v4.5.2

Test full `make build` on Travis

.jshintignore

@@ -1 +0,0 @@
-src/babel/transformation/templates

.jshintrc

@@ -1,27 +0,0 @@
-{
-  "esnext": true,
-  "indent": 2,
-  "freeze": true,
-  "validthis": true,
-  "camelcase": true,
-  "unused": true,
-  "eqnull": true,
-  "newcap": true,
-  "supernew": true,
-  "noyield": true,
-  "evil": true,
-  "node": true,
-  "boss": true,
-  "expr": true,
-  "undef": true,
-  "maxparams": 5,
-  "maxdepth": 4,
-
-  "globals": {
-    "window": true,
-    "suite": true,
-    "set": true,
-    "before": true,
-    "bench": true
-  }
-}

CHANGELOG.md

@@ -13,6 +13,22 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 See [CHANGELOG - 6to5](CHANGELOG-6to5.md) for the pre-4.0.0 version changelog.
 
+## 4.5.2
+
+ * **New Feature**
+  * `returnUsedHelpers` option and add whitelist to `buildHelpers`.
+ * **Bug Fix**
+  * Fix function arity on self referencing inferred named functions.
+ * **Internal**
+  * Bump `acorn-babel`.
+  * Start converting source to ES6...
+
+## 4.5.1
+
+**Babel now compiles itself!**
+
+![holy shit](http://gifsec.com/wp-content/uploads/GIF/2014/03/OMG-GIF_2.gif)
+
 ## 4.5.0
 
  * **New Feature**

Makefile

@@ -8,7 +8,7 @@ BABEL_CMD = node_modules/babel/bin/babel
 
 export NODE_ENV = test
 
-.PHONY: clean test test-cov test-clean lint test-travis test-simple test-all test-browser publish build bootstrap publish-core publish-runtime build-core watch-core
+.PHONY: clean test test-cov test-clean test-travis test-simple test-all test-browser publish build bootstrap publish-core publish-runtime build-core watch-core
 
 build-core:
 	node $(BABEL_CMD) src --out-dir lib --copy-files
@@ -36,13 +36,10 @@ build:
 clean:
 	rm -rf coverage templates.json test/tmp dist
 
-lint:
-	$(JSHINT_CMD) --reporter node_modules/jshint-stylish/stylish.js src bin
-
 test-clean:
 	rm -rf test/tmp
 
-test: lint
+test:
 	$(MOCHA_CMD)
 	make test-clean
 
@@ -60,7 +57,7 @@ test-cov:
 	export SIMPLE_BABEL_TESTS=1; \
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 
-test-travis: build-core bootstrap
+test-travis: bootstrap build
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 	if test -n "$$CODECLIMATE_REPO_TOKEN"; then codeclimate < coverage/lcov.info; fi
 

README.md

@@ -9,9 +9,7 @@
 </p>
 
 <p align="center">
-  For more information view the <a href="https://babeljs.io/">documentation</a>. For questions
-  and support please visit the <a href="https://gitter.im/babel/babel">gitter room</a> before
-  creating an issue.
+  For questions and support please visit the <a href="https://gitter.im/babel/babel">gitter room</a> before creating an issue.
 </p>
 
 <p align="center">

doc/index.md

@@ -1 +0,0 @@
-See [babel.github.io/docs](https://github.com/babel/babel.github.io/tree/master/docs).

package.json

@@ -1,7 +1,7 @@
 {
   "name": "babel",
   "description": "Turn ES6 code into readable vanilla ES5 with source maps",
-  "version": "4.5.1",
+  "version": "4.5.2",
   "author": "Sebastian McKenzie <sebmck@gmail.com>",
   "homepage": "https://babeljs.io/",
   "repository": "babel/babel",
@@ -36,7 +36,7 @@
     "test": "make test"
   },
   "dependencies": {
-    "acorn-babel": "0.11.1-34",
+    "acorn-babel": "0.11.1-35",
     "ast-types": "~0.6.1",
     "chalk": "^1.0.0",
     "chokidar": "^0.12.6",
@@ -67,13 +67,11 @@
     "trim-right": "^1.0.0"
   },
   "devDependencies": {
-    "babel": "4.5.0",
+    "babel": "4.5.1",
     "browserify": "^8.1.3",
     "chai": "^2.0.0",
     "esvalid": "^1.1.0",
     "istanbul": "^0.3.5",
-    "jshint": "^2.6.0",
-    "jshint-stylish": "^1.0.0",
     "matcha": "^0.6.0",
     "mocha": "^2.1.0",
     "rimraf": "^2.2.8",

packages/babel-runtime/package.json

@@ -1,7 +1,7 @@
 {
   "name": "babel-runtime",
   "description": "babel selfContained runtime",
-  "version": "4.5.0",
+  "version": "4.5.1",
   "repository": "babel/babel",
   "author": "Sebastian McKenzie <sebmck@gmail.com>"
 }

src/babel/api/browser.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var transform = module.exports = require("../transformation");
 
 transform.version = require("../../../package").version;
@@ -7,14 +5,14 @@ transform.version = require("../../../package").version;
 transform.transform = transform;
 
 transform.run = function (code, opts) {
-  opts = opts || {};
+  opts ||= {};
   opts.sourceMap = "inline";
   return new Function(transform(code, opts).code)();
 };
 
 transform.load = function (url, callback, opts, hold) {
-  opts = opts || {};
-  opts.filename = opts.filename || url;
+  opts ||= {};
+  opts.filename ||= url;
 
   var xhr = global.ActiveXObject ? new global.ActiveXObject("Microsoft.XMLHTTP") : new global.XMLHttpRequest();
   xhr.open("GET", url, true);

src/babel/api/node.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var isFunction = require("lodash/lang/isFunction");
 var transform  = require("../transformation");
 var util       = require("../util");
@@ -52,7 +50,7 @@ exports.transformFile = function (filename, opts, callback) {
 };
 
 exports.transformFileSync = function (filename, opts) {
-  opts = opts || {};
+  opts ||= {};
   opts.filename = filename;
   return transform(fs.readFileSync(filename), opts);
 };

src/babel/api/register/browser.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // required to safely use babel/register within a browserify codebase
 
 module.exports = function () {};

src/babel/api/register/cache.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var path = require("path");
 var os   = require("os");
 var fs   = require("fs");

src/babel/api/register/node.js

@@ -1,5 +1,3 @@
-"use strict";
-
 require("../../polyfill");
 
 var sourceMapSupport = require("source-map-support");
@@ -12,7 +10,7 @@ var util             = require("../../util");
 var fs               = require("fs");
 
 sourceMapSupport.install({
-  retrieveSourceMap: function (source) {
+  retrieveSourceMap(source) {
     var map = maps && maps[source];
     if (map) {
       return {
@@ -138,7 +136,7 @@ hookExtensions(util.canCompile.EXTENSIONS);
 
 module.exports = function (opts) {
   // normalize options
-  opts = opts || {};
+  opts ||= {};
 
   if (opts.only != null) onlyRegex = util.regexify(opts.only);
   if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);

src/babel/api/register/resolve-rc.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var merge = require("lodash/object/merge");
 var path  = require("path");
 var fs    = require("fs");
@@ -14,7 +12,7 @@ function exists(filename) {
 
 module.exports = function (loc, opts) {
   var rel = ".babelrc";
-  opts = opts || {};
+  opts ||= {};
 
   function find(start, rel) {
     var file = path.join(start, rel);

src/babel/build-external-helpers.js

@@ -1,11 +1,9 @@
-"use strict";
-
 var buildHelpers = require("./build-helpers");
 var generator    = require("./generation");
 var util         = require("./util");
 var t            = require("./types");
 
-module.exports = function () {
+module.exports = function (whitelist) {
   var namespace = t.identifier("babelHelpers");
 
   var body      = [];
@@ -19,7 +17,7 @@ module.exports = function () {
     )
   ]));
 
-  buildHelpers(body, namespace);
+  buildHelpers(body, namespace, whitelist);
 
   return generator(tree).code;
 };

src/babel/build-helpers.js

@@ -3,9 +3,11 @@ var util = require("./util");
 var each = require("lodash/collection/each");
 var t    = require("./types");
 
-module.exports = function (body, namespace) {
+module.exports = function (body, namespace, whitelist = []) {
   each(File.helpers, function (name) {
     var key = t.identifier(t.toIdentifier(name));
+    if (whitelist.length && whitelist.indexOf(key) >= 0) return;
+
     body.push(t.expressionStatement(
       t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))
     ));

src/babel/detection/index.js

@@ -15,7 +15,7 @@ function detect(ast) {
   };
 
   traverse(ast, {
-    enter: function (node, parent) {
+    enter(node, parent) {
       if (SYNTAX_KEYS[node.type]) {
         detectedSyntax(SYNTAX_KEYS[node.type]);
       }

src/babel/generation/buffer.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = Buffer;
 
 var repeating = require("repeating");
@@ -80,7 +78,7 @@ Buffer.prototype.newline = function (i, removeLast) {
     return;
   }
 
-  removeLast = removeLast || false;
+  removeLast ||= false;
 
   if (isNumber(i)) {
     i = Math.min(2, i);

src/babel/generation/generators/base.js

@@ -1,5 +1,3 @@
-"use strict";
-
 exports.File = function (node, print) {
   print(node.program);
 };

src/babel/generation/generators/classes.js

@@ -1,5 +1,3 @@
-"use strict";
-
 exports.ClassExpression =
 exports.ClassDeclaration = function (node, print) {
   this.push("class");

src/babel/generation/generators/comprehensions.js

@@ -1,5 +1,3 @@
-"use strict";
-
 exports.ComprehensionBlock = function (node, print) {
   this.keyword("for");
   this.push("(");

src/babel/generation/generators/expressions.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var isInteger = require("is-integer");
 var isNumber  = require("lodash/lang/isNumber");
 var t         = require("../../types");

src/babel/generation/generators/flow.js

@@ -1,5 +1,3 @@
-"use strict";
-
 exports.AnyTypeAnnotation =
 exports.ArrayTypeAnnotation =
 exports.BooleanTypeAnnotation =

src/babel/generation/generators/jsx.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t    = require("../../types");
 var each = require("lodash/collection/each");
 

src/babel/generation/generators/methods.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../types");
 
 exports._params = function (node, print) {

src/babel/generation/generators/modules.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t    = require("../../types");
 var each = require("lodash/collection/each");
 

src/babel/generation/generators/playground.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var each = require("lodash/collection/each");
 
 each(["BindMemberExpression", "BindFunctionExpression"], function (type) {

src/babel/generation/generators/statements.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var repeating = require("repeating");
 var t         = require("../../types");
 
@@ -151,7 +149,7 @@ exports.SwitchStatement = function (node, print) {
 
   print.sequence(node.cases, {
     indent: true,
-    addNewlines: function (leading, cas) {
+    addNewlines(leading, cas) {
       if (!leading && node.cases[node.cases.length - 1] === cas) return -1;
     }
   });

src/babel/generation/generators/template-literals.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var each = require("lodash/collection/each");
 
 exports.TaggedTemplateExpression = function (node, print) {

src/babel/generation/generators/types.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var each = require("lodash/collection/each");
 
 exports.Identifier = function (node) {

src/babel/generation/index.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = function (ast, opts, code) {
   var gen = new CodeGenerator(ast, opts, code);
   return gen.generate();
@@ -20,7 +18,7 @@ var n            = require("./node");
 var t            = require("../types");
 
 function CodeGenerator(ast, opts, code) {
-  opts = opts || {};
+  opts ||= {};
 
   this.comments = ast.comments || [];
   this.tokens   = ast.tokens || [];
@@ -110,7 +108,7 @@ CodeGenerator.prototype.buildPrint = function (parent) {
   };
 
   print.sequence = (nodes, opts) => {
-    opts = opts || {};
+    opts ||= {};
     opts.statement = true;
     return this.printJoin(print, nodes, opts);
   };
@@ -120,8 +118,8 @@ CodeGenerator.prototype.buildPrint = function (parent) {
   };
 
   print.list = function (items, opts) {
-    opts = opts || {};
-    opts.separator = opts.separator || ", ";
+    opts ||= {};
+    opts.separator ||= ", ";
     print.join(items, opts);
   };
 
@@ -148,7 +146,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
     this.format.concise = true;
   }
 
-  opts = opts || {};
+  opts ||= {};
 
   var newline = (leading) => {
     if (!opts.statement && !n.isUserWhitespacable(node, parent)) {
@@ -218,7 +216,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
   if (!nodes || !nodes.length) return;
 
-  opts = opts || {};
+  opts ||= {};
 
   var len = nodes.length;
 

src/babel/generation/node/index.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = Node;
 
 var whitespace = require("./whitespace");

src/babel/generation/node/parentheses.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t    = require("../../types");
 var each = require("lodash/collection/each");
 

src/babel/generation/node/whitespace.js

@@ -1,12 +1,10 @@
-"use strict";
-
 var isBoolean = require("lodash/lang/isBoolean");
 var each      = require("lodash/collection/each");
 var map       = require("lodash/collection/map");
 var t         = require("../../types");
 
 var crawl = function (node, state) {
-  state = state || {};
+  state ||= {};
 
   if (t.isMemberExpression(node)) {
     crawl(node.object, state);
@@ -20,7 +18,7 @@ var crawl = function (node, state) {
   } else if (t.isFunction(node)) {
     state.hasFunction = true;
   } else if (t.isIdentifier(node)) {
-    state.hasHelper = state.hasHelper || isHelper(node.callee);
+    state.hasHelper ||= isHelper(node.callee);
   }
 
   return state;
@@ -46,7 +44,7 @@ var isType = function (node) {
 };
 
 exports.nodes = {
-  AssignmentExpression: function (node) {
+  AssignmentExpression(node) {
     var state = crawl(node.right);
     if ((state.hasCall && state.hasHelper) || state.hasFunction) {
       return {
@@ -56,13 +54,13 @@ exports.nodes = {
     }
   },
 
-  SwitchCase: function (node, parent) {
+  SwitchCase(node, parent) {
     return {
       before: node.consequent.length || parent.cases[0] === node
     };
   },
 
-  LogicalExpression: function (node) {
+  LogicalExpression(node) {
     if (t.isFunction(node.left) || t.isFunction(node.right)) {
       return {
         after: true
@@ -70,7 +68,7 @@ exports.nodes = {
     }
   },
 
-  Literal: function (node) {
+  Literal(node) {
     if (node.value === "use strict") {
       return {
         after: true
@@ -78,7 +76,7 @@ exports.nodes = {
     }
   },
 
-  CallExpression: function (node) {
+  CallExpression(node) {
     if (t.isFunction(node.callee) || isHelper(node)) {
       return {
         before: true,
@@ -87,7 +85,7 @@ exports.nodes = {
     }
   },
 
-  VariableDeclaration: function (node) {
+  VariableDeclaration(node) {
     for (var i = 0; i < node.declarations.length; i++) {
       var declar = node.declarations[i];
 
@@ -106,7 +104,7 @@ exports.nodes = {
     }
   },
 
-  IfStatement: function (node) {
+  IfStatement(node) {
     if (t.isBlockStatement(node.consequent)) {
       return {
         before: true,
@@ -126,15 +124,15 @@ exports.nodes.SpreadProperty = function (node, parent) {
 };
 
 exports.list = {
-  VariableDeclaration: function (node) {
+  VariableDeclaration(node) {
     return map(node.declarations, "init");
   },
 
-  ArrayExpression: function (node) {
+  ArrayExpression(node) {
     return node.elements;
   },
 
-  ObjectExpression: function (node) {
+  ObjectExpression(node) {
     return node.properties;
   }
 };

src/babel/generation/position.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = Position;
 
 function Position() {

src/babel/generation/source-map.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = SourceMap;
 
 var sourceMap = require("source-map");

src/babel/generation/whitespace.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = Whitespace;
 
 var sortBy = require("lodash/collection/sortBy");

src/babel/helpers/code-frame.js

@@ -77,7 +77,7 @@ module.exports = function (lines, lineNumber, colNumber) {
     start: start + 1,
     before: "  ",
     after: " | ",
-    transform: function (params) {
+    transform(params) {
       if (params.number !== lineNumber) {
         return;
       }

src/babel/helpers/object.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = function () {
   return Object.create(null);
 };

src/babel/helpers/to-fast-properties.js

@@ -1,5 +1,3 @@
-"use strict";
-
 /**
  * A trick from Bluebird to force V8 to use fast properties for an object.
  * Read more: http://stackoverflow.com/questions/24987896/

src/babel/patch.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var extend = require("lodash/object/extend");
 var t      = require("./types");
 

src/babel/polyfill.js

@@ -1,5 +1,3 @@
-"use strict";
-
 if (global._babelPolyfill) {
   throw new Error("only one instance of babel/polyfill is allowed");
 }

src/babel/transformation/file.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = File;
 
 var sourceMapToComment = require("source-map-to-comment");
@@ -24,12 +22,13 @@ function File(opts) {
   this.dynamicImported          = [];
   this.dynamicImports           = [];
 
-  this.dynamicData      = {};
-  this.data             = {};
+  this.usedHelpers = {};
+  this.dynamicData = {};
+  this.data        = {};
 
-  this.lastStatements   = [];
-  this.opts             = this.normalizeOptions(opts);
-  this.ast              = {};
+  this.lastStatements = [];
+  this.opts           = this.normalizeOptions(opts);
+  this.ast            = {};
 
   this.buildTransformers();
 }
@@ -87,6 +86,7 @@ File.validOptions = [
   "externalHelpers",
   "auxiliaryComment",
   "compact",
+  "returnUsedHelpers",
 
   "resolveModuleSource",
   "moduleId",
@@ -113,6 +113,7 @@ File.prototype.normalizeOptions = function (opts) {
   defaults(opts, {
     keepModuleIdExtensions: false,
     resolveModuleSource:    null,
+    returnUsedHelpers:      false,
     externalHelpers:        false,
     auxilaryComment:        "",
     experimental:           false,
@@ -288,7 +289,7 @@ File.prototype.get = function (key) {
 };
 
 File.prototype.addImport = function (source, name, noDefault) {
-  name = name || source;
+  name ||= source;
   var id = this.dynamicImportIds[name];
 
   if (!id) {
@@ -314,7 +315,7 @@ File.prototype.isConsequenceExpressionStatement = function (node) {
 File.prototype.attachAuxiliaryComment = function (node) {
   var comment = this.opts.auxiliaryComment;
   if (comment) {
-    node.leadingComments = node.leadingComments || [];
+    node.leadingComments ||= [];
     node.leadingComments.push({
       type: "Line",
       value: " " + comment
@@ -333,6 +334,8 @@ File.prototype.addHelper = function (name) {
   var declar = program._declarations && program._declarations[name];
   if (declar) return declar.id;
 
+  this.usedHelpers[name] = true;
+
   var runtime = this.get("helpersNamespace");
   if (runtime) {
     name = t.identifier(t.toIdentifier(name));
@@ -355,7 +358,7 @@ File.prototype.logDeopt = function () {
 };
 
 File.prototype.errorWithNode = function (node, msg, Error) {
-  Error = Error || SyntaxError;
+  Error ||= SyntaxError;
 
   var loc = node.loc.start;
   var err = new Error("Line " + loc.line + ": " + msg);
@@ -417,7 +420,7 @@ File.prototype.call = function (key) {
 };
 
 var checkTransformerVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     checkNode(state.stack, node, scope);
   }
 };
@@ -431,7 +434,7 @@ var checkNode = function (stack, node, scope) {
 
 File.prototype.checkNode = function (node, scope) {
   var stack = this.transformerStack;
-  scope = scope || this.scope;
+  scope ||= this.scope;
 
   checkNode(stack, node, scope);
 
@@ -450,6 +453,10 @@ File.prototype.generate = function () {
     ast: null
   };
 
+  if (this.opts.returnUsedHelpers) {
+    result.usedHelpers = Object.keys(this.usedHelpers);
+  }
+
   if (opts.ast) result.ast = ast;
   if (!opts.code) return result;
 

src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var explode = require("./explode-assignable-expression");
 var t       = require("../../types");
 

src/babel/transformation/helpers/build-comprehension.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../types");
 
 module.exports = function build(node, buildBody) {

src/babel/transformation/helpers/build-conditional-assignment-operator-transformer.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var explode = require("./explode-assignable-expression");
 var t       = require("../../types");
 

src/babel/transformation/helpers/build-react-transformer.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // Based upon the excellent jsx-transpiler by Ingvar Stepanyan (RReverser)
 // https://github.com/RReverser/jsx-transpiler
 
@@ -33,7 +31,7 @@ module.exports = function (exports, opts) {
   };
 
   exports.JSXMemberExpression = {
-    exit: function (node) {
+    exit(node) {
       node.computed = t.isLiteral(node.property);
       node.type = "MemberExpression";
     }
@@ -44,21 +42,21 @@ module.exports = function (exports, opts) {
   };
 
   exports.JSXAttribute = {
-    enter: function (node) {
+    enter(node) {
       var value = node.value;
       if (t.isLiteral(value) && isString(value.value)) {
         value.value = value.value.replace(/\n\s+/g, " ");
       }
     },
 
-    exit: function (node) {
+    exit(node) {
       var value = node.value || t.literal(true);
       return t.inherits(t.property("init", node.name, value), node);
     }
   };
 
   exports.JSXOpeningElement = {
-    exit: function (node, parent, scope, file) {
+    exit(node, parent, scope, file) {
       var tagExpr = node.name;
       var args = [];
 
@@ -146,7 +144,7 @@ module.exports = function (exports, opts) {
   };
 
   exports.JSXElement = {
-    exit: function (node) {
+    exit(node) {
       var callExpr = node.openingElement;
 
       for (var i = 0; i < node.children.length; i++) {

src/babel/transformation/helpers/explode-assignable-expression.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../types");
 
 var getObjRef = function (node, nodes, file, scope) {

src/babel/transformation/helpers/get-function-arity.js

@@ -0,0 +1,9 @@
+var t = require("../../types");
+
+module.exports = function (node) {
+  var lastNonDefault = 0;
+  for (var i = 0; i < node.params.length; i++) {
+    if (!t.isAssignmentPattern(node.params[i])) lastNonDefault = i + 1;
+  }
+  return lastNonDefault;
+};

src/babel/transformation/helpers/name-method.js

@@ -1,10 +1,9 @@
-"use strict";
-
-var util = require("../../util");
-var t    = require("../../types");
+var getFunctionArity = require("./get-function-arity");
+var util             = require("../../util");
+var t                = require("../../types");
 
 var visitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     // check if this node is a referenced identifier that matches the same as our
     // function id
     if (!t.isReferencedIdentifier(node, parent, { name: state.name })) return;
@@ -23,12 +22,21 @@ var wrap = function (state, method, id, scope) {
   if (state.selfReference) {
     var templateName = "property-method-assignment-wrapper";
     if (method.generator) templateName += "-generator";
-    return util.template(templateName, {
+    var template = util.template(templateName, {
       FUNCTION: method,
       FUNCTION_ID: id,
       FUNCTION_KEY: scope.generateUidIdentifier(id.name),
       WRAPPER_KEY: scope.generateUidIdentifier(id.name + "Wrapper")
     });
+
+    // shim in dummy params to retain function arity, if you try to read the
+    // source then you'll get the original since it's proxied so it's all good
+    var params = template.callee.body.body[0].declarations[0].init.params;
+    for (var i = 0, len = getFunctionArity(method); i < len; i++) {
+      params.push(scope.generateUidIdentifier("x"));
+    }
+
+    return template;
   } else {
     method.id = id;
     return method;
@@ -99,7 +107,7 @@ exports.bare = function (node, parent, scope) {
 
   var id;
   if (t.isProperty(parent) && parent.kind === "init" && !parent.computed) {
-    // { foo: function () {} };
+    // { foo() {} };
     id = parent.key;
   } else if (t.isVariableDeclarator(parent)) {
     // var foo = function () {};

src/babel/transformation/helpers/remap-async-to-generator.js

@@ -1,9 +1,7 @@
-"use strict";
-
 var t = require("../../types");
 
 var visitor = {
-  enter: function (node) {
+  enter(node) {
     if (t.isFunction(node)) this.skip();
 
     if (t.isAwaitExpression(node)) {

src/babel/transformation/helpers/replace-supers.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = ReplaceSupers;
 
 var messages = require("../../messages");
@@ -96,7 +94,7 @@ ReplaceSupers.prototype.replace = function () {
 };
 
 var visitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     var topLevel = state.topLevel;
     var self = state.self;
 

src/babel/transformation/helpers/use-strict.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../types");
 
 exports.has = function (node) {

src/babel/transformation/index.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = transform;
 
 var normalizeAst = require("../helpers/normalize-ast");
@@ -60,7 +58,7 @@ var rawTransformers = require("./transformers");
 each(rawTransformers, function (transformer, key) {
   var namespace = key.split(".")[0];
 
-  transform.namespaces[namespace] = transform.namespaces[namespace] || [];
+  transform.namespaces[namespace] ||= [];
   transform.namespaces[namespace].push(key);
   transform.transformerNamespaces[key] = namespace;
 

src/babel/transformation/modules/_default.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = DefaultFormatter;
 
 var messages = require("../../messages");
@@ -35,12 +33,12 @@ DefaultFormatter.prototype.doDefaultExportInterop = function (node) {
 DefaultFormatter.prototype.bumpImportOccurences = function (node) {
   var source = node.source.value;
   var occurs = this.localImportOccurences;
-  occurs[source] = occurs[source] || 0;
+  occurs[source] ||= 0;
   occurs[source] += node.specifiers.length;
 };
 
 var exportsVisitor = {
-  enter: function (node, parent, scope, formatter) {
+  enter(node, parent, scope, formatter) {
     var declar = node && node.declaration;
     if (t.isExportDeclaration(node)) {
       formatter.hasLocalImports = true;
@@ -65,7 +63,7 @@ DefaultFormatter.prototype.getLocalExports = function () {
 };
 
 var importsVisitor = {
-  enter: function (node, parent, scope, formatter) {
+  enter(node, parent, scope, formatter) {
     if (t.isImportDeclaration(node)) {
       formatter.hasLocalImports = true;
       extend(formatter.localImports, t.getBindingIdentifiers(node));
@@ -79,7 +77,7 @@ DefaultFormatter.prototype.getLocalImports = function () {
 };
 
 var remapVisitor = {
-  enter: function (node, parent, scope, formatter) {
+  enter(node, parent, scope, formatter) {
     if (t.isUpdateExpression(node) && formatter.isLocalReference(node.argument, scope)) {
       this.skip();
 

src/babel/transformation/modules/_strict.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var util = require("../../util");
 
 module.exports = function (Parent) {

src/babel/transformation/modules/amd-strict.js

@@ -1,3 +1 @@
-"use strict";
-
 module.exports = require("./_strict")(require("./amd"));

src/babel/transformation/modules/amd.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = AMDFormatter;
 
 var DefaultFormatter = require("./_default");

src/babel/transformation/modules/common-strict.js

@@ -1,3 +1 @@
-"use strict";
-
 module.exports = require("./_strict")(require("./common"));

src/babel/transformation/modules/common.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = CommonJSFormatter;
 
 var DefaultFormatter = require("./_default");

src/babel/transformation/modules/ignore.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = IgnoreFormatter;
 
 var t = require("../../types");

src/babel/transformation/modules/system.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = SystemFormatter;
 
 var DefaultFormatter = require("./_default");
@@ -68,7 +66,7 @@ SystemFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
 };
 
 var runnerSettersVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (node._importSource === state.source) {
       if (t.isVariableDeclaration(node)) {
         each(node.declarations, function (declar) {
@@ -103,7 +101,7 @@ SystemFormatter.prototype.buildRunnerSetters = function (block, hoistDeclarators
 };
 
 var hoistVariablesVisitor = {
-  enter: function (node, parent, scope, hoistDeclarators) {
+  enter(node, parent, scope, hoistDeclarators) {
     if (t.isFunction(node)) {
       // nothing inside is accessible
       return this.skip();
@@ -148,7 +146,7 @@ var hoistVariablesVisitor = {
 };
 
 var hoistFunctionsVisitor = {
-  enter: function (node, parent, scope, handlerBody) {
+  enter(node, parent, scope, handlerBody) {
     if (t.isFunction(node)) this.skip();
 
     if (t.isFunctionDeclaration(node) || node._blockHoist) {

src/babel/transformation/modules/umd-strict.js

@@ -1,3 +1 @@
-"use strict";
-
 module.exports = require("./_strict")(require("./umd"));

src/babel/transformation/modules/umd.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = UMDFormatter;
 
 var AMDFormatter = require("./amd");

src/babel/transformation/transformer.js

@@ -1,5 +1,3 @@
-"use strict";
-
 module.exports = Transformer;
 
 var TransformerPass = require("./transformer-pass");
@@ -35,7 +33,7 @@ function Transformer(key, transformer, opts) {
   this.optional     = !!take("optional");
 
   this.handlers = this.normalize(transformer);
-  this.opts     = opts || {};
+  this.opts     ||= {};
   this.key      = key;
 }
 

src/babel/transformation/transformers/es3/member-expression-literals.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.MemberExpression = function (node) {

src/babel/transformation/transformers/es3/property-literals.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.Property = function (node) {

src/babel/transformation/transformers/es5/properties.mutators.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var defineMap = require("../../helpers/define-map");
 var t         = require("../../../types");
 

src/babel/transformation/transformers/es6/arrow-functions.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.check = t.isArrowFunctionExpression;

src/babel/transformation/transformers/es6/block-scoping-tdz.js

@@ -1,9 +1,7 @@
-"use strict";
-
 var t = require("../../../types");
 
 var visitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (!t.isReferencedIdentifier(node, parent)) return;
 
     var declared = state.letRefs[node.name];

src/babel/transformation/transformers/es6/block-scoping.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var traverse = require("../../../traversal");
 var object   = require("../../../helpers/object");
 var util     = require("../../../util");
@@ -20,7 +18,7 @@ var isLet = function (node, parent) {
   if (isLetInitable(node, parent)) {
     for (var i = 0; i < node.declarations.length; i++) {
       var declar = node.declarations[i];
-      declar.init = declar.init || t.identifier("undefined");
+      declar.init ||= t.identifier("undefined");
     }
   }
 
@@ -83,53 +81,6 @@ exports.BlockStatement = function (block, parent, scope, file) {
   }
 };
 
-/**
- * Description
- *
- * @param {Boolean|Node} loopParent
- * @param {Node} block
- * @param {Node} parent
- * @param {Scope} scope
- * @param {File} file
- */
-
-function BlockScoping(loopParent, block, parent, scope, file) {
-  this.loopParent = loopParent;
-  this.parent     = parent;
-  this.scope      = scope;
-  this.block      = block;
-  this.file       = file;
-
-  this.outsideLetReferences = object();
-  this.hasLetReferences     = false;
-  this.letReferences        = block._letReferences = object();
-  this.body                 = [];
-}
-
-/**
- * Start the ball rolling.
- */
-
-BlockScoping.prototype.run = function () {
-  var block = this.block;
-  if (block._letDone) return;
-  block._letDone = true;
-
-  var needsClosure = this.getLetReferences();
-
-  // this is a block within a `Function/Program` so we can safely leave it be
-  if (t.isFunction(this.parent) || t.isProgram(this.block)) return;
-
-  // we can skip everything
-  if (!this.hasLetReferences) return;
-
-  if (needsClosure) {
-    this.wrapClosure();
-  } else {
-    this.remap();
-  }
-};
-
 function replace(node, parent, scope, remaps) {
   if (!t.isReferencedIdentifier(node, parent)) return;
 
@@ -155,118 +106,17 @@ function traverseReplace(node, parent, scope, remaps) {
   scope.traverse(node, replaceVisitor, remaps);
 }
 
-/**
- * Description
- */
-
-BlockScoping.prototype.remap = function () {
-  var hasRemaps = false;
-  var letRefs   = this.letReferences;
-  var scope     = this.scope;
-
-  // alright, so since we aren't wrapping this block in a closure
-  // we have to check if any of our let variables collide with
-  // those in upper scopes and then if they do, generate a uid
-  // for them and replace all references with it
-  var remaps = object();
-
-  for (var key in letRefs) {
-    // just an Identifier node we collected in `getLetReferences`
-    // this is the defining identifier of a declaration
-    var ref = letRefs[key];
-
-    if (scope.parentHasBinding(key) || scope.hasGlobal(key)) {
-      var uid = scope.generateUidIdentifier(ref.name).name;
-      ref.name = uid;
-
-      hasRemaps = true;
-      remaps[key] = remaps[uid] = {
-        binding: ref,
-        uid: uid
-      };
+var letReferenceBlockVisitor = {
+  enter(node, parent, scope, state) {
+    if (t.isFunction(node)) {
+      scope.traverse(node, letReferenceFunctionVisitor, state);
+      return this.skip();
     }
   }
-
-  if (!hasRemaps) return;
-
-  //
-
-  var loopParent = this.loopParent;
-  if (loopParent) {
-    traverseReplace(loopParent.right, loopParent, scope, remaps);
-    traverseReplace(loopParent.test, loopParent, scope, remaps);
-    traverseReplace(loopParent.update, loopParent, scope, remaps);
-  }
-
-  scope.traverse(this.block, replaceVisitor, remaps);
-};
-
-/**
- * Description
- */
-
-BlockScoping.prototype.wrapClosure = function () {
-  var block = this.block;
-
-  var outsideRefs = this.outsideLetReferences;
-
-  // remap loop heads with colliding variables
-  if (this.loopParent) {
-    for (var name in outsideRefs) {
-      var id = outsideRefs[name];
-
-      if (this.scope.hasGlobal(id.name)) {
-        delete outsideRefs[id.name];
-        delete this.letReferences[id.name];
-
-        this.scope.rename(id.name);
-
-        this.letReferences[id.name] = id;
-        outsideRefs[id.name] = id;
-      }
-    }
-  }
-
-  // if we're inside of a for loop then we search to see if there are any
-  // `break`s, `continue`s, `return`s etc
-  this.has = this.checkLoop();
-
-  // hoist var references to retain scope
-  this.hoistVarDeclarations();
-
-  // turn outsideLetReferences into an array
-  var params = values(outsideRefs);
-
-  // build the closure that we're going to wrap the block with
-  var fn = t.functionExpression(null, params, t.blockStatement(block.body));
-  fn._aliasFunction = true;
-
-  // replace the current block body with the one we're going to build
-  block.body = this.body;
-
-  // build a call and a unique id that we can assign the return value to
-  var call = t.callExpression(fn, params);
-  var ret  = this.scope.generateUidIdentifier("ret");
-
-  // handle generators
-  var hasYield = traverse.hasType(fn.body, this.scope, "YieldExpression", t.FUNCTION_TYPES);
-  if (hasYield) {
-    fn.generator = true;
-    call = t.yieldExpression(call, true);
-  }
-
-  // handlers async functions
-  var hasAsync = traverse.hasType(fn.body, this.scope, "AwaitExpression", t.FUNCTION_TYPES);
-  if (hasAsync) {
-    fn.async = true;
-    call = t.awaitExpression(call, true);
-  }
-
-  this.build(ret, call);
 };
 
 var letReferenceFunctionVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     // not a direct reference
     if (!t.isReferencedIdentifier(node, parent)) return;
 
@@ -281,65 +131,30 @@ var letReferenceFunctionVisitor = {
   }
 };
 
-var letReferenceBlockVisitor = {
-  enter: function (node, parent, scope, state) {
-    if (t.isFunction(node)) {
-      scope.traverse(node, letReferenceFunctionVisitor, state);
+var hoistVarDeclarationsVisitor = {
+  enter(node, parent, scope, self) {
+    if (t.isForStatement(node)) {
+      if (isVar(node.init, node)) {
+        node.init = t.sequenceExpression(self.pushDeclar(node.init));
+      }
+    } else if (t.isFor(node)) {
+      if (isVar(node.left, node)) {
+        node.left = node.left.declarations[0].id;
+      }
+    } else if (isVar(node, parent)) {
+      return self.pushDeclar(node).map(t.expressionStatement);
+    } else if (t.isFunction(node)) {
       return this.skip();
     }
   }
 };
 
-/**
- * Description
- */
-
-BlockScoping.prototype.getLetReferences = function () {
-  var block = this.block;
-
-  var declarators = block._letDeclarators || [];
-  var declar;
-
-  //
-  for (var i = 0; i < declarators.length; i++) {
-    declar = declarators[i];
-    extend(this.outsideLetReferences, t.getBindingIdentifiers(declar));
-  }
-
-  //
-  if (block.body) {
-    for (i = 0; i < block.body.length; i++) {
-      declar = block.body[i];
-      if (isLet(declar, block)) {
-        declarators = declarators.concat(declar.declarations);
-      }
+var loopLabelVisitor = {
+  enter(node, parent, scope, state) {
+    if (t.isLabeledStatement(node)) {
+      state.innerLabels.push(node.label.name);
     }
   }
-
-  //
-  for (i = 0; i < declarators.length; i++) {
-    declar = declarators[i];
-    var keys = t.getBindingIdentifiers(declar);
-    extend(this.letReferences, keys);
-    this.hasLetReferences = true;
-  }
-
-  // no let references so we can just quit
-  if (!this.hasLetReferences) return;
-
-  // set let references to plain var references
-  standardizeLets(declarators);
-
-  var state = {
-    letReferences: this.letReferences,
-    closurify:     false
-  };
-
-  // traverse through this block, stopping on functions and checking if they
-  // contain any local let references
-  this.scope.traverse(this.block, letReferenceBlockVisitor, state);
-
-  return state.closurify;
 };
 
 var loopNodeTo = function (node) {
@@ -351,7 +166,7 @@ var loopNodeTo = function (node) {
 };
 
 var loopVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     var replace;
 
     if (t.isLoop(node)) {
@@ -402,160 +217,346 @@ var loopVisitor = {
   }
 };
 
-var loopLabelVisitor = {
-  enter: function (node, parent, scope, state) {
-    if (t.isLabeledStatement(node)) {
-      state.innerLabels.push(node.label.name);
-    }
-  }
-};
+class BlockScoping {
 
-/**
- * If we're inside of a loop then traverse it and check if it has one of
- * the following node types `ReturnStatement`, `BreakStatement`,
- * `ContinueStatement` and replace it with a return value that we can track
- * later on.
- *
- * @returns {Object}
- */
+  /**
+   * Description
+   *
+   * @param {Boolean|Node} loopParent
+   * @param {Node} block
+   * @param {Node} parent
+   * @param {Scope} scope
+   * @param {File} file
+   */
 
-BlockScoping.prototype.checkLoop = function () {
-  var state = {
-    hasBreakContinue: false,
-    ignoreLabeless:   false,
-    innerLabels:      [],
-    hasReturn:        false,
-    isLoop:           !!this.loopParent,
-    map:              {}
-  };
+  constructor(loopParent, block, parent, scope, file) {
+    this.loopParent = loopParent;
+    this.parent     = parent;
+    this.scope      = scope;
+    this.block      = block;
+    this.file       = file;
 
-  this.scope.traverse(this.block, loopLabelVisitor, state);
-  this.scope.traverse(this.block, loopVisitor, state);
-
-  return state;
-};
-
-var hoistVarDeclarationsVisitor = {
-  enter: function (node, parent, scope, self) {
-    if (t.isForStatement(node)) {
-      if (isVar(node.init, node)) {
-        node.init = t.sequenceExpression(self.pushDeclar(node.init));
-      }
-    } else if (t.isFor(node)) {
-      if (isVar(node.left, node)) {
-        node.left = node.left.declarations[0].id;
-      }
-    } else if (isVar(node, parent)) {
-      return self.pushDeclar(node).map(t.expressionStatement);
-    } else if (t.isFunction(node)) {
-      return this.skip();
-    }
-  }
-};
-
-/**
- * Hoist all var declarations in this block to before it so they retain scope
- * once we wrap everything in a closure.
- */
-
-BlockScoping.prototype.hoistVarDeclarations = function () {
-  traverse(this.block, hoistVarDeclarationsVisitor, this.scope, this);
-};
-
-/**
- * Turn a `VariableDeclaration` into an array of `AssignmentExpressions` with
- * their declarations hoisted to before the closure wrapper.
- *
- * @param {Node} node VariableDeclaration
- * @returns {Array}
- */
-
-BlockScoping.prototype.pushDeclar = function (node) {
-  this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
-    return t.variableDeclarator(declar.id);
-  })));
-
-  var replace = [];
-
-  for (var i = 0; i < node.declarations.length; i++) {
-    var declar = node.declarations[i];
-    if (!declar.init) continue;
-
-    var expr = t.assignmentExpression("=", declar.id, declar.init);
-    replace.push(t.inherits(expr, declar));
+    this.outsideLetReferences = object();
+    this.hasLetReferences     = false;
+    this.letReferences        = block._letReferences = object();
+    this.body                 = [];
   }
 
-  return replace;
-};
+  /**
+   * Start the ball rolling.
+   */
 
-/**
- * Push the closure to the body.
- *
- * @param {Node} ret Identifier
- * @param {Node} call CallExpression
- */
+  run() {
+    var block = this.block;
+    if (block._letDone) return;
+    block._letDone = true;
 
-BlockScoping.prototype.build = function (ret, call) {
-  var has = this.has;
-  if (has.hasReturn || has.hasBreakContinue) {
-    this.buildHas(ret, call);
-  } else {
-    this.body.push(t.expressionStatement(call));
-  }
-};
+    var needsClosure = this.getLetReferences();
 
-/**
- * Description
- *
- * @param {Node} ret Identifier
- * @param {Node} call CallExpression
- */
+    // this is a block within a `Function/Program` so we can safely leave it be
+    if (t.isFunction(this.parent) || t.isProgram(this.block)) return;
 
-BlockScoping.prototype.buildHas = function (ret, call) {
-  var body = this.body;
+    // we can skip everything
+    if (!this.hasLetReferences) return;
 
-  body.push(t.variableDeclaration("var", [
-    t.variableDeclarator(ret, call)
-  ]));
-
-  var loopParent = this.loopParent;
-  var retCheck;
-  var has = this.has;
-  var cases = [];
-
-  if (has.hasReturn) {
-    // typeof ret === "object"
-    retCheck = util.template("let-scoping-return", {
-      RETURN: ret
-    });
-  }
-
-  if (has.hasBreakContinue) {
-    if (!loopParent) {
-      throw new Error("Has no loop parent but we're trying to reassign breaks " +
-                      "and continues, something is going wrong here.");
-    }
-
-    for (var key in has.map) {
-      cases.push(t.switchCase(t.literal(key), [has.map[key]]));
-    }
-
-    if (has.hasReturn) {
-      cases.push(t.switchCase(null, [retCheck]));
-    }
-
-    if (cases.length === 1) {
-      var single = cases[0];
-      body.push(this.file.attachAuxiliaryComment(t.ifStatement(
-        t.binaryExpression("===", ret, single.test),
-        single.consequent[0]
-      )));
+    if (needsClosure) {
+      this.wrapClosure();
     } else {
-      body.push(this.file.attachAuxiliaryComment(t.switchStatement(ret, cases)));
-    }
-  } else {
-    if (has.hasReturn) {
-      body.push(this.file.attachAuxiliaryComment(retCheck));
+      this.remap();
     }
   }
-};
+
+  /**
+   * Description
+   */
+
+  remap() {
+    var hasRemaps = false;
+    var letRefs   = this.letReferences;
+    var scope     = this.scope;
+
+    // alright, so since we aren't wrapping this block in a closure
+    // we have to check if any of our let variables collide with
+    // those in upper scopes and then if they do, generate a uid
+    // for them and replace all references with it
+    var remaps = object();
+
+    for (var key in letRefs) {
+      // just an Identifier node we collected in `getLetReferences`
+      // this is the defining identifier of a declaration
+      var ref = letRefs[key];
+
+      if (scope.parentHasBinding(key) || scope.hasGlobal(key)) {
+        var uid = scope.generateUidIdentifier(ref.name).name;
+        ref.name = uid;
+
+        hasRemaps = true;
+        remaps[key] = remaps[uid] = {
+          binding: ref,
+          uid: uid
+        };
+      }
+    }
+
+    if (!hasRemaps) return;
+
+    //
+
+    var loopParent = this.loopParent;
+    if (loopParent) {
+      traverseReplace(loopParent.right, loopParent, scope, remaps);
+      traverseReplace(loopParent.test, loopParent, scope, remaps);
+      traverseReplace(loopParent.update, loopParent, scope, remaps);
+    }
+
+    scope.traverse(this.block, replaceVisitor, remaps);
+  }
+
+  /**
+   * Description
+   */
+
+  wrapClosure() {
+    var block = this.block;
+
+    var outsideRefs = this.outsideLetReferences;
+
+    // remap loop heads with colliding variables
+    if (this.loopParent) {
+      for (var name in outsideRefs) {
+        var id = outsideRefs[name];
+
+        if (this.scope.hasGlobal(id.name)) {
+          delete outsideRefs[id.name];
+          delete this.letReferences[id.name];
+
+          this.scope.rename(id.name);
+
+          this.letReferences[id.name] = id;
+          outsideRefs[id.name] = id;
+        }
+      }
+    }
+
+    // if we're inside of a for loop then we search to see if there are any
+    // `break`s, `continue`s, `return`s etc
+    this.has = this.checkLoop();
+
+    // hoist var references to retain scope
+    this.hoistVarDeclarations();
+
+    // turn outsideLetReferences into an array
+    var params = values(outsideRefs);
+
+    // build the closure that we're going to wrap the block with
+    var fn = t.functionExpression(null, params, t.blockStatement(block.body));
+    fn._aliasFunction = true;
+
+    // replace the current block body with the one we're going to build
+    block.body = this.body;
+
+    // build a call and a unique id that we can assign the return value to
+    var call = t.callExpression(fn, params);
+    var ret  = this.scope.generateUidIdentifier("ret");
+
+    // handle generators
+    var hasYield = traverse.hasType(fn.body, this.scope, "YieldExpression", t.FUNCTION_TYPES);
+    if (hasYield) {
+      fn.generator = true;
+      call = t.yieldExpression(call, true);
+    }
+
+    // handlers async functions
+    var hasAsync = traverse.hasType(fn.body, this.scope, "AwaitExpression", t.FUNCTION_TYPES);
+    if (hasAsync) {
+      fn.async = true;
+      call = t.awaitExpression(call, true);
+    }
+
+    this.build(ret, call);
+  }
+
+  /**
+   * Description
+   */
+
+  getLetReferences() {
+    var block = this.block;
+
+    var declarators = block._letDeclarators || [];
+    var declar;
+
+    //
+    for (var i = 0; i < declarators.length; i++) {
+      declar = declarators[i];
+      extend(this.outsideLetReferences, t.getBindingIdentifiers(declar));
+    }
+
+    //
+    if (block.body) {
+      for (i = 0; i < block.body.length; i++) {
+        declar = block.body[i];
+        if (isLet(declar, block)) {
+          declarators = declarators.concat(declar.declarations);
+        }
+      }
+    }
+
+    //
+    for (i = 0; i < declarators.length; i++) {
+      declar = declarators[i];
+      var keys = t.getBindingIdentifiers(declar);
+      extend(this.letReferences, keys);
+      this.hasLetReferences = true;
+    }
+
+    // no let references so we can just quit
+    if (!this.hasLetReferences) return;
+
+    // set let references to plain var references
+    standardizeLets(declarators);
+
+    var state = {
+      letReferences: this.letReferences,
+      closurify:     false
+    };
+
+    // traverse through this block, stopping on functions and checking if they
+    // contain any local let references
+    this.scope.traverse(this.block, letReferenceBlockVisitor, state);
+
+    return state.closurify;
+  }
+
+  /**
+   * If we're inside of a loop then traverse it and check if it has one of
+   * the following node types `ReturnStatement`, `BreakStatement`,
+   * `ContinueStatement` and replace it with a return value that we can track
+   * later on.
+   *
+   * @returns {Object}
+   */
+
+  checkLoop() {
+    var state = {
+      hasBreakContinue: false,
+      ignoreLabeless:   false,
+      innerLabels:      [],
+      hasReturn:        false,
+      isLoop:           !!this.loopParent,
+      map:              {}
+    };
+
+    this.scope.traverse(this.block, loopLabelVisitor, state);
+    this.scope.traverse(this.block, loopVisitor, state);
+
+    return state;
+  }
+
+  /**
+   * Hoist all var declarations in this block to before it so they retain scope
+   * once we wrap everything in a closure.
+   */
+
+  hoistVarDeclarations() {
+    traverse(this.block, hoistVarDeclarationsVisitor, this.scope, this);
+  }
+
+  /**
+   * Turn a `VariableDeclaration` into an array of `AssignmentExpressions` with
+   * their declarations hoisted to before the closure wrapper.
+   *
+   * @param {Node} node VariableDeclaration
+   * @returns {Array}
+   */
+
+  pushDeclar(node) {
+    this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
+      return t.variableDeclarator(declar.id);
+    })));
+
+    var replace = [];
+
+    for (var i = 0; i < node.declarations.length; i++) {
+      var declar = node.declarations[i];
+      if (!declar.init) continue;
+
+      var expr = t.assignmentExpression("=", declar.id, declar.init);
+      replace.push(t.inherits(expr, declar));
+    }
+
+    return replace;
+  }
+
+  /**
+   * Push the closure to the body.
+   *
+   * @param {Node} ret Identifier
+   * @param {Node} call CallExpression
+   */
+
+  build(ret, call) {
+    var has = this.has;
+    if (has.hasReturn || has.hasBreakContinue) {
+      this.buildHas(ret, call);
+    } else {
+      this.body.push(t.expressionStatement(call));
+    }
+  }
+
+  /**
+   * Description
+   *
+   * @param {Node} ret Identifier
+   * @param {Node} call CallExpression
+   */
+
+  buildHas(ret, call) {
+    var body = this.body;
+
+    body.push(t.variableDeclaration("var", [
+      t.variableDeclarator(ret, call)
+    ]));
+
+    var loopParent = this.loopParent;
+    var retCheck;
+    var has = this.has;
+    var cases = [];
+
+    if (has.hasReturn) {
+      // typeof ret === "object"
+      retCheck = util.template("let-scoping-return", {
+        RETURN: ret
+      });
+    }
+
+    if (has.hasBreakContinue) {
+      if (!loopParent) {
+        throw new Error("Has no loop parent but we're trying to reassign breaks " +
+                        "and continues, something is going wrong here.");
+      }
+
+      for (var key in has.map) {
+        cases.push(t.switchCase(t.literal(key), [has.map[key]]));
+      }
+
+      if (has.hasReturn) {
+        cases.push(t.switchCase(null, [retCheck]));
+      }
+
+      if (cases.length === 1) {
+        var single = cases[0];
+        body.push(this.file.attachAuxiliaryComment(t.ifStatement(
+          t.binaryExpression("===", ret, single.test),
+          single.consequent[0]
+        )));
+      } else {
+        body.push(this.file.attachAuxiliaryComment(t.switchStatement(ret, cases)));
+      }
+    } else {
+      if (has.hasReturn) {
+        body.push(this.file.attachAuxiliaryComment(retCheck));
+      }
+    }
+  }
+}

src/babel/transformation/transformers/es6/classes.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var ReplaceSupers = require("../../helpers/replace-supers");
 var nameMethod    = require("../../helpers/name-method");
 var defineMap     = require("../../helpers/define-map");
@@ -29,277 +27,280 @@ exports.ClassExpression = function (node, parent, scope, file) {
   return new ClassTransformer(node, file, scope, false).run();
 };
 
-/**
- * Description
- *
- * @param {Node} node
- * @param {File} file
- * @param {Scope} scope
- * @param {Boolean} isStatement
- */
+class ClassTransformer {
 
-function ClassTransformer(node, file, scope, isStatement) {
-  this.isStatement = isStatement;
-  this.scope       = scope;
-  this.node        = node;
-  this.file        = file;
+  /**
+   * Description
+   *
+   * @param {Node} node
+   * @param {File} file
+   * @param {Scope} scope
+   * @param {Boolean} isStatement
+   */
 
-  this.hasInstanceMutators = false;
-  this.hasStaticMutators   = false;
+  constructor(node, file, scope, isStatement) {
+    this.isStatement = isStatement;
+    this.scope       = scope;
+    this.node        = node;
+    this.file        = file;
 
-  this.instanceMutatorMap = {};
-  this.staticMutatorMap   = {};
-  this.hasConstructor     = false;
-  this.className          = node.id || scope.generateUidIdentifier("class");
-  this.superName          = node.superClass || t.identifier("Function");
-  this.hasSuper           = !!node.superClass;
-  this.isLoose            = file.isLoose("es6.classes");
-}
+    this.hasInstanceMutators = false;
+    this.hasStaticMutators   = false;
 
-/**
- * Description
- *
- * @returns {Array}
- */
-
-ClassTransformer.prototype.run = function () {
-  var superName = this.superName;
-  var className = this.className;
-  var classBody = this.node.body.body;
-  var file      = this.file;
-
-  //
-
-  var body = this.body = [];
-
-  var constructorBody = t.blockStatement([
-    t.expressionStatement(t.callExpression(file.addHelper("class-call-check"), [
-      t.thisExpression(),
-      className
-    ]))
-  ]);
-
-  var constructor;
-  if (this.node.id) {
-    constructor = t.functionDeclaration(className, [], constructorBody);
-    body.push(constructor);
-  } else {
-    var constructorName = null;
-    // when a class has no parent and there is only a constructor or no body
-    // then the constructor is not wrapped in a closure and needs to be named
-    var containsOnlyConstructor = classBody.length === 1 && classBody[0].key.name === "constructor";
-    if (!this.hasSuper && (classBody.length === 0 || containsOnlyConstructor)) {
-      constructorName = className;
-    }
-
-    constructor = t.functionExpression(constructorName, [], constructorBody);
-    body.push(t.variableDeclaration("var", [
-      t.variableDeclarator(className, constructor)
-    ]));
-  }
-  this.constructor = constructor;
-
-  var closureParams = [];
-  var closureArgs = [];
-
-  //
-
-  if (this.hasSuper) {
-    closureArgs.push(superName);
-
-    if (!t.isIdentifier(superName)) {
-      superName = this.scope.generateUidBasedOnNode(superName, this.file);
-    }
-
-    closureParams.push(superName);
-
-    this.superName = superName;
-    body.push(t.expressionStatement(t.callExpression(file.addHelper("inherits"), [className, superName])));
+    this.instanceMutatorMap = {};
+    this.staticMutatorMap   = {};
+    this.hasConstructor     = false;
+    this.className          = node.id || scope.generateUidIdentifier("class");
+    this.superName          = node.superClass || t.identifier("Function");
+    this.hasSuper           = !!node.superClass;
+    this.isLoose            = file.isLoose("es6.classes");
   }
 
-  this.buildBody();
+  /**
+   * Description
+   *
+   * @returns {Array}
+   */
 
-  t.inheritsComments(body[0], this.node);
+  run() {
+    var superName = this.superName;
+    var className = this.className;
+    var classBody = this.node.body.body;
+    var file      = this.file;
 
-  var init;
+    //
 
-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    init = t.toExpression(constructor);
-  } else {
-    body.push(t.returnStatement(className));
-    init = t.callExpression(
-      t.functionExpression(null, closureParams, t.blockStatement(body)),
-      closureArgs
-    );
-  }
+    var body = this.body = [];
 
-  if (this.isStatement) {
-    return t.variableDeclaration("let", [
-      t.variableDeclarator(className, init)
+    var constructorBody = t.blockStatement([
+      t.expressionStatement(t.callExpression(file.addHelper("class-call-check"), [
+        t.thisExpression(),
+        className
+      ]))
     ]);
-  } else {
-    return init;
-  }
-};
 
-/**
- * Description
- */
-
-ClassTransformer.prototype.buildBody = function () {
-  var constructor = this.constructor;
-  var className   = this.className;
-  var superName   = this.superName;
-  var classBody   = this.node.body.body;
-  var body        = this.body;
-
-  for (var i = 0; i < classBody.length; i++) {
-    var node = classBody[i];
-    if (t.isMethodDefinition(node)) {
-      var replaceSupers = new ReplaceSupers({
-        methodNode: node,
-        className:  this.className,
-        superName:  this.superName,
-        isStatic:   node.static,
-        isLoose:    this.isLoose,
-        scope:      this.scope,
-        file:       this.file
-      }, true);
-      replaceSupers.replace();
-
-      if ((!node.computed && t.isIdentifier(node.key, { name: "constructor" })) || t.isLiteral(node.key, { value: "constructor" })) {
-        this.pushConstructor(node);
-      } else {
-        this.pushMethod(node);
+    var constructor;
+    if (this.node.id) {
+      constructor = t.functionDeclaration(className, [], constructorBody);
+      body.push(constructor);
+    } else {
+      var constructorName = null;
+      // when a class has no parent and there is only a constructor or no body
+      // then the constructor is not wrapped in a closure and needs to be named
+      var containsOnlyConstructor = classBody.length === 1 && classBody[0].key.name === "constructor";
+      if (!this.hasSuper && (classBody.length === 0 || containsOnlyConstructor)) {
+        constructorName = className;
       }
-    } else if (t.isPrivateDeclaration(node)) {
-      this.closure = true;
-      body.unshift(node);
-    } else if (t.isClassProperty(node)) {
-      this.pushProperty(node);
+
+      constructor = t.functionExpression(constructorName, [], constructorBody);
+      body.push(t.variableDeclaration("var", [
+        t.variableDeclarator(className, constructor)
+      ]));
+    }
+    this.constructor = constructor;
+
+    var closureParams = [];
+    var closureArgs = [];
+
+    //
+
+    if (this.hasSuper) {
+      closureArgs.push(superName);
+
+      if (!t.isIdentifier(superName)) {
+        superName = this.scope.generateUidBasedOnNode(superName, this.file);
+      }
+
+      closureParams.push(superName);
+
+      this.superName = superName;
+      body.push(t.expressionStatement(t.callExpression(file.addHelper("inherits"), [className, superName])));
+    }
+
+    this.buildBody();
+
+    t.inheritsComments(body[0], this.node);
+
+    var init;
+
+    if (body.length === 1) {
+      // only a constructor so no need for a closure container
+      init = t.toExpression(constructor);
+    } else {
+      body.push(t.returnStatement(className));
+      init = t.callExpression(
+        t.functionExpression(null, closureParams, t.blockStatement(body)),
+        closureArgs
+      );
+    }
+
+    if (this.isStatement) {
+      return t.variableDeclaration("let", [
+        t.variableDeclarator(className, init)
+      ]);
+    } else {
+      return init;
     }
   }
 
-  // we have no constructor, we have a super, and the super doesn't appear to be falsy
-  if (!this.hasConstructor && this.hasSuper && !t.isFalsyExpression(superName)) {
-    var helperName = "class-super-constructor-call";
-    if (this.isLoose) helperName += "-loose";
-    constructor.body.body.push(util.template(helperName, {
-      CLASS_NAME: className,
-      SUPER_NAME: this.superName
-    }, true));
-  }
+  /**
+   * Description
+   */
 
-  var instanceProps;
-  var staticProps;
+  buildBody() {
+    var constructor = this.constructor;
+    var className   = this.className;
+    var superName   = this.superName;
+    var classBody   = this.node.body.body;
+    var body        = this.body;
 
-  if (this.hasInstanceMutators) {
-    instanceProps = defineMap.build(this.instanceMutatorMap);
-  }
+    for (var i = 0; i < classBody.length; i++) {
+      var node = classBody[i];
+      if (t.isMethodDefinition(node)) {
+        var replaceSupers = new ReplaceSupers({
+          methodNode: node,
+          className:  this.className,
+          superName:  this.superName,
+          isStatic:   node.static,
+          isLoose:    this.isLoose,
+          scope:      this.scope,
+          file:       this.file
+        }, true);
+        replaceSupers.replace();
 
-  if (this.hasStaticMutators) {
-    staticProps = defineMap.build(this.staticMutatorMap);
-  }
-
-  if (instanceProps || staticProps) {
-    staticProps = staticProps || t.literal(null);
-
-    var args = [className, staticProps];
-    if (instanceProps) args.push(instanceProps);
-
-    body.push(t.expressionStatement(
-      t.callExpression(this.file.addHelper("prototype-properties"), args)
-    ));
-  }
-};
-
-/**
- * Push a method to its respective mutatorMap.
- *
- * @param {Node} node MethodDefinition
- */
-
-ClassTransformer.prototype.pushMethod = function (node) {
-  var methodName = node.key;
-
-  var kind = node.kind;
-
-  if (kind === "") {
-    nameMethod.property(node, this.file, this.scope);
-
-    if (this.isLoose) {
-      // use assignments instead of define properties for loose classes
-
-      var className = this.className;
-      if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
-      methodName = t.memberExpression(className, methodName, node.computed);
-
-      var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
-      t.inheritsComments(expr, node);
-      this.body.push(expr);
-      return;
+        if ((!node.computed && t.isIdentifier(node.key, { name: "constructor" })) || t.isLiteral(node.key, { value: "constructor" })) {
+          this.pushConstructor(node);
+        } else {
+          this.pushMethod(node);
+        }
+      } else if (t.isPrivateDeclaration(node)) {
+        this.closure = true;
+        body.unshift(node);
+      } else if (t.isClassProperty(node)) {
+        this.pushProperty(node);
+      }
     }
 
-    kind = "value";
+    // we have no constructor, we have a super, and the super doesn't appear to be falsy
+    if (!this.hasConstructor && this.hasSuper && !t.isFalsyExpression(superName)) {
+      var helperName = "class-super-constructor-call";
+      if (this.isLoose) helperName += "-loose";
+      constructor.body.body.push(util.template(helperName, {
+        CLASS_NAME: className,
+        SUPER_NAME: this.superName
+      }, true));
+    }
+
+    var instanceProps;
+    var staticProps;
+
+    if (this.hasInstanceMutators) {
+      instanceProps = defineMap.build(this.instanceMutatorMap);
+    }
+
+    if (this.hasStaticMutators) {
+      staticProps = defineMap.build(this.staticMutatorMap);
+    }
+
+    if (instanceProps || staticProps) {
+      staticProps ||= t.literal(null);
+
+      var args = [className, staticProps];
+      if (instanceProps) args.push(instanceProps);
+
+      body.push(t.expressionStatement(
+        t.callExpression(this.file.addHelper("prototype-properties"), args)
+      ));
+    }
   }
 
-  var mutatorMap = this.instanceMutatorMap;
-  if (node.static) {
-    this.hasStaticMutators = true;
-    mutatorMap = this.staticMutatorMap;
-  } else {
-    this.hasInstanceMutators = true;
+  /**
+   * Push a method to its respective mutatorMap.
+   *
+   * @param {Node} node MethodDefinition
+   */
+
+  pushMethod(node) {
+    var methodName = node.key;
+
+    var kind = node.kind;
+
+    if (kind === "") {
+      nameMethod.property(node, this.file, this.scope);
+
+      if (this.isLoose) {
+        // use assignments instead of define properties for loose classes
+
+        var className = this.className;
+        if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
+        methodName = t.memberExpression(className, methodName, node.computed);
+
+        var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
+        t.inheritsComments(expr, node);
+        this.body.push(expr);
+        return;
+      }
+
+      kind = "value";
+    }
+
+    var mutatorMap = this.instanceMutatorMap;
+    if (node.static) {
+      this.hasStaticMutators = true;
+      mutatorMap = this.staticMutatorMap;
+    } else {
+      this.hasInstanceMutators = true;
+    }
+
+    defineMap.push(mutatorMap, methodName, kind, node.computed, node);
+    defineMap.push(mutatorMap, methodName, "enumerable", node.computed, false);
   }
 
-  defineMap.push(mutatorMap, methodName, kind, node.computed, node);
-  defineMap.push(mutatorMap, methodName, "enumerable", node.computed, false);
-};
+  /**
+   * Description
+   *
+   * @param {Node} node
+   */
 
-/**
- * Description
- *
- * @param {Node} node
- */
+  pushProperty(node) {
+    if (!node.value) return;
 
-ClassTransformer.prototype.pushProperty = function (node) {
-  if (!node.value) return;
+    var key;
 
-  var key;
-
-  if (node.static) {
-    key = t.memberExpression(this.className, node.key);
-    this.body.push(
-      t.expressionStatement(t.assignmentExpression("=", key, node.value))
-    );
-  } else {
-    key = t.memberExpression(t.thisExpression(), node.key);
-    this.constructor.body.body.unshift(
-      t.expressionStatement(t.assignmentExpression("=", key, node.value))
-    );
-  }
-};
-
-/**
- * Replace the constructor body of our class.
- *
- * @param {Node} method MethodDefinition
- */
-
-ClassTransformer.prototype.pushConstructor = function (method) {
-  if (method.kind) {
-    throw this.file.errorWithNode(method, messages.get("classesIllegalConstructorKind"));
+    if (node.static) {
+      key = t.memberExpression(this.className, node.key);
+      this.body.push(
+        t.expressionStatement(t.assignmentExpression("=", key, node.value))
+      );
+    } else {
+      key = t.memberExpression(t.thisExpression(), node.key);
+      this.constructor.body.body.unshift(
+        t.expressionStatement(t.assignmentExpression("=", key, node.value))
+      );
+    }
   }
 
-  var construct = this.constructor;
-  var fn        = method.value;
+  /**
+   * Replace the constructor body of our class.
+   *
+   * @param {Node} method MethodDefinition
+   */
 
-  this.hasConstructor = true;
+  pushConstructor(method) {
+    if (method.kind) {
+      throw this.file.errorWithNode(method, messages.get("classesIllegalConstructorKind"));
+    }
 
-  t.inherits(construct, fn);
-  t.inheritsComments(construct, method);
+    var construct = this.constructor;
+    var fn        = method.value;
 
-  construct._ignoreUserWhitespace = true;
-  construct.params                = fn.params;
-  construct.body.body             = construct.body.body.concat(fn.body.body);
-};
+    this.hasConstructor = true;
+
+    t.inherits(construct, fn);
+    t.inheritsComments(construct, method);
+
+    construct._ignoreUserWhitespace = true;
+    construct.params                = fn.params;
+    construct.body.body             = construct.body.body.concat(fn.body.body);
+  }
+}

src/babel/transformation/transformers/es6/constants.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var messages = require("../../../messages");
 var t        = require("../../../types");
 
@@ -8,7 +6,7 @@ exports.check = function (node) {
 };
 
 var visitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isAssignmentExpression(node) || t.isUpdateExpression(node)) {
       var ids = t.getBindingIdentifiers(node);
 

src/babel/transformation/transformers/es6/destructuring.js

@@ -1,273 +1,8 @@
-"use strict";
-
 var messages = require("../../../messages");
 var t        = require("../../../types");
 
 exports.check = t.isPattern;
 
-function DestructuringTransformer(opts) {
-  this.blockHoist = opts.blockHoist;
-  this.operator   = opts.operator;
-  this.nodes      = opts.nodes;
-  this.scope      = opts.scope;
-  this.file       = opts.file;
-  this.kind       = opts.kind;
-}
-
-DestructuringTransformer.prototype.buildVariableAssignment = function (id, init) {
-  var op = this.operator;
-  if (t.isMemberExpression(id)) op = "=";
-
-  var node;
-
-  if (op) {
-    node = t.expressionStatement(t.assignmentExpression(op, id, init));
-  } else {
-    node = t.variableDeclaration(this.kind, [
-      t.variableDeclarator(id, init)
-    ]);
-  }
-
-  node._blockHoist = this.blockHoist;
-
-  return node;
-};
-
-DestructuringTransformer.prototype.buildVariableDeclaration = function (id, init) {
-  var declar = t.variableDeclaration("var", [
-    t.variableDeclarator(id, init)
-  ]);
-  declar._blockHoist = this.blockHoist;
-  return declar;
-};
-
-DestructuringTransformer.prototype.push = function (id, init) {
-  if (t.isObjectPattern(id)) {
-    this.pushObjectPattern(id, init);
-  } else if (t.isArrayPattern(id)) {
-    this.pushArrayPattern(id, init);
-  } else if (t.isAssignmentPattern(id)) {
-    this.pushAssignmentPattern(id, init);
-  } else {
-    this.nodes.push(this.buildVariableAssignment(id, init));
-  }
-};
-
-DestructuringTransformer.prototype.get = function () {
-
-};
-
-DestructuringTransformer.prototype.pushAssignmentPattern = function (pattern, valueRef) {
-  // we need to assign the current value of the assignment to avoid evaluating
-  // it more than once
-
-  var tempValueRef = this.scope.generateUidBasedOnNode(valueRef);
-
-  var declar = t.variableDeclaration("var", [
-    t.variableDeclarator(tempValueRef, valueRef)
-  ]);
-  declar._blockHoist = this.blockHoist;
-  this.nodes.push(declar);
-
-  //
-
-  this.nodes.push(this.buildVariableAssignment(
-    pattern.left,
-    t.conditionalExpression(
-      t.binaryExpression("===", tempValueRef, t.identifier("undefined")),
-      pattern.right,
-      tempValueRef
-    )
-  ));
-};
-
-DestructuringTransformer.prototype.pushObjectSpread = function (pattern, objRef, spreadProp, spreadPropIndex) {
-  // get all the keys that appear in this object before the current spread
-
-  var keys = [];
-
-  for (var i = 0; i < pattern.properties.length; i++) {
-    var prop = pattern.properties[i];
-
-    // we've exceeded the index of the spread property to all properties to the
-    // right need to be ignored
-    if (i >= spreadPropIndex) break;
-
-    // ignore other spread properties
-    if (t.isSpreadProperty(prop)) continue;
-
-    var key = prop.key;
-    if (t.isIdentifier(key)) key = t.literal(prop.key.name);
-    keys.push(key);
-  }
-
-  keys = t.arrayExpression(keys);
-
-  //
-
-  var value = t.callExpression(this.file.addHelper("object-without-properties"), [objRef, keys]);
-  this.nodes.push(this.buildVariableAssignment(spreadProp.argument, value));
-};
-
-DestructuringTransformer.prototype.pushObjectProperty = function (prop, propRef) {
-  if (t.isLiteral(prop.key)) prop.computed = true;
-
-  var pattern = prop.value;
-  var objRef  = t.memberExpression(propRef, prop.key, prop.computed);
-
-  if (t.isPattern(pattern)) {
-    this.push(pattern, objRef);
-  } else {
-    this.nodes.push(this.buildVariableAssignment(pattern, objRef));
-  }
-};
-
-DestructuringTransformer.prototype.pushObjectPattern = function (pattern, objRef) {
-  // https://github.com/babel/babel/issues/681
-
-  if (!pattern.properties.length) {
-    this.nodes.push(t.expressionStatement(
-      t.callExpression(this.file.addHelper("object-destructuring-empty"), [objRef])
-    ));
-  }
-
-  // if we have more than one properties in this pattern and the objectRef is a
-  // member expression then we need to assign it to a temporary variable so it's
-  // only evaluated once
-
-  if (pattern.properties.length > 1 && t.isMemberExpression(objRef)) {
-    var temp = this.scope.generateUidBasedOnNode(objRef, this.file);
-    this.nodes.push(this.buildVariableDeclaration(temp, objRef));
-    objRef = temp;
-  }
-
-  //
-
-  for (var i = 0; i < pattern.properties.length; i++) {
-    var prop = pattern.properties[i];
-    if (t.isSpreadProperty(prop)) {
-      this.pushObjectSpread(pattern, objRef, prop, i);
-    } else {
-      this.pushObjectProperty(prop, objRef);
-    }
-  }
-};
-
-var hasRest = function (pattern) {
-  for (var i = 0; i < pattern.elements.length; i++) {
-    if (t.isRestElement(pattern.elements[i])) {
-      return true;
-    }
-  }
-  return false;
-};
-
-DestructuringTransformer.prototype.canUnpackArrayPattern = function (pattern, arr) {
-  // not an array so there's no way we can deal with this
-  if (!t.isArrayExpression(arr)) return false;
-
-  // pattern has less elements than the array and doesn't have a rest so some
-  // elements wont be evaluated
-  if (pattern.elements.length > arr.elements.length) return;
-  if (pattern.elements.length < arr.elements.length && !hasRest(pattern)) return false;
-
-  // deopt on holes
-  for (var i = 0; i < pattern.elements.length; i++) {
-    if (!pattern.elements[i]) return false;
-  }
-
-  return true;
-};
-
-DestructuringTransformer.prototype.pushUnpackedArrayPattern = function (pattern, arr) {
-  for (var i = 0; i < pattern.elements.length; i++) {
-    var elem = pattern.elements[i];
-    if (t.isRestElement(elem)) {
-      this.push(elem.argument, t.arrayExpression(arr.elements.slice(i)));
-    } else {
-      this.push(elem, arr.elements[i]);
-    }
-  }
-};
-
-DestructuringTransformer.prototype.pushArrayPattern = function (pattern, arrayRef) {
-  if (!pattern.elements) return;
-
-  // optimise basic array destructuring of an array expression
-  //
-  // we can't do this to a pattern of unequal size to it's right hand
-  // array expression as then there will be values that wont be evaluated
-  //
-  // eg: var [a, b] = [1, 2];
-
-  if (this.canUnpackArrayPattern(pattern, arrayRef)) {
-    return this.pushUnpackedArrayPattern(pattern, arrayRef);
-  }
-
-  // if we have a rest then we need all the elements so don't tell
-  // `scope.toArray` to only get a certain amount
-
-  var count = !hasRest(pattern) && pattern.elements.length;
-
-  // so we need to ensure that the `arrayRef` is an array, `scope.toArray` will
-  // return a locally bound identifier if it's been inferred to be an array,
-  // otherwise it'll be a call to a helper that will ensure it's one
-
-  var toArray = this.scope.toArray(arrayRef, count);
-
-  if (t.isIdentifier(toArray)) {
-    // we've been given an identifier so it must have been inferred to be an
-    // array
-    arrayRef = toArray;
-  } else {
-    arrayRef = this.scope.generateUidBasedOnNode(arrayRef);
-    this.nodes.push(this.buildVariableDeclaration(arrayRef, toArray));
-    this.scope.assignTypeGeneric(arrayRef.name, "Array");
-  }
-
-  //
-
-  for (var i = 0; i < pattern.elements.length; i++) {
-    var elem = pattern.elements[i];
-
-    // hole
-    if (!elem) continue;
-
-    var elemRef;
-
-    if (t.isRestElement(elem)) {
-      elemRef = this.scope.toArray(arrayRef);
-
-      if (i > 0) {
-        elemRef = t.callExpression(t.memberExpression(elemRef, t.identifier("slice")), [t.literal(i)]);
-      }
-
-      // set the element to the rest element argument since we've dealt with it
-      // being a rest already
-      elem = elem.argument;
-    } else {
-      elemRef = t.memberExpression(arrayRef, t.literal(i), true);
-    }
-
-    this.push(elem, elemRef);
-  }
-};
-
-DestructuringTransformer.prototype.init = function (pattern, ref) {
-  // trying to destructure a value that we can't evaluate more than once so we
-  // need to save it to a variable
-
-  if (!t.isArrayExpression(ref) && !t.isMemberExpression(ref) && !t.isIdentifier(ref)) {
-    var key = this.scope.generateUidBasedOnNode(ref);
-    this.nodes.push(this.buildVariableDeclaration(key, ref));
-    ref = key;
-  }
-
-  //
-
-  this.push(pattern, ref);
-};
-
 exports.ForInStatement =
 exports.ForOfStatement = function (node, parent, scope, file) {
   var left = node.left;
@@ -469,7 +204,7 @@ exports.VariableDeclaration = function (node, parent, scope, file) {
 
     for (i = 0; i < nodes.length; i++) {
       node = nodes[i];
-      declar = declar || t.variableDeclaration(node.kind, []);
+      declar ||= t.variableDeclaration(node.kind, []);
 
       if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
         throw file.errorWithNode(node, messages.get("invalidParentForThisNode"));
@@ -483,3 +218,264 @@ exports.VariableDeclaration = function (node, parent, scope, file) {
 
   return nodes;
 };
+
+var hasRest = function (pattern) {
+  for (var i = 0; i < pattern.elements.length; i++) {
+    if (t.isRestElement(pattern.elements[i])) {
+      return true;
+    }
+  }
+  return false;
+};
+
+class DestructuringTransformer {
+  constructor(opts) {
+    this.blockHoist = opts.blockHoist;
+    this.operator   = opts.operator;
+    this.nodes      = opts.nodes;
+    this.scope      = opts.scope;
+    this.file       = opts.file;
+    this.kind       = opts.kind;
+  }
+
+  buildVariableAssignment(id, init) {
+    var op = this.operator;
+    if (t.isMemberExpression(id)) op = "=";
+
+    var node;
+
+    if (op) {
+      node = t.expressionStatement(t.assignmentExpression(op, id, init));
+    } else {
+      node = t.variableDeclaration(this.kind, [
+        t.variableDeclarator(id, init)
+      ]);
+    }
+
+    node._blockHoist = this.blockHoist;
+
+    return node;
+  }
+
+  buildVariableDeclaration(id, init) {
+    var declar = t.variableDeclaration("var", [
+      t.variableDeclarator(id, init)
+    ]);
+    declar._blockHoist = this.blockHoist;
+    return declar;
+  }
+
+  push(id, init) {
+    if (t.isObjectPattern(id)) {
+      this.pushObjectPattern(id, init);
+    } else if (t.isArrayPattern(id)) {
+      this.pushArrayPattern(id, init);
+    } else if (t.isAssignmentPattern(id)) {
+      this.pushAssignmentPattern(id, init);
+    } else {
+      this.nodes.push(this.buildVariableAssignment(id, init));
+    }
+  }
+
+  pushAssignmentPattern(pattern, valueRef) {
+    // we need to assign the current value of the assignment to avoid evaluating
+    // it more than once
+
+    var tempValueRef = this.scope.generateUidBasedOnNode(valueRef);
+
+    var declar = t.variableDeclaration("var", [
+      t.variableDeclarator(tempValueRef, valueRef)
+    ]);
+    declar._blockHoist = this.blockHoist;
+    this.nodes.push(declar);
+
+    //
+
+    this.nodes.push(this.buildVariableAssignment(
+      pattern.left,
+      t.conditionalExpression(
+        t.binaryExpression("===", tempValueRef, t.identifier("undefined")),
+        pattern.right,
+        tempValueRef
+      )
+    ));
+  }
+
+  pushObjectSpread(pattern, objRef, spreadProp, spreadPropIndex) {
+    // get all the keys that appear in this object before the current spread
+
+    var keys = [];
+
+    for (var i = 0; i < pattern.properties.length; i++) {
+      var prop = pattern.properties[i];
+
+      // we've exceeded the index of the spread property to all properties to the
+      // right need to be ignored
+      if (i >= spreadPropIndex) break;
+
+      // ignore other spread properties
+      if (t.isSpreadProperty(prop)) continue;
+
+      var key = prop.key;
+      if (t.isIdentifier(key)) key = t.literal(prop.key.name);
+      keys.push(key);
+    }
+
+    keys = t.arrayExpression(keys);
+
+    //
+
+    var value = t.callExpression(this.file.addHelper("object-without-properties"), [objRef, keys]);
+    this.nodes.push(this.buildVariableAssignment(spreadProp.argument, value));
+  }
+
+  pushObjectProperty(prop, propRef) {
+    if (t.isLiteral(prop.key)) prop.computed = true;
+
+    var pattern = prop.value;
+    var objRef  = t.memberExpression(propRef, prop.key, prop.computed);
+
+    if (t.isPattern(pattern)) {
+      this.push(pattern, objRef);
+    } else {
+      this.nodes.push(this.buildVariableAssignment(pattern, objRef));
+    }
+  }
+
+  pushObjectPattern(pattern, objRef) {
+    // https://github.com/babel/babel/issues/681
+
+    if (!pattern.properties.length) {
+      this.nodes.push(t.expressionStatement(
+        t.callExpression(this.file.addHelper("object-destructuring-empty"), [objRef])
+      ));
+    }
+
+    // if we have more than one properties in this pattern and the objectRef is a
+    // member expression then we need to assign it to a temporary variable so it's
+    // only evaluated once
+
+    if (pattern.properties.length > 1 && t.isMemberExpression(objRef)) {
+      var temp = this.scope.generateUidBasedOnNode(objRef, this.file);
+      this.nodes.push(this.buildVariableDeclaration(temp, objRef));
+      objRef = temp;
+    }
+
+    //
+
+    for (var i = 0; i < pattern.properties.length; i++) {
+      var prop = pattern.properties[i];
+      if (t.isSpreadProperty(prop)) {
+        this.pushObjectSpread(pattern, objRef, prop, i);
+      } else {
+        this.pushObjectProperty(prop, objRef);
+      }
+    }
+  }
+
+  canUnpackArrayPattern(pattern, arr) {
+    // not an array so there's no way we can deal with this
+    if (!t.isArrayExpression(arr)) return false;
+
+    // pattern has less elements than the array and doesn't have a rest so some
+    // elements wont be evaluated
+    if (pattern.elements.length > arr.elements.length) return;
+    if (pattern.elements.length < arr.elements.length && !hasRest(pattern)) return false;
+
+    // deopt on holes
+    for (var i = 0; i < pattern.elements.length; i++) {
+      if (!pattern.elements[i]) return false;
+    }
+
+    return true;
+  }
+
+  pushUnpackedArrayPattern(pattern, arr) {
+    for (var i = 0; i < pattern.elements.length; i++) {
+      var elem = pattern.elements[i];
+      if (t.isRestElement(elem)) {
+        this.push(elem.argument, t.arrayExpression(arr.elements.slice(i)));
+      } else {
+        this.push(elem, arr.elements[i]);
+      }
+    }
+  }
+
+  pushArrayPattern(pattern, arrayRef) {
+    if (!pattern.elements) return;
+
+    // optimise basic array destructuring of an array expression
+    //
+    // we can't do this to a pattern of unequal size to it's right hand
+    // array expression as then there will be values that wont be evaluated
+    //
+    // eg: var [a, b] = [1, 2];
+
+    if (this.canUnpackArrayPattern(pattern, arrayRef)) {
+      return this.pushUnpackedArrayPattern(pattern, arrayRef);
+    }
+
+    // if we have a rest then we need all the elements so don't tell
+    // `scope.toArray` to only get a certain amount
+
+    var count = !hasRest(pattern) && pattern.elements.length;
+
+    // so we need to ensure that the `arrayRef` is an array, `scope.toArray` will
+    // return a locally bound identifier if it's been inferred to be an array,
+    // otherwise it'll be a call to a helper that will ensure it's one
+
+    var toArray = this.scope.toArray(arrayRef, count);
+
+    if (t.isIdentifier(toArray)) {
+      // we've been given an identifier so it must have been inferred to be an
+      // array
+      arrayRef = toArray;
+    } else {
+      arrayRef = this.scope.generateUidBasedOnNode(arrayRef);
+      this.nodes.push(this.buildVariableDeclaration(arrayRef, toArray));
+      this.scope.assignTypeGeneric(arrayRef.name, "Array");
+    }
+
+    //
+
+    for (var i = 0; i < pattern.elements.length; i++) {
+      var elem = pattern.elements[i];
+
+      // hole
+      if (!elem) continue;
+
+      var elemRef;
+
+      if (t.isRestElement(elem)) {
+        elemRef = this.scope.toArray(arrayRef);
+
+        if (i > 0) {
+          elemRef = t.callExpression(t.memberExpression(elemRef, t.identifier("slice")), [t.literal(i)]);
+        }
+
+        // set the element to the rest element argument since we've dealt with it
+        // being a rest already
+        elem = elem.argument;
+      } else {
+        elemRef = t.memberExpression(arrayRef, t.literal(i), true);
+      }
+
+      this.push(elem, elemRef);
+    }
+  }
+
+  init(pattern, ref) {
+    // trying to destructure a value that we can't evaluate more than once so we
+    // need to save it to a variable
+
+    if (!t.isArrayExpression(ref) && !t.isMemberExpression(ref) && !t.isIdentifier(ref)) {
+      var key = this.scope.generateUidBasedOnNode(ref);
+      this.nodes.push(this.buildVariableDeclaration(key, ref));
+      ref = key;
+    }
+
+    //
+
+    this.push(pattern, ref);
+  }
+}

src/babel/transformation/transformers/es6/for-of.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var messages = require("../../../messages");
 var util     = require("../../../util");
 var t        = require("../../../types");
@@ -38,7 +36,7 @@ exports.ForOfStatement = function (node, parent, scope, file) {
 };
 
 var breakVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isLoop(node)) {
       state.ignoreLabeless = true;
       scope.traverse(node, breakVisitor, state);

src/babel/transformation/transformers/es6/modules.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.check = require("../internal/modules").check;

src/babel/transformation/transformers/es6/object-super.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var ReplaceSupers = require("../../helpers/replace-supers");
 var t             = require("../../../types");
 

src/babel/transformation/transformers/es6/parameters.default.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var util = require("../../../util");
 var t    = require("../../../types");
 
@@ -15,7 +13,7 @@ var hasDefaults = function (node) {
 };
 
 var iifeVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (!t.isReferencedIdentifier(node, parent)) return;
     if (!state.scope.hasOwnBinding(node.name)) return;
     if (state.scope.bindingIdentifierEquals(node.name, node)) return;

src/babel/transformation/transformers/es6/parameters.rest.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var util = require("../../../util");
 var t    = require("../../../types");
 

src/babel/transformation/transformers/es6/properties.computed.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.check = function (node) {

src/babel/transformation/transformers/es6/properties.shorthand.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var clone = require("lodash/lang/clone");
 var t     = require("../../../types");
 

src/babel/transformation/transformers/es6/spread.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var includes = require("lodash/collection/includes");
 var t        = require("../../../types");
 

src/babel/transformation/transformers/es6/tail-call.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var reduceRight = require("lodash/collection/reduceRight");
 var messages    = require("../../../messages");
 var flatten     = require("lodash/array/flatten");
@@ -7,305 +5,18 @@ var util        = require("../../../util");
 var map         = require("lodash/collection/map");
 var t           = require("../../../types");
 
+exports.Function = function (node, parent, scope, file) {
+  var tailCall = new TailCallTransformer(node, scope, file);
+  tailCall.run();
+};
+
 function returnBlock(expr) {
   return t.blockStatement([t.returnStatement(expr)]);
 }
 
-function TailCallTransformer(node, scope, file) {
-  this.hasTailRecursion = false;
-  this.needsArguments   = false;
-  this.setsArguments    = false;
-  this.needsThis        = false;
-  this.ownerId          = node.id;
-  this.vars             = [];
-
-  this.scope = scope;
-  this.file  = file;
-  this.node  = node;
-}
-
-TailCallTransformer.prototype.getArgumentsId = function () {
-  return this.argumentsId = this.argumentsId || this.scope.generateUidIdentifier("arguments");
-};
-
-TailCallTransformer.prototype.getThisId = function () {
-  return this.thisId = this.thisId || this.scope.generateUidIdentifier("this");
-};
-
-TailCallTransformer.prototype.getLeftId = function () {
-  return this.leftId = this.leftId || this.scope.generateUidIdentifier("left");
-};
-
-TailCallTransformer.prototype.getFunctionId = function () {
-  return this.functionId = this.functionId || this.scope.generateUidIdentifier("function");
-};
-
-TailCallTransformer.prototype.getAgainId = function () {
-  return this.againId = this.againId || this.scope.generateUidIdentifier("again");
-};
-
-TailCallTransformer.prototype.getParams = function () {
-  var params = this.params;
-
-  if (!params) {
-    params = this.node.params;
-    this.paramDecls = [];
-
-    for (var i = 0; i < params.length; i++) {
-      var param = params[i];
-      if (!param._isDefaultPlaceholder) {
-        this.paramDecls.push(t.variableDeclarator(
-          param,
-          params[i] = this.scope.generateUidIdentifier("x")
-        ));
-      }
-    }
-  }
-
-  return this.params = params;
-};
-
-TailCallTransformer.prototype.hasDeopt = function () {
-  // check if the ownerId has been reassigned, if it has then it's not safe to
-  // perform optimisations
-  var ownerIdInfo = this.scope.getBindingInfo(this.ownerId.name);
-  return ownerIdInfo && ownerIdInfo.reassigned;
-};
-
-TailCallTransformer.prototype.run = function () {
-  var scope = this.scope;
-  var node  = this.node;
-
-  // only tail recursion can be optimized as for now, so we can skip anonymous
-  // functions entirely
-  var ownerId = this.ownerId;
-  if (!ownerId) return;
-
-  // traverse the function and look for tail recursion
-  scope.traverse(node, firstPass, this);
-
-  if (!this.hasTailRecursion) return;
-
-  if (this.hasDeopt()) {
-    this.file.logDeopt(node, messages.get("tailCallReassignmentDeopt"));
-    return;
-  }
-
-  //
-
-  scope.traverse(node, secondPass, this);
-
-  if (!this.needsThis || !this.needsArguments) {
-    scope.traverse(node, thirdPass, this);
-  }
-
-  var body = t.ensureBlock(node).body;
-
-  if (this.vars.length > 0) {
-    var declarations = flatten(map(this.vars, function (decl) {
-      return decl.declarations;
-    }, this));
-    var statement = reduceRight(declarations, function (expr, decl) {
-      return t.assignmentExpression("=", decl.id, expr);
-    }, t.identifier("undefined"));
-    body.unshift(t.expressionStatement(statement));
-  }
-
-  var paramDecls = this.paramDecls;
-  if (paramDecls.length > 0) {
-    body.unshift(t.variableDeclaration("var", paramDecls));
-  }
-
-  body.unshift(t.expressionStatement(
-    t.assignmentExpression("=", this.getAgainId(), t.literal(false)))
-  );
-
-  node.body = util.template("tail-call-body", {
-    AGAIN_ID:      this.getAgainId(),
-    THIS_ID:       this.thisId,
-    ARGUMENTS_ID:  this.argumentsId,
-    FUNCTION_ID:   this.getFunctionId(),
-    BLOCK:         node.body
-  });
-
-  var topVars = [];
-
-  if (this.needsThis) {
-    topVars.push(t.variableDeclarator(this.getThisId(), t.thisExpression()));
-  }
-
-  if (this.needsArguments || this.setsArguments) {
-    var decl = t.variableDeclarator(this.getArgumentsId());
-    if (this.needsArguments) {
-      decl.init = t.identifier("arguments");
-    }
-    topVars.push(decl);
-  }
-
-  var leftId = this.leftId;
-  if (leftId) {
-    topVars.push(t.variableDeclarator(leftId));
-  }
-
-  if (topVars.length > 0) {
-    node.body.body.unshift(t.variableDeclaration("var", topVars));
-  }
-};
-
-TailCallTransformer.prototype.subTransform = function (node) {
-  if (!node) return;
-
-  var handler = this["subTransform" + node.type];
-  if (handler) return handler.call(this, node);
-};
-
-TailCallTransformer.prototype.subTransformConditionalExpression = function (node) {
-  var callConsequent = this.subTransform(node.consequent);
-  var callAlternate = this.subTransform(node.alternate);
-  if (!callConsequent && !callAlternate) {
-    return;
-  }
-
-  // if ternary operator had tail recursion in value, convert to optimized if-statement
-  node.type = "IfStatement";
-  node.consequent = callConsequent ? t.toBlock(callConsequent) : returnBlock(node.consequent);
-
-  if (callAlternate) {
-    node.alternate = t.isIfStatement(callAlternate) ? callAlternate : t.toBlock(callAlternate);
-  } else {
-    node.alternate = returnBlock(node.alternate);
-  }
-
-  return [node];
-};
-
-TailCallTransformer.prototype.subTransformLogicalExpression = function (node) {
-  // only call in right-value of can be optimized
-  var callRight = this.subTransform(node.right);
-  if (!callRight) return;
-
-  // cache left value as it might have side-effects
-  var leftId = this.getLeftId();
-  var testExpr = t.assignmentExpression(
-    "=",
-    leftId,
-    node.left
-  );
-
-  if (node.operator === "&&") {
-    testExpr = t.unaryExpression("!", testExpr);
-  }
-
-  return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
-};
-
-TailCallTransformer.prototype.subTransformSequenceExpression = function (node) {
-  var seq = node.expressions;
-
-  // only last element can be optimized
-  var lastCall = this.subTransform(seq[seq.length - 1]);
-  if (!lastCall) {
-    return;
-  }
-
-  // remove converted expression from sequence
-  // and convert to regular expression if needed
-  if (--seq.length === 1) {
-    node = seq[0];
-  }
-
-  return [t.expressionStatement(node)].concat(lastCall);
-};
-
-TailCallTransformer.prototype.subTransformCallExpression = function (node) {
-  var callee = node.callee, thisBinding, args;
-
-  if (t.isMemberExpression(callee, { computed: false }) && t.isIdentifier(callee.property)) {
-    switch (callee.property.name) {
-      case "call":
-        args = t.arrayExpression(node.arguments.slice(1));
-        break;
-
-      case "apply":
-        args = node.arguments[1] || t.identifier("undefined");
-        break;
-
-      default:
-        return;
-    }
-
-    thisBinding = node.arguments[0];
-    callee = callee.object;
-  }
-
-  // only tail recursion can be optimized as for now
-  if (!t.isIdentifier(callee) || !this.scope.bindingIdentifierEquals(callee.name, this.ownerId)) {
-    return;
-  }
-
-  this.hasTailRecursion = true;
-
-  if (this.hasDeopt()) return;
-
-  var body = [];
-
-  if (!t.isThisExpression(thisBinding)) {
-    body.push(t.expressionStatement(t.assignmentExpression(
-      "=",
-      this.getThisId(),
-      thisBinding || t.identifier("undefined")
-    )));
-  }
-
-  if (!args) {
-    args = t.arrayExpression(node.arguments);
-  }
-
-  var argumentsId = this.getArgumentsId();
-  var params = this.getParams();
-
-  body.push(t.expressionStatement(t.assignmentExpression(
-    "=",
-    argumentsId,
-    args
-  )));
-
-  var i, param;
-
-  if (t.isArrayExpression(args)) {
-    var elems = args.elements;
-    for (i = 0; i < elems.length && i < params.length; i++) {
-      param = params[i];
-      var elem = elems[i] || (elems[i] = t.identifier("undefined"));
-      if (!param._isDefaultPlaceholder) {
-        elems[i] = t.assignmentExpression("=", param, elem);
-      }
-    }
-  } else {
-    this.setsArguments = true;
-    for (i = 0; i < params.length; i++) {
-      param = params[i];
-      if (!param._isDefaultPlaceholder) {
-        body.push(t.expressionStatement(t.assignmentExpression(
-          "=",
-          param,
-          t.memberExpression(argumentsId, t.literal(i), true)
-        )));
-      }
-    }
-  }
-
-  body.push(t.expressionStatement(
-    t.assignmentExpression("=", this.getAgainId(), t.literal(true))
-  ));
-  body.push(t.continueStatement(this.getFunctionId()));
-
-  return body;
-};
-
 // looks for and replaces tail recursion calls
 var firstPass = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isIfStatement(node)) {
       if (t.isReturnStatement(node.alternate)) {
         t.ensureBlock(node, "alternate");
@@ -335,7 +46,7 @@ var firstPass = {
 // hoists up function declarations, replaces `this` and `arguments` and marks
 // them as needed
 var secondPass = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isThisExpression(node)) {
       state.needsThis = true;
       return state.getThisId();
@@ -357,7 +68,7 @@ var secondPass = {
 
 // optimizes recursion by removing `this` and `arguments` if they aren't used
 var thirdPass = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (!t.isExpressionStatement(node)) return;
 
     var expr = node.expression;
@@ -373,7 +84,296 @@ var thirdPass = {
   }
 };
 
-exports.Function = function (node, parent, scope, file) {
-  var tailCall = new TailCallTransformer(node, scope, file);
-  tailCall.run();
-};
+class TailCallTransformer {
+  constructor(node, scope, file) {
+    this.hasTailRecursion = false;
+    this.needsArguments   = false;
+    this.setsArguments    = false;
+    this.needsThis        = false;
+    this.ownerId          = node.id;
+    this.vars             = [];
+
+    this.scope = scope;
+    this.file  = file;
+    this.node  = node;
+  }
+
+  getArgumentsId() {
+    return this.argumentsId ||= this.scope.generateUidIdentifier("arguments");
+  }
+
+  getThisId() {
+    return this.thisId ||= this.scope.generateUidIdentifier("this");
+  }
+
+  getLeftId() {
+    return this.leftId ||= this.scope.generateUidIdentifier("left");
+  }
+
+  getFunctionId() {
+    return this.functionId ||= this.scope.generateUidIdentifier("function");
+  }
+
+  getAgainId() {
+    return this.againId ||= this.scope.generateUidIdentifier("again");
+  }
+
+  getParams() {
+    var params = this.params;
+
+    if (!params) {
+      params = this.node.params;
+      this.paramDecls = [];
+
+      for (var i = 0; i < params.length; i++) {
+        var param = params[i];
+        if (!param._isDefaultPlaceholder) {
+          this.paramDecls.push(t.variableDeclarator(
+            param,
+            params[i] = this.scope.generateUidIdentifier("x")
+          ));
+        }
+      }
+    }
+
+    return this.params = params;
+  }
+
+  hasDeopt() {
+    // check if the ownerId has been reassigned, if it has then it's not safe to
+    // perform optimisations
+    var ownerIdInfo = this.scope.getBindingInfo(this.ownerId.name);
+    return ownerIdInfo && ownerIdInfo.reassigned;
+  }
+
+  run() {
+    var scope = this.scope;
+    var node  = this.node;
+
+    // only tail recursion can be optimized as for now, so we can skip anonymous
+    // functions entirely
+    var ownerId = this.ownerId;
+    if (!ownerId) return;
+
+    // traverse the function and look for tail recursion
+    scope.traverse(node, firstPass, this);
+
+    if (!this.hasTailRecursion) return;
+
+    if (this.hasDeopt()) {
+      this.file.logDeopt(node, messages.get("tailCallReassignmentDeopt"));
+      return;
+    }
+
+    //
+
+    scope.traverse(node, secondPass, this);
+
+    if (!this.needsThis || !this.needsArguments) {
+      scope.traverse(node, thirdPass, this);
+    }
+
+    var body = t.ensureBlock(node).body;
+
+    if (this.vars.length > 0) {
+      var declarations = flatten(map(this.vars, function (decl) {
+        return decl.declarations;
+      }, this));
+      var statement = reduceRight(declarations, function (expr, decl) {
+        return t.assignmentExpression("=", decl.id, expr);
+      }, t.identifier("undefined"));
+      body.unshift(t.expressionStatement(statement));
+    }
+
+    var paramDecls = this.paramDecls;
+    if (paramDecls.length > 0) {
+      body.unshift(t.variableDeclaration("var", paramDecls));
+    }
+
+    body.unshift(t.expressionStatement(
+      t.assignmentExpression("=", this.getAgainId(), t.literal(false)))
+    );
+
+    node.body = util.template("tail-call-body", {
+      AGAIN_ID:      this.getAgainId(),
+      THIS_ID:       this.thisId,
+      ARGUMENTS_ID:  this.argumentsId,
+      FUNCTION_ID:   this.getFunctionId(),
+      BLOCK:         node.body
+    });
+
+    var topVars = [];
+
+    if (this.needsThis) {
+      topVars.push(t.variableDeclarator(this.getThisId(), t.thisExpression()));
+    }
+
+    if (this.needsArguments || this.setsArguments) {
+      var decl = t.variableDeclarator(this.getArgumentsId());
+      if (this.needsArguments) {
+        decl.init = t.identifier("arguments");
+      }
+      topVars.push(decl);
+    }
+
+    var leftId = this.leftId;
+    if (leftId) {
+      topVars.push(t.variableDeclarator(leftId));
+    }
+
+    if (topVars.length > 0) {
+      node.body.body.unshift(t.variableDeclaration("var", topVars));
+    }
+  }
+
+  subTransform(node) {
+    if (!node) return;
+
+    var handler = this["subTransform" + node.type];
+    if (handler) return handler.call(this, node);
+  }
+
+  subTransformConditionalExpression(node) {
+    var callConsequent = this.subTransform(node.consequent);
+    var callAlternate = this.subTransform(node.alternate);
+    if (!callConsequent && !callAlternate) {
+      return;
+    }
+
+    // if ternary operator had tail recursion in value, convert to optimized if-statement
+    node.type = "IfStatement";
+    node.consequent = callConsequent ? t.toBlock(callConsequent) : returnBlock(node.consequent);
+
+    if (callAlternate) {
+      node.alternate = t.isIfStatement(callAlternate) ? callAlternate : t.toBlock(callAlternate);
+    } else {
+      node.alternate = returnBlock(node.alternate);
+    }
+
+    return [node];
+  }
+
+  subTransformLogicalExpression(node) {
+    // only call in right-value of can be optimized
+    var callRight = this.subTransform(node.right);
+    if (!callRight) return;
+
+    // cache left value as it might have side-effects
+    var leftId = this.getLeftId();
+    var testExpr = t.assignmentExpression(
+      "=",
+      leftId,
+      node.left
+    );
+
+    if (node.operator === "&&") {
+      testExpr = t.unaryExpression("!", testExpr);
+    }
+
+    return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
+  }
+
+  subTransformSequenceExpression(node) {
+    var seq = node.expressions;
+
+    // only last element can be optimized
+    var lastCall = this.subTransform(seq[seq.length - 1]);
+    if (!lastCall) {
+      return;
+    }
+
+    // remove converted expression from sequence
+    // and convert to regular expression if needed
+    if (--seq.length === 1) {
+      node = seq[0];
+    }
+
+    return [t.expressionStatement(node)].concat(lastCall);
+  }
+
+  subTransformCallExpression(node) {
+    var callee = node.callee, thisBinding, args;
+
+    if (t.isMemberExpression(callee, { computed: false }) && t.isIdentifier(callee.property)) {
+      switch (callee.property.name) {
+        case "call":
+          args = t.arrayExpression(node.arguments.slice(1));
+          break;
+
+        case "apply":
+          args = node.arguments[1] || t.identifier("undefined");
+          break;
+
+        default:
+          return;
+      }
+
+      thisBinding = node.arguments[0];
+      callee = callee.object;
+    }
+
+    // only tail recursion can be optimized as for now
+    if (!t.isIdentifier(callee) || !this.scope.bindingIdentifierEquals(callee.name, this.ownerId)) {
+      return;
+    }
+
+    this.hasTailRecursion = true;
+
+    if (this.hasDeopt()) return;
+
+    var body = [];
+
+    if (!t.isThisExpression(thisBinding)) {
+      body.push(t.expressionStatement(t.assignmentExpression(
+        "=",
+        this.getThisId(),
+        thisBinding || t.identifier("undefined")
+      )));
+    }
+
+    if (!args) {
+      args = t.arrayExpression(node.arguments);
+    }
+
+    var argumentsId = this.getArgumentsId();
+    var params = this.getParams();
+
+    body.push(t.expressionStatement(t.assignmentExpression(
+      "=",
+      argumentsId,
+      args
+    )));
+
+    var i, param;
+
+    if (t.isArrayExpression(args)) {
+      var elems = args.elements;
+      for (i = 0; i < elems.length && i < params.length; i++) {
+        param = params[i];
+        var elem = elems[i] || (elems[i] = t.identifier("undefined"));
+        if (!param._isDefaultPlaceholder) {
+          elems[i] = t.assignmentExpression("=", param, elem);
+        }
+      }
+    } else {
+      this.setsArguments = true;
+      for (i = 0; i < params.length; i++) {
+        param = params[i];
+        if (!param._isDefaultPlaceholder) {
+          body.push(t.expressionStatement(t.assignmentExpression(
+            "=",
+            param,
+            t.memberExpression(argumentsId, t.literal(i), true)
+          )));
+        }
+      }
+    }
+
+    body.push(t.expressionStatement(
+      t.assignmentExpression("=", this.getAgainId(), t.literal(true))
+    ));
+    body.push(t.continueStatement(this.getFunctionId()));
+
+    return body;
+  }
+}

src/babel/transformation/transformers/es6/template-literals.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 var buildBinaryExpression = function (left, right) {

src/babel/transformation/transformers/es6/unicode-regex.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var rewritePattern = require("regexpu/rewrite-pattern");
 var pull           = require("lodash/array/pull");
 var t              = require("../../../types");

src/babel/transformation/transformers/es7/abstract-references.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // https://github.com/zenparsing/es-abstract-refs
 
 var util = require("../../../util");

src/babel/transformation/transformers/es7/comprehensions.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var buildComprehension = require("../../helpers/build-comprehension");
 var traverse           = require("../../../traversal");
 var util               = require("../../../util");

src/babel/transformation/transformers/es7/exponentiation-operator.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // https://github.com/rwaldron/exponentiation-operator
 
 exports.experimental = true;
@@ -12,7 +10,7 @@ var MATH_POW = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
 build(exports, {
   operator: "**",
 
-  build: function (left, right) {
+  build(left, right) {
     return t.callExpression(MATH_POW, [left, right]);
   }
 });

src/babel/transformation/transformers/es7/object-rest-spread.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // https://github.com/sebmarkbage/ecmascript-rest-spread
 
 var t = require("../../../types");

src/babel/transformation/transformers/index.js

@@ -1,13 +1,14 @@
 module.exports = {
   useStrict:                               require("./other/use-strict"),
 
-  // this goes at the start so we only transform the original user code
-  "spec.functionName":                     require("./spec/function-name"),
-
   "validation.undeclaredVariableCheck":    require("./validation/undeclared-variable-check"),
   "validation.noForInOfAssignment":        require("./validation/no-for-in-of-assignment"),
   "validation.setters":                    require("./validation/setters"),
   "validation.react":                      require("./validation/react"),
+
+  // this goes at the start so we only transform the original user code
+  "spec.functionName":                     require("./spec/function-name"),
+
   "spec.blockScopedFunctions":             require("./spec/block-scoped-functions"),
 
   // needs to be before `_aliasFunction`

src/babel/transformation/transformers/internal/alias-functions.js

@@ -1,9 +1,7 @@
-"use strict";
-
 var t = require("../../../types");
 
 var functionChildrenVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (t.isFunction(node) && !node._aliasFunction) {
       return this.skip();
     }
@@ -25,7 +23,7 @@ var functionChildrenVisitor = {
 };
 
 var functionVisitor = {
-  enter: function (node, parent, scope, state) {
+  enter(node, parent, scope, state) {
     if (!node._aliasFunction) {
       if (t.isFunction(node)) {
         // stop traversal of this node as it'll be hit again by this transformer
@@ -47,11 +45,12 @@ var go = function (getBody, node, scope) {
   var thisId;
 
   var state = {
-    getArgumentsId: function () {
-      return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
+    getArgumentsId() {
+      return argumentsId ||= scope.generateUidIdentifier("arguments");
     },
-    getThisId: function () {
-      return thisId = thisId || scope.generateUidIdentifier("this");
+
+    getThisId() {
+      return thisId ||= scope.generateUidIdentifier("this");
     }
   };
 
@@ -62,7 +61,7 @@ var go = function (getBody, node, scope) {
   var body;
 
   var pushDeclaration = function (id, init) {
-    body = body || getBody();
+    body ||= getBody();
     body.unshift(t.variableDeclaration("var", [
       t.variableDeclarator(id, init)
     ]));

src/babel/transformation/transformers/internal/block-hoist.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var groupBy = require("lodash/collection/groupBy");
 var flatten = require("lodash/array/flatten");
 var values  = require("lodash/object/values");
@@ -13,7 +11,7 @@ var values  = require("lodash/object/values");
 
 exports.BlockStatement =
 exports.Program = {
-  exit: function (node) {
+  exit(node) {
     var hasChange = false;
     for (var i = 0; i < node.body.length; i++) {
       var bodyNode = node.body[i];

src/babel/transformation/transformers/internal/declarations.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var useStrict = require("../../helpers/use-strict");
 var t         = require("../../../types");
 
@@ -22,7 +20,7 @@ exports.Program = function (node, parent, scope, file) {
       if (declar.init) {
         node.body.unshift(file.attachAuxiliaryComment(t.variableDeclaration(kind, [declarNode])));
       } else {
-        kinds[kind] = kinds[kind] || [];
+        kinds[kind] ||= [];
         kinds[kind].push(declarNode);
       }
     }

src/babel/transformation/transformers/internal/module-formatter.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var useStrict = require("../../helpers/use-strict");
 
 exports.Program = function (program, parent, scope, file) {

src/babel/transformation/transformers/internal/modules.js

@@ -1,5 +1,3 @@
-"use strict";
-
 // in this transformer we have to split up classes and function declarations
 // from their exports. why? because sometimes we need to replace classes with
 // nodes that aren't allowed in the same contexts. also, if you're exporting

src/babel/transformation/transformers/internal/use-strict.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 exports.Program = function (program, parent, scope, file) {

src/babel/transformation/transformers/minification/dead-code-elimination.js

@@ -17,7 +17,7 @@ exports.ExpressionStatement = function (node) {
 };
 
 exports.IfStatement = {
-  exit: function (node) {
+  exit(node) {
     // todo: in scenarios where we can just return the consequent or
     // alternate we should drop the block statement if it contains no
     // block scoped variables

src/babel/transformation/transformers/minification/remove-console-calls.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var t = require("../../../types");
 
 var isConsole = t.buildMatchMemberExpression("console", true);

src/babel/transformation/transformers/other/async-to-generator.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var remapAsyncToGenerator = require("../../helpers/remap-async-to-generator");
 var bluebirdCoroutines    = require("./bluebird-coroutines");
 

src/babel/transformation/transformers/other/bluebird-coroutines.js

@@ -1,5 +1,3 @@
-"use strict";
-
 var remapAsyncToGenerator = require("../../helpers/remap-async-to-generator");
 var t                     = require("../../../types");