) {
-  t[type.toUpperCase() + "_TYPES"] = types;
-
-  var is = t["is" + type] = function (node, opts) {
-    return node && types.indexOf(node.type) >= 0 && t.shallowEqual(node, opts);
-  };
-
-  addAssert(type, is);
-});
-
 /**
  * Description
  *
@@ -139,17 +172,17 @@ t.toSequenceExpression = function (nodes, scope) {
 //
 
 t.shallowEqual = function (actual, expected) {
-  var same = true;
+  var keys = Object.keys(expected);
+  var key;
 
-  if (expected) {
-    _.each(expected, function (val, key) {
-      if (actual[key] !== val) {
-        return same = false;
-      }
-    });
+  for (var i = 0; i < keys.length; i++) {
+    key = keys[i];
+
+    if (actual[key] !== expected[key])
+      return false;
   }
 
-  return same;
+  return true;
 };
 
 /**
@@ -198,7 +231,11 @@ t.isReferenced = function (node, parent) {
     if (_.contains(parent.params, node)) return false;
 
     // we're a rest parameter
-    if (_.contains(parent.params, node)) return false;
+    if (parent.rest === node) return false;
+  }
+
+  if (t.isMethodDefinition(parent) && parent.key === node && !parent.computed) {
+    return false;
   }
 
   // we're a catch clause param
@@ -403,7 +440,7 @@ t.getIds = function (node, map, ignoreTypes) {
     if (t.isIdentifier(id)) {
       ids[id.name] = id;
     } else if (nodeKeys) {
-      for (i in nodeKeys) {
+      for (i = 0; i < nodeKeys.length; i++) {
         key = nodeKeys[i];
         if (id[key]) {
           search.push(id[key]);
@@ -411,7 +448,7 @@ t.getIds = function (node, map, ignoreTypes) {
         }
       }
     } else if (arrKeys) {
-      for (i in arrKeys) {
+      for (i = 0; i < arrKeys.length; i++) {
         key = arrKeys[i];
         search = search.concat(id[key] || []);
       }

package.json

@@ -1,16 +1,10 @@
 {
   "name": "6to5",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "2.12.2",
+  "version": "2.12.4",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
-  "homepage": "https://github.com/6to5/6to5",
-  "repository": {
-    "type": "git",
-    "url": "https://github.com/6to5/6to5.git"
-  },
-  "bugs": {
-    "url": "https://github.com/6to5/6to5/issues"
-  },
+  "homepage": "https://6to5.org/",
+  "repository": "6to5/6to5",
   "preferGlobal": true,
   "main": "lib/6to5/index.js",
   "bin": {
@@ -39,7 +33,7 @@
     "test": "make test"
   },
   "dependencies": {
-    "acorn-6to5": "0.11.1-14",
+    "acorn-6to5": "0.11.1-16",
     "ast-types": "~0.6.1",
     "chokidar": "0.11.1",
     "commander": "2.5.0",
@@ -50,7 +44,7 @@
     "fs-readdir-recursive": "0.1.0",
     "jshint": "2.5.10",
     "lodash": "2.4.1",
-    "mkdirp": "0.5.0",
+    "output-file-sync": "^1.1.0",
     "private": "0.1.6",
     "regenerator": "0.8.3",
     "regexpu": "0.3.0",

test/bin.js

@@ -1,15 +1,15 @@
 if (process.env.running_under_istanbul) return;
 
-var readdir = require("fs-readdir-recursive");
-var helper  = require("./_helper");
-var assert  = require("assert");
-var rimraf  = require("rimraf");
-var mkdirp  = require("mkdirp");
-var child   = require("child_process");
-var path    = require("path");
-var chai    = require("chai");
-var fs      = require("fs");
-var _       = require("lodash");
+var readdir        = require("fs-readdir-recursive");
+var helper         = require("./_helper");
+var assert         = require("assert");
+var rimraf         = require("rimraf");
+var outputFileSync = require("output-file-sync");
+var child          = require("child_process");
+var path           = require("path");
+var chai           = require("chai");
+var fs             = require("fs");
+var _              = require("lodash");
 
 var fixtureLoc = __dirname + "/fixtures/bin";
 var tmpLoc = __dirname + "/tmp";
@@ -27,10 +27,7 @@ var readDir = function (loc) {
 
 var saveInFiles = function (files) {
   _.each(files, function (content, filename) {
-    var up = path.normalize(filename + "/..");
-    mkdirp.sync(up);
-
-    fs.writeFileSync(filename, content);
+    outputFileSync(filename, content);
   });
 };
 

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

@@ -1,11 +1,6 @@
 "use strict";
 
 var _slice = Array.prototype.slice;
-var _prototypeProperties = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
 var _inherits = function (subClass, superClass) {
   if (typeof superClass !== "function" && superClass !== null) {
     throw new TypeError("Super expression must either be null or a function, not " + typeof superClass);
@@ -37,21 +32,19 @@ var Test = (function (Foo) {
 
   _inherits(Test, Foo);
 
-  Test.prototype.test = function () {
+  Test.prototype.test = function test() {
     var _Foo$prototype$test3, _Foo$prototype$test4;
     Foo.prototype.test.call(this);
     (_Foo$prototype$test3 = Foo.prototype.test).call.apply(_Foo$prototype$test3, [this].concat(_slice.call(arguments)));
     (_Foo$prototype$test4 = Foo.prototype.test).call.apply(_Foo$prototype$test4, [this, "test"].concat(_slice.call(arguments)));
   };
 
-  Test.foo = function () {
+  Test.foo = function foo() {
     var _Foo$foo, _Foo$foo2;
     Foo.foo.call(this);
     (_Foo$foo = Foo.foo).call.apply(_Foo$foo, [this].concat(_slice.call(arguments)));
     (_Foo$foo2 = Foo.foo).call.apply(_Foo$foo2, [this, "test"].concat(_slice.call(arguments)));
   };
 
-  _prototypeProperties(Test, {}, {});
-
   return Test;
 })(Foo);

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

@@ -1,10 +1,5 @@
 "use strict";
 
-var _prototypeProperties = function (child, staticProps, instanceProps) {
-  if (staticProps) Object.defineProperties(child, staticProps);
-  if (instanceProps) Object.defineProperties(child.prototype, instanceProps);
-};
-
 var _inherits = function (subClass, superClass) {
   if (typeof superClass !== "function" && superClass !== null) {
     throw new TypeError("Super expression must either be null or a function, not " + typeof superClass);
@@ -28,11 +23,9 @@ var Test = (function (Foo) {
 
   _inherits(Test, Foo);
 
-  Test.test = function () {
+  Test.test = function test() {
     return Foo.wow.call(this);
   };
 
-  _prototypeProperties(Test, {});
-
   return Test;
 })(Foo);

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

@@ -61,7 +61,7 @@ var Test = (function (Foo) {
 
   _prototypeProperties(Test, {
     foo: {
-      value: function () {
+      value: function foo() {
         var _get4;
         _get(Object.getPrototypeOf(Test), "foo", this).call(this);
         _get(Object.getPrototypeOf(Test), "foo", this).apply(this, arguments);
@@ -73,7 +73,7 @@ var Test = (function (Foo) {
     }
   }, {
     test: {
-      value: function () {
+      value: function test() {
         var _get5;
         _get(Object.getPrototypeOf(Test.prototype), "test", this).call(this);
         _get(Object.getPrototypeOf(Test.prototype), "test", this).apply(this, arguments);

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

@@ -52,7 +52,7 @@ var Test = (function (Foo) {
 
   _prototypeProperties(Test, {
     test: {
-      value: function () {
+      value: function test() {
         return _get(Object.getPrototypeOf(Test), "wow", this).call(this);
       },
       writable: true,

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

@@ -10,7 +10,7 @@ var Test = (function () {
 
   _prototypeProperties(Test, null, {
     test: {
-      value: function () {
+      value: function test() {
         return 5 + 5;
       },
       writable: true,

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

@@ -9,16 +9,16 @@ var BaseView = function BaseView() {
   this.autoRender = true;
 };
 
-var BaseView = function () {
+var BaseView = function BaseView() {
   this.autoRender = true;
 };
 
 var BaseView = (function () {
-  var _class2 = function () {};
+  function BaseView() {}
 
-  _prototypeProperties(_class2, null, {
+  _prototypeProperties(BaseView, null, {
     foo: {
-      value: function () {
+      value: function foo() {
         this.autoRender = true;
       },
       writable: true,
@@ -27,5 +27,5 @@ var BaseView = (function () {
     }
   });
 
-  return _class2;
+  return BaseView;
 })();

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

@@ -10,7 +10,7 @@ var A = (function () {
 
   _prototypeProperties(A, {
     a: {
-      value: function () {},
+      value: function a() {},
       writable: true,
       enumerable: true,
       configurable: true

test/fixtures/transformation/es6-rest-parameters/arrow-functions/expected.js

@@ -1,9 +1,9 @@
 "use strict";
 
 var concat = function () {
-  var arrs = [];
-
-  for (var _key = 0; _key < arguments.length; _key++) {
+  for (var _len = arguments.length,
+      arrs = Array(_len),
+      _key = 0; _key < _len; _key++) {
     arrs[_key] = arguments[_key];
   }
 };

test/fixtures/transformation/es6-rest-parameters/multiple/expected.js

@@ -1,17 +1,17 @@
 "use strict";
 
 var t = function (f) {
-  var items = [];
-
-  for (var _key = 1; _key < arguments.length; _key++) {
+  for (var _len = arguments.length,
+      items = Array(_len > 1 ? _len - 1 : 0),
+      _key = 1; _key < _len; _key++) {
     items[_key - 1] = arguments[_key];
   }
 };
 
 function t(f) {
-  var items = [];
-
-  for (var _key2 = 1; _key2 < arguments.length; _key2++) {
+  for (var _len2 = arguments.length,
+      items = Array(_len2 > 1 ? _len2 - 1 : 0),
+      _key2 = 1; _key2 < _len2; _key2++) {
     items[_key2 - 1] = arguments[_key2];
   }
 }

test/fixtures/transformation/es6-rest-parameters/single/expected.js

@@ -1,17 +1,17 @@
 "use strict";
 
 var t = function () {
-  var items = [];
-
-  for (var _key = 0; _key < arguments.length; _key++) {
+  for (var _len = arguments.length,
+      items = Array(_len),
+      _key = 0; _key < _len; _key++) {
     items[_key] = arguments[_key];
   }
 };
 
 function t() {
-  var items = [];
-
-  for (var _key2 = 0; _key2 < arguments.length; _key2++) {
+  for (var _len2 = arguments.length,
+      items = Array(_len2),
+      _key2 = 0; _key2 < _len2; _key2++) {
     items[_key2] = arguments[_key2];
   }
 }

test/fixtures/transformation/es7-abstract-references/private/expected.js

@@ -16,7 +16,7 @@ var H = (function () {
   var J = new WeakMap(),
       K = new WeakMap();
   var I = new WeakMap();
-  var _class = function () {};
+  function H() {}
 
-  return _class;
+  return H;
 })();

test/fixtures/transformation/optional-typeof-symbol/basic/expected.js

@@ -5,4 +5,4 @@ var _typeof = function (obj) {
 };
 
 var s = Symbol("s");
-assert.equal(_typeof(s), "symbol");
+assert.equal(typeof s === "undefined" ? "undefined" : _typeof(s), "symbol");

test/traceur.js

@@ -14,6 +14,7 @@ require("./_transformation-helper")({
   loc: traceurLoc + "/test/feature",
 
   ignoreSuites: [
+    // these are all internal traceur tests or non-standard features
     "ObjectMixin",
     "Annotations",
     "TestRunner",
@@ -40,10 +41,13 @@ require("./_transformation-helper")({
     "Syntax/UseStrictEscapeSequence",
     "Syntax/UseStrictLineContinuation",
 
-    // the spec for these doesn't define syntax (as far as i could tell)
+    // experimental es7 - the spec hasn't been finalised yet
     // these both fail because of filter between blocks
     "ArrayComprehension/Simple",
-    "GeneratorComprehension/Simple"
+    "GeneratorComprehension/Simple",
+
+    // yield has been added as a keyword in ES6 so this test is actually incorrect
+    "Yield/YieldIdentifier"
   ]
 }, {
   optional: ["typeofSymbol"],