v3.6.3

Conflicts:
	lib/6to5/transformation/transformers/minification/dead-code-elimination.js

.6to5rc

@@ -0,0 +1,5 @@
+{
+  "experimental": true,
+  "playground": true,
+  "loose": true
+}

.editorconfig

@@ -6,6 +6,6 @@ charset = utf-8
 trim_trailing_whitespace = true
 insert_final_newline = true
 
-[*.js]
+[*.{js,json}]
 indent_style = space
 indent_size = 2

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "vendor/test262"]
 	path = vendor/test262
 	url = https://github.com/tc39/test262
+[submodule "vendor/compat-table"]
+	path = vendor/compat-table
+	url = https://github.com/kangax/compat-table

.istanbul.yml

@@ -0,0 +1,2 @@
+instrumentation:
+  root: lib

.jscsrc

@@ -14,7 +14,6 @@
   },
   "disallowSpacesInsideArrayBrackets": true,
   "disallowSpacesInsideParentheses": true,
-  "disallowQuotedKeysInObjects": true,
   "disallowSpaceAfterObjectKeys": true,
   "disallowSpaceAfterPrefixUnaryOperators": true,
   "disallowSpaceBeforePostfixUnaryOperators": true,
@@ -33,10 +32,8 @@
   "requireCommaBeforeLineBreak": true,
   "requireSpaceBeforeBinaryOperators": true,
   "requireSpaceAfterBinaryOperators": true,
-  "requireCamelCaseOrUpperCaseIdentifiers": true,
   "requireLineFeedAtFileEnd": true,
   "requireCapitalizedConstructors": true,
-  "requireDotNotation": true,
   "requireSpacesInForStatement": true,
   "requireCurlyBraces": [
     "do"
@@ -52,7 +49,8 @@
     "return",
     "try",
     "catch",
-    "typeof"
+    "typeof",
+    "function"
   ],
   "validateLineBreaks": "LF",
   "validateQuoteMarks": "\"",

.jshintrc

@@ -2,6 +2,7 @@
   "esnext": true,
   "indent": 2,
   "freeze": true,
+  "validthis": true,
   "camelcase": true,
   "unused": true,
   "eqnull": true,

.travis.yml

@@ -3,6 +3,7 @@ language: node_js
 node_js:
   - "0.10"
   - "0.11"
+  - "0.12"
 
 branches:
   except:

CHANGELOG.md

@@ -11,6 +11,198 @@
 
 _Note: Gaps between patch versions are faulty/broken releases._
 
+## 3.6.3
+
+ * **Internal**
+  * Upgrade `acorn-6to5`.
+
+## 3.6.2
+
+ * **Polish**
+  * Use better iterator detection in `slicedToArray` helper and add support for it to the `selfContained` transformer.
+
+## 3.6.1
+
+ * **Bug Fix**
+  * Multiline JSX string literals are now supported.
+  * Fix scope tracking import specifiers incorrectly.
+  * Fix templates incorrectly recursing into their replacements.
+ * **Internal**
+  * Type inferrence now extends to function return types.
+  * Upgrade `acorn-6to5`.
+
+## 3.6.0
+
+ * **New Feature**
+  * Add playground class property initializers.
+ * **Polish**
+  * Completely reimplemented scope tracking, can now track types and optimise certain helpers based on it.
+  * Extremely fast tail recursion optimisation implementation. Thanks [@RReverser](https://github.com/RReverser)!
+ * **Internal**
+  * `kexec` has been removed as an optional dependency and must be user installed.
+  * Upgrade `regenerator-6to5`.
+  * Upgrade `acorn-6to5`.
+  * Upgrade `core-js`.
+
+## 3.5.3
+
+ * Enable `es6.tailCall` transformer with the first implementation that only works with self referencing calls until we can implement nested tail calls elegantly.
+
+## 3.5.2
+
+ * Disable `es6.tailCall` temporairly after reports of it breaking.
+
+## 3.5.1
+
+ * **Polish**
+  * Allow tail calls to work across files without the runtime.
+ * **Internal**
+  * Upgrade `acorn-6to5`.
+
+## 3.5.0
+
+ * **Bug Fix**
+  * Destructuring patterns as the left operator in `ForInStatement`/`ForOfStatement`.
+ * **Polish**
+  * Make default parameter IIFE invocation smarter.
+  * Make `__esModule` flag non-enumerable. Thanks [@daliwali](https://github.com/daliwali)!
+ * **Internal**
+  * More performance improvements.
+  * Parsing is now ~30% faster thanks to [marijnh/acorn@7264bc0178e7e6af7cfe02e9e0c6b26ee0e6007f](https://github.com/marijnh/acorn/commit/7264bc0178e7e6af7cfe02e9e0c6b26ee0e6007f).
+ * **New Feature**
+  * Optional `es6.blockScopingTDZ` is now completely functional and handles all edgecases.
+  * `super` in object literals.
+  * Tail call optimisation. Thanks [@RReverser](https://github.com/RReverser)!
+
+## 3.4.1
+
+ * **Bug Fix**
+  * Fix conflicting `--module-ids` shorthand arg in `$ 6to5`.
+  * Add require hook options to cache key.
+  * Fix strict module formatter.
+
+## 3.4.0
+
+ * **New Feature**
+  * Add `commonStandard` module formatter.
+ * **Bug Fix**
+  * Fix conflicting `--module-ids` shorthand arg in `$ 6to5`.
+ * **Internal**
+  * Lots of internal refactoring with scope tracking and traversal.
+ * **Polish**
+  * Don't return `map` in the API result if `sourceMap` was set to `"inline"`.
+
+## 3.3.12
+
+ * **Bug Fix**
+  * Don't override `MemberExpression`s with `core-js` in `selfContained` if a local binding exists.
+
+## 3.3.11
+
+ * **Bug Fix**
+  * Fix the require cache.
+
+## 3.3.10
+
+ * **Internal**
+  * Restructure transformers so they're only ran if the AST contains nodes that they need to worry about. Improves transpilation speed significantly.
+ * **Bug Fix**
+  * Fix source maps not tracking end of node locations.
+ * **Spec Compliancy**
+  * Use static super references as the home object is actually done at definition time.
+ * **Polish**
+  * Force the `es6.destructuring` transformer to be whitelisted when the `es7.objectSpread` transformer is.
+  * Join sibling string literals when creating JSX.
+
+## 3.3.9
+
+ * **Bug Fix**
+  * Fix super inside of functions.
+  * Fix super constructor inheritance.
+
+## 3.3.7
+
+ * **Bug Fix**
+  * Add `--use-strict` to valid node flags in `6to5-node`.
+  * Fix booleans not being properly stripped from the arguments in `6to5-node`.
+  * Force `.js` extension when writing files to directories with `6to5`.
+
+## 3.3.5
+
+ * **Bug Fix**
+  * Fix block scoping inside of while loops.
+  * Make module name regex more conservative. Thanks [@johlrich](https://github.com/johlrich)!
+  * Fix block scoping of constants.
+  * Fix istanbul interop.
+  * Make JSX transforming more inline with the official transformer with spaces after non-empty last lines.
+ * **Polish**
+  * Make it illegal to export a property called `__esModule`.
+
+## 3.3.4
+
+ * **Polish**
+  * Add istanbul `require` interop.
+ * **Bug Fix**
+  * Fix incorrect source map column tracking in specific scenarios.
+
+## 3.3.3
+
+ * **Polish**
+  * Remap top level `this` to `undefined` instead of throwing an error.
+ * **Bug Fix**
+  * Run `selfContained` transformer over the regenerator runtime when building `6to5-runtime`.
+  * Fix `t.isReferenced` not properly allowing `value` nodes.
+
+## 3.3.1
+
+ * **Bug Fix**
+  * Block hoist assignment pattern destructuring.
+
+## 3.3.0
+
+ * **Bug Fix**
+  * Do all transforms before the regenerator transform is ran.
+ * **New Feature**
+  * Added back the 2.x optional runtime.
+
+## 3.2.1
+
+ * **Bug Fix**
+  * Fix block scoping transformer rewriting breaks and continues to inner labels.
+
+## 3.2.0
+
+ * **Bug Fix**
+  * Fixed scope tracking for default parameters IIFE.
+  * Fixed block scoped functions.
+  * Improved `bin/6to5` path resolution.
+ * **New Feature**
+  * You can now trigger super setters in classes. Thanks [@kruppel](https://github.com/kruppel)!
+  * Add `resolveSourceMap` option.
+  * Better support and output for block scoping loops with labels.
+
+## 3.1.1
+
+ * **Polish**
+  * Drop `enumerable: false` clause from class method definitions as `enumerable` already defaults to `false`.
+ * **Bug Fix**
+  * Properly transform `XJSIdentifier` nodes referencing `this` into a `ThisExpression`.
+
+## 3.1.0
+
+ * **Breaking Change**
+  * [Make class methods unenumerable](https://esdiscuss.org/topic/classes-and-enumerability#content-61).
+
+## 3.0.16
+
+ * **Bug Fix**
+  * Don't ignore dynamic import specifiers.
+ * **Internal**
+  * Upgrade `regenerator-6to5`.
+ * **Polish**
+  * Use `Object.assign` in place of extends helper if it exists.
+  * Require individual `lodash` methods. Thanks [@stefanpenner](https://github.com/stefanpenner)!
+
 ## 3.0.15
 
  * **Bug Fix**
@@ -268,8 +460,8 @@ _Note: Gaps between patch versions are faulty/broken releases._
  * **Polish**
   * Rest parameters now allocate the array before populating.
  * **Internal**
-  * `for...in` loops have been changed to optimised `for` loops - better performance and no enumeration of protoype keys.
-  * Parts of the code generator have now been optimised thanks to [gaearon](https://github.com/gaearon).
+  * `for...in` loops have been changed to optimized `for` loops - better performance and no enumeration of protoype keys.
+  * Parts of the code generator have now been optimized thanks to [gaearon](https://github.com/gaearon).
 
 ## 2.12.3
 
@@ -292,7 +484,7 @@ _Note: Gaps between patch versions are faulty/broken releases._
  * **Bug Fix**
   * Support non-string JSX literals.
  * **New Feature**
-  * Loose mode for some transformers that enables non-spec behaviour.
+  * Loose mode for some transformers that enables non-spec behavior.
  * **Internal**
   * Uglify `--mangle sort` has been added to the build script, cutting minified scripts in half.
 
@@ -730,7 +922,7 @@ _Note: Gaps between patch versions are faulty/broken releases._
 
 ## 1.13.2
 
- * Optimise `Array.from` usage by adding a helper method.
+ * Optimize `Array.from` usage by adding a helper method.
  * Upgrade `acorn-6to5`.
 
 ## 1.13.1

CONTRIBUTING.md

@@ -1,6 +1,12 @@
 # Contributing
 
-Contributions are always welcome, no matter how large or small. Before contributing, please read the [code of conduct](https://github.com/6to5/6to5/blob/master/CODE_OF_CONDUCT.md).
+Contributions are always welcome, no matter how large or small. Before
+contributing, please read the
+[code of conduct](https://github.com/6to5/6to5/blob/master/CODE_OF_CONDUCT.md).
+
+**NOTE:** Please do not send pull requests that fix linting issues. It's highly
+likely that they've already been fixed by the time it's submitted and it just
+pollutes the git tree.
 
 ## Developing
 
@@ -12,7 +18,8 @@ Contributions are always welcome, no matter how large or small. Before contribut
 * Link your forked clone (`npm link`)
 * Develop your changes ensuring you're fetching updates from upstream often
 * Ensure the test are passing (`make test`)
-* Create new pull request explaining your proposed change or reference an issue in your commit message
+* Create new pull request explaining your proposed change or reference an issue
+  in your commit message
 
 #### Code Standards
 

Makefile

@@ -5,10 +5,17 @@ UGLIFY_CMD = node_modules/uglify-js/bin/uglifyjs
 JSHINT_CMD = node_modules/jshint/bin/jshint
 MOCHA_CMD = node_modules/mocha/bin/_mocha
 JSCS_CMD = node_modules/jscs/bin/jscs
+6TO5_CMD = node_modules/6to5/bin/6to5
 
 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
+.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
+
+build-core:
+	#node $(6TO5_CMD) src --out-dir lib
+
+watch-core:
+	#node $(6TO5_CMD) src --out-dir lib --watch
 
 build:
 	mkdir -p dist
@@ -18,9 +25,12 @@ build:
 	node $(BROWSERIFY_CMD) -e lib/6to5/polyfill.js >dist/polyfill.js
 	node $(UGLIFY_CMD) dist/polyfill.js >dist/polyfill.min.js
 
-	node $(BROWSERIFY_CMD) lib/6to5/browser.js -s to5 >dist/6to5.js
+	node $(BROWSERIFY_CMD) lib/6to5/api/browser.js -s to5 >dist/6to5.js
 	node $(UGLIFY_CMD) dist/6to5.js >dist/6to5.min.js
 
+	node bin/6to5-runtime >dist/runtime.js
+	node $(UGLIFY_CMD) dist/runtime.js >dist/runtime.min.js
+
 	rm -rf templates.json
 
 clean:
@@ -52,7 +62,7 @@ test-cov:
 	export SIMPLE_6TO5_TESTS=1; \
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 
-test-travis: bootstrap
+test-travis: build-core bootstrap
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 	if test -n "$$CODECLIMATE_REPO_TOKEN"; then codeclimate < coverage/lcov.info; fi
 
@@ -77,6 +87,7 @@ publish:
 	make build
 	cp dist/6to5.min.js browser.js
 	cp dist/polyfill.min.js browser-polyfill.js
+	cp dist/runtime.min.js runtime.js
 
 	node tools/cache-templates
 	test -f templates.json
@@ -88,7 +99,7 @@ publish:
 	make publish-core
 	make publish-runtime
 
-	rm -rf templates.json browser.js browser-polyfill.js
+	rm -rf templates.json browser.js browser-polyfill.js runtime.js
 
 publish-runtime:
 	cd packages; \
@@ -110,3 +121,4 @@ bootstrap:
 	npm install
 	git submodule update --init
 	cd vendor/regenerator; npm install
+	cd vendor/compat-table; npm install object-assign

NOTES.md

@@ -1,3 +1,3 @@
 # Notes
 
- * Wildcard exports/imports wont normalise if `export default` is a non-object. See [#224](https://github.com/6to5/6to5/issues/224).
+ * Wildcard exports/imports wont normalize if `export default` is a non-object. See [#224](https://github.com/6to5/6to5/issues/224).

appveyor.yml

@@ -1,17 +0,0 @@
-environment:
-  matrix:
-    - nodejs_version: "0.10"
-    - nodejs_version: "0.11"
-
-install:
- - "npm install"
- - "cinst make"
-
-test_script:
- - "node --version"
- - "npm --version"
- - "make test-spec"
-
-build: "off"
-
-version: "{build}"

bin/6to5-minify

@@ -0,0 +1,7 @@
+#!/usr/bin/env node
+
+var opts = require("./6to5").opts;
+opts.optional = (opts.optional || []).concat("minification");
+opts.format = {
+  compact: true
+};

bin/6to5-node

@@ -5,7 +5,7 @@
  * when found, before invoking the "real" _6to5-node(1) executable.
  */
 
-var args  = ["--harmony", __dirname + "/_6to5-node"];
+var args  = [__dirname + "/_6to5-node"];
 
 process.argv.slice(2).forEach(function(arg){
   var flag = arg.split("=")[0];
@@ -35,6 +35,7 @@ process.argv.slice(2).forEach(function(arg){
     case "--prof":
     case "--throw-deprecation":
     case "--trace-deprecation":
+    case "--use-strict":
       args.unshift(arg);
       break;
 

bin/6to5-runtime

@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+
+var runtime = require("../lib/6to5/build-runtime");
+console.log(runtime());

bin/6to5/dir.js

@@ -11,9 +11,14 @@ module.exports = function (commander, filenames, opts) {
   }
 
   var write = function (src, relative) {
+    // remove extension and then append back on .js
+    relative = relative.replace(/\.(\w*?)$/, "") + ".js";
+
     var dest = path.join(commander.outDir, relative);
 
-    var data = util.compile(src, { sourceMapName: dest });
+    var data = util.compile(src, {
+      sourceFileName: path.relative(dest + "/..", src)
+    });
 
     if (commander.sourceMaps) {
       var mapLoc = dest + ".map";
@@ -34,8 +39,13 @@ module.exports = function (commander, filenames, opts) {
     if (stat.isDirectory(filename)) {
       var dirname = filename;
 
-      _.each(util.readdirFilter(dirname), function (filename) {
-        write(path.join(dirname, filename), filename);
+      _.each(util.readdir(dirname), function (filename) {
+        var src = path.join(dirname, filename);
+        if (util.canCompile(filename)) {
+          write(src, filename);
+        } else {
+          outputFileSync(path.join(commander.outDir, filename), fs.readFileSync(src));
+        }
       });
     } else {
       write(filename, filename);
@@ -53,10 +63,7 @@ module.exports = function (commander, filenames, opts) {
 
       _.each(["add", "change"], function (type) {
         watcher.on(type, function (filename) {
-          // chop off the dirname plus the path separator
-          var relative = filename.slice(dirname.length + 1);
-
-          console.log(type, filename);
+          var relative = path.relative(dirname, filename) || filename;
           write(filename, relative);
         });
       });

bin/6to5/index.js

@@ -1,15 +1,17 @@
 #!/usr/bin/env node
 
 var commander = require("commander");
-var transform = require("../../lib/6to5/transformation/transform");
+var transform = require("../../lib/6to5/transformation");
 var util      = require("../../lib/6to5/util");
 var fs        = require("fs");
-var _         = require("lodash");
+var each      = require("lodash/collection/each");
+var keys      = require("lodash/object/keys");
 
 commander.option("-t, --source-maps-inline", "Append sourceMappingURL comment to bottom of code");
 commander.option("-s, --source-maps", "Save source map alongside the compiled code");
 commander.option("-f, --filename [filename]", "Filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]", "stdin");
 commander.option("-w, --watch", "Recompile files on changes");
+commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
 commander.option("-e, --experimental", "Enable experimental support for proposed ES7 features");
 commander.option("-p, --playground", "Enable playground support");
 
@@ -21,7 +23,7 @@ commander.option("-L, --loose [list]", "List of transformers to enable loose mod
 commander.option("-o, --out-file [out]", "Compile all input files into a single file");
 commander.option("-d, --out-dir [out]", "Compile an input directory of modules into an output directory");
 commander.option("-c, --remove-comments", "Remove comments from the compiled code", false);
-commander.option("-m, --module-ids", "Insert module id in modules", false);
+commander.option("-M, --module-ids", "Insert module id in modules", false);
 commander.option("-R, --react-compat", "Makes the react transformer produce pre-v0.12 code");
 commander.option("--keep-module-id-extensions", "Keep extensions when generating module ids", false);
 
@@ -30,7 +32,7 @@ commander.on("--help", function () {
     console.log("  " + title + ":");
     console.log();
 
-    _.each(_.keys(obj).sort(), function (key) {
+    each(keys(obj).sort(), function (key) {
       if (key[0] === "_") return;
 
       if (obj[key].optional) {
@@ -58,7 +60,7 @@ var errors = [];
 
 var filenames = commander.args;
 
-_.each(filenames, function (filename) {
+each(filenames, function (filename) {
   if (!fs.existsSync(filename)) {
     errors.push(filename + " doesn't exist");
   }
@@ -107,16 +109,22 @@ exports.opts = {
   sourceMap:              commander.sourceMaps || commander.sourceMapsInline,
   optional:               commander.optional,
   comments:               !commander.removeComments,
+  runtime:                commander.runtime,
   modules:                commander.modules,
   loose:                  commander.loose
 };
 
-var fn;
+setTimeout(function () {
+  // this is just a hack to give `6to5-minify` and other files including this
+  // time to modify `exports.opts`
 
-if (commander.outDir) {
-  fn = require("./dir");
-} else {
-  fn = require("./file");
-}
+  var fn;
 
-fn(commander, filenames, exports.opts);
+  if (commander.outDir) {
+    fn = require("./dir");
+  } else {
+    fn = require("./file");
+  }
+
+  fn(commander, filenames, exports.opts);
+}, 0);

bin/6to5/util.js

@@ -2,7 +2,7 @@ var readdir = require("fs-readdir-recursive");
 var index   = require("./index");
 var util    = require("../../lib/6to5/util");
 var path    = require("path");
-var to5     = require("../../lib/6to5");
+var to5     = require("../../lib/6to5/api/node");
 var fs      = require("fs");
 var _       = require("lodash");
 
@@ -12,12 +12,16 @@ exports.readdirFilter = function (filename) {
   });
 };
 
+exports.readdir = readdir;
+
+exports.canCompile = util.canCompile;
+
 exports.addSourceMappingUrl = function (code, loc) {
   return code + "\n//# sourceMappingURL=" + path.basename(loc);
 };
 
 exports.transform = function (filename, code, opts) {
-  opts = _.extend(opts || {}, index.opts);
+  opts = _.defaults(opts || {}, index.opts);
   opts.filename = filename;
 
   var result;

bin/_6to5-node

@@ -4,7 +4,7 @@ var commander = require("commander");
 var Module    = require("module");
 var path      = require("path");
 var repl      = require("repl");
-var to5       = require("../lib/6to5");
+var to5       = require("../lib/6to5/api/node");
 var util      = require("../lib/6to5/util");
 var vm        = require("vm");
 var _         = require("lodash");
@@ -72,7 +72,8 @@ if (program.eval || program.print) {
       }
 
       if (arg[0] === "-") {
-        if (program[arg.slice(2)]) {
+        var parsedArg = program[arg.slice(2)];
+        if (parsedArg && parsedArg !== true) {
           ignoreNext = true;
         }
       } else {

lib/6to5/api/browser.js

@@ -1,8 +1,8 @@
 "use strict";
 
-var transform = module.exports = require("./transformation/transform");
+var transform = module.exports = require("../transformation");
 
-transform.version = require("../../package").version;
+transform.version = require("../../../package").version;
 
 transform.transform = transform;
 

lib/6to5/api/node.js

@@ -1,22 +1,24 @@
 "use strict";
 
-var transform = require("./transformation/transform");
-var util      = require("./util");
-var fs        = require("fs");
-var _         = require("lodash");
+var isFunction = require("lodash/lang/isFunction");
+var transform  = require("../transformation");
+var util       = require("../util");
+var fs         = require("fs");
 
-exports.version = require("../../package").version;
+exports.version = require("../../../package").version;
 
-exports.types = require("./types");
+exports.runtime = require("../build-runtime");
+
+exports.types = require("../types");
 
 exports.register = function (opts) {
-  var register = require("./register");
+  var register = require("./register/node");
   if (opts != null) register(opts);
   return register;
 };
 
 exports.polyfill = function () {
-  require("./polyfill");
+  require("../polyfill");
 };
 
 exports.canCompile = util.canCompile;
@@ -27,7 +29,7 @@ exports._util = util;
 exports.transform = transform;
 
 exports.transformFile = function (filename, opts, callback) {
-  if (_.isFunction(opts)) {
+  if (isFunction(opts)) {
     callback = opts;
     opts = {};
   }

lib/6to5/api/register/browser.js

@@ -4,4 +4,4 @@
 
 module.exports = function () {};
 
-require("./polyfill");
+require("../../polyfill");

lib/6to5/api/register/cache.js

@@ -12,14 +12,6 @@ exports.save = function () {
 };
 
 exports.load = function () {
-  if (!fs.existsSync(FILENAME)) return;
-
-  try {
-    data = JSON.parse(fs.readFileSync(FILENAME));
-  } catch (err) {
-    return;
-  }
-
   process.on("exit", exports.save);
 
   var sigint = function () {
@@ -29,6 +21,14 @@ exports.load = function () {
   };
 
   process.on("SIGINT", sigint);
+
+  if (!fs.existsSync(FILENAME)) return;
+
+  try {
+    data = JSON.parse(fs.readFileSync(FILENAME));
+  } catch (err) {
+    return;
+  }
 };
 
 exports.get = function () {

lib/6to5/api/register/node.js

@@ -0,0 +1,152 @@
+"use strict";
+
+require("../../polyfill");
+
+var sourceMapSupport = require("source-map-support");
+var registerCache    = require("./cache");
+var extend           = require("lodash/object/extend");
+var each             = require("lodash/collection/each");
+var util             = require("../../util");
+var to5              = require("../node");
+var fs               = require("fs");
+
+sourceMapSupport.install({
+  retrieveSourceMap: function (source) {
+    var map = maps && maps[source];
+    if (map) {
+      return {
+        url: null,
+        map: map
+      };
+    } else {
+      return null;
+    }
+  }
+});
+
+//
+
+registerCache.load();
+var cache = registerCache.get();
+
+//
+
+var transformOpts = {};
+var ignoreRegex   = /node_modules/;
+var onlyRegex;
+var exts          = {};
+var maps          = {};
+
+var mtime = function (filename) {
+  return +fs.statSync(filename).mtime;
+};
+
+var compile = function (filename) {
+  var result;
+
+  var cacheKey = filename + ":" + JSON.stringify(transformOpts);
+
+  if (cache) {
+    var cached = cache[cacheKey];
+    if (cached && cached.mtime === mtime(filename)) {
+      result = cached;
+    }
+  }
+
+  if (!result) {
+    result = to5.transformFileSync(filename, extend({
+      sourceMap: true,
+      ast:       false
+    }, transformOpts));
+  }
+
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[cacheKey] = result;
+  }
+
+  maps[filename] = result.map;
+
+  return result.code;
+};
+
+var shouldIgnore = function (filename) {
+  return (ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename));
+};
+
+var istanbulMonkey = {};
+
+if (process.env.running_under_istanbul) { // jshint ignore:line
+  // we need to monkey patch fs.readFileSync so we can hook into
+  // what istanbul gets, it's extremely dirty but it's the only way
+  var _readFileSync = fs.readFileSync;
+
+  fs.readFileSync = function (filename) {
+    if (istanbulMonkey[filename]) {
+      delete istanbulMonkey[filename];
+      var code = compile(filename);
+      istanbulMonkey[filename] = true;
+      return code;
+    } else {
+      return _readFileSync.apply(this, arguments);
+    }
+  };
+}
+
+var istanbulLoader = function (m, filename, old) {
+  istanbulMonkey[filename] = true;
+  old(m, filename);
+};
+
+var normalLoader = function (m, filename) {
+  m._compile(compile(filename), filename);
+};
+
+var registerExtension = function (ext) {
+  var old = require.extensions[ext];
+
+  var loader = normalLoader;
+  if (process.env.running_under_istanbul) loader = istanbulLoader; // jshint ignore:line
+
+  require.extensions[ext] = function (m, filename) {
+    if (shouldIgnore(filename)) {
+      old(m, filename);
+    } else {
+      loader(m, filename, old);
+    }
+  };
+};
+
+var hookExtensions = function (_exts) {
+  each(exts, function (old, ext) {
+    require.extensions[ext] = old;
+  });
+
+  exts = {};
+
+  each(_exts, function (ext) {
+    exts[ext] = require.extensions[ext];
+    registerExtension(ext);
+  });
+};
+
+hookExtensions(util.canCompile.EXTENSIONS);
+
+module.exports = function (opts) {
+  // normalize options
+  opts = opts || {};
+
+  if (opts.only != null) onlyRegex = util.regexify(opts.only);
+  if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);
+
+  if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
+
+  if (opts.cache === false) cache = null;
+
+  delete opts.extensions;
+  delete opts.ignore;
+  delete opts.cache;
+  delete opts.only;
+
+  extend(transformOpts, opts);
+};

lib/6to5/build-helpers.js

@@ -0,0 +1,13 @@
+var File = require("./transformation/file");
+var util = require("./util");
+var each = require("lodash/collection/each");
+var t    = require("./types");
+
+module.exports = function (body, namespace) {
+  each(File.helpers, function (name) {
+    var key = t.identifier(t.toIdentifier(name));
+    body.push(t.expressionStatement(
+      t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))
+    ));
+  });
+};

lib/6to5/build-runtime.js

@@ -0,0 +1,25 @@
+"use strict";
+
+var buildHelpers = require("./build-helpers");
+var generator    = require("./generation");
+var util         = require("./util");
+var t            = require("./types");
+
+module.exports = function () {
+  var namespace = t.identifier("to5Runtime");
+
+  var body      = [];
+  var container = t.functionExpression(null, [t.identifier("global")], t.blockStatement(body));
+  var tree      = t.program([t.expressionStatement(t.callExpression(container, [util.template("self-global")]))]);
+
+  body.push(t.variableDeclaration("var", [
+    t.variableDeclarator(
+      namespace,
+      t.assignmentExpression("=", t.memberExpression(t.identifier("global"), namespace), t.objectExpression([]))
+    )
+  ]));
+
+  buildHelpers(body, namespace);
+
+  return generator(tree).code;
+};

lib/6to5/detection/index.js

@@ -0,0 +1,29 @@
+module.exports = detect;
+
+var SYNTAX_KEYS = require("./syntax-keys");
+var traverse    = require("../traversal");
+var visitors    = traverse.explode(require("./visitors"));
+
+function detect(ast) {
+  var stats = {
+    syntax: {},
+    builtins: {}
+  };
+
+  var detectedSyntax = function (name) {
+    stats.syntax[name] = true;
+  };
+
+  traverse(ast, {
+    enter: function (node, parent) {
+      if (SYNTAX_KEYS[node.type]) {
+        detectedSyntax(SYNTAX_KEYS[node.type]);
+      }
+
+      var visitor = visitors[node.type];
+      if (visitor) visitor(node, parent, detectedSyntax);
+    }
+  });
+
+  return stats;
+}

lib/6to5/detection/syntax-keys.json

@@ -0,0 +1,84 @@
+{
+  "ArrowFunctionExpression":   "es6.arrowFunctions",
+
+  "AwaitExpression":           "es7.asyncFunctions",
+
+  "ClassBody":                 "es6.classes",
+  "ClassDeclaration":          "es6.classes",
+  "ClassExpression":           "es6.classes",
+  "MethodDefinition":          "es6.classes",
+
+  "ComprehensionBlock":        "es7.comprehensions",
+  "ComprehensionExpression":   "es7.comprehensions",
+
+  "ForOfStatement":            "es6.forOf",
+
+  "ExportBatchSpecifier":      "es6.modules",
+  "ExportDeclaration":         "es6.modules",
+  "ExportSpecifier":           "es6.modules",
+  "ImportBatchSpecifier":      "es6.modules",
+  "ImportDeclaration":         "es6.modules",
+  "ImportSpecifier":           "es6.modules",
+
+  "ArrayPattern":              "es6.destructuring",
+  "AssignmentPattern":         "es6.destructuring",
+  "ObjectPattern":             "es6.destructuring",
+
+  "RestElement":               "es6.parameters.rest",
+
+  "SpreadElement":             "es6.spread",
+
+  "SpreadProperty":            "es7.objectSpread",
+
+  "TaggedTemplateExpression":  "es6.templateLiterals",
+  "TemplateElement":           "es6.templateLiterals",
+  "TemplateLiteral":           "es6.templateLiterals",
+
+  "VirtualPropertyExpression": "es7.abstractReferences",
+  "PrivateDeclaration":        "es7.abstractReferences",
+
+  "YieldExpression":           "es6.generators",
+
+  "AnyTypeAnnotation":           "flow",
+  "ArrayTypeAnnotation":         "flow",
+  "BooleanTypeAnnotation":       "flow",
+  "ClassProperty":               "flow",
+  "DeclareClass":                "flow",
+  "DeclareFunction":             "flow",
+  "DeclareModule":               "flow",
+  "DeclareVariable":             "flow",
+  "FunctionTypeAnnotation":      "flow",
+  "FunctionTypeParam":           "flow",
+  "GenericTypeAnnotation":       "flow",
+  "InterfaceExtends":            "flow",
+  "InterfaceDeclaration":        "flow",
+  "IntersectionTypeAnnotation":  "flow",
+  "NullableTypeAnnotation":      "flow",
+  "NumberTypeAnnotation":        "flow",
+  "StringLiteralTypeAnnotation": "flow",
+  "StringTypeAnnotation":        "flow",
+  "TupleTypeAnnotation":         "flow",
+  "TypeofTypeAnnotation":        "flow",
+  "TypeAlias":                   "flow",
+  "TypeAnnotation":              "flow",
+  "TypeParameterDeclaration":    "flow",
+  "TypeParameterInstantiation":  "flow",
+  "ObjectTypeAnnotation":        "flow",
+  "ObjectTypeCallProperty":      "flow",
+  "ObjectTypeIndexer":           "flow",
+  "ObjectTypeProperty":          "flow",
+  "QualifiedTypeIdentifier":     "flow",
+  "UnionTypeAnnotation":         "flow",
+  "VoidTypeAnnotation":          "flow",
+
+  "JSXAttribute":              "jsx",
+  "JSXClosingElement":         "jsx",
+  "JSXElement":                "jsx",
+  "JSXEmptyExpression":        "jsx",
+  "JSXExpressionContainer":    "jsx",
+  "JSXIdentifier":             "jsx",
+  "JSXMemberExpression":       "jsx",
+  "JSXNamespacedName":         "jsx",
+  "JSXOpeningElement":         "jsx",
+  "JSXSpreadAttribute":        "jsx"
+}

lib/6to5/detection/visitors.js

@@ -0,0 +1,54 @@
+var t = require("../types");
+var includes = require("lodash/collection/includes");
+
+exports.AssignmentExpression = function (node, parent, detected) {
+  if (node.operator === "**=") {
+    detected("es6.exponentation");
+  }
+};
+
+exports.BinaryExpression = function (node, parent, detected) {
+  if (node.operator === "**") {
+    detected("es6.exponentation");
+  }
+};
+
+exports.VariableDeclaration = function (node, parent, detected) {
+  if (node.kind === "let" || node.kind === "const") {
+    detected("es6.blockScoping");
+  }
+
+  if (node.kind === "const") {
+    detected("es6.constants");
+  }
+};
+
+exports.Property = function (node, parent, detected) {
+  if (node.shorthand || node.method) {
+    detected("es6.properties.shorthand");
+  }
+
+  if (node.kind === "set" || node.kind === "get") {
+    detected("es5.properties.mutators");
+  }
+
+  if (node.computed) {
+    detected("es6.properties.computed");
+  }
+};
+
+exports.AssignmentPattern = function (node, parent, detected) {
+  if (t.isFunction(parent) && includes(parent.params, node)) {
+    detected("es6.parameters.default");
+  }
+};
+
+exports.Function = function (node, parent, detected) {
+  if (node.generator) {
+    detected("es6.generators");
+  }
+
+  if (node.async) {
+    detected("es7.asyncFunctions");
+  }
+};

lib/6to5/generation/buffer.js

@@ -2,8 +2,10 @@
 
 module.exports = Buffer;
 
-var util = require("../util");
-var _    = require("lodash");
+var isBoolean = require("lodash/lang/isBoolean");
+var includes  = require("lodash/collection/includes");
+var isNumber  = require("lodash/lang/isNumber");
+var util      = require("../util");
 
 function Buffer(position, format) {
   this.position = position;
@@ -17,7 +19,7 @@ Buffer.prototype.get = function () {
 };
 
 Buffer.prototype.getIndent = function () {
-  if (this.format.compact) {
+  if (this.format.compact || this.format.concise) {
     return "";
   } else {
     return util.repeat(this._indent, this.format.indent.style);
@@ -51,10 +53,12 @@ Buffer.prototype.rightBrace = function () {
 
 Buffer.prototype.keyword = function (name) {
   this.push(name);
-  this.push(" ");
+  this.space();
 };
 
 Buffer.prototype.space = function () {
+  if (this.format.compact) return;
+
   if (this.buf && !this.isLast([" ", "\n"])) {
     this.push(" ");
   }
@@ -68,14 +72,14 @@ Buffer.prototype.removeLast = function (cha) {
 };
 
 Buffer.prototype.newline = function (i, removeLast) {
-  if (this.format.compact) {
+  if (this.format.compact || this.format.concise) {
     this.space();
     return;
   }
 
   removeLast = removeLast || false;
 
-  if (_.isNumber(i)) {
+  if (isNumber(i)) {
     if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
@@ -85,7 +89,7 @@ Buffer.prototype.newline = function (i, removeLast) {
     return;
   }
 
-  if (_.isBoolean(i)) {
+  if (isBoolean(i)) {
     removeLast = i;
   }
 
@@ -155,7 +159,7 @@ Buffer.prototype.isLast = function (cha, trimRight) {
   var last = buf[buf.length - 1];
 
   if (Array.isArray(cha)) {
-    return _.contains(cha, last);
+    return includes(cha, last);
   } else {
     return cha === last;
   }

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

@@ -1,8 +1,8 @@
 "use strict";
 
-var util = require("../../util");
-var t    = require("../../types");
-var _    = require("lodash");
+var util     = require("../../util");
+var t        = require("../../types");
+var isNumber = require("lodash/lang/isNumber");
 
 exports.UnaryExpression = function (node, print) {
   var hasSpace = /[a-z]$/.test(node.operator);
@@ -17,7 +17,7 @@ exports.UnaryExpression = function (node, print) {
   }
 
   this.push(node.operator);
-  if (hasSpace) this.space();
+  if (hasSpace) this.push(" ");
   print(node.argument);
 };
 
@@ -33,9 +33,13 @@ exports.UpdateExpression = function (node, print) {
 
 exports.ConditionalExpression = function (node, print) {
   print(node.test);
-  this.push(" ? ");
+  this.space();
+  this.push("?");
+  this.space();
   print(node.consequent);
-  this.push(" : ");
+  this.space();
+  this.push(":");
+  this.space();
   print(node.alternate);
 };
 
@@ -44,13 +48,13 @@ exports.NewExpression = function (node, print) {
   print(node.callee);
   if (node.arguments.length || this.format.parentheses) {
     this.push("(");
-    print.join(node.arguments, { separator: ", " });
+    print.list(node.arguments);
     this.push(")");
   }
 };
 
 exports.SequenceExpression = function (node, print) {
-  print.join(node.expressions, { separator: ", " });
+  print.list(node.expressions);
 };
 
 exports.ThisExpression = function () {
@@ -72,9 +76,7 @@ exports.CallExpression = function (node, print) {
     separator += " ";
   }
 
-  print.join(node.arguments, {
-    separator: separator
-  });
+  print.list(node.arguments, { separator: separator });
 
   if (node._prettyCall) {
     this.newline();
@@ -115,10 +117,11 @@ exports.BinaryExpression =
 exports.LogicalExpression =
 exports.AssignmentPattern =
 exports.AssignmentExpression = function (node, print) {
+  // todo: add cases where the spaces can be dropped when in compact mode
   print(node.left);
-  this.space();
+  this.push(" ");
   this.push(node.operator);
-  this.space();
+  this.push(" ");
   print(node.right);
 };
 
@@ -133,7 +136,7 @@ exports.MemberExpression = function (node, print) {
   }
 
   var computed = node.computed;
-  if (t.isLiteral(node.property) && _.isNumber(node.property.value)) {
+  if (t.isLiteral(node.property) && isNumber(node.property.value)) {
     computed = true;
   }
 

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

@@ -1,7 +1,7 @@
 "use strict";
 
-var t = require("../../types");
-var _ = require("lodash");
+var t    = require("../../types");
+var each = require("lodash/collection/each");
 
 exports.JSXAttribute = function (node, print) {
   print(node.name);
@@ -47,7 +47,7 @@ exports.JSXElement = function (node, print) {
   if (open.selfClosing) return;
 
   this.indent();
-  _.each(node.children, function (child) {
+  each(node.children, function (child) {
     if (t.isLiteral(child)) {
       self.push(child.value);
     } else {
@@ -75,6 +75,4 @@ exports.JSXClosingElement = function (node, print) {
   this.push(">");
 };
 
-exports.JSXEmptyExpression = function () {
-
-};
+exports.JSXEmptyExpression = function () {};

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

@@ -4,11 +4,7 @@ var t = require("../../types");
 
 exports._params = function (node, print) {
   this.push("(");
-
-  print.join(node.params, {
-    separator: ", "
-  });
-
+  print.list(node.params);
   this.push(")");
 };
 
@@ -45,11 +41,14 @@ exports.FunctionExpression = function (node, print) {
   if (node.async) this.push("async ");
   this.push("function");
   if (node.generator) this.push("*");
-  this.push(" ");
+
   if (node.id) {
-    this.space();
+    this.push(" ");
     print(node.id);
+  } else {
+    this.space();
   }
+
   this._params(node, print);
   this.space();
   print(node.body);

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

@@ -1,7 +1,7 @@
 "use strict";
 
-var t = require("../../types");
-var _ = require("lodash");
+var t    = require("../../types");
+var each = require("lodash/collection/each");
 
 exports.ImportSpecifier = function (node, print) {
   if (t.isSpecifierDefault(node)) {
@@ -66,7 +66,7 @@ exports.ImportDeclaration = function (node, print) {
   if (specfiers && specfiers.length) {
     var foundImportSpecifier = false;
 
-    _.each(node.specifiers, function (spec, i) {
+    each(node.specifiers, function (spec, i) {
       if (+i > 0) {
         self.push(", ");
       }

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

@@ -1,8 +1,8 @@
 "use strict";
 
-var _ = require("lodash");
+var each = require("lodash/collection/each");
 
-_.each(["BindMemberExpression", "BindFunctionExpression"], function (type) {
+each(["BindMemberExpression", "BindFunctionExpression"], function (type) {
   exports[type] = function () {
     throw new ReferenceError("Trying to render non-standard playground node " + JSON.stringify(type));
   };

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

@@ -21,8 +21,13 @@ exports.IfStatement = function (node, print) {
   print.indentOnComments(node.consequent);
 
   if (node.alternate) {
-    if (this.isLast("}")) this.push(" ");
+    if (this.isLast("}")) this.space();
     this.keyword("else");
+
+    if (this.format.format && !t.isBlockStatement(node.alternate)) {
+      this.push(" ");
+    }
+
     print.indentOnComments(node.alternate);
   }
 };
@@ -190,7 +195,7 @@ exports.VariableDeclaration = function (node, print, parent) {
     sep += " ";
   }
 
-  print.join(node.declarations, { separator: sep });
+  print.list(node.declarations, { separator: sep });
 
   if (!t.isFor(parent)) {
     this.semicolon();

lib/6to5/generation/generators/template-literals.js

@@ -1,6 +1,6 @@
 "use strict";
 
-var _ = require("lodash");
+var each = require("lodash/collection/each");
 
 exports.TaggedTemplateExpression = function (node, print) {
   print(node.tag);
@@ -18,7 +18,7 @@ exports.TemplateLiteral = function (node, print) {
   var self   = this;
   var len    = quasis.length;
 
-  _.each(quasis, function (quasi, i) {
+  each(quasis, function (quasi, i) {
     print(quasi);
 
     if (i + 1 < len) {

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

@@ -1,6 +1,6 @@
 "use strict";
 
-var _ = require("lodash");
+var each = require("lodash/collection/each");
 
 exports.Identifier = function (node) {
   this.push(node.name);
@@ -27,7 +27,7 @@ exports.ObjectPattern = function (node, print) {
     this.push("{");
     this.space();
 
-    print.join(props, { separator: ", ", indent: true });
+    print.list(props, { indent: true });
 
     this.space();
     this.push("}");
@@ -49,7 +49,8 @@ exports.Property = function (node, print) {
       if (node.shorthand) return;
     }
 
-    this.push(": ");
+    this.push(":");
+    this.space();
     print(node.value);
   }
 };
@@ -62,7 +63,7 @@ exports.ArrayPattern = function (node, print) {
 
   this.push("[");
 
-  _.each(elems, function (elem, i) {
+  each(elems, function (elem, i) {
     if (!elem) {
       // If the array expression ends with a hole, that hole
       // will be ignored by the interpreter, but if it ends with
@@ -71,7 +72,7 @@ exports.ArrayPattern = function (node, print) {
       // both (all) of the holes.
       self.push(",");
     } else {
-      if (i > 0) self.push(" ");
+      if (i > 0 && !self.format.compact) self.push(" ");
       print(elem);
       if (i < len - 1) self.push(",");
     }
@@ -93,8 +94,10 @@ exports.Literal = function (node) {
     });
 
     this.push(val);
-  } else if (type === "boolean" || type === "number") {
-    this.push(JSON.stringify(val));
+  } else if (type === "number") {
+    this.push(val + "");
+  } else if (type === "boolean") {
+    this.push(val ? "true" : "false");
   } else if (node.regex) {
     this.push("/" + node.regex.pattern + "/" + node.regex.flags);
   } else if (val === null) {

lib/6to5/generation/index.js

@@ -12,17 +12,20 @@ var Whitespace   = require("./whitespace");
 var SourceMap    = require("./source-map");
 var Position     = require("./position");
 var Buffer       = require("./buffer");
+var extend       = require("lodash/object/extend");
+var merge        = require("lodash/object/merge");
+var each         = require("lodash/collection/each");
 var util         = require("../util");
 var n            = require("./node");
 var t            = require("../types");
-var _            = require("lodash");
 
 function CodeGenerator(ast, opts, code) {
   opts = opts || {};
 
   this.comments = ast.comments || [];
   this.tokens   = ast.tokens || [];
-  this.format   = CodeGenerator.normaliseOptions(code, opts);
+  this.format   = CodeGenerator.normalizeOptions(code, opts);
+  this.opts     = opts;
   this.ast      = ast;
 
   this.whitespace = new Whitespace(this.tokens, this.comments);
@@ -31,21 +34,24 @@ function CodeGenerator(ast, opts, code) {
   this.buffer     = new Buffer(this.position, this.format);
 }
 
-_.each(Buffer.prototype, function (fn, key) {
+each(Buffer.prototype, function (fn, key) {
   CodeGenerator.prototype[key] = function () {
     return fn.apply(this.buffer, arguments);
   };
 });
 
-CodeGenerator.normaliseOptions = function (code, opts) {
-  var indent = detectIndent(code);
-  var style  = indent.indent;
-  if (!style || style === " ") style = "  ";
+CodeGenerator.normalizeOptions = function (code, opts) {
+  var style = "  ";
+  if (code) {
+    var indent = detectIndent(code).indent;
+    if (indent && indent !== " ") style = indent;
+  }
 
-  return _.merge({
+  return merge({
     parentheses: true,
     comments: opts.comments == null || opts.comments,
     compact: false,
+    concise: false,
     indent: {
       adjustMultilineComment: true,
       style: style,
@@ -69,8 +75,8 @@ CodeGenerator.generators = {
   jsx:              require("./generators/jsx")
 };
 
-_.each(CodeGenerator.generators, function (generator) {
-  _.extend(CodeGenerator.prototype, generator);
+each(CodeGenerator.generators, function (generator) {
+  extend(CodeGenerator.prototype, generator);
 });
 
 CodeGenerator.prototype.generate = function () {
@@ -79,7 +85,7 @@ CodeGenerator.prototype.generate = function () {
   this.print(ast);
 
   var comments = [];
-  _.each(ast.comments, function (comment) {
+  each(ast.comments, function (comment) {
     if (!comment._displayed) comments.push(comment);
   });
   this._printComments(comments);
@@ -107,6 +113,16 @@ CodeGenerator.prototype.buildPrint = function (parent) {
     return self.printJoin(print, nodes, opts);
   };
 
+  print.list = function (items, opts) {
+    opts = opts || {};
+
+    var sep = opts.separator || ", ";
+    if (self.format.compact) sep = ",";
+    opts.separator = sep;
+
+    print.join(items, opts);
+  };
+
   print.block = function (node) {
     return self.printBlock(print, node);
   };
@@ -125,9 +141,9 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
     node._compact = true;
   }
 
-  var oldCompact = this.format.compact;
+  var oldConcise = this.format.concise;
   if (node._compact) {
-    this.format.compact = true;
+    this.format.concise = true;
   }
 
   var self = this;
@@ -195,7 +211,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
     throw new ReferenceError("unknown node of type " + JSON.stringify(node.type) + " with constructor " + JSON.stringify(node && node.constructor.name));
   }
 
-  this.format.compact = oldCompact;
+  this.format.concise = oldConcise;
 };
 
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
@@ -208,7 +224,7 @@ CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
 
   if (opts.indent) self.indent();
 
-  _.each(nodes, function (node, i) {
+  each(nodes, function (node, i) {
     print(node, {
       statement: opts.statement,
       after: function () {
@@ -273,7 +289,7 @@ CodeGenerator.prototype.getComments = function (key, node, parent) {
     nodes.push(node.argument);
   }
 
-  _.each(nodes, function (node) {
+  each(nodes, function (node) {
     comments = comments.concat(self._getComments(key, node));
   });
 
@@ -291,11 +307,11 @@ CodeGenerator.prototype._printComments = function (comments) {
 
   var self = this;
 
-  _.each(comments, function (comment) {
+  each(comments, function (comment) {
     var skip = false;
 
     // find the original comment in the ast and set it as displayed
-    _.each(self.ast.comments, function (origComment) {
+    each(self.ast.comments, function (origComment) {
       if (origComment.start === comment.start) {
         // comment has already been output
         if (origComment._displayed) skip = true;

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

@@ -5,7 +5,8 @@ module.exports = Node;
 var whitespace = require("./whitespace");
 var parens     = require("./parentheses");
 var t          = require("../../types");
-var _          = require("lodash");
+var each       = require("lodash/collection/each");
+var some       = require("lodash/collection/some");
 
 var find = function (obj, node, parent) {
   if (!obj) return;
@@ -44,7 +45,7 @@ Node.needsWhitespace = function (node, parent, type) {
   var lines = find(whitespace[type].nodes, node, parent);
   if (lines) return lines;
 
-  _.each(find(whitespace[type].list, node, parent), function (expr) {
+  each(find(whitespace[type].list, node, parent), function (expr) {
     lines = Node.needsWhitespace(expr, node, type);
     if (lines) return false;
   });
@@ -65,7 +66,7 @@ Node.needsParens = function (node, parent) {
   if (t.isNewExpression(parent) && parent.callee === node) {
     if (t.isCallExpression(node)) return true;
 
-    var hasCall = _.some(node, function (val) {
+    var hasCall = some(node, function (val) {
       return t.isCallExpression(val);
     });
     if (hasCall) return true;
@@ -94,7 +95,7 @@ Node.needsParensNoLineTerminator = function (node, parent) {
   return false;
 };
 
-_.each(Node, function (fn, key) {
+each(Node, function (fn, key) {
   Node.prototype[key] = function () {
     // Avoid leaking arguments to prevent deoptimization
     var args = new Array(arguments.length + 2);

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

@@ -1,11 +1,11 @@
 "use strict";
 
-var t = require("../../types");
-var _ = require("lodash");
+var t    = require("../../types");
+var each = require("lodash/collection/each");
 
 var PRECEDENCE = {};
 
-_.each([
+each([
   ["||"],
   ["&&"],
   ["|"],
@@ -18,7 +18,7 @@ _.each([
   ["*", "/", "%"],
   ["**"]
 ], function (tier, i) {
-  _.each(tier, function (op) {
+  each(tier, function (op) {
     PRECEDENCE[op] = i;
   });
 });

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

@@ -1,7 +1,9 @@
 "use strict";
 
-var _ = require("lodash");
-var t = require("../../types");
+var t        = require("../../types");
+var each     = require("lodash/collection/each");
+var map      = require("lodash/collection/map");
+var isNumber = require("lodash/lang/isNumber");
 
 exports.before = {
   nodes: {
@@ -31,6 +33,10 @@ exports.before = {
 
 exports.after = {
   nodes: {
+    LogicalExpression: function (node) {
+      return t.isFunction(node.left) || t.isFunction(node.right);
+    },
+
     AssignmentExpression: function (node) {
       if (t.isFunction(node.right)) {
         return 1;
@@ -40,7 +46,7 @@ exports.after = {
 
   list: {
     VariableDeclaration: function (node) {
-      return _.map(node.declarations, "init");
+      return map(node.declarations, "init");
     },
 
     ArrayExpression: function (node) {
@@ -53,7 +59,7 @@ exports.after = {
   }
 };
 
-_.each({
+each({
   Function: 1,
   Class: 1,
   For: 1,
@@ -64,12 +70,12 @@ _.each({
   CallExpression: { after: 1 },
   Literal: { after: 1 }
 }, function (amounts, type) {
-  if (_.isNumber(amounts)) {
+  if (isNumber(amounts)) {
     amounts = { after: amounts, before: amounts };
   }
 
-  _.each([type].concat(t.FLIPPED_ALIAS_KEYS[type] || []), function (type) {
-    _.each(amounts, function (amount, key) {
+  each([type].concat(t.FLIPPED_ALIAS_KEYS[type] || []), function (type) {
+    each(amounts, function (amount, key) {
       exports[key].nodes[type] = function () {
         return amount;
       };

lib/6to5/generation/source-map.js

@@ -48,8 +48,6 @@ SourceMap.prototype.mark = function (node, type) {
 
   var original = loc[type];
 
-  if (generated.line === original.line && generated.column === original.column) return; // nothing to map
-
   map.addMapping({
     source: this.opts.sourceFileName,
     generated: generated,

lib/6to5/generation/whitespace.js

@@ -2,7 +2,7 @@
 
 module.exports = Whitespace;
 
-var _    = require("lodash");
+var sortBy = require("lodash/collection/sortBy");
 
 /**
  * Returns `i`th number from `base`, continuing from 0 when `max` is reached.
@@ -23,7 +23,7 @@ function getLookupIndex(i, base, max) {
 }
 
 function Whitespace(tokens, comments) {
-  this.tokens = _.sortBy(tokens.concat(comments), "start");
+  this.tokens = sortBy(tokens.concat(comments), "start");
   this.used   = {};
 
   // Profiling this code shows that while generator passes over it, indexes

lib/6to5/helpers/code-frame.js

@@ -47,7 +47,7 @@ module.exports = function (lines, lineNumber, colNumber) {
     lines = highlight(lines);
   }
 
-  lines = lines.split("\n");
+  lines = lines.split(/\r\n|[\n\r\u2028\u2029]/);
 
   var start = Math.max(lineNumber - 3, 0);
   var end   = Math.min(lines.length, lineNumber + 3);

lib/6to5/helpers/levenshtein.js

@@ -0,0 +1,38 @@
+// taken from stackoverflow, it's crap i know.
+
+module.exports = function (a, b) {
+  if (a.length === 0) return b.length;
+  if (b.length === 0) return a.length;
+
+  var matrix = [];
+
+  // increment along the first column of each row
+  var i;
+  for (i = 0; i <= b.length; i++) {
+    matrix[i] = [i];
+  }
+
+  // increment each column in the first row
+  var j;
+  for (j = 0; j <= a.length; j++) {
+    matrix[0][j] = j;
+  }
+
+  // Fill in the rest of the matrix
+  for (i = 1; i <= b.length; i++) {
+    for (j = 1; j <= a.length; j++) {
+      if (b.charAt(i - 1) == a.charAt(j - 1)) {
+        matrix[i][j] = matrix[i - 1][j - 1];
+      } else {
+        matrix[i][j] = Math.min(
+          matrix[i - 1][j - 1] + 1, // substitution
+          Math.min(
+            matrix[i][j - 1] + 1, // insertion
+            matrix[i - 1][j] + 1) // deletion
+          );
+      }
+    }
+  }
+
+  return matrix[b.length][a.length];
+};

lib/6to5/helpers/normalize-ast.js

@@ -0,0 +1,9 @@
+var t = require("../types");
+
+module.exports = function (ast, comments, tokens) {
+  if (ast && ast.type === "Program") {
+    return t.file(ast, comments || [], tokens || []);
+  } else {
+    throw new Error("Not a valid ast?");
+  }
+};

lib/6to5/helpers/parse.js

@@ -0,0 +1,49 @@
+var normalizeAst = require("./normalize-ast");
+var estraverse   = require("estraverse");
+var codeFrame    = require("./code-frame");
+var acorn        = require("acorn-6to5");
+
+module.exports = function (opts, code, callback) {
+  try {
+    var comments = [];
+    var tokens   = [];
+
+    var ast = acorn.parse(code, {
+      allowImportExportEverywhere: opts.allowImportExportEverywhere,
+      allowReturnOutsideFunction:  !opts._anal,
+      ecmaVersion:                 opts.experimental ? 7 : 6,
+      playground:                  opts.playground,
+      strictMode:                  opts.strictMode,
+      onComment:                   comments,
+      locations:                   true,
+      onToken:                     tokens,
+      ranges:                      true
+    });
+
+    estraverse.attachComments(ast, comments, tokens);
+
+    ast = normalizeAst(ast, comments, tokens);
+
+    if (callback) {
+      return callback(ast);
+    } else {
+      return ast;
+    }
+  } catch (err) {
+    if (!err._6to5) {
+      err._6to5 = true;
+      var message = opts.filename + ": " + err.message;
+
+      var loc = err.loc;
+      if (loc) {
+        var frame = codeFrame(code, loc.line, loc.column + 1);
+        message += frame;
+      }
+
+      if (err.stack) err.stack = err.stack.replace(err.message, message);
+      err.message = message;
+    }
+
+    throw err;
+  }
+};

lib/6to5/messages.js

@@ -0,0 +1,48 @@
+var util = require("util");
+
+exports.messages = {
+  tailCallReassignmentDeopt: "Function reference has been reassigned so it's probably be dereferenced so we can't optimise this with confidence",
+  JSXNamespacedTags: "Namespace tags are not supported. ReactJSX is not XML.",
+  classesIllegalBareSuper: "Illegal use of bare super",
+  classesIllegalSuperCall: "Direct super call is illegal in non-constructor, use super.$1() instead",
+  classesIllegalConstructorKind: "Illegal kind for constructor method",
+  scopeDuplicateDeclaration: "Duplicate declaration $1",
+  undeclaredVariable: "Reference to undeclared variable $1",
+  undeclaredVariableSuggestion: "Reference to undeclared variable $1 - did you mean $2?",
+  settersInvalidParamLength: "Setters must have only one parameter",
+  noAssignmentsInForHead: "No assignments allowed in for-in/of head",
+  expectedMemberExpressionOrIdentifier: "Expected type MemeberExpression or Identifier",
+  invalidParentForThisNode: "We don't know how to handle this node within the current parent - please open an issue",
+  readOnly: "$1 is read-only",
+  modulesIllegalExportName: "Illegal export $1",
+  unknownForHead: "Unknown node type $1 in ForStatement"
+};
+
+exports.get = function (key) {
+  var msg = exports.messages[key];
+  if (!msg) throw new ReferenceError("Unknown message `" + key + "`");
+
+  var args = [];
+  for (var i = 1; i < arguments.length; i++) {
+    args.push(arguments[i]);
+  }
+  args = exports.parseArgs(args);
+
+  return msg.replace(/\$(\d+)/g, function (str, i) {
+    return args[--i];
+  });
+};
+
+exports.parseArgs = function (args) {
+  return args.map(function (val) {
+    if (val != null && val.inspect) {
+      return val.inspect();
+    } else {
+      try {
+        return JSON.stringify(val) || val + "";
+      } catch (e) {
+        return util.inspect(val);
+      }
+    }
+  });
+};

lib/6to5/patch.js

@@ -1,14 +1,12 @@
 "use strict";
 
-var t = require("./types");
-var _ = require("lodash");
-
-require("./types/node");
+var extend = require("lodash/object/extend");
+var t      = require("./types");
 
 // estraverse
 
 var estraverse = require("estraverse");
-_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
 
 // regenerator-6to5/ast-types
 

lib/6to5/register.js

@@ -1,107 +0,0 @@
-"use strict";
-
-require("./polyfill");
-
-var sourceMapSupport = require("source-map-support");
-var registerCache    = require("./register-cache");
-var util             = require("./util");
-var to5              = require("./index");
-var fs               = require("fs");
-var _                = require("lodash");
-
-sourceMapSupport.install({
-  retrieveSourceMap: function (source) {
-    var map = maps && maps[source];
-    if (map) {
-      return {
-        url: null,
-        map: map
-      };
-    } else {
-      return null;
-    }
-  }
-});
-
-//
-
-registerCache.load();
-var cache = registerCache.get();
-
-//
-
-var transformOpts = {};
-var ignoreRegex   = /node_modules/;
-var onlyRegex;
-var whitelist     = [];
-var exts          = {};
-var maps          = {};
-var old           = require.extensions[".js"];
-
-var mtime = function (filename) {
-  return +fs.statSync(filename).mtime;
-};
-
-var loader = function (m, filename) {
-  if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
-    return old.apply(this, arguments);
-  }
-
-  var result;
-
-  if (cache) {
-    var cached = cache[filename];
-    if (cached && cached.mtime === mtime(filename)) {
-      result = cached;
-    }
-  }
-
-  result = result || to5.transformFileSync(filename, _.extend({
-    whitelist: whitelist,
-    sourceMap: true,
-    ast:       false
-  }, transformOpts));
-
-  if (cache) {
-    result.mtime = mtime(filename);
-    cache[filename] = result;
-  }
-
-  maps[filename] = result.map;
-
-  m._compile(result.code, filename);
-};
-
-var hookExtensions = function (_exts) {
-  _.each(exts, function (old, ext) {
-    require.extensions[ext] = old;
-  });
-
-  exts = {};
-
-  _.each(_exts, function (ext) {
-    exts[ext] = require.extensions[ext];
-    require.extensions[ext] = loader;
-  });
-};
-
-hookExtensions(util.canCompile.EXTENSIONS);
-
-module.exports = function (opts) {
-  // normalise options
-  opts = opts || {};
-
-  if (opts.only != null) onlyRegex = util.regexify(opts.only);
-  if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);
-
-  if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
-
-  if (opts.cache === false) cache = null;
-
-  delete opts.extensions;
-  delete opts.ignore;
-  delete opts.cache;
-  delete opts.only;
-
-  _.extend(transformOpts, opts);
-};

lib/6to5/transformation/file.js

@@ -4,24 +4,30 @@ module.exports = File;
 
 var SHEBANG_REGEX = /^\#\!.*/;
 
-var transform = require("./transformation/transform");
-var generate  = require("./generation/generator");
-var clone     = require("./helpers/clone");
-var Scope     = require("./traverse/scope");
-var util      = require("./util");
-var t         = require("./types");
-var _         = require("lodash");
+var isFunction = require("lodash/lang/isFunction");
+var transform  = require("./index");
+var generate   = require("../generation");
+var defaults   = require("lodash/object/defaults");
+var includes   = require("lodash/collection/includes");
+var clone      = require("../helpers/clone");
+var parse      = require("../helpers/parse");
+var Scope      = require("../traversal/scope");
+var util       = require("../util");
+var path       = require("path");
+var each       = require("lodash/collection/each");
+var t          = require("../types");
 
 function File(opts) {
-  this.dynamicImportIds = {};
-  this.dynamicImported  = [];
-  this.dynamicImports   = [];
+  this.dynamicImportedNoDefault = [];
+  this.dynamicImportIds         = {};
+  this.dynamicImported          = [];
+  this.dynamicImports           = [];
 
   this.dynamicData      = {};
   this.data             = {};
 
   this.lastStatements   = [];
-  this.opts             = File.normaliseOptions(opts);
+  this.opts             = this.normalizeOptions(opts);
   this.ast              = {};
 
   this.buildTransformers();
@@ -36,6 +42,7 @@ File.helpers = [
   "tagged-template-literal-loose",
   "interop-require",
   "to-array",
+  "to-consumable-array",
   "sliced-to-array",
   "object-without-properties",
   "has-own",
@@ -46,7 +53,13 @@ File.helpers = [
   "interop-require-wildcard",
   "typeof",
   "extends",
-  "get"
+  "get",
+  "set",
+  "class-call-check",
+  "object-destructuring-empty",
+  "temporal-undefined",
+  "temporal-assert-defined",
+  "tail-call"
 ];
 
 File.validOptions = [
@@ -71,14 +84,17 @@ File.validOptions = [
   "format",
   "playground",
   "experimental",
+  "resolveModuleSource",
+  "runtime",
 
   // these are used by plugins
   "ignore",
   "only",
-  "extensions"
+  "extensions",
+  "accept"
 ];
 
-File.normaliseOptions = function (opts) {
+File.prototype.normalizeOptions = function (opts) {
   opts = clone(opts);
 
   for (var key in opts) {
@@ -87,8 +103,9 @@ File.normaliseOptions = function (opts) {
     }
   }
 
-  _.defaults(opts, {
+  defaults(opts, {
     keepModuleIdExtensions: false,
+    resolveModuleSource:    null,
     experimental:           false,
     reactCompat:            false,
     playground:             false,
@@ -101,36 +118,42 @@ File.normaliseOptions = function (opts) {
     comments:               true,
     filename:               "unknown",
     modules:                "common",
+    runtime:                false,
     loose:                  [],
     code:                   true,
     ast:                    true
   });
 
-  // normalise windows path separators to unix
-  opts.filename = opts.filename.replace(/\\/g, "/");
+  // normalize windows path separators to unix
+  opts.filename = util.normalisePathSeparator(opts.filename);
+  if (opts.sourceRoot) {
+    opts.sourceRoot = util.normalisePathSeparator(opts.sourceRoot);
+  }
+
+  opts.basename = path.basename(opts.filename, path.extname(opts.filename));
 
   opts.blacklist = util.arrayify(opts.blacklist);
   opts.whitelist = util.arrayify(opts.whitelist);
   opts.optional  = util.arrayify(opts.optional);
   opts.loose     = util.arrayify(opts.loose);
 
-  if (_.contains(opts.loose, "all")) {
+  if (includes(opts.loose, "all") || includes(opts.loose, true)) {
     opts.loose = Object.keys(transform.transformers);
   }
 
-  _.defaults(opts, {
+  defaults(opts, {
     moduleRoot: opts.sourceRoot
   });
 
-  _.defaults(opts, {
+  defaults(opts, {
     sourceRoot: opts.moduleRoot
   });
 
-  _.defaults(opts, {
+  defaults(opts, {
     filenameRelative: opts.filename
   });
 
-  _.defaults(opts, {
+  defaults(opts, {
     sourceFileName: opts.filenameRelative,
     sourceMapName:  opts.filenameRelative
   });
@@ -139,16 +162,35 @@ File.normaliseOptions = function (opts) {
     opts.experimental = true;
   }
 
+  if (opts.runtime) {
+    this.set("runtimeIdentifier", t.identifier("to5Runtime"));
+  }
+
   opts.blacklist = transform._ensureTransformerNames("blacklist", opts.blacklist);
   opts.whitelist = transform._ensureTransformerNames("whitelist", opts.whitelist);
-  opts.optional = transform._ensureTransformerNames("optional", opts.optional);
-  opts.loose = transform._ensureTransformerNames("loose", opts.loose);
+  opts.optional  = transform._ensureTransformerNames("optional", opts.optional);
+  opts.loose     = transform._ensureTransformerNames("loose", opts.loose);
+
+  if (opts.reactCompat) {
+    opts.optional.push("reactCompat");
+    console.error("The reactCompat option has been moved into the optional transformer " +
+                  "`reactCompat` - backwards compatibility will be removed in v4.0.0");
+  }
+
+  var ensureEnabled = function (key) {
+    var namespace = transform.transformerNamespaces[key];
+    if (namespace === "es7") opts.experimental = true;
+    if (namespace === "playground") opts.playground = true;
+  };
+
+  each(opts.whitelist, ensureEnabled);
+  each(opts.optional, ensureEnabled);
 
   return opts;
 };
 
 File.prototype.isLoose = function (key) {
-  return _.contains(this.opts.loose, key);
+  return includes(this.opts.loose, key);
 };
 
 File.prototype.buildTransformers = function () {
@@ -159,11 +201,12 @@ File.prototype.buildTransformers = function () {
   var secondaryStack = [];
   var stack = [];
 
-  _.each(transform.transformers, function (transformer, key) {
+  each(transform.transformers, function (transformer, key) {
     var pass = transformers[key] = transformer.buildPass(file);
 
     if (pass.canRun(file)) {
       stack.push(pass);
+
       if (transformer.secondPass) {
         secondaryStack.push(pass);
       }
@@ -178,24 +221,14 @@ File.prototype.buildTransformers = function () {
   this.transformers = transformers;
 };
 
-File.prototype.toArray = function (node, i) {
-  if (t.isArrayExpression(node)) {
-    return node;
-  } else if (t.isIdentifier(node) && node.name === "arguments") {
-    return t.callExpression(t.memberExpression(this.addHelper("slice"), t.identifier("call")), [node]);
-  } else {
-    var declarationName = "to-array";
-    var args = [node];
-    if (i) {
-      args.push(t.literal(i));
-      declarationName = "sliced-to-array";
-    }
-    return t.callExpression(this.addHelper(declarationName), args);
-  }
+File.prototype.debug = function (msg) {
+  var parts = this.opts.filename;
+  if (msg) parts += ": " + msg;
+  util.debug(parts);
 };
 
 File.prototype.getModuleFormatter = function (type) {
-  var ModuleFormatter = _.isFunction(type) ? type : transform.moduleFormatters[type];
+  var ModuleFormatter = isFunction(type) ? type : transform.moduleFormatters[type];
 
   if (!ModuleFormatter) {
     var loc = util.resolve(type);
@@ -241,17 +274,19 @@ File.prototype.get = function (key) {
   }
 };
 
-File.prototype.addImport = function (source, name) {
+File.prototype.addImport = function (source, name, noDefault) {
   name = name || source;
   var id = this.dynamicImportIds[name];
 
   if (!id) {
-    id = this.dynamicImportIds[name] = this.generateUidIdentifier(name);
+    id = this.dynamicImportIds[name] = this.scope.generateUidIdentifier(name);
 
     var specifiers = [t.importSpecifier(t.identifier("default"), id)];
     var declar = t.importDeclaration(specifiers, t.literal(source));
     declar._blockHoist = 3;
+
     this.dynamicImported.push(declar);
+    if (noDefault) this.dynamicImportedNoDefault.push(declar);
 
     this.moduleFormatter.importSpecifier(specifiers[0], declar, this.dynamicImports);
   }
@@ -264,8 +299,8 @@ File.prototype.isConsequenceExpressionStatement = function (node) {
 };
 
 File.prototype.addHelper = function (name) {
-  if (!_.contains(File.helpers, name)) {
-    throw new ReferenceError("unknown declaration " + name);
+  if (!includes(File.helpers, name)) {
+    throw new ReferenceError("Unknown helper " + name);
   }
 
   var program = this.ast.program;
@@ -280,7 +315,7 @@ File.prototype.addHelper = function (name) {
   } else {
     var ref = util.template(name);
     ref._compact = true;
-    var uid = this.generateUidIdentifier(name);
+    var uid = this.scope.generateUidIdentifier(name);
     this.scope.push({
       key: name,
       id: uid,
@@ -290,6 +325,10 @@ File.prototype.addHelper = function (name) {
   }
 };
 
+File.prototype.logDeopt = function () {
+  // todo, (node, msg)
+};
+
 File.prototype.errorWithNode = function (node, msg, Error) {
   Error = Error || SyntaxError;
 
@@ -313,36 +352,69 @@ File.prototype.parse = function (code) {
   var opts = this.opts;
 
   opts.allowImportExportEverywhere = this.isLoose("es6.modules");
+  //opts.strictMode = this.transformers.useStrict.canRun();
 
-  return util.parse(opts, code, function (tree) {
+  return parse(opts, code, function (tree) {
     self.transform(tree);
     return self.generate();
   });
 };
 
 File.prototype.transform = function (ast) {
-  var self = this;
-
-  util.debug(this.opts.filename);
+  this.debug();
 
   this.ast = ast;
   this.lastStatements = t.getLastStatements(ast.program);
   this.scope = new Scope(ast.program, ast, null, this);
-  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
 
-  var astRun = function (key) {
-    _.each(self.transformerStack, function (pass) {
-      pass.astRun(key);
-    });
-  };
+  var modFormatter = this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
+  if (modFormatter.init && this.transformers["es6.modules"].canRun()) {
+    modFormatter.init();
+  }
 
-  astRun("enter");
+  this.checkNode(ast);
 
-  _.each(this.transformerStack, function (pass) {
+  this.call("pre");
+
+  each(this.transformerStack, function (pass) {
     pass.transform();
   });
 
-  astRun("exit");
+  this.call("post");
+};
+
+File.prototype.call = function (key) {
+  var stack = this.transformerStack;
+  for (var i = 0; i < stack.length; i++) {
+    var transformer = stack[i].transformer;
+    if (transformer[key]) {
+      transformer[key](this);
+    }
+  }
+};
+
+var checkTransformerVisitor = {
+  enter: function (node, parent, scope, state) {
+    checkNode(state.stack, node, scope);
+  }
+};
+
+var checkNode = function (stack, node, scope) {
+  each(stack, function (pass) {
+    if (pass.shouldRun) return;
+    pass.checkNode(node, scope);
+  });
+};
+
+File.prototype.checkNode = function (node, scope) {
+  var stack = this.transformerStack;
+  scope = scope || this.scope;
+
+  checkNode(stack, node, scope);
+
+  scope.traverse(node, checkTransformerVisitor, {
+    stack: stack
+  });
 };
 
 File.prototype.generate = function () {
@@ -369,34 +441,8 @@ File.prototype.generate = function () {
 
   if (opts.sourceMap === "inline") {
     result.code += "\n" + util.sourceMapToComment(result.map);
+    result.map = null;
   }
 
   return result;
 };
-
-File.prototype.generateUid = function (name, scope) {
-  name = t.toIdentifier(name).replace(/^_+/, "");
-
-  scope = scope || this.scope;
-
-  var uid;
-  var i = 0;
-  do {
-    uid = this._generateUid(name, i);
-    i++;
-  } while (scope.has(uid));
-  return uid;
-};
-
-File.prototype.generateUidIdentifier = function (name, scope) {
-  scope = scope || this.scope;
-  var id = t.identifier(this.generateUid(name, scope));
-  scope.add(id);
-  return id;
-};
-
-File.prototype._generateUid = function (name, i) {
-  var id = name;
-  if (i > 1) id += i;
-  return "_" + id;
-};

lib/6to5/transformation/helpers/build-binary-assignment-operator-transformer.js

@@ -12,7 +12,7 @@ module.exports = function (exports, opts) {
     return t.assignmentExpression("=", left, right);
   };
 
-  exports.ExpressionStatement = function (node, parent, scope, context, file) {
+  exports.ExpressionStatement = function (node, parent, scope, file) {
     // hit the `AssignmentExpression` one below
     if (file.isConsequenceExpressionStatement(node)) return;
 
@@ -29,7 +29,7 @@ module.exports = function (exports, opts) {
     return nodes;
   };
 
-  exports.AssignmentExpression = function (node, parent, scope, context, file) {
+  exports.AssignmentExpression = function (node, parent, scope, file) {
     if (!isAssignment(node)) return;
 
     var nodes    = [];

lib/6to5/transformation/helpers/build-conditional-assignment-operator-transformer.js

@@ -8,7 +8,7 @@ module.exports = function (exports, opts) {
     return t.assignmentExpression("=", left, right);
   };
 
-  exports.ExpressionStatement = function (node, parent, scope, context, file) {
+  exports.ExpressionStatement = function (node, parent, scope, file) {
     // hit the `AssignmentExpression` one below
     if (file.isConsequenceExpressionStatement(node)) return;
 
@@ -27,7 +27,7 @@ module.exports = function (exports, opts) {
     return nodes;
   };
 
-  exports.AssignmentExpression = function (node, parent, scope, context, file) {
+  exports.AssignmentExpression = function (node, parent, scope, file) {
     if (!opts.is(node, file)) return;
 
     var nodes    = [];

lib/6to5/transformation/helpers/build-react-transformer.js

@@ -0,0 +1,284 @@
+"use strict";
+
+// Based upon the excellent jsx-transpiler by Ingvar Stepanyan (RReverser)
+// https://github.com/RReverser/jsx-transpiler
+
+// jsx
+
+var isString = require("lodash/lang/isString");
+var messages = require("../../messages");
+var esutils  = require("esutils");
+var react    = require("./react");
+var t        = require("../../types");
+
+module.exports = function (exports, opts) {
+  exports.check = function (node) {
+    if (t.isJSX(node)) return true;
+    if (react.isCreateClass(node)) return true;
+    return false;
+  };
+
+  exports.JSXIdentifier = function (node, parent) {
+    if (node.name === "this" && t.isReferenced(node, parent)) {
+      return t.thisExpression();
+    } else if (esutils.keyword.isIdentifierName(node.name)) {
+      node.type = "Identifier";
+    } else {
+      return t.literal(node.name);
+    }
+  };
+
+  exports.JSXNamespacedName = function (node, parent, scope, file) {
+    throw file.errorWithNode(node, messages.get("JSXNamespacedTags"));
+  };
+
+  exports.JSXMemberExpression = {
+    exit: function (node) {
+      node.computed = t.isLiteral(node.property);
+      node.type = "MemberExpression";
+    }
+  };
+
+  exports.JSXExpressionContainer = function (node) {
+    return node.expression;
+  };
+
+  exports.JSXAttribute = {
+    exit: function (node) {
+      var value = node.value || t.literal(true);
+
+      if (t.isLiteral(value) && isString(value.value)) {
+        value.value = value.value.replace(/\n\s+/g, " ");
+      }
+
+      return t.inherits(t.property("init", node.name, value), node);
+    }
+  };
+  exports.JSXOpeningElement = {
+    exit: function (node, parent, scope, file) {
+      var tagExpr = node.name;
+      var args = [];
+
+      var tagName;
+      if (t.isIdentifier(tagExpr)) {
+        tagName = tagExpr.name;
+      } else if (t.isLiteral(tagExpr)) {
+        tagName = tagExpr.value;
+      }
+
+      var state = {
+        tagExpr: tagExpr,
+        tagName: tagName,
+        args:    args
+      };
+
+      if (opts.pre) {
+        opts.pre(state);
+      }
+
+      var attribs = node.attributes;
+      if (attribs.length) {
+        attribs = buildJSXOpeningElementAttributes(attribs, file);
+      } else {
+        attribs = t.literal(null);
+      }
+
+      args.push(attribs);
+
+      if (opts.post) {
+        opts.post(state);
+      }
+
+      return state.call || t.callExpression(state.callee, args);
+    }
+  };
+
+  /**
+   * The logic for this is quite terse. It's because we need to
+   * support spread elements. We loop over all attributes,
+   * breaking on spreads, we then push a new object containg
+   * all prior attributes to an array for later processing.
+   */
+
+  var buildJSXOpeningElementAttributes = function (attribs, file) {
+    var _props = [];
+    var objs = [];
+
+    var pushProps = function () {
+      if (!_props.length) return;
+
+      objs.push(t.objectExpression(_props));
+      _props = [];
+    };
+
+    while (attribs.length) {
+      var prop = attribs.shift();
+      if (t.isJSXSpreadAttribute(prop)) {
+        pushProps();
+        objs.push(prop.argument);
+      } else {
+        _props.push(prop);
+      }
+    }
+
+    pushProps();
+
+    if (objs.length === 1) {
+      // only one object
+      attribs = objs[0];
+    } else {
+      // looks like we have multiple objects
+      if (!t.isObjectExpression(objs[0])) {
+        objs.unshift(t.objectExpression([]));
+      }
+
+      // spread it
+      attribs = t.callExpression(
+        file.addHelper("extends"),
+        objs
+      );
+    }
+
+    return attribs;
+  };
+
+  exports.JSXElement = {
+    exit: function (node) {
+      var callExpr = node.openingElement;
+
+      for (var i = 0; i < node.children.length; i++) {
+        var child = node.children[i];
+
+        if (t.isLiteral(child) && typeof child.value === "string") {
+          cleanJSXElementLiteralChild(child, callExpr.arguments);
+          continue;
+        } else if (t.isJSXEmptyExpression(child)) {
+          continue;
+        }
+
+        callExpr.arguments.push(child);
+      }
+
+      callExpr.arguments = flatten(callExpr.arguments);
+
+      if (callExpr.arguments.length >= 3) {
+        callExpr._prettyCall = true;
+      }
+
+      return t.inherits(callExpr, node);
+    }
+  };
+
+  var isStringLiteral = function (node) {
+    return t.isLiteral(node) && isString(node.value);
+  };
+
+  var flatten = function (args) {
+    var flattened = [];
+    var last;
+
+    for (var i = 0; i < args.length; i++) {
+      var arg = args[i];
+      if (isStringLiteral(arg) && isStringLiteral(last)) {
+        last.value += arg.value;
+      } else {
+        last = arg;
+        flattened.push(arg);
+      }
+    }
+
+    return flattened;
+  };
+
+  var cleanJSXElementLiteralChild = function (child, args) {
+    var lines = child.value.split(/\r\n|\n|\r/);
+
+    var lastNonEmptyLine = 0;
+    var i;
+
+    for (i = 0; i < lines.length; i++) {
+      if (lines[i].match(/[^ \t]/)) {
+        lastNonEmptyLine = i;
+      }
+    }
+
+    for (i = 0; i < lines.length; i++) {
+      var line = lines[i];
+
+      var isFirstLine = i === 0;
+      var isLastLine = i === lines.length - 1;
+      var isLastNonEmptyLine = i === lastNonEmptyLine;
+
+      // replace rendered whitespace tabs with spaces
+      var trimmedLine = line.replace(/\t/g, " ");
+
+      // trim whitespace touching a newline
+      if (!isFirstLine) {
+        trimmedLine = trimmedLine.replace(/^[ ]+/, "");
+      }
+
+      // trim whitespace touching an endline
+      if (!isLastLine) {
+        trimmedLine = trimmedLine.replace(/[ ]+$/, "");
+      }
+
+      if (trimmedLine) {
+        if (!isLastNonEmptyLine) {
+          trimmedLine += " ";
+        }
+
+        args.push(t.literal(trimmedLine));
+      }
+    }
+  };
+
+  // display names
+
+  var addDisplayName = function (id, call) {
+    var props = call.arguments[0].properties;
+    var safe = true;
+
+    for (var i = 0; i < props.length; i++) {
+      var prop = props[i];
+      if (t.isIdentifier(prop.key, { name: "displayName" })) {
+        safe = false;
+        break;
+      }
+    }
+
+    if (safe) {
+      props.unshift(t.property("init", t.identifier("displayName"), t.literal(id)));
+    }
+  };
+
+  exports.ExportDeclaration = function (node, parent, scope, file) {
+    if (node.default && react.isCreateClass(node.declaration)) {
+      addDisplayName(file.opts.basename, node.declaration);
+    }
+  };
+
+  exports.AssignmentExpression =
+  exports.Property =
+  exports.VariableDeclarator = function (node) {
+    var left, right;
+
+    if (t.isAssignmentExpression(node)) {
+      left = node.left;
+      right = node.right;
+    } else if (t.isProperty(node)) {
+      left = node.key;
+      right = node.value;
+    } else if (t.isVariableDeclarator(node)) {
+      left = node.id;
+      right = node.init;
+    }
+
+    if (t.isMemberExpression(left)) {
+      left = left.property;
+    }
+
+    if (t.isIdentifier(left) && react.isCreateClass(right)) {
+      addDisplayName(left.name, right);
+    }
+  };
+};

lib/6to5/transformation/helpers/define-map.js

@@ -0,0 +1,73 @@
+var cloneDeep = require("lodash/lang/cloneDeep");
+var traverse  = require("../../traversal");
+var clone     = require("lodash/lang/clone");
+var each      = require("lodash/collection/each");
+var has       = require("lodash/object/has");
+var t         = require("../../types");
+
+exports.push = function (mutatorMap, key, kind, computed, value) {
+  var alias;
+
+  if (t.isIdentifier(key)) {
+    alias = key.name;
+    if (computed) alias = "computed:" + alias;
+  } else if (t.isLiteral(key)) {
+    alias = String(key.value);
+  } else {
+    alias = JSON.stringify(traverse.removeProperties(cloneDeep(key)));
+  }
+
+  var map;
+  if (has(mutatorMap, alias)) {
+    map = mutatorMap[alias];
+  } else {
+    map = {};
+  }
+  mutatorMap[alias] = map;
+
+  map._key = key;
+  if (computed) {
+    map._computed = true;
+  }
+
+  map[kind] = value;
+};
+
+exports.build = function (mutatorMap) {
+  var objExpr = t.objectExpression([]);
+
+  each(mutatorMap, function (map) {
+    var mapNode = t.objectExpression([]);
+
+    var propNode = t.property("init", map._key, mapNode, map._computed);
+
+    if (!map.get && !map.set) {
+      map.writable = t.literal(true);
+    }
+
+    if (map.enumerable === false) {
+      delete map.enumerable;
+    } else {
+      map.enumerable = t.literal(true);
+    }
+
+    map.configurable = t.literal(true);
+
+    each(map, function (node, key) {
+      if (key[0] === "_") return;
+
+      node = clone(node);
+      var inheritNode = node;
+      if (t.isMethodDefinition(node)) node = node.value;
+
+      var prop = t.property("init", t.identifier(key), node);
+      t.inheritsComments(prop, inheritNode);
+      t.removeComments(inheritNode);
+      mapNode.properties.push(prop);
+    });
+
+    objExpr.properties.push(propNode);
+  });
+
+  return objExpr;
+};

lib/6to5/transformation/helpers/explode-assignable-expression.js

@@ -5,7 +5,7 @@ var t = require("../../types");
 var getObjRef = function (node, nodes, file, scope) {
   var ref;
   if (t.isIdentifier(node)) {
-    if (scope.has(node.name, true)) {
+    if (scope.hasBinding(node.name)) {
       // this variable is declared in scope so we can be 100% sure
       // that evaluating it multiple times wont trigger a getter
       // or something else
@@ -18,7 +18,7 @@ var getObjRef = function (node, nodes, file, scope) {
   } else if (t.isMemberExpression(node)) {
     ref = node.object;
 
-    if (t.isIdentifier(ref) && scope.has(ref.name)) {
+    if (t.isIdentifier(ref) && scope.hasGlobal(ref.name)) {
       // the object reference that we need to save is locally declared
       // so as per the previous comment we can be 100% sure evaluating
       // it multiple times will be safe

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

@@ -1,11 +1,10 @@
 "use strict";
 
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
+var util = require("../../util");
+var t    = require("../../types");
 
 var visitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     // check if this node is an identifier that matches the same as our function id
     if (!t.isIdentifier(node, { name: state.id })) return;
 
@@ -14,11 +13,11 @@ var visitor = {
 
     // check that we don't have a local variable declared as that removes the need
     // for the wrapper
-    var localDeclar = scope.get(state.id, true);
+    var localDeclar = scope.getBindingIdentifier(state.id);
     if (localDeclar !== state.outerDeclar) return;
 
     state.selfReference = true;
-    context.stop();
+    this.stop();
   }
 };
 
@@ -32,20 +31,23 @@ exports.property = function (node, file, scope) {
   var state = {
     id: id,
     selfReference: false,
-    outerDeclar: scope.get(id, true),
+    outerDeclar: scope.getBindingIdentifier(id),
   };
 
-  traverse(node, visitor, scope, state);
+  scope.traverse(node, visitor, state);
+
+  var method = node.value;
 
   if (state.selfReference) {
-    // todo: support generators
-    node.value = util.template("property-method-assignment-wrapper", {
-      FUNCTION: node.value,
+    var templateName = "property-method-assignment-wrapper";
+    if (method.generator) templateName += "-generator";
+    node.value = util.template(templateName, {
+      FUNCTION: method,
       FUNCTION_ID: key,
       FUNCTION_KEY: scope.generateUidIdentifier(id),
       WRAPPER_KEY: scope.generateUidIdentifier(id + "Wrapper")
     });
   } else {
-    node.value.id = key;
+    method.id = key;
   }
 };

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

@@ -0,0 +1,26 @@
+var t = require("../../types");
+
+var isCreateClassCallExpression = t.buildMatchMemberExpression("React.createClass");
+
+exports.isCreateClass = function (node) {
+  if (!node || !t.isCallExpression(node)) return false;
+
+  // not React.createClass call member object
+  if (!isCreateClassCallExpression(node.callee)) return false;
+
+  // no call arguments
+  var args = node.arguments;
+  if (args.length !== 1) return false;
+
+  // first node arg is not an object
+  var first = args[0];
+  if (!t.isObjectExpression(first)) return false;
+
+  return true;
+};
+
+exports.isReactComponent = t.buildMatchMemberExpression("React.Component");
+
+exports.isCompatTag = function (tagName) {
+  return tagName && /^[a-z]|\-/.test(tagName);
+};

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

@@ -1,11 +1,10 @@
 "use strict";
 
-var traverse = require("../../traverse");
-var t        = require("../../types");
+var t = require("../../types");
 
 var visitor = {
-  enter: function (node, parent, scope, context) {
-    if (t.isFunction(node)) context.skip();
+  enter: function (node) {
+    if (t.isFunction(node)) this.skip();
 
     if (t.isAwaitExpression(node)) {
       node.type = "YieldExpression";
@@ -23,7 +22,7 @@ module.exports = function (node, callId, scope) {
   node.async = false;
   node.generator = true;
 
-  traverse(node, visitor, scope);
+  scope.traverse(node, visitor);
 
   var call = t.callExpression(callId, [node]);
   var id = node.id;

lib/6to5/transformation/helpers/replace-supers.js

@@ -2,25 +2,61 @@
 
 module.exports = ReplaceSupers;
 
-var traverse = require("../../traverse");
+var messages = require("../../messages");
 var t        = require("../../types");
 
 /**
  * Description
  *
  * @param {Object} opts
+ * @param {Boolean} [inClass]
  */
 
-function ReplaceSupers(opts) {
-  this.topLevelThisReference = null;
+function ReplaceSupers(opts, inClass) {
+  this.topLevelThisReference = opts.topLevelThisReference;
   this.methodNode            = opts.methodNode;
   this.className             = opts.className;
   this.superName             = opts.superName;
+  this.isStatic              = opts.isStatic;
+  this.hasSuper              = false;
+  this.inClass               = inClass;
   this.isLoose               = opts.isLoose;
   this.scope                 = opts.scope;
   this.file                  = opts.file;
 }
 
+/**
+ * Sets a super class value of the named property.
+ *
+ * @example
+ *
+ *   _set(Object.getPrototypeOf(CLASS.prototype), "METHOD", "VALUE", this)
+ *
+ * @param {Node} property
+ * @param {Node} value
+ * @param {Boolean} isComputed
+ * @param {Node} thisExpression
+ *
+ * @returns {Node}
+ */
+
+ReplaceSupers.prototype.setSuperProperty = function (property, value, isComputed, thisExpression) {
+  return t.callExpression(
+    this.file.addHelper("set"),
+    [
+      t.callExpression(
+        t.memberExpression(t.identifier("Object"), t.identifier("getPrototypeOf")),
+        [
+          this.isStatic ? this.className : t.memberExpression(this.className, t.identifier("prototype"))
+        ]
+      ),
+      isComputed ? property : t.literal(property.name),
+      value,
+      thisExpression
+    ]
+  );
+};
+
 /**
  * Gets a node representing the super class value of the named property.
  *
@@ -29,20 +65,20 @@ function ReplaceSupers(opts) {
  *   _get(Object.getPrototypeOf(CLASS.prototype), "METHOD", this)
  *
  * @param {Node} property
- * @param {boolean} isStatic
- * @param {boolean} isComputed
+ * @param {Boolean} isComputed
+ * @param {Node} thisExpression
  *
  * @returns {Node}
  */
 
-ReplaceSupers.prototype.superProperty = function (property, isStatic, isComputed, thisExpression) {
+ReplaceSupers.prototype.getSuperProperty = function (property, isComputed, thisExpression) {
   return t.callExpression(
     this.file.addHelper("get"),
     [
       t.callExpression(
         t.memberExpression(t.identifier("Object"), t.identifier("getPrototypeOf")),
         [
-          isStatic ? this.className : t.memberExpression(this.className, t.identifier("prototype"))
+          this.isStatic ? this.className : t.memberExpression(this.className, t.identifier("prototype"))
         ]
       ),
       isComputed ? property : t.literal(property.name),
@@ -51,6 +87,70 @@ ReplaceSupers.prototype.superProperty = function (property, isStatic, isComputed
   );
 };
 
+/**
+ * Description
+ */
+
+ReplaceSupers.prototype.replace = function () {
+  this.traverseLevel(this.methodNode.value, true);
+};
+
+var visitor = {
+  enter: function (node, parent, scope, state) {
+    var topLevel = state.topLevel;
+    var self = state.self;
+
+    if (t.isFunction(node) && !t.isArrowFunctionExpression(node)) {
+      // we need to call traverseLevel again so we're context aware
+      self.traverseLevel(node, false);
+      return this.skip();
+    }
+
+    if (t.isProperty(node, { method: true }) || t.isMethodDefinition(node)) {
+      // break on object methods
+      return this.skip();
+    }
+
+    var getThisReference = topLevel ?
+      // top level so `this` is the instance
+      t.thisExpression :
+      // not in the top level so we need to create a reference
+      self.getThisReference.bind(self);
+
+    var callback = self.specHandle;
+    if (self.isLoose) callback = self.looseHandle;
+    return callback.call(self, getThisReference, node, parent);
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Object} node
+ * @param {Boolean} topLevel
+ */
+
+ReplaceSupers.prototype.traverseLevel = function (node, topLevel) {
+  var state = { self: this, topLevel: topLevel };
+  this.scope.traverse(node, visitor, state);
+};
+
+/**
+ * Description
+ */
+
+ReplaceSupers.prototype.getThisReference = function () {
+  if (this.topLevelThisReference) {
+    return this.topLevelThisReference;
+  } else {
+    var ref = this.topLevelThisReference = this.scope.generateUidIdentifier("this");
+    this.methodNode.value.body.body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(this.topLevelThisReference, t.thisExpression())
+    ]));
+    return ref;
+  }
+};
+
 /**
  * Description
  *
@@ -60,7 +160,8 @@ ReplaceSupers.prototype.superProperty = function (property, isStatic, isComputed
  * @returns {Object}
  */
 
-ReplaceSupers.prototype.looseSuperProperty = function (methodNode, id, parent) {
+ReplaceSupers.prototype.getLooseSuperProperty = function (id, parent) {
+  var methodNode = this.methodNode;
   var methodName = methodNode.key;
   var superName  = this.superName || t.identifier("Function");
 
@@ -92,70 +193,6 @@ ReplaceSupers.prototype.looseSuperProperty = function (methodNode, id, parent) {
   }
 };
 
-/**
- * Description
- */
-
-ReplaceSupers.prototype.replace = function () {
-  this.traverseLevel(this.methodNode.value, true);
-};
-
-var visitor = {
-  enter: function (node, parent, scope, context, state) {
-    var topLevel = state.topLevel;
-    var self = state.self;
-
-    if (t.isFunction(node) && !t.isArrowFunctionExpression(node)) {
-      // we need to call traverseLevel again so we're context aware
-      self.traverseLevel(node, false);
-      return context.skip();
-    }
-
-    if (t.isProperty(node, { method: true }) || t.isMethodDefinition(node)) {
-      // break on object methods
-      return context.skip();
-    }
-
-    var getThisReference = topLevel ?
-      // top level so `this` is the instance
-      t.thisExpression :
-      // not in the top level so we need to create a reference
-      self.getThisReference;
-
-    var callback = self.specHandle;
-    if (self.isLoose) callback = self.looseHandle;
-    return callback.call(self, getThisReference, node, parent);
-  }
-};
-
-/**
- * Description
- *
- * @param {Object} node
- * @param {Boolean} topLevel
- */
-
-ReplaceSupers.prototype.traverseLevel = function (node, topLevel) {
-  var state = { self: this, topLevel: topLevel };
-  traverse(node, visitor, this.scope, state);
-};
-
-/**
- * Description
- */
-
-ReplaceSupers.prototype.getThisReference = function () {
-  if (this.topLevelThisReference) {
-    return this.topLevelThisReference;
-  } else {
-    var ref = this.topLevelThisReference = this.file.generateUidIdentifier("this");
-    this.methodNode.value.body.body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(this.topLevelThisReference, t.thisExpression())
-    ]));
-    return ref;
-  }
-};
-
 /**
  * Description
  *
@@ -166,13 +203,15 @@ ReplaceSupers.prototype.getThisReference = function () {
 
 ReplaceSupers.prototype.looseHandle = function (getThisReference, node, parent) {
   if (t.isIdentifier(node, { name: "super" })) {
-    return this.looseSuperProperty(this.methodNode, node, parent);
+    this.hasSuper = true;
+    return this.getLooseSuperProperty(node, parent);
   } else if (t.isCallExpression(node)) {
     var callee = node.callee;
     if (!t.isMemberExpression(callee)) return;
     if (callee.object.name !== "super") return;
 
     // super.test(); -> ClassName.prototype.MethodName.call(this);
+    this.hasSuper = true;
     t.appendToMemberExpression(callee, t.identifier("call"));
     node.arguments.unshift(getThisReference());
   }
@@ -191,14 +230,15 @@ ReplaceSupers.prototype.specHandle = function (getThisReference, node, parent) {
   var property;
   var computed;
   var args;
+  var thisReference;
 
-  if (t.isIdentifier(node, { name: "super" })) {
-    if (!(t.isMemberExpression(parent) && !parent.computed && parent.property === node)) {
-      throw this.file.errorWithNode(node, "illegal use of bare super");
-    }
-  } else if (t.isCallExpression(node)) {
+  if (isIllegalBareSuper(node, parent)) {
+    throw this.file.errorWithNode(node, messages.get("classesIllegalBareSuper"));
+  }
+
+  if (t.isCallExpression(node)) {
     var callee = node.callee;
-    if (t.isIdentifier(callee, { name: "super" })) {
+    if (isSuper(callee, node)) {
       // super(); -> _get(Object.getPrototypeOf(ClassName), "MethodName", this).call(this);
       property = methodNode.key;
       computed = methodNode.computed;
@@ -207,31 +247,32 @@ ReplaceSupers.prototype.specHandle = function (getThisReference, node, parent) {
       // bare `super` call is illegal inside non-constructors
       //  - https://esdiscuss.org/topic/super-call-in-methods
       //  - https://twitter.com/wycats/status/544553184396836864
-      if (methodNode.key.name !== "constructor") {
+      if (methodNode.key.name !== "constructor" || !this.inClass) {
         var methodName = methodNode.key.name || "METHOD_NAME";
-        throw this.file.errorWithNode(node, "Direct super call is illegal in non-constructor, use super." + methodName + "() instead");
+        throw this.file.errorWithNode(node, messages.get("classesIllegalSuperCall", methodName));
       }
-    } else {
-      if (!t.isMemberExpression(callee)) return;
-      if (callee.object.name !== "super") return;
-
+    } else if (t.isMemberExpression(callee) && isSuper(callee.object, callee)) {
       // super.test(); -> _get(Object.getPrototypeOf(ClassName.prototype), "test", this).call(this);
       property = callee.property;
       computed = callee.computed;
       args = node.arguments;
     }
-  } else if (t.isMemberExpression(node)) {
-    if (!t.isIdentifier(node.object, { name: "super" })) return;
-
+  } else if (t.isMemberExpression(node) && isSuper(node.object, node)) {
     // super.name; -> _get(Object.getPrototypeOf(ClassName.prototype), "name", this);
     property = node.property;
     computed = node.computed;
+  } else if (t.isAssignmentExpression(node) && isSuper(node.left.object, node.left) && methodNode.kind === "set") {
+    // super.name = "val"; -> _set(Object.getPrototypeOf(ClassName.prototype), "name", this);
+    this.hasSuper = true;
+    return this.setSuperProperty(node.left.property, node.right, node.left.computed, getThisReference());
   }
 
   if (!property) return;
 
-  var thisReference = getThisReference();
-  var superProperty = this.superProperty(property, methodNode.static, computed, thisReference);
+  this.hasSuper = true;
+
+  thisReference = getThisReference();
+  var superProperty = this.getSuperProperty(property, computed, thisReference);
   if (args) {
     if (args.length === 1 && t.isSpreadElement(args[0])) {
       // super(...arguments);
@@ -249,3 +290,14 @@ ReplaceSupers.prototype.specHandle = function (getThisReference, node, parent) {
     return superProperty;
   }
 };
+
+var isIllegalBareSuper = function (node, parent) {
+  if (!isSuper(node, parent)) return false;
+  if (t.isMemberExpression(parent, { computed: false })) return false;
+  if (t.isCallExpression(parent, { callee: node })) return false;
+  return true;
+};
+
+var isSuper = function (node, parent) {
+  return t.isIdentifier(node, { name: "super" }) && t.isReferenced(node, parent);
+};

lib/6to5/transformation/index.js

@@ -2,11 +2,11 @@
 
 module.exports = transform;
 
-var Transformer = require("./transformer");
-var object      = require("../helpers/object");
-var File        = require("../file");
-var util        = require("../util");
-var _           = require("lodash");
+var normalizeAst = require("../helpers/normalize-ast");
+var Transformer  = require("./transformer");
+var object       = require("../helpers/object");
+var File         = require("./file");
+var each         = require("lodash/collection/each");
 
 function transform(code, opts) {
   var file = new File(opts);
@@ -14,7 +14,7 @@ function transform(code, opts) {
 }
 
 transform.fromAst = function (ast, code, opts) {
-  ast = util.normaliseAst(ast);
+  ast = normalizeAst(ast);
 
   var file = new File(opts);
   file.addCode(code);
@@ -56,18 +56,21 @@ transform._ensureTransformerNames = function (type, rawKeys) {
   return keys;
 };
 
-transform.transformers = object();
-transform.namespaces   = object();
+transform.transformerNamespaces = object();
+transform.transformers          = object();
+transform.namespaces            = object();
 
 transform.deprecatedTransformerMap = require("./transformers/deprecated");
 transform.moduleFormatters = require("./modules");
 
 var rawTransformers = require("./transformers");
 
-_.each(rawTransformers, function (transformer, key) {
+each(rawTransformers, function (transformer, key) {
   var namespace = key.split(".")[0];
+
   transform.namespaces[namespace] = transform.namespaces[namespace] || [];
   transform.namespaces[namespace].push(key);
+  transform.transformerNamespaces[key] = namespace;
 
   transform.transformers[key] = new Transformer(key, transformer);
 });

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

@@ -2,15 +2,16 @@
 
 module.exports = DefaultFormatter;
 
-var traverse = require("../../traverse");
+var messages = require("../../messages");
+var extend   = require("lodash/object/extend");
 var object   = require("../../helpers/object");
 var util     = require("../../util");
 var t        = require("../../types");
-var _        = require("lodash");
 
 function DefaultFormatter(file) {
-  this.file = file;
-  this.ids  = object();
+  this.scope = file.scope;
+  this.file  = file;
+  this.ids   = object();
 
   this.hasNonDefaultExports = false;
 
@@ -28,7 +29,7 @@ function DefaultFormatter(file) {
 }
 
 DefaultFormatter.prototype.doDefaultExportInterop = function (node) {
-  return node.default && !this.noInteropRequire && !this.hasNonDefaultExports;
+  return node.default && !this.noInteropRequireExport && !this.hasNonDefaultExports;
 };
 
 DefaultFormatter.prototype.bumpImportOccurences = function (node) {
@@ -39,13 +40,13 @@ DefaultFormatter.prototype.bumpImportOccurences = function (node) {
 };
 
 var exportsVisitor = {
-  enter: function (node, parent, scope, context, formatter) {
+  enter: function (node, parent, scope, formatter) {
     var declar = node && node.declaration;
     if (t.isExportDeclaration(node)) {
       formatter.hasLocalImports = true;
 
       if (declar && t.isStatement(declar)) {
-        _.extend(formatter.localExports, t.getIds(declar, true));
+        extend(formatter.localExports, t.getBindingIdentifiers(declar));
       }
 
       if (!node.default) {
@@ -60,27 +61,27 @@ var exportsVisitor = {
 };
 
 DefaultFormatter.prototype.getLocalExports = function () {
-  traverse(this.file.ast, exportsVisitor, this.file.scope, this);
+  this.file.scope.traverse(this.file.ast, exportsVisitor, this);
 };
 
 var importsVisitor = {
-  enter: function (node, parent, scope, context, formatter) {
+  enter: function (node, parent, scope, formatter) {
     if (t.isImportDeclaration(node)) {
       formatter.hasLocalImports = true;
-      _.extend(formatter.localImports, t.getIds(node, true));
+      extend(formatter.localImports, t.getBindingIdentifiers(node));
       formatter.bumpImportOccurences(node);
     }
   }
 };
 
 DefaultFormatter.prototype.getLocalImports = function () {
-  traverse(this.file.ast, importsVisitor, this.file.scope, this);
+  this.file.scope.traverse(this.file.ast, importsVisitor, this);
 };
 
 var remapVisitor = {
-  enter: function (node, parent, scope, context, formatter) {
+  enter: function (node, parent, scope, formatter) {
     if (t.isUpdateExpression(node) && formatter.isLocalReference(node.argument, scope)) {
-      context.skip();
+      this.skip();
 
       // expand to long file assignment expression
       var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
@@ -108,7 +109,7 @@ var remapVisitor = {
     }
 
     if (t.isAssignmentExpression(node) && formatter.isLocalReference(node.left, scope)) {
-      context.skip();
+      this.skip();
       return formatter.remapExportAssignment(node);
     }
   }
@@ -116,7 +117,7 @@ var remapVisitor = {
 
 DefaultFormatter.prototype.remapAssignments = function () {
   if (this.hasLocalImports) {
-    traverse(this.file.ast, remapVisitor, this.file.scope, this);
+    this.file.scope.traverse(this.file.ast, remapVisitor, this);
   }
 };
 
@@ -125,13 +126,6 @@ DefaultFormatter.prototype.isLocalReference = function (node) {
   return t.isIdentifier(node) && localImports[node.name] && localImports[node.name] !== node;
 };
 
-DefaultFormatter.prototype.checkLocalReference = function (node) {
-  var file = this.file;
-  if (this.isLocalReference(node)) {
-    throw file.errorWithNode(node, "Illegal assignment of module import");
-  }
-};
-
 DefaultFormatter.prototype.remapExportAssignment = function (node) {
   return t.assignmentExpression(
     "=",
@@ -147,7 +141,7 @@ DefaultFormatter.prototype.remapExportAssignment = function (node) {
 DefaultFormatter.prototype.isLocalReference = function (node, scope) {
   var localExports = this.localExports;
   var name = node.name;
-  return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
+  return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.getBindingIdentifier(name);
 };
 
 DefaultFormatter.prototype.getModuleName = function () {
@@ -171,12 +165,12 @@ DefaultFormatter.prototype.getModuleName = function () {
 
   if (!opts.keepModuleIdExtensions) {
     // remove extension
-    filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+    filenameRelative = filenameRelative.replace(/\.(\w*?)$/, "");
   }
 
   moduleName += filenameRelative;
 
-  // normalise path separators
+  // normalize path separators
   moduleName = moduleName.replace(/\\/g, "/");
 
   return moduleName;
@@ -212,10 +206,13 @@ DefaultFormatter.prototype.getExternalReference = function (node, nodes) {
   }
 };
 
-DefaultFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  var inherits = false;
-  if (node.specifiers.length === 1) inherits = node;
+DefaultFormatter.prototype.checkExportIdentifier = function (node) {
+  if (t.isIdentifier(node, { name: "__esModule" })) {
+    throw this.file.errorWithNode(node, messages.get("modulesIllegalExportName", node.name));
+  }
+};
 
+DefaultFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
   if (node.source) {
     var ref = this.getExternalReference(node, nodes);
 
@@ -223,8 +220,8 @@ DefaultFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
       // export * from "foo";
       nodes.push(this.buildExportsWildcard(ref, node));
     } else {
-      if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
-        // importing a default so we need to normalise it
+      if (t.isSpecifierDefault(specifier) && !this.noInteropRequireExport) {
+        // importing a default so we need to normalize it
         ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
       } else {
         ref = t.memberExpression(ref, t.getSpecifierId(specifier));
@@ -251,6 +248,7 @@ DefaultFormatter.prototype.buildExportsWildcard = function (objectIdentifier) {
 };
 
 DefaultFormatter.prototype.buildExportsAssignment = function (id, init) {
+  this.checkExportIdentifier(id);
   return util.template("exports-assign", {
     VALUE: init,
     KEY:   id

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

@@ -4,7 +4,7 @@ var util = require("../../util");
 
 module.exports = function (Parent) {
   var Constructor = function () {
-    this.noInteropRequire = true;
+    this.noInteropRequireExport = true;
     Parent.apply(this, arguments);
   };
 

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

@@ -4,9 +4,10 @@ module.exports = AMDFormatter;
 
 var DefaultFormatter = require("./_default");
 var CommonFormatter  = require("./common");
+var includes         = require("lodash/collection/includes");
+var values           = require("lodash/object/values");
 var util             = require("../../util");
 var t                = require("../../types");
-var _                = require("lodash");
 
 function AMDFormatter() {
   CommonFormatter.apply(this, arguments);
@@ -14,6 +15,8 @@ function AMDFormatter() {
 
 util.inherits(AMDFormatter, DefaultFormatter);
 
+AMDFormatter.prototype.init = CommonFormatter.prototype.init;
+
 AMDFormatter.prototype.buildDependencyLiterals = function () {
   var names = [];
   for (var name in this.ids) {
@@ -26,9 +29,8 @@ AMDFormatter.prototype.buildDependencyLiterals = function () {
  * Wrap the entire body in a `define` wrapper.
  */
 
-AMDFormatter.prototype.transform = function (ast) {
-  var program = ast.program;
-  var body    = program.body;
+AMDFormatter.prototype.transform = function (program) {
+  var body = program.body;
 
   // build an array of module names
 
@@ -39,7 +41,7 @@ AMDFormatter.prototype.transform = function (ast) {
 
   // build up define container
 
-  var params = _.values(this.ids);
+  var params = values(this.ids);
   if (this.passModuleArg) params.unshift(t.identifier("module"));
   params.unshift(t.identifier("exports"));
 
@@ -68,7 +70,7 @@ AMDFormatter.prototype.getModuleName = function () {
 };
 
 AMDFormatter.prototype._getExternalReference = function (node) {
-  return this.file.generateUidIdentifier(node.source.value);
+  return this.scope.generateUidIdentifier(node.source.value);
 };
 
 AMDFormatter.prototype.importDeclaration = function (node) {
@@ -79,13 +81,12 @@ AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var key = t.getSpecifierName(specifier);
   var ref = this.getExternalReference(node);
 
-  if (_.contains(this.file.dynamicImported, node)) {
+  if (includes(this.file.dynamicImportedNoDefault, node)) {
     // Prevent unnecessary renaming of dynamic imports.
-    this.ids[node.source.value] = key;
-    return;
+    this.ids[node.source.value] = ref;
   } else if (t.isImportBatchSpecifier(specifier)) {
     // import * as bar from "foo";
-  } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
+  } else if (!includes(this.file.dynamicImported, node) && t.isSpecifierDefault(specifier) && !this.noInteropRequireImport) {
     // import foo from "foo";
     ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
   } else {

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

@@ -0,0 +1,13 @@
+"use strict";
+
+module.exports = CommonStandardFormatter;
+
+var CommonStrictFormatter = require("./common-strict");
+var util = require("../../util");
+
+function CommonStandardFormatter() {
+  this.noInteropRequireImport = true;
+  CommonStrictFormatter.apply(this, arguments);
+}
+
+util.inherits(CommonStandardFormatter, CommonStrictFormatter);

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

@@ -3,20 +3,27 @@
 module.exports = CommonJSFormatter;
 
 var DefaultFormatter = require("./_default");
+var includes         = require("lodash/collection/includes");
 var util             = require("../../util");
 var t                = require("../../types");
-var _                = require("lodash");
 
-function CommonJSFormatter(file) {
+function CommonJSFormatter() {
   DefaultFormatter.apply(this, arguments);
-
-  if (this.hasNonDefaultExports) {
-    file.ast.program.body.push(util.template("exports-module-declaration", true));
-  }
 }
 
 util.inherits(CommonJSFormatter, DefaultFormatter);
 
+CommonJSFormatter.prototype.init = function () {
+  var file  = this.file;
+  var scope = file.scope;
+
+  scope.rename("module");
+
+  if (!this.noInteropRequireImport && this.hasNonDefaultExports) {
+    file.ast.program.body.push(util.template("exports-module-declaration", true));
+  }
+};
+
 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var variableName = t.getSpecifierName(specifier);
 
@@ -24,20 +31,24 @@ CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes)
 
   // import foo from "foo";
   if (t.isSpecifierDefault(specifier)) {
-    if (!_.contains(this.file.dynamicImported, node)) {
-      ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
+    if (!includes(this.file.dynamicImportedNoDefault, node)) {
+      if (this.noInteropRequireImport || includes(this.file.dynamicImported, node)) {
+        ref = t.memberExpression(ref, t.identifier("default"));
+      } else {
+        ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
+      }
     }
     nodes.push(t.variableDeclaration("var", [t.variableDeclarator(variableName, ref)]));
   } else {
     if (specifier.type === "ImportBatchSpecifier") {
+
+      if (!this.noInteropRequireImport) {
+        ref = t.callExpression(this.file.addHelper("interop-require-wildcard"), [ref]);
+      }
+
       // import * as bar from "foo";
       nodes.push(t.variableDeclaration("var", [
-        t.variableDeclarator(
-          variableName,
-          t.callExpression(this.file.addHelper("interop-require-wildcard"), [
-            ref
-          ])
-        )
+        t.variableDeclarator(variableName, ref)
       ]));
     } else {
       // import { foo } from "foo";
@@ -82,7 +93,7 @@ CommonJSFormatter.prototype._getExternalReference = function (node, nodes) {
   var call = t.callExpression(t.identifier("require"), [node.source]);
 
   if (this.localImportOccurences[source] > 1) {
-    var uid = this.file.generateUidIdentifier(source);
+    var uid = this.scope.generateUidIdentifier(source);
     nodes.push(t.variableDeclaration("var", [
       t.variableDeclarator(uid, call)
     ]));

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

@@ -1,10 +1,11 @@
 module.exports = {
-  commonStrict: require("./common-strict"),
-  amdStrict:    require("./amd-strict"),
-  umdStrict:    require("./umd-strict"),
-  common:       require("./common"),
-  system:       require("./system"),
-  ignore:       require("./ignore"),
-  amd:          require("./amd"),
-  umd:          require("./umd")
+  commonStandard: require("./common-standard"),
+  commonStrict:   require("./common-strict"),
+  amdStrict:      require("./amd-strict"),
+  umdStrict:      require("./umd-strict"),
+  common:         require("./common"),
+  system:         require("./system"),
+  ignore:         require("./ignore"),
+  amd:            require("./amd"),
+  umd:            require("./umd")
 };

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

@@ -5,27 +5,31 @@ module.exports = SystemFormatter;
 var DefaultFormatter = require("./_default");
 var AMDFormatter     = require("./amd");
 var useStrict        = require("../helpers/use-strict");
-var traverse         = require("../../traverse");
 var util             = require("../../util");
 var t                = require("../../types");
-var _                = require("lodash");
+var last             = require("lodash/array/last");
+var each             = require("lodash/collection/each");
+var map              = require("lodash/collection/map");
 
 function SystemFormatter(file) {
-  this.exportIdentifier = file.generateUidIdentifier("export");
-  this.noInteropRequire = true;
+  this.exportIdentifier = file.scope.generateUidIdentifier("export");
+  this.noInteropRequireExport = true;
+  this.noInteropRequireImport = true;
 
   DefaultFormatter.apply(this, arguments);
 }
 
 util.inherits(SystemFormatter, AMDFormatter);
 
+SystemFormatter.prototype.init = function () {};
+
 SystemFormatter.prototype._addImportSource = function (node, exportNode) {
   node._importSource = exportNode.source && exportNode.source.value;
   return node;
 };
 
 SystemFormatter.prototype.buildExportsWildcard = function (objectIdentifier, node) {
-  var leftIdentifier = this.file.generateUidIdentifier("key");
+  var leftIdentifier = this.scope.generateUidIdentifier("key");
   var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
 
   var left = t.variableDeclaration("var", [
@@ -61,14 +65,14 @@ SystemFormatter.prototype.buildExportCall = function (id, init, isStatement) {
 
 SystemFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   AMDFormatter.prototype.importSpecifier.apply(this, arguments);
-  this._addImportSource(_.last(nodes), node);
+  this._addImportSource(last(nodes), node);
 };
 
 var runnerSettersVisitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     if (node._importSource === state.source) {
       if (t.isVariableDeclaration(node)) {
-        _.each(node.declarations, function (declar) {
+        each(node.declarations, function (declar) {
           state.hoistDeclarators.push(t.variableDeclarator(declar.id));
           state.nodes.push(t.expressionStatement(
             t.assignmentExpression("=", declar.id, declar.init)
@@ -78,7 +82,7 @@ var runnerSettersVisitor = {
         state.nodes.push(node);
       }
 
-      context.remove();
+      this.remove();
     }
   }
 };
@@ -86,24 +90,24 @@ var runnerSettersVisitor = {
 SystemFormatter.prototype.buildRunnerSetters = function (block, hoistDeclarators) {
   var scope = this.file.scope;
 
-  return t.arrayExpression(_.map(this.ids, function (uid, source) {
+  return t.arrayExpression(map(this.ids, function (uid, source) {
     var state = {
       source:           source,
       nodes:            [],
       hoistDeclarators: hoistDeclarators
     };
 
-    traverse(block, runnerSettersVisitor, scope, state);
+    scope.traverse(block, runnerSettersVisitor, state);
 
     return t.functionExpression(null, [uid], t.blockStatement(state.nodes));
   }));
 };
 
 var hoistVariablesVisitor = {
-  enter: function (node, parent, scope, context, hoistDeclarators) {
+  enter: function (node, parent, scope, hoistDeclarators) {
     if (t.isFunction(node)) {
       // nothing inside is accessible
-      return context.skip();
+      return this.skip();
     }
 
     if (t.isVariableDeclaration(node)) {
@@ -145,19 +149,17 @@ var hoistVariablesVisitor = {
 };
 
 var hoistFunctionsVisitor = {
-  enter: function (node, parent, scope, context, handlerBody) {
-    if (t.isFunction(node)) context.skip();
+  enter: function (node, parent, scope, handlerBody) {
+    if (t.isFunction(node)) this.skip();
 
     if (t.isFunctionDeclaration(node) || node._blockHoist) {
       handlerBody.push(node);
-      context.remove();
+      this.remove();
     }
   }
 };
 
-SystemFormatter.prototype.transform = function (ast) {
-  var program = ast.program;
-
+SystemFormatter.prototype.transform = function (program) {
   var hoistDeclarators = [];
   var moduleName = this.getModuleName();
   var moduleNameLiteral = t.literal(moduleName);
@@ -178,7 +180,7 @@ SystemFormatter.prototype.transform = function (ast) {
   var returnStatement = handlerBody.pop();
 
   // hoist up all variable declarations
-  traverse(block, hoistVariablesVisitor, this.file.scope, hoistDeclarators);
+  this.file.scope.traverse(block, hoistVariablesVisitor, hoistDeclarators);
 
   if (hoistDeclarators.length) {
     var hoistDeclar = t.variableDeclaration("var", hoistDeclarators);
@@ -187,7 +189,7 @@ SystemFormatter.prototype.transform = function (ast) {
   }
 
   // hoist up function declarations for circular references
-  traverse(block, hoistFunctionsVisitor, this.file.scope, handlerBody);
+  this.file.scope.traverse(block, hoistFunctionsVisitor, handlerBody);
 
   handlerBody.push(returnStatement);
 

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

@@ -5,7 +5,7 @@ module.exports = UMDFormatter;
 var AMDFormatter = require("./amd");
 var util         = require("../../util");
 var t            = require("../../types");
-var _            = require("lodash");
+var values       = require("lodash/object/values");
 
 function UMDFormatter() {
   AMDFormatter.apply(this, arguments);
@@ -13,9 +13,8 @@ function UMDFormatter() {
 
 util.inherits(UMDFormatter, AMDFormatter);
 
-UMDFormatter.prototype.transform = function (ast) {
-  var program = ast.program;
-  var body    = program.body;
+UMDFormatter.prototype.transform = function (program) {
+  var body = program.body;
 
   // build an array of module names
 
@@ -26,7 +25,7 @@ UMDFormatter.prototype.transform = function (ast) {
 
   // factory
 
-  var ids  = _.values(this.ids);
+  var ids  = values(this.ids);
   var args = [t.identifier("exports")];
   if (this.passModuleArg) args.push(t.identifier("module"));
   args = args.concat(ids);

lib/6to5/transformation/templates/.6to5rc

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["useStrict"]
+}

lib/6to5/transformation/templates/class-call-check.js

@@ -0,0 +1,5 @@
+(function (instance, Constructor) {
+  if (!(instance instanceof Constructor)) {
+    throw new TypeError("Cannot call a class as a function");
+  }
+});

lib/6to5/transformation/templates/class-super-constructor-call.js

@@ -1,3 +1,3 @@
-if (Object.getPrototypeOf(CLASS_NAME) !== null) {
-  Object.getPrototypeOf(CLASS_NAME).apply(this, arguments);
+if (SUPER_NAME != null) {
+  SUPER_NAME.apply(this, arguments);
 }

lib/6to5/transformation/templates/corejs-is-iterator.js

@@ -0,0 +1 @@
+CORE_ID.$for.isIterable(VALUE);

lib/6to5/transformation/templates/default-parameter.js

@@ -1 +1 @@
-var VARIABLE_NAME = ARGUMENTS[ARGUMENT_KEY] === undefined ? DEFAULT_VALUE : ARGUMENTS[ARGUMENT_KEY];
+let VARIABLE_NAME = ARGUMENTS[ARGUMENT_KEY] === undefined ? DEFAULT_VALUE : ARGUMENTS[ARGUMENT_KEY];

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

@@ -1,7 +1,10 @@
 (function (obj, defaults) {
-  for (var key in defaults) {
-    if (obj[key] === undefined) {
-      obj[key] = defaults[key];
+  var keys = Object.getOwnPropertyNames(defaults);
+  for (var i = 0; i < keys.length; i++) {
+    var key = keys[i];
+    var value = Object.getOwnPropertyDescriptor(defaults, key);
+    if (value && value.configurable && obj[key] === undefined) {
+      Object.defineProperty(obj, key, value);
     }
   }
   return obj;

lib/6to5/transformation/templates/exports-module-declaration.js

@@ -1 +1,3 @@
-exports.__esModule = true;
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});

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

@@ -1,4 +1,4 @@
-(function (target) {
+Object.assign || (function (target) {
   for (var i = 1; i < arguments.length; i++) {
     var source = arguments[i];
     for (var key in source) {

lib/6to5/transformation/templates/object-destructuring-empty.js

@@ -0,0 +1,3 @@
+(function (obj) {
+  if (obj == null) throw new TypeError("Cannot destructure undefined");
+});

lib/6to5/transformation/templates/property-method-assignment-wrapper-generator.js

@@ -0,0 +1,11 @@
+(function (FUNCTION_KEY) {
+  var WRAPPER_KEY = function* FUNCTION_ID() {
+    return yield* FUNCTION_KEY.apply(this, arguments);
+  };
+
+  WRAPPER_KEY.toString = function () {
+    return FUNCTION_KEY.toString();
+  };
+
+  return WRAPPER_KEY;
+})(FUNCTION)

lib/6to5/transformation/templates/self-contained-helpers-head.js

@@ -0,0 +1,2 @@
+var helpers = exports.default = {};
+exports.__esModule = true;

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

@@ -0,0 +1,19 @@
+(function set(object, property, value, receiver) {
+  var desc = Object.getOwnPropertyDescriptor(object, property);
+
+  if (desc === undefined) {
+    var parent = Object.getPrototypeOf(object);
+
+    if (parent !== null) {
+      return set(parent, property, value, receiver);
+    }
+  } else if ("value" in desc && desc.writable) {
+    return desc.value = value;
+  } else {
+    var setter = desc.set;
+
+    if (setter !== undefined) {
+      return setter.call(receiver, value);
+    }
+  }
+});

lib/6to5/transformation/templates/sliced-to-array.js

@@ -1,12 +1,14 @@
 (function (arr, i) {
   if (Array.isArray(arr)) {
     return arr;
-  } else {
+  } else if (Symbol.iterator in Object(arr)) {
     var _arr = [];
     for (var _iterator = arr[Symbol.iterator](), _step; !(_step = _iterator.next()).done;) {
       _arr.push(_step.value);
       if (i && _arr.length === i) break;
     }
     return _arr;
+  } else {
+    throw new TypeError("Invalid attempt to destructure non-iterable instance");
   }
 });

lib/6to5/transformation/templates/tail-call-body.js

@@ -0,0 +1,3 @@
+{
+  FUNCTION_ID:while (true) BLOCK
+}

lib/6to5/transformation/templates/tail-call.js

@@ -0,0 +1,23 @@
+(function () {
+  function Tail(func, args, context) {
+    this.func = func;
+    this.args = args;
+    this.context = context;
+  }
+
+  Tail.prototype._isTailDescriptor = true;
+
+  var isRunning = false;
+
+  return function (func, args, context) {
+    var result = new Tail(func, args, context);
+    if (!isRunning) {
+      isRunning = true;
+      do {
+        result = result.func.apply(result.context, result.args);
+      } while (result instanceof Tail || (result && result._isTailDescriptor));
+      isRunning = false;
+    }
+    return result;
+  };
+})()

lib/6to5/transformation/templates/temporal-assert-defined.js

@@ -0,0 +1,6 @@
+(function (val, name, undef) {
+  if (val === undef) {
+    throw new ReferenceError(name + " is not defined - temporal dead zone");
+  }
+  return true;
+})

lib/6to5/transformation/templates/temporal-undefined.js

@@ -0,0 +1 @@
+({})

lib/6to5/transformation/templates/to-consumable-array.js

@@ -0,0 +1,8 @@
+(function (arr) {
+  if (Array.isArray(arr)) {
+    for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) arr2[i] = arr[i];
+    return arr2;
+  } else {
+    return Array.from(arr);
+  }
+});

lib/6to5/transformation/transformer-pass.js

@@ -1,8 +1,6 @@
 module.exports = TransformerPass;
 
-var traverse = require("../traverse");
-var util     = require("../util");
-var _        = require("lodash");
+var includes = require("lodash/collection/includes");
 
 /**
  * This class is responsible for traversing over the provided `File`s
@@ -11,62 +9,55 @@ var _        = require("lodash");
 
 function TransformerPass(file, transformer) {
   this.transformer = transformer;
+  this.shouldRun   = !transformer.check;
   this.handlers    = transformer.handlers;
   this.file        = file;
 }
 
-TransformerPass.prototype.astRun = function (key) {
-  var handlers = this.handlers;
-  var file = this.file;
-
-  if (handlers.ast && handlers.ast[key]) {
-    handlers.ast[key](file.ast, file);
-  }
-};
-
 TransformerPass.prototype.canRun = function () {
   var transformer = this.transformer;
 
   var opts = this.file.opts;
   var key  = transformer.key;
+
+  // internal
   if (key[0] === "_") return true;
 
+  // blacklist
   var blacklist = opts.blacklist;
-  if (blacklist.length && _.contains(blacklist, key)) return false;
+  if (blacklist.length && includes(blacklist, key)) return false;
 
+  // whitelist
   var whitelist = opts.whitelist;
-  if (whitelist.length && !_.contains(whitelist, key)) return false;
+  if (whitelist.length) return includes(whitelist, key);
 
-  if (transformer.optional && !_.contains(opts.optional, key)) return false;
+  // optional
+  if (transformer.optional && !includes(opts.optional, key)) return false;
 
+  // experimental
   if (transformer.experimental && !opts.experimental) return false;
 
+  // playground
+  if (transformer.playground && !opts.playground) return false;
+
   return true;
 };
 
-var transformVisitor = {
-  enter: function (node, parent, scope, context, state) {
-    var fns = state.handlers[node.type];
-    if (!fns) return;
-    return fns.enter(node, parent, scope, context, state.file, state.pass);
-  },
-
-  exit: function (node, parent, scope, context, state) {
-    var fns = state.handlers[node.type];
-    if (!fns) return;
-    return fns.exit(node, parent, scope, context, state.file, state.pass);
+TransformerPass.prototype.checkNode = function (node) {
+  var check = this.transformer.check;
+  if (check) {
+    return this.shouldRun = check(node);
+  } else {
+    return true;
   }
 };
 
 TransformerPass.prototype.transform = function () {
+  if (!this.shouldRun) return;
+
   var file = this.file;
 
-  util.debug(file.opts.filename + ": Running transformer " + this.transformer.key);
+  file.debug("Running transformer " + this.transformer.key);
 
-  this.astRun("before");
-
-  var state = { file: file, handlers: this.handlers, pass: this };
-  traverse(file.ast, transformVisitor, file.scope, state);
-
-  this.astRun("after");
+  file.scope.traverse(file.ast, this.handlers, file);
 };

lib/6to5/transformation/transformer.js

@@ -3,8 +3,11 @@
 module.exports = Transformer;
 
 var TransformerPass = require("./transformer-pass");
-var t               = require("../types");
-var _               = require("lodash");
+var isFunction      = require("lodash/lang/isFunction");
+var traverse        = require("../traversal");
+var isObject        = require("lodash/lang/isObject");
+var clone           = require("../helpers/clone");
+var each            = require("lodash/collection/each");
 
 /**
  * This is the class responsible for normalising a transformers handlers
@@ -13,44 +16,55 @@ var _               = require("lodash");
  */
 
 function Transformer(key, transformer, opts) {
-  this.manipulateOptions = transformer.manipulateOptions;
-  this.experimental      = !!transformer.experimental;
-  this.secondPass        = !!transformer.secondPass;
-  this.optional          = !!transformer.optional;
-  this.handlers          = this.normalise(transformer);
-  this.opts              = opts || {};
-  this.key               = key;
+  transformer = clone(transformer);
+
+  var take = function (key) {
+    var val = transformer[key];
+    delete transformer[key];
+    return val;
+  };
+
+  this.manipulateOptions = take("manipulateOptions");
+  this.check             = take("check");
+  this.post              = take("post");
+  this.pre               = take("pre");
+
+  this.experimental = !!take("experimental");
+  this.playground   = !!take("playground");
+  this.secondPass   = !!take("secondPass");
+  this.optional     = !!take("optional");
+
+  this.handlers = this.normalize(transformer);
+  this.opts     = opts || {};
+  this.key      = key;
 }
 
-Transformer.prototype.normalise = function (transformer) {
+Transformer.prototype.normalize = function (transformer) {
   var self = this;
 
-  if (_.isFunction(transformer)) {
+  if (isFunction(transformer)) {
     transformer = { ast: transformer };
   }
 
-  _.each(transformer, function (fns, type) {
+  traverse.explode(transformer);
+
+  each(transformer, function (fns, type) {
     // hidden property
     if (type[0] === "_") {
       self[type] = fns;
       return;
     }
 
-    if (_.isFunction(fns)) fns = { enter: fns };
+    if (type === "enter" || type === "exit") return;
 
-    if (!_.isObject(fns)) return;
+    if (isFunction(fns)) fns = { enter: fns };
 
-    if (!fns.enter) fns.enter = _.noop;
-    if (!fns.exit) fns.exit = _.noop;
+    if (!isObject(fns)) return;
+
+    if (!fns.enter) fns.enter = function () { };
+    if (!fns.exit) fns.exit = function () { };
 
     transformer[type] = fns;
-
-    var aliases = t.FLIPPED_ALIAS_KEYS[type];
-    if (aliases) {
-      _.each(aliases, function (alias) {
-        transformer[alias] = fns;
-      });
-    }
   });
 
   return transformer;

lib/6to5/transformation/transformers/deprecated.json

@@ -12,7 +12,8 @@
   "generatorComprehension": "es7.comprehensions",
   "arrowFunctions": "es6.arrowFunctions",
   "classes": "es6.classes",
-  "objectSpread": "es7.objectSpread",
+  "objectSpread": "es7.objectRestSpread",
+  "es7.objectSpread": "es7.objectRestSpread",
   "exponentiationOperator": "es7.exponentiationOperator",
   "spread": "es6.spread",
   "templateLiterals": "es6.templateLiterals",
@@ -33,6 +34,8 @@
   "coreAliasing": "selfContained",
   "undefinedToVoid": "spec.undefinedToVoid",
   "undeclaredVariableCheck": "validation.undeclaredVariableCheck",
-  "specPropertyLiterals": "minification.propertyLiterals",
-  "specMemberExpressionLiterals": "minification.memberExpressionLiterals"
+  "specPropertyLiterals": "es3.propertyLiterals",
+  "specMemberExpressionLiterals": "es3.memberExpressionLiterals",
+  "minification.propertyLiterals": "es3.propertyLiterals",
+  "minification.memberExpressionLiterals": "es3.memberExpressionLiterals"
 }

lib/6to5/transformation/transformers/es5/properties.mutators.js

@@ -1,7 +1,11 @@
 "use strict";
 
-var util = require("../../../util");
-var t    = require("../../../types");
+var defineMap = require("../../helpers/define-map");
+var t         = require("../../../types");
+
+exports.check = function (node) {
+  return t.isProperty(node) && (node.kind === "get" || node.kind === "set");
+};
 
 exports.ObjectExpression = function (node) {
   var mutatorMap = {};
@@ -10,7 +14,7 @@ exports.ObjectExpression = function (node) {
   node.properties = node.properties.filter(function (prop) {
     if (prop.kind === "get" || prop.kind === "set") {
       hasAny = true;
-      util.pushMutatorMap(mutatorMap, prop.key, prop.kind, prop.computed, prop.value);
+      defineMap.push(mutatorMap, prop.key, prop.kind, prop.computed, prop.value);
       return false;
     } else {
       return true;
@@ -21,6 +25,6 @@ exports.ObjectExpression = function (node) {
 
   return t.callExpression(
     t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
-    [node, util.buildDefineProperties(mutatorMap)]
+    [node, defineMap.build(mutatorMap)]
   );
 };

lib/6to5/transformation/transformers/es6/arrow-functions.js

@@ -2,6 +2,8 @@
 
 var t = require("../../../types");
 
+exports.check = t.isArrowFunctionExpression;
+
 exports.ArrowFunctionExpression = function (node) {
   t.ensureBlock(node);
 

lib/6to5/transformation/transformers/es6/block-scoping-tdz.js

@@ -1,34 +1,29 @@
 "use strict";
 
-var traverse = require("../../../traverse");
-var t        = require("../../../types");
+var t = require("../../../types");
 
 var visitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     if (!t.isReferencedIdentifier(node, parent)) return;
 
     var declared = state.letRefs[node.name];
     if (!declared) return;
 
     // declared node is different in this scope
-    if (scope.get(node.name, true) !== declared) return;
+    if (scope.getBindingIdentifier(node.name) !== declared) return;
 
-    var declaredLoc  = declared.loc;
-    var referenceLoc = node.loc;
+    var assert = t.callExpression(
+      state.file.addHelper("temporal-assert-defined"),
+      [node, t.literal(node.name), state.file.addHelper("temporal-undefined")]
+    );
 
-    if (!declaredLoc || !referenceLoc) return;
+    this.skip();
 
-    // does this reference appear on a line before the declaration?
-    var before = referenceLoc.start.line < declaredLoc.start.line;
-
-    if (referenceLoc.start.line === declaredLoc.start.line) {
-      // this reference appears on the same line
-      // check it appears before the declaration
-      before = referenceLoc.start.col < declaredLoc.start.col;
-    }
-
-    if (before) {
-      throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
+    if (t.isAssignmentExpression(parent) || t.isUpdateExpression(parent)) {
+      if (parent._ignoreBlockScopingTDZ) return;
+      this.parentPath.replaceNode(t.sequenceExpression([assert, parent]));
+    } else {
+      return t.logicalExpression("&&", assert, node);
     }
   }
 };
@@ -37,7 +32,7 @@ exports.optional = true;
 
 exports.Loop =
 exports.Program =
-exports.BlockStatement = function (node, parent, scope, context, file) {
+exports.BlockStatement = function (node, parent, scope, file) {
   var letRefs = node._letReferences;
   if (!letRefs) return;
 
@@ -46,5 +41,5 @@ exports.BlockStatement = function (node, parent, scope, context, file) {
     file:    file
   };
 
-  traverse(node, visitor, scope, state);
+  scope.traverse(node, visitor, state);
 };

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

@@ -1,10 +1,15 @@
 "use strict";
 
-var traverse = require("../../../traverse");
+var traverse = require("../../../traversal");
 var object   = require("../../../helpers/object");
 var util     = require("../../../util");
 var t        = require("../../../types");
-var _        = require("lodash");
+var values   = require("lodash/object/values");
+var extend   = require("lodash/object/extend");
+
+exports.check = function (node) {
+  return t.isVariableDeclaration(node) && (node.kind === "let" || node.kind === "const");
+};
 
 var isLet = function (node, parent) {
   if (!t.isVariableDeclaration(node)) return false;
@@ -12,7 +17,7 @@ var isLet = function (node, parent) {
   if (node.kind !== "let") return false;
 
   // https://github.com/6to5/6to5/issues/255
-  if (!t.isFor(parent) || t.isFor(parent) && parent.left !== node) {
+  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");
@@ -24,46 +29,57 @@ var isLet = function (node, parent) {
   return true;
 };
 
+var isLetInitable = function (node, parent) {
+  return !t.isFor(parent) || t.isFor(parent) && parent.left !== node;
+};
+
 var isVar = function (node, parent) {
   return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node, parent);
 };
 
-var standardiseLets = function (declars) {
+var standardizeLets = function (declars) {
   for (var i = 0; i < declars.length; i++) {
     delete declars[i]._let;
   }
 };
 
-exports.VariableDeclaration = function (node, parent) {
-  isLet(node, parent);
+exports.VariableDeclaration = function (node, parent, scope, file) {
+  if (!isLet(node, parent)) return;
+
+  if (isLetInitable(node) && file.transformers["es6.blockScopingTDZ"].canRun()) {
+    var nodes = [node];
+
+    for (var i = 0; i < node.declarations.length; i++) {
+      var decl = node.declarations[i];
+      if (decl.init) {
+        var assign = t.assignmentExpression("=", decl.id, decl.init);
+        assign._ignoreBlockScopingTDZ = true;
+        nodes.push(t.expressionStatement(assign));
+      }
+      decl.init = file.addHelper("temporal-undefined");
+    }
+
+    node._blockHoist = 2;
+
+    return nodes;
+  }
 };
 
-exports.Loop = function (node, parent, scope, context, file) {
+exports.Loop = function (node, parent, scope, file) {
   var init = node.left || node.init;
   if (isLet(init, node)) {
     t.ensureBlock(node);
     node.body._letDeclarators = [init];
   }
-
-  if (t.isLabeledStatement(parent)) {
-    // set label so `run` has access to it
-    node.label = parent.label;
-  }
-
-  var letScoping = new LetScoping(node, node.body, parent, scope, file);
-  letScoping.run();
-
-  if (node.label && !t.isLabeledStatement(parent)) {
-    // we've been given a label so let's wrap ourselves
-    return t.labeledStatement(node.label, node);
-  }
+  var blockScoping = new BlockScoping(node, node.body, parent, scope, file);
+  blockScoping.run();
 };
 
 exports.Program =
-exports.BlockStatement = function (block, parent, scope, context, file) {
+exports.BlockStatement = function (block, parent, scope, file) {
   if (!t.isLoop(parent)) {
-    var letScoping = new LetScoping(false, block, parent, scope, file);
-    letScoping.run();
+    var blockScoping = new BlockScoping(false, block, parent, scope, file);
+    blockScoping.run();
   }
 };
 
@@ -77,7 +93,7 @@ exports.BlockStatement = function (block, parent, scope, context, file) {
  * @param {File} file
  */
 
-function LetScoping(loopParent, block, parent, scope, file) {
+function BlockScoping(loopParent, block, parent, scope, file) {
   this.loopParent = loopParent;
   this.parent     = parent;
   this.scope      = scope;
@@ -94,7 +110,7 @@ function LetScoping(loopParent, block, parent, scope, file) {
  * Start the ball rolling.
  */
 
-LetScoping.prototype.run = function () {
+BlockScoping.prototype.run = function () {
   var block = this.block;
   if (block._letDone) return;
   block._letDone = true;
@@ -114,19 +130,19 @@ LetScoping.prototype.run = function () {
   }
 };
 
-function replace(node, parent, scope, context, remaps) {
+function replace(node, parent, scope, remaps) {
   if (!t.isReferencedIdentifier(node, parent)) return;
 
   var remap = remaps[node.name];
   if (!remap) return;
 
-  var own = scope.get(node.name, true);
-  if (own === remap.node) {
+  var ownBinding = scope.getBindingIdentifier(node.name);
+  if (ownBinding === remap.binding) {
     node.name = remap.uid;
   } else {
-    // scope already has it's own declaration that doesn't
+    // scope already has it's own binding that doesn't
     // match the one we have a stored replacement for
-    if (context) context.skip();
+    if (this) this.skip();
   }
 }
 
@@ -135,15 +151,15 @@ var replaceVisitor = {
 };
 
 function traverseReplace(node, parent, scope, remaps) {
-  replace(node, parent, scope, null, remaps);
-  traverse(node, replaceVisitor, scope, remaps);
+  replace(node, parent, scope, remaps);
+  scope.traverse(node, replaceVisitor, remaps);
 }
 
 /**
  * Description
  */
 
-LetScoping.prototype.remap = function () {
+BlockScoping.prototype.remap = function () {
   var hasRemaps = false;
   var letRefs   = this.letReferences;
   var scope     = this.scope;
@@ -159,13 +175,13 @@ LetScoping.prototype.remap = function () {
     // this is the defining identifier of a declaration
     var ref = letRefs[key];
 
-    if (scope.parentHas(key)) {
+    if (scope.parentHasBinding(key) || scope.hasGlobal(key)) {
       var uid = scope.generateUidIdentifier(ref.name).name;
       ref.name = uid;
 
       hasRemaps = true;
       remaps[key] = remaps[uid] = {
-        node: ref,
+        binding: ref,
         uid: uid
       };
     }
@@ -182,14 +198,14 @@ LetScoping.prototype.remap = function () {
     traverseReplace(loopParent.update, loopParent, scope, remaps);
   }
 
-  traverse(this.block, replaceVisitor, scope, remaps);
+  scope.traverse(this.block, replaceVisitor, remaps);
 };
 
 /**
  * Description
  */
 
-LetScoping.prototype.needsClosure = function () {
+BlockScoping.prototype.needsClosure = function () {
   var block = this.block;
 
   // if we're inside of a for loop then we search to see if there are any
@@ -200,7 +216,7 @@ LetScoping.prototype.needsClosure = function () {
   this.hoistVarDeclarations();
 
   // turn outsideLetReferences into an array
-  var params = _.values(this.outsideLetReferences);
+  var params = values(this.outsideLetReferences);
 
   // build the closure that we're going to wrap the block with
   var fn = t.functionExpression(null, params, t.blockStatement(block.body));
@@ -231,13 +247,13 @@ LetScoping.prototype.needsClosure = function () {
 };
 
 var letReferenceFunctionVisitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     // not a direct reference
     if (!t.isReferencedIdentifier(node, parent)) return;
 
     // this scope has a variable with the same name so it couldn't belong
     // to our let scope
-    if (scope.hasOwn(node.name, true)) return;
+    if (scope.hasOwnBinding(node.name)) return;
 
     // not a part of our scope
     if (!state.letReferences[node.name]) return;
@@ -247,10 +263,10 @@ var letReferenceFunctionVisitor = {
 };
 
 var letReferenceBlockVisitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     if (t.isFunction(node)) {
-      traverse(node, letReferenceFunctionVisitor, scope, state);
-      return context.skip();
+      scope.traverse(node, letReferenceFunctionVisitor, state);
+      return this.skip();
     }
   }
 };
@@ -259,7 +275,7 @@ var letReferenceBlockVisitor = {
  * Description
  */
 
-LetScoping.prototype.getLetReferences = function () {
+BlockScoping.prototype.getLetReferences = function () {
   var block = this.block;
 
   var declarators = block._letDeclarators || [];
@@ -268,7 +284,7 @@ LetScoping.prototype.getLetReferences = function () {
   //
   for (var i = 0; i < declarators.length; i++) {
     declar = declarators[i];
-    _.extend(this.outsideLetReferences, t.getIds(declar, true));
+    extend(this.outsideLetReferences, t.getBindingIdentifiers(declar));
   }
 
   //
@@ -284,8 +300,8 @@ LetScoping.prototype.getLetReferences = function () {
   //
   for (i = 0; i < declarators.length; i++) {
     declar = declarators[i];
-    var keys = t.getIds(declar, true);
-    _.extend(this.letReferences, keys);
+    var keys = t.getBindingIdentifiers(declar);
+    extend(this.letReferences, keys);
     this.hasLetReferences = true;
   }
 
@@ -293,7 +309,7 @@ LetScoping.prototype.getLetReferences = function () {
   if (!this.hasLetReferences) return;
 
   // set let references to plain var references
-  standardiseLets(declarators);
+  standardizeLets(declarators);
 
   var state = {
     letReferences: this.letReferences,
@@ -302,39 +318,76 @@ LetScoping.prototype.getLetReferences = function () {
 
   // traverse through this block, stopping on functions and checking if they
   // contain any local let references
-  traverse(this.block, letReferenceBlockVisitor, this.scope, state);
+  this.scope.traverse(this.block, letReferenceBlockVisitor, state);
 
   return state.closurify;
 };
 
+var loopNodeTo = function (node) {
+  if (t.isBreakStatement(node)) {
+    return "break";
+  } else if (t.isContinueStatement(node)) {
+    return "continue";
+  }
+};
+
 var loopVisitor = {
-  enter: function (node, parent, scope, context, state) {
+  enter: function (node, parent, scope, state) {
     var replace;
 
-    if (t.isFunction(node) || t.isLoop(node)) {
-      return context.skip();
+    if (t.isLoop(node)) {
+      state.ignoreLabeless = true;
+      scope.traverse(node, loopVisitor, state);
+      state.ignoreLabeless = false;
     }
 
-    if (node && !node.label && state.isLoop) {
-      if (t.isBreakStatement(node)) {
-        if (t.isSwitchCase(parent)) return;
+    if (t.isFunction(node) || t.isLoop(node)) {
+      return this.skip();
+    }
 
-        state.hasBreak = true;
-        replace = t.returnStatement(t.literal("break"));
-      } else if (t.isContinueStatement(node)) {
-        state.hasContinue = true;
-        replace = t.returnStatement(t.literal("continue"));
+    var loopText = loopNodeTo(node);
+
+    if (loopText) {
+      if (node.label) {
+        // we shouldn't be transforming this because it exists somewhere inside
+        if (state.innerLabels.indexOf(node.label.name) >= 0) {
+          return;
+        }
+
+        loopText = loopText + "|" + node.label.name;
+      } else {
+        // we shouldn't be transforming these statements because
+        // they don't refer to the actual loop we're scopifying
+        if (state.ignoreLabeless) return;
+
+        // break statements mean something different in this context
+        if (t.isBreakStatement(node) && t.isSwitchCase(parent)) return;
       }
+
+      state.hasBreakContinue = true;
+      state.map[loopText] = node;
+      replace = t.literal(loopText);
     }
 
     if (t.isReturnStatement(node)) {
       state.hasReturn = true;
-      replace = t.returnStatement(t.objectExpression([
+      replace = t.objectExpression([
         t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
-      ]));
+      ]);
     }
 
-    if (replace) return t.inherits(replace, node);
+    if (replace) {
+      replace = t.returnStatement(replace);
+      return t.inherits(replace, node);
+    }
+  }
+};
+
+var loopLabelVisitor = {
+  enter: function (node, parent, scope, state) {
+    if (t.isLabeledStatement(node)) {
+      state.innerLabels.push(node.label.name);
+    }
   }
 };
 
@@ -347,20 +400,24 @@ var loopVisitor = {
  * @returns {Object}
  */
 
-LetScoping.prototype.checkLoop = function () {
+BlockScoping.prototype.checkLoop = function () {
   var state = {
-    hasContinue: false,
-    hasReturn:   false,
-    hasBreak:    false,
-    isLoop:      !!this.loopParent
+    hasBreakContinue: false,
+    ignoreLabeless:   false,
+    innerLabels:      [],
+    hasReturn:        false,
+    isLoop:           !!this.loopParent,
+    map:              {}
   };
 
-  traverse(this.block, loopVisitor, this.scope, state);
+  this.scope.traverse(this.block, loopLabelVisitor, state);
+  this.scope.traverse(this.block, loopVisitor, state);
+
   return state;
 };
 
 var hoistVarDeclarationsVisitor = {
-  enter: function (node, parent, scope, context, self) {
+  enter: function (node, parent, scope, self) {
     if (t.isForStatement(node)) {
       if (isVar(node.init, node)) {
         node.init = t.sequenceExpression(self.pushDeclar(node.init));
@@ -372,7 +429,7 @@ var hoistVarDeclarationsVisitor = {
     } else if (isVar(node, parent)) {
       return self.pushDeclar(node).map(t.expressionStatement);
     } else if (t.isFunction(node)) {
-      return context.skip();
+      return this.skip();
     }
   }
 };
@@ -382,7 +439,7 @@ var hoistVarDeclarationsVisitor = {
  * once we wrap everything in a closure.
  */
 
-LetScoping.prototype.hoistVarDeclarations = function () {
+BlockScoping.prototype.hoistVarDeclarations = function () {
   traverse(this.block, hoistVarDeclarationsVisitor, this.scope, this);
 };
 
@@ -394,7 +451,7 @@ LetScoping.prototype.hoistVarDeclarations = function () {
  * @returns {Array}
  */
 
-LetScoping.prototype.pushDeclar = function (node) {
+BlockScoping.prototype.pushDeclar = function (node) {
   this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
     return t.variableDeclarator(declar.id);
   })));
@@ -419,9 +476,9 @@ LetScoping.prototype.pushDeclar = function (node) {
  * @param {Node} call CallExpression
  */
 
-LetScoping.prototype.build = function (ret, call) {
+BlockScoping.prototype.build = function (ret, call) {
   var has = this.has;
-  if (has.hasReturn || has.hasBreak || has.hasContinue) {
+  if (has.hasReturn || has.hasBreakContinue) {
     this.buildHas(ret, call);
   } else {
     this.body.push(t.expressionStatement(call));
@@ -435,7 +492,7 @@ LetScoping.prototype.build = function (ret, call) {
  * @param {Node} call CallExpression
  */
 
-LetScoping.prototype.buildHas = function (ret, call) {
+BlockScoping.prototype.buildHas = function (ret, call) {
   var body = this.body;
 
   body.push(t.variableDeclaration("var", [
@@ -454,22 +511,14 @@ LetScoping.prototype.buildHas = function (ret, call) {
     });
   }
 
-  if (has.hasBreak || has.hasContinue) {
+  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.");
     }
 
-    // ensure that the parent has a label as we're building a switch and we
-    // need to be able to access it
-    var label = loopParent.label = loopParent.label || this.scope.generateUidIdentifier("loop");
-
-    if (has.hasBreak) {
-      cases.push(t.switchCase(t.literal("break"), [t.breakStatement(label)]));
-    }
-
-    if (has.hasContinue) {
-      cases.push(t.switchCase(t.literal("continue"), [t.continueStatement(label)]));
+    for (var key in has.map) {
+      cases.push(t.switchCase(t.literal(key), [has.map[key]]));
     }
 
     if (has.hasReturn) {

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

@@ -2,14 +2,18 @@
 
 var ReplaceSupers = require("../../helpers/replace-supers");
 var nameMethod    = require("../../helpers/name-method");
+var defineMap     = require("../../helpers/define-map");
+var messages      = require("../../../messages");
 var util          = require("../../../util");
 var t             = require("../../../types");
 
-exports.ClassDeclaration = function (node, parent, scope, context, file) {
-  return new Class(node, file, scope, true).run();
+exports.check = t.isClass;
+
+exports.ClassDeclaration = function (node, parent, scope, file) {
+  return new ClassTransformer(node, file, scope, true).run();
 };
 
-exports.ClassExpression = function (node, parent, scope, context, file) {
+exports.ClassExpression = function (node, parent, scope, file) {
   if (!node.id) {
     if (t.isProperty(parent) && parent.value === node && !parent.computed && t.isIdentifier(parent.key)) {
       // var o = { foo: class {} };
@@ -22,7 +26,7 @@ exports.ClassExpression = function (node, parent, scope, context, file) {
     }
   }
 
-  return new Class(node, file, scope, false).run();
+  return new ClassTransformer(node, file, scope, false).run();
 };
 
 /**
@@ -31,10 +35,10 @@ exports.ClassExpression = function (node, parent, scope, context, file) {
  * @param {Node} node
  * @param {File} file
  * @param {Scope} scope
- * @param {Boolean} closure
+ * @param {Boolean} isStatement
  */
 
-function Class(node, file, scope, isStatement) {
+function ClassTransformer(node, file, scope, isStatement) {
   this.isStatement = isStatement;
   this.scope       = scope;
   this.node        = node;
@@ -47,7 +51,8 @@ function Class(node, file, scope, isStatement) {
   this.staticMutatorMap   = {};
   this.hasConstructor     = false;
   this.className          = node.id || scope.generateUidIdentifier("class");
-  this.superName          = node.superClass;
+  this.superName          = node.superClass || t.identifier("Function");
+  this.hasSuper           = !!node.superClass;
   this.isLoose            = file.isLoose("es6.classes");
 }
 
@@ -57,7 +62,7 @@ function Class(node, file, scope, isStatement) {
  * @returns {Array}
  */
 
-Class.prototype.run = function () {
+ClassTransformer.prototype.run = function () {
   var superName = this.superName;
   var className = this.className;
   var file      = this.file;
@@ -66,12 +71,19 @@ Class.prototype.run = function () {
 
   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, [], t.blockStatement([]));
+    constructor = t.functionDeclaration(className, [], constructorBody);
     body.push(constructor);
   } else {
-    constructor = t.functionExpression(null, [], t.blockStatement([]));
+    constructor = t.functionExpression(null, [], constructorBody);
     body.push(t.variableDeclaration("var", [
       t.variableDeclarator(className, constructor)
     ]));
@@ -83,12 +95,11 @@ Class.prototype.run = function () {
 
   //
 
-  if (superName) {
+  if (this.hasSuper) {
     closureArgs.push(superName);
 
     if (!t.isIdentifier(superName)) {
-      var superRef = this.scope.generateUidBasedOnNode(superName, this.file);
-      superName = superRef;
+      superName = this.scope.generateUidBasedOnNode(superName, this.file);
     }
 
     closureParams.push(superName);
@@ -127,7 +138,7 @@ Class.prototype.run = function () {
  * Description
  */
 
-Class.prototype.buildBody = function () {
+ClassTransformer.prototype.buildBody = function () {
   var constructor = this.constructor;
   var className   = this.className;
   var superName   = this.superName;
@@ -141,10 +152,11 @@ Class.prototype.buildBody = function () {
         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.key.name === "constructor") {
@@ -155,15 +167,16 @@ Class.prototype.buildBody = function () {
     } else if (t.isPrivateDeclaration(node)) {
       this.closure = true;
       body.unshift(node);
+    } else if (t.isClassProperty(node)) {
+      this.pushProperty(node);
     }
   }
 
   // we have no constructor, we have a super, and the super doesn't appear to be falsy
-  if (!this.hasConstructor && superName && !t.isFalsyExpression(superName)) {
-    var defaultConstructorTemplate = "class-super-constructor-call";
-    if (this.isLoose) defaultConstructorTemplate += "-loose";
-
-    constructor.body.body.push(util.template(defaultConstructorTemplate, {
+  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));
@@ -173,11 +186,11 @@ Class.prototype.buildBody = function () {
   var staticProps;
 
   if (this.hasInstanceMutators) {
-    instanceProps = util.buildDefineProperties(this.instanceMutatorMap);
+    instanceProps = defineMap.build(this.instanceMutatorMap);
   }
 
   if (this.hasStaticMutators) {
-    staticProps = util.buildDefineProperties(this.staticMutatorMap);
+    staticProps = defineMap.build(this.staticMutatorMap);
   }
 
   if (instanceProps || staticProps) {
@@ -193,12 +206,12 @@ Class.prototype.buildBody = function () {
 };
 
 /**
- * Push a method to it's respective mutatorMap.
+ * Push a method to its respective mutatorMap.
  *
  * @param {Node} node MethodDefinition
  */
 
-Class.prototype.pushMethod = function (node) {
+ClassTransformer.prototype.pushMethod = function (node) {
   var methodName = node.key;
 
   var kind = node.kind;
@@ -230,7 +243,32 @@ Class.prototype.pushMethod = function (node) {
     this.hasInstanceMutators = true;
   }
 
-  util.pushMutatorMap(mutatorMap, methodName, kind, node.computed, node);
+  defineMap.push(mutatorMap, methodName, kind, node.computed, node);
+  defineMap.push(mutatorMap, methodName, "enumerable", node.computed, false);
+};
+
+/**
+ * Description
+ *
+ * @param {Node} node
+ */
+
+ClassTransformer.prototype.pushProperty = function (node) {
+  if (!node.value) return;
+
+  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))
+    );
+  }
 };
 
 /**
@@ -239,9 +277,9 @@ Class.prototype.pushMethod = function (node) {
  * @param {Node} method MethodDefinition
  */
 
-Class.prototype.pushConstructor = function (method) {
+ClassTransformer.prototype.pushConstructor = function (method) {
   if (method.kind) {
-    throw this.file.errorWithNode(method, "illegal kind for constructor method");
+    throw this.file.errorWithNode(method, messages.get("classesIllegalConstructorKind"));
   }
 
   var construct = this.constructor;
@@ -254,5 +292,5 @@ Class.prototype.pushConstructor = function (method) {
 
   construct._ignoreUserWhitespace = true;
   construct.params                = fn.params;
-  construct.body                  = fn.body;
+  construct.body.body             = construct.body.body.concat(fn.body.body);
 };

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

@@ -1,37 +1,46 @@
 "use strict";
 
-var traverse = require("../../../traverse");
+var messages = require("../../../messages");
 var t        = require("../../../types");
 
+exports.check = function (node) {
+  return t.isVariableDeclaration(node, { kind: "const" });
+};
+
 var visitor = {
-  enter: function (node, parent, scope, context, state) {
-    if (t.isDeclaration(node) || t.isAssignmentExpression(node)) {
-      var ids = t.getIds(node, true);
+  enter: function (node, parent, scope, state) {
+    if (t.isAssignmentExpression(node) || t.isUpdateExpression(node)) {
+      var ids = t.getBindingIdentifiers(node);
 
-      for (var key in ids) {
-        var id = ids[key];
+      for (var name in ids) {
+        var id = ids[name];
 
-        var constant = state.constants[key];
+        var constant = state.constants[name];
 
         // no constant exists
         if (!constant) continue;
 
+        var constantIdentifier = constant.identifier;
+
         // check if the assignment id matches the constant declaration id
         // if it does then it was the id used to initially declare the
         // constant so we can just ignore it
-        if (id === constant) continue;
+        if (id === constantIdentifier) continue;
 
-        throw state.file.errorWithNode(id, key + " is read-only");
+        // check if there's been a local binding that shadows this constant
+        if (!scope.bindingIdentifierEquals(name, constantIdentifier)) continue;
+
+        throw state.file.errorWithNode(id, messages.get("readOnly", name));
       }
-    } else if (t.isScope(node)) {
-      context.skip();
+    } else if (t.isScope(node, parent)) {
+      this.skip();
     }
   }
 };
 
-exports.Scope = function (node, parent, scope, context, file) {
-  traverse(node, visitor, scope, {
-    constants: scope.getAllOfKind("const"),
+exports.Scopable = function (node, parent, scope, file) {
+  scope.traverse(node, visitor, {
+    constants: scope.getAllBindingsOfKind("const"),
     file:      file
   });
 };

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

@@ -1,11 +1,21 @@
 "use strict";
 
-// TODO: Clean up
+var messages = require("../../../messages");
+var t        = require("../../../types");
 
-var t = require("../../../types");
+exports.check = t.isPattern;
 
-var buildVariableAssign = function (opts, id, init) {
-  var op = opts.operator;
+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;
@@ -13,45 +23,46 @@ var buildVariableAssign = function (opts, id, init) {
   if (op) {
     node = t.expressionStatement(t.assignmentExpression(op, id, init));
   } else {
-    node = t.variableDeclaration(opts.kind, [
+    node = t.variableDeclaration(this.kind, [
       t.variableDeclarator(id, init)
     ]);
   }
 
-  node._blockHoist = opts.blockHoist;
+  node._blockHoist = this.blockHoist;
 
   return node;
 };
 
-var buildVariableDeclar = function (opts, id, init) {
+DestructuringTransformer.prototype.buildVariableDeclaration = function (id, init) {
   var declar = t.variableDeclaration("var", [
     t.variableDeclarator(id, init)
   ]);
-  declar._blockHoist = opts.blockHoist;
+  declar._blockHoist = this.blockHoist;
   return declar;
 };
 
-var push = function (opts, nodes, elem, parentId) {
+DestructuringTransformer.prototype.push = function (elem, parentId) {
   if (t.isObjectPattern(elem)) {
-    pushObjectPattern(opts, nodes, elem, parentId);
+    this.pushObjectPattern(elem, parentId);
   } else if (t.isArrayPattern(elem)) {
-    pushArrayPattern(opts, nodes, elem, parentId);
+    this.pushArrayPattern(elem, parentId);
   } else if (t.isAssignmentPattern(elem)) {
-    pushAssignmentPattern(opts, nodes, elem, parentId);
+    this.pushAssignmentPattern(elem, parentId);
   } else {
-    nodes.push(buildVariableAssign(opts, elem, parentId));
+    this.nodes.push(this.buildVariableAssignment(elem, parentId));
   }
 };
 
-var pushAssignmentPattern = function (opts, nodes, pattern, parentId) {
-  var tempParentId = opts.scope.generateUidBasedOnNode(parentId, opts.file);
+DestructuringTransformer.prototype.pushAssignmentPattern = function (pattern, parentId) {
+  var tempParentId = this.scope.generateUidBasedOnNode(parentId);
 
-  nodes.push(t.variableDeclaration("var", [
+  var declar = t.variableDeclaration("var", [
     t.variableDeclarator(tempParentId, parentId)
-  ]));
+  ]);
+  declar._blockHoist = this.blockHoist;
+  this.nodes.push(declar);
 
-  nodes.push(buildVariableAssign(
-    opts,
+  this.nodes.push(this.buildVariableAssignment(
     pattern.left,
     t.conditionalExpression(
       t.binaryExpression("===", tempParentId, t.identifier("undefined")),
@@ -61,72 +72,96 @@ var pushAssignmentPattern = function (opts, nodes, pattern, parentId) {
   ));
 };
 
-var pushObjectPattern = function (opts, nodes, pattern, parentId) {
+DestructuringTransformer.prototype.pushObjectSpread = function (pattern, parentId, prop, i) {
+  // get all the keys that appear in this object before the current spread
+  var keys = [];
+  for (var i2 = 0; i2 < pattern.properties.length; i2++) {
+    var prop2 = pattern.properties[i2];
+
+    if (i2 >= i) break;
+    if (t.isSpreadProperty(prop2)) continue;
+
+    var key = prop2.key;
+    if (t.isIdentifier(key)) {
+      key = t.literal(prop2.key.name);
+    }
+    keys.push(key);
+  }
+  keys = t.arrayExpression(keys);
+
+  var value = t.callExpression(this.file.addHelper("object-without-properties"), [parentId, keys]);
+  this.nodes.push(this.buildVariableAssignment(prop.argument, value));
+};
+
+DestructuringTransformer.prototype.pushObjectProperty = function (prop, parentId) {
+  if (t.isLiteral(prop.key)) prop.computed = true;
+
+  var pattern2   = prop.value;
+  var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
+
+  if (t.isPattern(pattern2)) {
+    this.push(pattern2, patternId2);
+  } else {
+    this.nodes.push(this.buildVariableAssignment(pattern2, patternId2));
+  }
+};
+
+DestructuringTransformer.prototype.pushObjectPattern = function (pattern, parentId) {
+  if (!pattern.properties.length) {
+    this.nodes.push(t.expressionStatement(
+      t.callExpression(this.file.addHelper("object-destructuring-empty"), [parentId])
+    ));
+  }
+
+  if (pattern.properties.length > 1 && t.isMemberExpression(parentId)) {
+    var temp = this.scope.generateUidBasedOnNode(parentId, this.file);
+    this.nodes.push(this.buildVariableDeclaration(temp, parentId));
+    parentId = temp;
+  }
+
   for (var i = 0; i < pattern.properties.length; i++) {
     var prop = pattern.properties[i];
     if (t.isSpreadProperty(prop)) {
-      // get all the keys that appear in this object before the current spread
-      var keys = [];
-      for (var i2 = 0; i2 < pattern.properties.length; i2++) {
-        var prop2 = pattern.properties[i2];
-
-        if (i2 >= i) break;
-        if (t.isSpreadProperty(prop2)) continue;
-
-        var key = prop2.key;
-        if (t.isIdentifier(key)) {
-          key = t.literal(prop2.key.name);
-        }
-        keys.push(key);
-      }
-      keys = t.arrayExpression(keys);
-
-      var value = t.callExpression(opts.file.addHelper("object-without-properties"), [parentId, keys]);
-      nodes.push(buildVariableAssign(opts, prop.argument, value));
+      this.pushObjectSpread(pattern, parentId, prop, i);
     } else {
-      if (t.isLiteral(prop.key)) prop.computed = true;
-
-      var pattern2   = prop.value;
-      var patternId2 = t.memberExpression(parentId, prop.key, prop.computed);
-
-      if (t.isPattern(pattern2)) {
-        push(opts, nodes, pattern2, patternId2);
-      } else {
-        nodes.push(buildVariableAssign(opts, pattern2, patternId2));
-      }
+      this.pushObjectProperty(prop, parentId);
     }
   }
 };
 
-var pushArrayPattern = function (opts, nodes, pattern, parentId) {
-  if (!pattern.elements) return;
-
-  var i;
-
-  var hasRest = false;
-  for (i = 0; i < pattern.elements.length; i++) {
+var hasRest = function (pattern) {
+  for (var i = 0; i < pattern.elements.length; i++) {
     if (t.isRestElement(pattern.elements[i])) {
-      hasRest = true;
-      break;
+      return true;
     }
   }
+  return false;
+};
 
-  var toArray = opts.file.toArray(parentId, !hasRest && pattern.elements.length);
+DestructuringTransformer.prototype.pushArrayPattern = function (pattern, parentId) {
+  if (!pattern.elements) return;
 
-  var _parentId = opts.scope.generateUidBasedOnNode(parentId, opts.file);
-  nodes.push(buildVariableDeclar(opts, _parentId, toArray));
+  // if we have a rest then we need all the elements
+  var count = !hasRest(pattern) && pattern.elements.length;
+
+  var toArray = this.scope.toArray(parentId, count);
+
+  var _parentId = this.scope.generateUidBasedOnNode(parentId);
+  this.nodes.push(this.buildVariableDeclaration(_parentId, toArray));
   parentId = _parentId;
 
-  for (i = 0; i < pattern.elements.length; i++) {
-    var elem = pattern.elements[i];
-    if (!elem) continue;
+  this.scope.assignTypeGeneric(parentId.name, "Array");
 
-    i = +i;
+  for (var i = 0; i < pattern.elements.length; i++) {
+    var elem = pattern.elements[i];
+
+    // hole
+    if (!elem) continue;
 
     var newPatternId;
 
     if (t.isRestElement(elem)) {
-      newPatternId = opts.file.toArray(parentId);
+      newPatternId = this.scope.toArray(parentId);
 
       if (i > 0) {
         newPatternId = t.callExpression(t.memberExpression(newPatternId, t.identifier("slice")), [t.literal(i)]);
@@ -137,45 +172,62 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
       newPatternId = t.memberExpression(parentId, t.literal(i), true);
     }
 
-    push(opts, nodes, elem, newPatternId);
+    this.push(elem, newPatternId);
   }
 };
 
-var pushPattern = function (opts) {
-  var nodes = opts.nodes;
-  var pattern = opts.pattern;
-  var parentId = opts.id;
-  var scope = opts.scope;
-
+DestructuringTransformer.prototype.init = function (pattern, parentId) {
   if (!t.isArrayExpression(parentId) && !t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = scope.generateUidBasedOnNode(parentId);
-    nodes.push(buildVariableDeclar(opts, key, parentId));
+    var key = this.scope.generateUidBasedOnNode(parentId);
+    this.nodes.push(this.buildVariableDeclaration(key, parentId));
     parentId = key;
   }
 
-  push(opts, nodes, pattern, parentId);
+  this.push(pattern, parentId);
 };
 
 exports.ForInStatement =
-exports.ForOfStatement = function (node, parent, scope, context, file) {
-  var declar = node.left;
-  if (!t.isVariableDeclaration(declar)) return;
+exports.ForOfStatement = function (node, parent, scope, file) {
+  var left = node.left;
 
-  var pattern = declar.declarations[0].id;
+  if (t.isPattern(left)) {
+    // for ({ length: k } in { abc: 3 });
+
+    var temp = scope.generateUidIdentifier("ref");
+
+    node.left = t.variableDeclaration("var", [
+      t.variableDeclarator(temp)
+    ]);
+
+    t.ensureBlock(node);
+
+    node.body.body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(left, temp)
+    ]));
+
+    return;
+  }
+
+  if (!t.isVariableDeclaration(left)) return;
+
+  var pattern = left.declarations[0].id;
   if (!t.isPattern(pattern)) return;
 
   var key = scope.generateUidIdentifier("ref");
-  node.left = t.variableDeclaration(declar.kind, [
+  node.left = t.variableDeclaration(left.kind, [
     t.variableDeclarator(key, null)
   ]);
 
   var nodes = [];
 
-  push({
-    kind: declar.kind,
+  var destructuring = new DestructuringTransformer({
+    kind: left.kind,
     file: file,
-    scope: scope
-  }, nodes, pattern, key);
+    scope: scope,
+    nodes: nodes
+  });
+
+  destructuring.init(pattern, key);
 
   t.ensureBlock(node);
 
@@ -183,31 +235,30 @@ exports.ForOfStatement = function (node, parent, scope, context, file) {
   block.body = nodes.concat(block.body);
 };
 
-exports.Function = function (node, parent, scope, context, file) {
+exports.Function = function (node, parent, scope, file) {
   var nodes = [];
 
-  var hasDestructuring = false;
+  var hasDestructuringTransformer = false;
 
   node.params = node.params.map(function (pattern, i) {
     if (!t.isPattern(pattern)) return pattern;
 
-    hasDestructuring = true;
+    hasDestructuringTransformer = true;
     var parentId = scope.generateUidIdentifier("ref");
 
-    pushPattern({
+    var destructuring = new DestructuringTransformer({
       blockHoist: node.params.length - i,
-      pattern:    pattern,
       nodes:      nodes,
       scope:      scope,
       file:       file,
       kind:       "var",
-      id:         parentId
     });
+    destructuring.init(pattern, parentId);
 
     return parentId;
   });
 
-  if (!hasDestructuring) return;
+  if (!hasDestructuringTransformer) return;
 
   t.ensureBlock(node);
 
@@ -215,7 +266,7 @@ exports.Function = function (node, parent, scope, context, file) {
   block.body = nodes.concat(block.body);
 };
 
-exports.CatchClause = function (node, parent, scope, context, file) {
+exports.CatchClause = function (node, parent, scope, file) {
   var pattern = node.param;
   if (!t.isPattern(pattern)) return;
 
@@ -224,16 +275,20 @@ exports.CatchClause = function (node, parent, scope, context, file) {
 
   var nodes = [];
 
-  push({
-    kind: "var",
+  var destructuring = new DestructuringTransformer({
+    kind: "let",
     file: file,
-    scope: scope
-  }, nodes, pattern, ref);
+    scope: scope,
+    nodes: nodes
+  });
+  destructuring.init(pattern, ref);
 
   node.body.body = nodes.concat(node.body.body);
+
+  return node;
 };
 
-exports.ExpressionStatement = function (node, parent, scope, context, file) {
+exports.ExpressionStatement = function (node, parent, scope, file) {
   var expr = node.expression;
   if (expr.type !== "AssignmentExpression") return;
   if (!t.isPattern(expr.left)) return;
@@ -246,16 +301,18 @@ exports.ExpressionStatement = function (node, parent, scope, context, file) {
     t.variableDeclarator(ref, expr.right)
   ]));
 
-  push({
+  var destructuring = new DestructuringTransformer({
     operator: expr.operator,
     file: file,
-    scope: scope
-  }, nodes, expr.left, ref);
+    scope: scope,
+    nodes: nodes
+  });
+  destructuring.init(expr.left, ref);
 
   return nodes;
 };
 
-exports.AssignmentExpression = function (node, parent, scope, context, file) {
+exports.AssignmentExpression = function (node, parent, scope, file) {
   if (!t.isPattern(node.left)) return;
 
   var ref = scope.generateUidIdentifier("temp");
@@ -267,50 +324,50 @@ exports.AssignmentExpression = function (node, parent, scope, context, file) {
   var nodes = [];
   nodes.push(t.assignmentExpression("=", ref, node.right));
 
-  push({
+  var destructuring = new DestructuringTransformer({
     operator: node.operator,
     file: file,
-    scope: scope
-  }, nodes, node.left, ref);
+    scope: scope,
+    nodes: nodes
+  });
+  destructuring.init(node.left, ref);
 
   nodes.push(ref);
 
   return t.toSequenceExpression(nodes, scope);
 };
 
-exports.VariableDeclaration = function (node, parent, scope, context, file) {
-  if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
-
-  var nodes = [];
-  var i;
-  var declar;
-
-  var hasPattern = false;
-  for (i = 0; i < node.declarations.length; i++) {
-    declar = node.declarations[i];
-    if (t.isPattern(declar.id)) {
-      hasPattern = true;
-      break;
+var variableDeclarationhasPattern = function (node) {
+  for (var i = 0; i < node.declarations.length; i++) {
+    if (t.isPattern(node.declarations[i].id)) {
+      return true;
     }
   }
-  if (!hasPattern) return;
+  return false;
+};
 
-  for (i = 0; i < node.declarations.length; i++) {
+exports.VariableDeclaration = function (node, parent, scope, file) {
+  if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
+  if (!variableDeclarationhasPattern(node)) return;
+
+  var nodes = [];
+  var declar;
+
+  for (var i = 0; i < node.declarations.length; i++) {
     declar = node.declarations[i];
 
     var patternId = declar.init;
     var pattern   = declar.id;
-    var opts = {
-      pattern: pattern,
-      nodes:   nodes,
-      scope:   scope,
-      kind:    node.kind,
-      file:    file,
-      id:      patternId,
-    };
+
+    var destructuring = new DestructuringTransformer({
+      nodes: nodes,
+      scope: scope,
+      kind:  node.kind,
+      file:  file
+    });
 
     if (t.isPattern(pattern) && patternId) {
-      pushPattern(opts);
+      destructuring.init(pattern, patternId);
 
       if (+i !== node.declarations.length - 1) {
         // we aren't the last declarator so let's just make the
@@ -318,11 +375,14 @@ exports.VariableDeclaration = function (node, parent, scope, context, file) {
         t.inherits(nodes[nodes.length - 1], declar);
       }
     } else {
-      nodes.push(t.inherits(buildVariableAssign(opts, declar.id, declar.init), declar));
+      nodes.push(t.inherits(destructuring.buildVariableAssignment(declar.id, declar.init), declar));
     }
   }
 
   if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
+    // https://github.com/6to5/6to5/issues/113
+    // for (let [x] = [0]; false;) {}
+
     declar = null;
 
     for (i = 0; i < nodes.length; i++) {
@@ -330,7 +390,7 @@ exports.VariableDeclaration = function (node, parent, scope, context, file) {
       declar = declar || t.variableDeclaration(node.kind, []);
 
       if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
-        throw file.errorWithNode(node, "Cannot use this node within the current parent");
+        throw file.errorWithNode(node, messages.get("invalidParentForThisNode"));
       }
 
       declar.declarations = declar.declarations.concat(node.declarations);