v3.0.1

Conflicts:
	package.json

.gitignore

@@ -11,3 +11,5 @@ test/tmp
 coverage
 dist
 .package.json
+packages/6to5-runtime/*.js
+packages/6to5-runtime/regenerator/*.js

.gitmodules

@@ -3,7 +3,7 @@
 	url = https://github.com/google/traceur-compiler
 [submodule "vendor/regenerator"]
 	path = vendor/regenerator
-	url = https://github.com/facebook/regenerator
+	url = https://github.com/6to5/regenerator-6to5
 [submodule "vendor/test262"]
 	path = vendor/test262
 	url = https://github.com/tc39/test262

.jscsrc

@@ -0,0 +1,60 @@
+{
+  "excludeFiles": ["lib/6to5/transformation/templates"],
+  "disallowSpacesInNamedFunctionExpression": {
+    "beforeOpeningRoundBrace": true
+  },
+  "requireSpacesInAnonymousFunctionExpression": {
+    "beforeOpeningRoundBrace": true
+  },
+  "requireSpacesInAnonymousFunctionExpression": {
+    "beforeOpeningRoundBrace": true
+  },
+  "disallowSpacesInFunctionDeclaration": {
+    "beforeOpeningRoundBrace": true
+  },
+  "disallowSpacesInsideArrayBrackets": true,
+  "disallowSpacesInsideParentheses": true,
+  "disallowQuotedKeysInObjects": true,
+  "disallowSpaceAfterObjectKeys": true,
+  "disallowSpaceAfterPrefixUnaryOperators": true,
+  "disallowSpaceBeforePostfixUnaryOperators": true,
+  "disallowSpaceBeforeBinaryOperators": [
+    ","
+  ],
+  "disallowMixedSpacesAndTabs": true,
+  "disallowTrailingWhitespace": true,
+  "disallowYodaConditions": true,
+  "disallowKeywords": [ "with" ],
+  "disallowMultipleLineBreaks": true,
+  "requireSpaceBeforeBlockStatements": true,
+  "requireParenthesesAroundIIFE": true,
+  "requireSpacesInConditionalExpression": true,
+  "requireBlocksOnNewline": 1,
+  "requireCommaBeforeLineBreak": true,
+  "requireSpaceBeforeBinaryOperators": true,
+  "requireSpaceAfterBinaryOperators": true,
+  "requireCamelCaseOrUpperCaseIdentifiers": true,
+  "requireLineFeedAtFileEnd": true,
+  "requireCapitalizedConstructors": true,
+  "requireDotNotation": true,
+  "requireSpacesInForStatement": true,
+  "requireCurlyBraces": [
+    "do"
+  ],
+  "requireSpaceAfterKeywords": [
+    "if",
+    "else",
+    "for",
+    "while",
+    "do",
+    "switch",
+    "case",
+    "return",
+    "try",
+    "catch",
+    "typeof"
+  ],
+  "validateLineBreaks": "LF",
+  "validateQuoteMarks": "\"",
+  "validateIndentation": 2
+}

.jshintignore

@@ -1,3 +1 @@
-node_modules
-test
 lib/6to5/transformation/templates

.npmignore

@@ -10,3 +10,6 @@ dist
 tests.json
 CHANGELOG.md
 .package.json
+coverage
+vendor
+packages

.travis.yml

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

CHANGELOG.md

@@ -11,6 +11,182 @@
 
 _Note: Gaps between patch versions are faulty/broken releases._
 
+## 3.0.0
+
+ * **Polish**
+  * Generated code autoindentation.
+  * Moved global uid registry to a scope registry resulting in nicer uids.
+  * `this` is now illegal in the top level scope when using the default `useStrict` transformer.
+  * New `asyncToGenerator` helper that's much more compact.
+  * Throw errors on unknown options.
+  * More reliable default parameter scope.
+  * Helpers are now compact and have no newlines.
+ * **Internal**
+  * Rewritten a lot of the internals to much simpler.
+  * Removed TDZ from default parameters as it was very wonky and unreliable.
+  * Upgrade `core-js` to `0.4.6`.
+  * Upgrade `acorn-6to5`.
+   * JSX support is now on-par with react-tools/esprima.
+   * Shorthand destructuring.
+ * **Bug Fix**
+  * Generators now work flawlessly with any parameter transformers.
+  * Optional async function transformers should not name their functions.
+  * Remove `unlink` event watching in `bin/6to5`.
+  * Fix regenerator variable declarations being incorrectly hoisted breaking scope.
+  * Transformers that attempted to simplify expressions that had no consequence now take into account whether it's one of the last statements/expressions in the script.
+ * **New Feature**
+  * New `selfContained` transformer.
+  * New `undeclaredVariableCheck` optional transformer.
+  * Added `--blacklist` and `--whitelist` options to `6to5-node`.
+ * **Breaking Change**
+  * Caching is now always enabled for the require hook. It also now no longer caches require resolutions.
+  * Bare `super();` only works inside of constructors.
+  * Removed the optional runtime in favor of the `selfContained` transformer.
+  * This shorthand has been removed from the playground.
+  * `6to5/polyfill` can now only be required **once**.
+  * **CLI**
+   * `--indent` option has been removed.
+   * `--include-regenerator` option has been removed.
+   * `--amd-modules-id` option has been removed, use `--module-ids` instead.
+  * **Options**
+   * `amdModuleIds` option has been removed, use `moduleIds` instead.
+   * `includeRegenerator` has been removed.
+   * `ignoreRegex` fallback has now been dropped from the require hook. `register(/foo/);`, `register({ ignoreRegex: /foo/ })` -> `register({ ignore: /foo/ })`.
+  * **Modules**
+    * Module interop now only collapses to `module.exports` when there's a **single** export that's default.
+    * Imports and exports are now illegal anywhere except the root level by default. Set `modules` to [loose mode](http://6to5.org/docs/usage/loose) to allow them everywhere.
+  * **Transformers**
+    * Optional fast transformer backwards compatibility support has been removed. Use [loose mode](https://6to5.org/docs/usage/loose).
+    * Removed the `coreAliasing` transformer in favor of `selfContained`.
+    * Renamed transformers:
+     * `specNoForInOfAssignment` -> `validation.noForInOfAssignment`
+     * `specSetters` -> `validation.setters`
+     * `specBlockScopedFunctions` -> `spec.blockScopedFunctions`
+     * `malletOperator` -> `playground.malletOperator`
+     * `methodBinding` -> `playground.methodBinding`
+     * `memoizationOperator` -> `playground.memoizationOperator`
+     * `objectGetterMemoization` -> `playground.objectGetterMemoization`
+     * `modules` -> `es6.modules`
+     * `propertyNameShorthand` -> `es6.properties.shorthand`
+     * `arrayComprehension` -> `es7.comprehensions`
+     * `generatorComprehension` -> `es7.comprehensions`
+     * `arrowFunctions` -> `es6.arrowFunctions`
+     * `classes` -> `es6.classes`
+     * `objectSpread` -> `es7.objectSpread`
+     * `exponentiationOperator` -> `es7.exponentiationOperator`
+     * `spread` -> `es6.spread`
+     * `templateLiterals` -> `es6.templateLiterals`
+     * `propertyMethodAssignment` -> `es6.properties.shorthand`
+     * `computedPropertyNames` -> `es6.properties.computed`
+     * `defaultParameters` -> `es6.parameters.default`
+     * `restParameters` -> `es6.parameters.rest`
+     * `destructuring` -> `es6.destructuring`
+     * `forOf` -> `es6.forOf`
+     * `unicodeRegex` -> `es6.unicodeRegex`
+     * `abstractReferences` -> `es7.abstractReferences`
+     * `constants` -> `es6.constants`
+     * `letScoping` -> `es6.blockScoping`
+     * `blockScopingTDZ` -> `es6.blockScopingTDZ`
+     * `generators` -> `regenerator`
+     * `protoToAssign` -> `spec.protoToAssign`
+     * `typeofSymbol` -> `spec.typeofSymbol`
+     * `coreAliasing` -> `selfContained`
+     * `undefinedToVoid` -> `spec.undefinedToVoid`
+     * `undeclaredVariableCheck` -> `validation.undeclaredVariableCheck`
+     * `specPropertyLiterals` -> `minification.propertyLiterals`
+     * `specMemberExpressionLiterals` -> `minification.memberExpressionLiterals`
+
+## 2.13.7
+
+ * **Bug Fix**
+  * Don't realias variables that are already declared in optional `coreAliasing` transformer.
+
+## 2.13.6
+
+ * **Bug Fix**
+  * Add `NewExpression` as a valid parent for parentheses insertion for `ConditionalExpression`.
+
+## 2.13.5
+
+ * **Bug Fix**
+  * Allow rest parameters to be destructuring patterns.
+ * **Internal**
+  * Upgrade `kexec` to `1.1.0`.
+
+## 2.13.4
+
+ * **Bug Fix**
+  * Fix ordering of destructuring and default params.
+  * Fix loop body scope.
+  * Fix `for...of` transformation not retaining it's scope.
+  * Add destructuring assignment support to scope tracking.
+ * **Polish**
+  * More reliable newlines for pretty printing variable declarations.
+
+## 2.13.3
+
+ * **Internal**
+  * Add `coverage` and `vendor` to npmignore.
+
+## 2.13.2
+
+ * **Bug Fix**
+  * Fix `super` inside of nested functions.
+ * **Internal**
+  * Move let scoping TDZ into a separate transformer until it's more solid.
+  * Use `process.stdin.write` instead of `console.log` in `bin` to avoid sprintfification.
+
+## 2.13.1
+
+ * **New Feature**
+  * Temporal dead zone for block binding.
+
+## 2.13.0
+
+ * **New Feature**
+  * Block scoped functions.
+  * Add `--loose all` option.
+  * Add playground mallet operator thanks to [@jridgewell](https://github.com/jridgewell).
+ * **Bug Fix**
+  * Rewrote large parts of the let scoping transformer. Now passes all known tests.
+ * **Internal**
+  * Even more optimisations thanks to the awesome [@gaearon](https://github.com/gaearon).
+  * Upgrade `acorn-6to5`.
+    * Fixes exponentation operator thanks to [@charliesome](https://github.com/charliesome).
+    * Fix flow optional parameters with types.
+  * Upgrade `chokidar` to `0.12.6`.
+  * Upgrade `commander` to `2.6.0`.
+  * Upgrade `core-js` to `0.4.5`.
+  * Upgrade `estraverse` to `1.9.1`.
+  * Upgrade `jshint` to `2.5.11`.
+  * Upgrade `regenerator` to `0.8.9`.
+  * Upgrade `regexpu` to `1.0.0`.
+  * Upgrade `source-map` to `0.1.43`.
+  * Upgrade `source-map-support` to `0.2.9`.
+  * Upgrade `browserify` to `8.1.1`.
+  * Upgrade `chai` to `1.10.0`.
+  * Upgrade `istanbul` to `0.3.5`.
+  * Upgrade `mocha` to `2.1.0`.
+  * Upgrade `uglify-js` to `2.4.16`.
+
+## 2.12.6
+
+ * **Bug Fix**
+  * Add missing flow type traversal keys.
+
+## 2.12.5
+
+ * **Internal**
+  * Fix incorrect `for...in` loop still causing `ember-script` issues.
+
+## 2.12.4
+
+ * **Polish**
+  * Rest parameters now allocate the array before populating.
+ * **Internal**
+  * `for...in` loops have been changed to optimised `for` loops - better performance and no enumeration of protoype keys.
+  * Parts of the code generator have now been optimised thanks to [gaearon](https://github.com/gaearon).
+
 ## 2.12.3
 
  * **Spec Compliancy**

CONTRIBUTING.md

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

Makefile

@@ -1,17 +1,19 @@
 BROWSERIFY_CMD = node_modules/browserify/bin/cmd.js
 ISTANBUL_CMD = node_modules/istanbul/lib/cli.js cover
-UGLIFY_CMD = node_modules/uglify-js/bin/uglifyjs --mangle sort
+UGLIFY_CMD = node_modules/uglify-js/bin/uglifyjs
+#UGLIFY_CMD = node_modules/uglify-js/bin/uglifyjs --mangle sort
 JSHINT_CMD = node_modules/jshint/bin/jshint
 MOCHA_CMD = node_modules/mocha/bin/_mocha
+JSCS_CMD = node_modules/jscs/bin/jscs
 
 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
+.PHONY: clean test test-cov test-clean lint test-travis test-simple test-all test-browser publish build bootstrap publish-core publish-runtime
 
 build:
 	mkdir -p dist
 
-	node bin/cache-templates
+	node tools/cache-templates
 
 	node $(BROWSERIFY_CMD) -e lib/6to5/polyfill.js >dist/polyfill.js
 	node $(UGLIFY_CMD) dist/polyfill.js >dist/polyfill.min.js
@@ -19,9 +21,6 @@ build:
 	node $(BROWSERIFY_CMD) lib/6to5/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:
@@ -29,6 +28,7 @@ clean:
 
 lint:
 	$(JSHINT_CMD) --reporter node_modules/jshint-stylish/stylish.js lib bin
+	$(JSCS_CMD) lib bin
 
 test-clean:
 	rm -rf test/tmp
@@ -39,17 +39,17 @@ test: lint
 
 test-simple:
 	# excludes test262
-	export SIMPLE_6TO5_TESTS=1
+	export SIMPLE_6TO5_TESTS=1; \
 	make test
 
 test-all:
 	# includes traceur, esnext, regenerator
-	export ALL_6TO5_TESTS=1
+	export ALL_6TO5_TESTS=1; \
 	make test
 
 test-cov:
-	export SIMPLE_6TO5_TESTS=1
 	rm -rf coverage
+	export SIMPLE_6TO5_TESTS=1; \
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) --
 
 test-travis: bootstrap
@@ -59,8 +59,8 @@ test-travis: bootstrap
 test-browser:
 	mkdir -p dist
 
-	node bin/cache-templates
-	node bin/cache-tests
+	node tools/cache-templates
+	node tools/cache-tests
 	node $(BROWSERIFY_CMD) -e test/_browser.js >dist/6to5-test.js
 	rm -rf templates.json tests.json
 
@@ -77,28 +77,35 @@ 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 bin/cache-templates
+	node tools/cache-templates
 	test -f templates.json
 
 	npm publish
 
 	git push --follow-tags
 
-	# generate
-	bin/generate-core-package-json >package2.json
+	make publish-core
+	make publish-runtime
+
+	rm -rf templates.json browser.js browser-polyfill.js
+
+publish-runtime:
+	cd packages; \
+	node build-runtime.js; \
+	cd 6to5-runtime; \
+	npm publish
+
+publish-core:
+	tools/generate-core-package-json >package2.json
 	mv package.json .package.json
 	mv package2.json package.json
 
 	npm publish
 
-	# restore
 	rm -rf package.json
 	mv .package.json package.json
 
-	rm -rf templates.json browser.js runtime.js browser-polyfill.js
-
 bootstrap:
 	npm install
 	git submodule update --init

NOTES.md

@@ -1,13 +1,3 @@
 # Notes
 
  * Wildcard exports/imports wont normalise if `export default` is a non-object. See [#224](https://github.com/6to5/6to5/issues/224).
-
-## 3.0.0 breaking changes
-
- * Remove `allowImportExportEverywhere` option from acorn.
- * Remove this shorthand from playground.
- * Remove `super()` inside non-constructors - add descriptive error message.
- * Split up ES5 getter/setter transforming and ES6 property methods into separate transformers.
- * Add autoindentation.
- * Move `super` transformation from classes into a separate transformer that also supports object expressions.
- * Remove fast transformer backwards compatibility.

bin/6to5-runtime

@@ -1,4 +0,0 @@
-#!/usr/bin/env node
-
-var runtime = require("../lib/6to5/runtime-generator");
-console.log(runtime(process.argv[2]));

bin/6to5/dir.js

@@ -1,9 +1,9 @@
-var chokidar = require("chokidar");
-var mkdirp   = require("mkdirp");
-var path     = require("path");
-var util     = require("./util");
-var fs       = require("fs");
-var _        = require("lodash");
+var outputFileSync = require("output-file-sync");
+var chokidar       = require("chokidar");
+var path           = require("path");
+var util           = require("./util");
+var fs             = require("fs");
+var _              = require("lodash");
 
 module.exports = function (commander, filenames, opts) {
   if (commander.sourceMapsInline) {
@@ -15,16 +15,13 @@ module.exports = function (commander, filenames, opts) {
 
     var data = util.compile(src, { sourceMapName: dest });
 
-    var up = path.normalize(dest + "/..");
-    mkdirp.sync(up);
-
     if (commander.sourceMaps) {
       var mapLoc = dest + ".map";
       data.code = util.addSourceMappingUrl(data.code, mapLoc);
-      fs.writeFileSync(mapLoc, JSON.stringify(data.map));
+      outputFileSync(mapLoc, JSON.stringify(data.map));
     }
 
-    fs.writeFileSync(dest, data.code);
+    outputFileSync(dest, data.code);
 
     console.log(src + " -> " + dest);
   };
@@ -54,7 +51,7 @@ module.exports = function (commander, filenames, opts) {
         ignoreInitial: true
       });
 
-      _.each(["add", "change", "unlink"], function (type) {
+      _.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);

bin/6to5/file.js

@@ -28,7 +28,7 @@ module.exports = function (commander, filenames) {
         map.setSourceContent(filename, result.actual);
 
         consumer.eachMapping(function (mapping) {
-          map._mappings.push({
+          map._mappings.add({
             generatedLine: mapping.generatedLine + offset,
             generatedColumn: mapping.generatedColumn,
             originalLine: mapping.originalLine,
@@ -63,7 +63,7 @@ module.exports = function (commander, filenames) {
 
       fs.writeFileSync(commander.outFile, result.code);
     } else {
-      console.log(result.code);
+      process.stdout.write(result.code + "\n");
     }
   };
 
@@ -77,7 +77,7 @@ module.exports = function (commander, filenames) {
       if (chunk !== null) code += chunk;
     });
 
-    process.stdin.on("end", function() {
+    process.stdin.on("end", function () {
       results.push(util.transform(commander.filename, code));
       output();
     });
@@ -117,7 +117,7 @@ module.exports = function (commander, filenames) {
         persistent: true,
         ignoreInitial: true
       }).on("all", function (type, filename) {
-        if (type === "add" || type === "change" || type === "unlink" ) {
+        if (type === "add" || type === "change") {
           console.log(type, filename);
           walk();
         }

bin/6to5/index.js

@@ -10,7 +10,6 @@ commander.option("-t, --source-maps-inline", "Append sourceMappingURL comment to
 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");
 
@@ -18,29 +17,23 @@ commander.option("-m, --modules [modules]", "Module formatter type to use [commo
 commander.option("-l, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
 commander.option("-b, --blacklist [blacklist]", "Blacklist of transformers to NOT use", util.list);
 commander.option("-i, --optional [list]", "List of optional transformers to enable", util.list);
-commander.option("--loose [list]", "List of transformers to enable their loose mode", util.list);
+commander.option("-L, --loose [list]", "List of transformers to enable loose mode ON", util.list);
 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("-I, --indent [width]", "Indent width [2]", 2);
-commander.option("-a, --amd-module-ids", "Insert module id in AMD modules", false); // todo: remove in 3.0.0
 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("-E, --include-regenerator", "Include the regenerator runtime if necessary", false);
 commander.option("--keep-module-id-extensions", "Keep extensions when generating module ids", false);
 
-commander.on("--help", function(){
+commander.on("--help", function () {
   var outKeys = function (title, obj) {
     console.log("  " + title + ":");
     console.log();
 
-    var hasOptional = true;
-
     _.each(_.keys(obj).sort(), function (key) {
       if (key[0] === "_") return;
 
       if (obj[key].optional) {
-        hasOptional = true;
         key = "[" + key + "]";
       }
 
@@ -104,25 +97,18 @@ if (errors.length) {
 
 exports.opts = {
   keepModuleIdExtensions: commander.keepModuleIdExtensions,
-  includeRegenerator:     commander.includeRegenerator,
   sourceMapName:          commander.outFile,
   experimental:           commander.experimental,
   reactCompat:            commander.reactCompat,
   playground:             commander.playground,
-  moduleIds:              commander.amdModuleIds || commander.moduleIds,
+  moduleIds:              commander.moduleIds,
   blacklist:              commander.blacklist,
   whitelist:              commander.whitelist,
   sourceMap:              commander.sourceMaps || commander.sourceMapsInline,
   optional:               commander.optional,
   comments:               !commander.removeComments,
-  runtime:                commander.runtime,
   modules:                commander.modules,
-  loose:                  commander.loose,
-  format: {
-    indent: {
-      style:     util.repeat(parseInt(commander.indent))
-    }
-  }
+  loose:                  commander.loose
 };
 
 var fn;

bin/_6to5-node

@@ -1,40 +1,39 @@
 #!/usr/bin/env node
 
-var roadrunner = require("roadrunner");
-var commander  = require("commander");
-var Module     = require("module");
-var path       = require("path");
-var repl       = require("repl");
-var to5        = require("../lib/6to5");
-var util       = require("../lib/6to5/util");
-var vm         = require("vm");
-var _          = require("lodash");
+var commander = require("commander");
+var Module    = require("module");
+var path      = require("path");
+var repl      = require("repl");
+var to5       = require("../lib/6to5");
+var util      = require("../lib/6to5/util");
+var vm        = require("vm");
+var _         = require("lodash");
 
 var program = new commander.Command("6to5-node");
 
 program.option("-e, --eval [script]", "Evaluate script");
-program.option("-p, --print", "Evaluate script and print result");
+program.option("-p, --print [code]", "Evaluate script and print result");
 program.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
-program.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
+program.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js,.es,.jsx]");
 program.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
 program.option("-g, --playground", "Enable playground support");
-program.option("-c, --cache", "Cache compiled files and require paths");
+program.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
+program.option("-b, --blacklist [blacklist]", "Blacklist of transformers to NOT use", util.list);
 
 var pkg = require("../package.json");
 program.version(pkg.version);
 program.usage("[options] [ -e script | script.js ] [arguments]");
 program.parse(process.argv);
 
-if (program.cache) roadrunner.load();
-
 //
 
 to5.register({
   experimental: program.experimental,
   extensions:   program.extensions,
   playground:   program.playground,
-  ignore:       program.ignore,
-  cache:        program.cache && roadrunner.get("6to5")
+  blacklist:    program.blacklist,
+  whitelist:    program.whitelist,
+  ignore:       program.ignore
 });
 
 //
@@ -42,15 +41,19 @@ to5.register({
 var _eval = function (code, filename) {
   code = to5.transform(code, {
     filename: filename,
-    blacklist: ["useStrict"],
+    blacklist: ["useStrict"].concat(program.blacklist || []),
+    whitelist: program.whitelist,
     experimental: program.experimental,
     playground: program.playground
   }).code;
   return vm.runInThisContext(code, filename);
 };
 
-if (program.eval) {
-  var result = _eval(program.eval, "eval");
+if (program.eval || program.print) {
+  var code = program.eval;
+  if (!code || code === true) code = program.print;
+
+  var result = _eval(code, "eval");
   if (program.print) console.log(result);
 } else {
   if (program.args.length) {
@@ -79,8 +82,6 @@ if (program.eval) {
   }
 }
 
-if (program.cache) roadrunner.save();
-
 function replStart() {
   repl.start({
     prompt: "> ",

lib/6to5/browser.js

@@ -1,3 +1,5 @@
+"use strict";
+
 var transform = module.exports = require("./transformation/transform");
 
 transform.version = require("../../package").version;

lib/6to5/file.js

@@ -1,21 +1,30 @@
+"use strict";
+
 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");
 
 function File(opts) {
-  this.dynamicImports   = [];
   this.dynamicImportIds = {};
+  this.dynamicImported  = [];
+  this.dynamicImports   = [];
+
+  this.dynamicData      = {};
+  this.data             = {};
+
+  this.lastStatements   = [];
   this.opts             = File.normaliseOptions(opts);
-  this.transformers     = this.getTransformers();
-  this.uids             = {};
   this.ast              = {};
+
+  this.buildTransformers();
 }
 
 File.helpers = [
@@ -40,23 +49,46 @@ File.helpers = [
   "get"
 ];
 
-File.excludeHelpersFromRuntime = [
-  "async-to-generator",
-  "typeof",
-  "tagged-template-literal-loose"
+File.validOptions = [
+  "filename",
+  "filenameRelative",
+  "blacklist",
+  "whitelist",
+  "loose",
+  "optional",
+  "modules",
+  "sourceMap",
+  "sourceMapName",
+  "sourceFileName",
+  "sourceRoot",
+  "moduleRoot",
+  "moduleIds",
+  "comments",
+  "reactCompat",
+  "keepModuleIdExtensions",
+  "code",
+  "ast",
+  "format",
+  "playground",
+  "experimental"
 ];
 
 File.normaliseOptions = function (opts) {
-  opts = _.cloneDeep(opts || {});
+  opts = clone(opts);
+
+  for (var key in opts) {
+    if (File.validOptions.indexOf(key) < 0) {
+      throw new ReferenceError("Unknown option: " + key);
+    }
+  }
 
   _.defaults(opts, {
     keepModuleIdExtensions: false,
-    includeRegenerator:     false,
     experimental:           false,
     reactCompat:            false,
     playground:             false,
     whitespace:             true,
-    moduleIds:              opts.amdModuleIds || false,
+    moduleIds:              false,
     blacklist:              [],
     whitelist:              [],
     sourceMap:              false,
@@ -64,7 +96,6 @@ File.normaliseOptions = function (opts) {
     comments:               true,
     filename:               "unknown",
     modules:                "common",
-    runtime:                false,
     loose:                  [],
     code:                   true,
     ast:                    true
@@ -78,16 +109,9 @@ File.normaliseOptions = function (opts) {
   opts.optional  = util.arrayify(opts.optional);
   opts.loose     = util.arrayify(opts.loose);
 
-  // todo: remove in 3.0.0
-  _.each({
-    fastForOf: "forOf",
-    classesFastSuper: "classes"
-  }, function (newTransformer, oldTransformer) {
-    if (_.contains(opts.optional, oldTransformer)) {
-      _.pull(opts.optional, oldTransformer);
-      opts.loose.push(newTransformer);
-    }
-  });
+  if (_.contains(opts.loose, "all")) {
+    opts.loose = Object.keys(transform.transformers);
+  }
 
   _.defaults(opts, {
     moduleRoot: opts.sourceRoot
@@ -106,18 +130,14 @@ File.normaliseOptions = function (opts) {
     sourceMapName:  opts.filenameRelative
   });
 
-  if (opts.runtime === true) {
-    opts.runtime = "to5Runtime";
-  }
-
   if (opts.playground) {
     opts.experimental = true;
   }
 
-  transform._ensureTransformerNames("blacklist", opts.blacklist);
-  transform._ensureTransformerNames("whitelist", opts.whitelist);
-  transform._ensureTransformerNames("optional", opts.optional);
-  transform._ensureTransformerNames("loose", opts.loose);
+  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);
 
   return opts;
 };
@@ -126,17 +146,21 @@ File.prototype.isLoose = function (key) {
   return _.contains(this.opts.loose, key);
 };
 
-File.prototype.getTransformers = function () {
+File.prototype.buildTransformers = function () {
   var file = this;
-  var transformers = [];
-  var secondPassTransformers = [];
 
-  _.each(transform.transformers, function (transformer) {
-    if (transformer.canRun(file)) {
-      transformers.push(transformer);
+  var transformers = {};
 
+  var secondaryStack = [];
+  var stack = [];
+
+  _.each(transform.transformers, function (transformer, key) {
+    var pass = transformers[key] = transformer.buildPass(file);
+
+    if (pass.canRun(file)) {
+      stack.push(pass);
       if (transformer.secondPass) {
-        secondPassTransformers.push(transformer);
+        secondaryStack.push(pass);
       }
 
       if (transformer.manipulateOptions) {
@@ -145,7 +169,8 @@ File.prototype.getTransformers = function () {
     }
   });
 
-  return transformers.concat(secondPassTransformers);
+  this.transformerStack = stack.concat(secondaryStack);
+  this.transformers = transformers;
 };
 
 File.prototype.toArray = function (node, i) {
@@ -191,6 +216,26 @@ File.prototype.parseShebang = function (code) {
   return code;
 };
 
+File.prototype.set = function (key, val) {
+  return this.data[key] = val;
+};
+
+File.prototype.setDynamic = function (key, fn) {
+  this.dynamicData[key] = fn;
+};
+
+File.prototype.get = function (key) {
+  var data = this.data[key];
+  if (data) {
+    return data;
+  } else {
+    var dynamic = this.dynamicData[key];
+    if (dynamic) {
+      return this.set(key, dynamic());
+    }
+  }
+};
+
 File.prototype.addImport = function (source, name) {
   name = name || source;
   var id = this.dynamicImportIds[name];
@@ -201,12 +246,18 @@ File.prototype.addImport = function (source, name) {
     var specifiers = [t.importSpecifier(t.identifier("default"), id)];
     var declar = t.importDeclaration(specifiers, t.literal(source));
     declar._blockHoist = 3;
-    this.dynamicImports.push(declar);
+    this.dynamicImported.push(declar);
+
+    this.moduleFormatter.importSpecifier(specifiers[0], declar, this.dynamicImports);
   }
 
   return id;
 };
 
+File.prototype.isConsequenceExpressionStatement = function (node) {
+  return t.isExpressionStatement(node) && this.lastStatements.indexOf(node) >= 0;
+};
+
 File.prototype.addHelper = function (name) {
   if (!_.contains(File.helpers, name)) {
     throw new ReferenceError("unknown declaration " + name);
@@ -217,22 +268,21 @@ File.prototype.addHelper = function (name) {
   var declar = program._declarations && program._declarations[name];
   if (declar) return declar.id;
 
-  var ref;
-  var runtimeNamespace = this.opts.runtime;
-  if (runtimeNamespace && !_.contains(File.excludeHelpersFromRuntime, name)) {
+  var runtime = this.get("runtimeIdentifier");
+  if (runtime) {
     name = t.identifier(t.toIdentifier(name));
-    return t.memberExpression(t.identifier(runtimeNamespace), name);
+    return t.memberExpression(runtime, name);
   } else {
-    ref = util.template(name);
+    var ref = util.template(name);
+    ref._compact = true;
+    var uid = this.generateUidIdentifier(name);
+    this.scope.push({
+      key: name,
+      id: uid,
+      init: ref
+    });
+    return uid;
   }
-
-  var uid = this.generateUidIdentifier(name);
-  this.scope.push({
-    key: name,
-    id: uid,
-    init: ref
-  });
-  return uid;
 };
 
 File.prototype.errorWithNode = function (node, msg, Error) {
@@ -255,7 +305,11 @@ File.prototype.parse = function (code) {
 
   code = this.addCode(code);
 
-  return util.parse(this.opts, code, function (tree) {
+  var opts = this.opts;
+
+  opts.allowImportExportEverywhere = this.isLoose("modules");
+
+  return util.parse(opts, code, function (tree) {
     self.transform(tree);
     return self.generate();
   });
@@ -265,19 +319,20 @@ File.prototype.transform = function (ast) {
   var self = this;
 
   this.ast = ast;
-  this.scope = new Scope(ast.program);
+  this.lastStatements = t.getLastStatements(ast.program);
+  this.scope = new Scope(ast.program, null, this);
   this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
 
   var astRun = function (key) {
-    _.each(self.transformers, function (transformer) {
-      transformer.astRun(self, key);
+    _.each(self.transformerStack, function (pass) {
+      pass.astRun(key);
     });
   };
 
   astRun("enter");
 
-  _.each(this.transformers, function (transformer) {
-    transformer.transform(self);
+  _.each(this.transformerStack, function (pass) {
+    pass.transform();
   });
 
   astRun("exit");
@@ -289,6 +344,7 @@ File.prototype.generate = function () {
 
   var result = {
     code: "",
+    opts: opts,
     map: null,
     ast: null
   };
@@ -318,22 +374,23 @@ File.prototype.generateUid = function (name, scope) {
   scope = scope || this.scope;
 
   var uid;
+  var i = 0;
   do {
-    uid = this._generateUid(name);
+    uid = this._generateUid(name, i);
+    i++;
   } while (scope.has(uid));
   return uid;
 };
 
 File.prototype.generateUidIdentifier = function (name, scope) {
-  return t.identifier(this.generateUid(name, scope));
+  scope = scope || this.scope;
+  var id = t.identifier(this.generateUid(name, scope));
+  scope.add(id);
+  return id;
 };
 
-File.prototype._generateUid = function (name) {
-  var uids = this.uids;
-  var i = uids[name] || 1;
-
+File.prototype._generateUid = function (name, i) {
   var id = name;
   if (i > 1) id += i;
-  uids[name] = i + 1;
   return "_" + id;
 };

lib/6to5/generation/buffer.js

@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = Buffer;
 
 var util = require("../util");
@@ -66,33 +68,62 @@ Buffer.prototype.removeLast = function (cha) {
 };
 
 Buffer.prototype.newline = function (i, removeLast) {
-  if (this.format.compact) return;
-
-  if (_.isBoolean(i)) {
-    removeLast = i;
-    i = null;
+  if (this.format.compact) {
+    this.space();
+    return;
   }
 
+  removeLast = removeLast || false;
+
   if (_.isNumber(i)) {
     if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
-    for (var j = 0; j < i; j++) {
-      this.newline(null, removeLast);
+    while (i--) {
+      this._newline(removeLast);
     }
     return;
   }
 
+  if (_.isBoolean(i)) {
+    removeLast = i;
+  }
+
+  this._newline(removeLast);
+};
+
+Buffer.prototype._newline = function (removeLast) {
   if (removeLast && this.isLast("\n")) this.removeLast("\n");
 
   this.removeLast(" ");
 
   // remove whitespace if last character was a newline
-  this.buf = this.buf.replace(/\n +$/, "\n");
-
+  this._removeSpacesAfterLastNewline();
   this._push("\n");
 };
 
+/**
+ * If buffer ends with a newline and some spaces after it, trim those spaces.
+ */
+Buffer.prototype._removeSpacesAfterLastNewline = function () {
+  var lastNewlineIndex = this.buf.lastIndexOf("\n");
+  if (lastNewlineIndex === -1)
+    return;
+
+  var index = this.buf.length - 1;
+  while (index > lastNewlineIndex) {
+    if (this.buf[index] !== " ") {
+      break;
+    }
+
+    index--;
+  }
+
+  if (index === lastNewlineIndex) {
+    this.buf = this.buf.substring(0, index + 1);
+  }
+};
+
 Buffer.prototype.push = function (str, noIndent) {
   if (this._indent && !noIndent && str !== "\n") {
     // we have an indent level and we aren't pushing a newline

lib/6to5/generation/generator.js

@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = function (ast, opts, code) {
   var gen = new CodeGenerator(ast, opts, code);
   return gen.generate();
@@ -5,21 +7,22 @@ module.exports = function (ast, opts, code) {
 
 module.exports.CodeGenerator = CodeGenerator;
 
-var Whitespace = require("./whitespace");
-var SourceMap  = require("./source-map");
-var Position   = require("./position");
-var Buffer     = require("./buffer");
-var util       = require("../util");
-var n          = require("./node");
-var t          = require("../types");
-var _          = require("lodash");
+var detectIndent = require("detect-indent");
+var Whitespace   = require("./whitespace");
+var SourceMap    = require("./source-map");
+var Position     = require("./position");
+var Buffer       = require("./buffer");
+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(opts);
+  this.format   = CodeGenerator.normaliseOptions(code, opts);
   this.ast      = ast;
 
   this.whitespace = new Whitespace(this.tokens, this.comments);
@@ -34,14 +37,18 @@ _.each(Buffer.prototype, function (fn, key) {
   };
 });
 
-CodeGenerator.normaliseOptions = function (opts) {
+CodeGenerator.normaliseOptions = function (code, opts) {
+  var indent = detectIndent(code);
+  var style  = indent.indent;
+  if (!style || style === " ") style = "  ";
+
   return _.merge({
     parentheses: true,
     comments: opts.comments == null || opts.comments,
     compact: false,
     indent: {
       adjustMultilineComment: true,
-      style: "  ",
+      style: style,
       base: 0
     }
   }, opts.format || {});
@@ -114,6 +121,15 @@ CodeGenerator.prototype.buildPrint = function (parent) {
 CodeGenerator.prototype.print = function (node, parent, opts) {
   if (!node) return "";
 
+  if (parent && parent._compact) {
+    node._compact = true;
+  }
+
+  var oldCompact = this.format.compact;
+  if (node._compact) {
+    this.format.compact = true;
+  }
+
   var self = this;
 
   opts = opts || {};
@@ -178,6 +194,8 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
   } else {
     throw new ReferenceError("unknown node of type " + JSON.stringify(node.type) + " with constructor " + JSON.stringify(node && node.constructor.name));
   }
+
+  this.format.compact = oldCompact;
 };
 
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {

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

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

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

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

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

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

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

@@ -1,3 +1,5 @@
+"use strict";
+
 var util = require("../../util");
 var t    = require("../../types");
 var _    = require("lodash");
@@ -110,7 +112,9 @@ exports.LogicalExpression =
 exports.AssignmentPattern =
 exports.AssignmentExpression = function (node, print) {
   print(node.left);
-  this.push(" " + node.operator + " ");
+  this.space();
+  this.push(node.operator);
+  this.space();
   print(node.right);
 };
 

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

@@ -1,3 +1,35 @@
-exports.ClassProperty = function () {
-  throw new Error("not implemented");
+"use strict";
+
+exports.AnyTypeAnnotation =
+exports.ArrayTypeAnnotation =
+exports.BooleanTypeAnnotation =
+exports.ClassProperty =
+exports.DeclareClass =
+exports.DeclareFunction =
+exports.DeclareModule =
+exports.DeclareVariable =
+exports.FunctionTypeAnnotation =
+exports.FunctionTypeParam =
+exports.GenericTypeAnnotation =
+exports.InterfaceExtends =
+exports.InterfaceDeclaration =
+exports.IntersectionTypeAnnotation =
+exports.NullableTypeAnnotation =
+exports.NumberTypeAnnotation =
+exports.StringLiteralTypeAnnotation =
+exports.StringTypeAnnotation =
+exports.TupleTypeAnnotation =
+exports.TypeofTypeAnnotation =
+exports.TypeAlias =
+exports.TypeAnnotation =
+exports.TypeParameterDeclaration =
+exports.TypeParameterInstantiation =
+exports.ObjectTypeAnnotation =
+exports.ObjectTypeCallProperty =
+exports.ObjectTypeIndexer =
+exports.ObjectTypeProperty =
+exports.QualifiedTypeIdentifier =
+exports.UnionTypeAnnotation =
+exports.VoidTypeAnnotation = function () {
+  // todo: implement these once we have a `--keep-types` option
 };

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

@@ -1,7 +1,9 @@
+"use strict";
+
 var t = require("../../types");
 var _ = require("lodash");
 
-exports.XJSAttribute = function (node, print) {
+exports.JSXAttribute = function (node, print) {
   print(node.name);
   if (node.value) {
     this.push("=");
@@ -9,35 +11,35 @@ exports.XJSAttribute = function (node, print) {
   }
 };
 
-exports.XJSIdentifier = function (node) {
+exports.JSXIdentifier = function (node) {
   this.push(node.name);
 };
 
-exports.XJSNamespacedName = function (node, print) {
+exports.JSXNamespacedName = function (node, print) {
   print(node.namespace);
   this.push(":");
   print(node.name);
 };
 
-exports.XJSMemberExpression = function (node, print) {
+exports.JSXMemberExpression = function (node, print) {
   print(node.object);
   this.push(".");
   print(node.property);
 };
 
-exports.XJSSpreadAttribute = function (node, print) {
+exports.JSXSpreadAttribute = function (node, print) {
   this.push("{...");
   print(node.argument);
   this.push("}");
 };
 
-exports.XJSExpressionContainer = function (node, print) {
+exports.JSXExpressionContainer = function (node, print) {
   this.push("{");
   print(node.expression);
   this.push("}");
 };
 
-exports.XJSElement = function (node, print) {
+exports.JSXElement = function (node, print) {
   var self = this;
 
   var open = node.openingElement;
@@ -57,22 +59,22 @@ exports.XJSElement = function (node, print) {
   print(node.closingElement);
 };
 
-exports.XJSOpeningElement = function (node, print) {
+exports.JSXOpeningElement = function (node, print) {
   this.push("<");
   print(node.name);
   if (node.attributes.length > 0) {
-    this.space();
+    this.push(" ");
     print.join(node.attributes, { separator: " " });
   }
   this.push(node.selfClosing ? " />" : ">");
 };
 
-exports.XJSClosingElement = function (node, print) {
+exports.JSXClosingElement = function (node, print) {
   this.push("</");
   print(node.name);
   this.push(">");
 };
 
-exports.XJSEmptyExpression = function () {
+exports.JSXEmptyExpression = function () {
 
 };

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

@@ -1,30 +1,14 @@
+"use strict";
+
 var t = require("../../types");
 
 exports._params = function (node, print) {
-  var self = this;
-
   this.push("(");
 
   print.join(node.params, {
-    separator: ", ",
-    iterator: function (param, i) {
-      var def = node.defaults && node.defaults[i];
-      if (def) {
-        self.push(" = ");
-        print(def);
-      }
-    }
+    separator: ", "
   });
 
-  if (node.rest) {
-    if (node.params.length) {
-      this.push(", ");
-    }
-
-    this.push("...");
-    print(node.rest);
-  }
-
   this.push(")");
 };
 
@@ -52,7 +36,7 @@ exports._method = function (node, print) {
   }
 
   this._params(value, print);
-  this.space();
+  this.push(" ");
   print(value.body);
 };
 
@@ -61,8 +45,11 @@ exports.FunctionExpression = function (node, print) {
   if (node.async) this.push("async ");
   this.push("function");
   if (node.generator) this.push("*");
-  this.space();
-  if (node.id) print(node.id);
+  this.push(" ");
+  if (node.id) {
+    this.space();
+    print(node.id);
+  }
   this._params(node, print);
   this.space();
   print(node.body);
@@ -71,7 +58,7 @@ exports.FunctionExpression = function (node, print) {
 exports.ArrowFunctionExpression = function (node, print) {
   if (node.async) this.push("async ");
 
-  if (node.params.length === 1 && !node.defaults.length && !node.rest && t.isIdentifier(node.params[0])) {
+  if (node.params.length === 1 && t.isIdentifier(node.params[0])) {
     print(node.params[0]);
   } else {
     this._params(node, print);

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

@@ -1,9 +1,11 @@
+"use strict";
+
 var t = require("../../types");
 var _ = require("lodash");
 
 exports.ImportSpecifier = function (node, print) {
-  if (node.id && node.id.name === "default") {
-    print(node.name);
+  if (t.isSpecifierDefault(node)) {
+    print(t.getSpecifierName(node));
   } else {
     return exports.ExportSpecifier.apply(this, arguments);
   }
@@ -69,7 +71,7 @@ exports.ImportDeclaration = function (node, print) {
         self.push(", ");
       }
 
-      var isDefault = spec.id && spec.id.name === "default";
+      var isDefault = t.isSpecifierDefault(spec);
 
       if (!isDefault && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
         foundImportSpecifier = true;

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

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

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

@@ -1,3 +1,5 @@
+"use strict";
+
 var util = require("../../util");
 var t    = require("../../types");
 
@@ -13,12 +15,13 @@ exports.IfStatement = function (node, print) {
   this.keyword("if");
   this.push("(");
   print(node.test);
-  this.push(") ");
+  this.push(")");
+  this.space();
 
   print.indentOnComments(node.consequent);
 
   if (node.alternate) {
-    if (this.isLast("}")) this.space();
+    if (this.isLast("}")) this.push(" ");
     this.keyword("else");
     print.indentOnComments(node.alternate);
   }
@@ -32,13 +35,13 @@ exports.ForStatement = function (node, print) {
   this.push(";");
 
   if (node.test) {
-    this.space();
+    this.push(" ");
     print(node.test);
   }
   this.push(";");
 
   if (node.update) {
-    this.space();
+    this.push(" ");
     print(node.update);
   }
 
@@ -85,7 +88,7 @@ var buildLabelStatement = function (prefix, key) {
 
     var label = node[key || "label"];
     if (label) {
-      this.space();
+      this.push(" ");
       print(label);
     }
 
@@ -142,7 +145,9 @@ exports.SwitchStatement = function (node, print) {
   this.keyword("switch");
   this.push("(");
   print(node.discriminant);
-  this.push(") {");
+  this.push(")");
+  this.space();
+  this.push("{");
   print.sequence(node.cases, { indent: true });
   this.push("}");
 };
@@ -167,18 +172,19 @@ exports.DebuggerStatement = function () {
 exports.VariableDeclaration = function (node, print, parent) {
   this.push(node.kind + " ");
 
-  var inits = 0;
-  var noInits = 0;
-  for (var i in node.declarations) {
-    if (node.declarations[i].init) {
-      inits++;
-    } else {
-      noInits++;
+  var hasInits = false;
+  // don't add whitespace to loop heads
+  if (!t.isFor(parent)) {
+    for (var i = 0; i < node.declarations.length; i++) {
+      if (node.declarations[i].init) {
+        // has an init so let's split it up over multiple lines
+        hasInits = true;
+      }
     }
   }
 
   var sep = ",";
-  if (inits > noInits) { // more inits than noinits
+  if (hasInits) {
     sep += "\n" + util.repeat(node.kind.length + 1);
   } else {
     sep += " ";
@@ -200,7 +206,9 @@ exports.PrivateDeclaration = function (node, print) {
 exports.VariableDeclarator = function (node, print) {
   if (node.init) {
     print(node.id);
-    this.push(" = ");
+    this.space();
+    this.push("=");
+    this.space();
     print(node.init);
   } else {
     print(node.id);

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

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

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

@@ -1,9 +1,12 @@
+"use strict";
+
 var _ = require("lodash");
 
 exports.Identifier = function (node) {
   this.push(node.name);
 };
 
+exports.RestElement =
 exports.SpreadElement =
 exports.SpreadProperty = function (node, print) {
   this.push("...");

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

@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = Node;
 
 var whitespace = require("./whitespace");
@@ -13,7 +15,7 @@ var find = function (obj, node, parent) {
   for (var i = 0; i < types.length; i++) {
     var type = types[i];
 
-    if (t["is" + type](node)) {
+    if (t.is(type, node)) {
       var fn = obj[type];
       result = fn(node, parent);
       if (result != null) break;
@@ -28,13 +30,11 @@ function Node(node, parent) {
   this.node   = node;
 }
 
-Node.prototype.isUserWhitespacable = function () {
-  return t.isUserWhitespacable(this.node);
+Node.isUserWhitespacable = function (node) {
+  return t.isUserWhitespacable(node);
 };
 
-Node.prototype.needsWhitespace = function (type) {
-  var parent = this.parent;
-  var node   = this.node;
+Node.needsWhitespace = function (node, parent, type) {
   if (!node) return 0;
 
   if (t.isExpressionStatement(node)) {
@@ -51,18 +51,15 @@ Node.prototype.needsWhitespace = function (type) {
   return lines || 0;
 };
 
-Node.prototype.needsWhitespaceBefore = function () {
-  return this.needsWhitespace("before");
+Node.needsWhitespaceBefore = function (node, parent) {
+  return Node.needsWhitespace(node, parent, "before");
 };
 
-Node.prototype.needsWhitespaceAfter = function () {
-  return this.needsWhitespace("after");
+Node.needsWhitespaceAfter = function (node, parent) {
+  return Node.needsWhitespace(node, parent, "after");
 };
 
-Node.prototype.needsParens = function () {
-  var parent = this.parent;
-  var node   = this.node;
-
+Node.needsParens = function (node, parent) {
   if (!parent) return false;
 
   if (t.isNewExpression(parent) && parent.callee === node) {
@@ -77,10 +74,7 @@ Node.prototype.needsParens = function () {
   return find(parens, node, parent);
 };
 
-Node.prototype.needsParensNoLineTerminator = function () {
-  var parent = this.parent;
-  var node   = this.node;
-
+Node.needsParensNoLineTerminator = function (node, parent) {
   if (!parent) return false;
 
   // no comments
@@ -100,17 +94,18 @@ Node.prototype.needsParensNoLineTerminator = function () {
   return false;
 };
 
-_.each(Node.prototype, function (fn, key) {
-  Node[key] = function (node, parent) {
-    var n = new Node(node, parent);
-
+_.each(Node, function (fn, key) {
+  Node.prototype[key] = function () {
     // Avoid leaking arguments to prevent deoptimization
-    var skipCount = 2;
-    var args = new Array(arguments.length - skipCount);
+    var args = new Array(arguments.length + 2);
+
+    args[0] = this.node;
+    args[1] = this.parent;
+
     for (var i = 0; i < args.length; i++) {
-      args[i] = arguments[i + 2];
+      args[i + 2] = arguments[i];
     }
 
-    return n[key].apply(n, args);
+    return Node[key].apply(null, args);
   };
 });

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

@@ -1,3 +1,5 @@
+"use strict";
+
 var t = require("../../types");
 var _ = require("lodash");
 
@@ -149,8 +151,10 @@ exports.ConditionalExpression = function (node, parent) {
     return true;
   }
 
-  if (t.isCallExpression(parent) && parent.callee === node) {
-    return true;
+  if (t.isCallExpression(parent) || t.isNewExpression(parent)) {
+    if (parent.callee === node) {
+      return true;
+    }
   }
 
   if (t.isConditionalExpression(parent) && parent.test === node) {

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

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

lib/6to5/generation/position.js

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

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

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

lib/6to5/generation/whitespace.js

@@ -1,10 +1,40 @@
+"use strict";
+
 module.exports = Whitespace;
 
-var _ = require("lodash");
+var _    = require("lodash");
+
+/**
+ * Returns `i`th number from `base`, continuing from 0 when `max` is reached.
+ * Useful for shifting `for` loop by a fixed number but going over all items.
+ *
+ * @param {Number} i Current index in the loop
+ * @param {Number} base Start index for which to return 0
+ * @param {Number} max Array length
+ * @returns {Number} shiftedIndex
+ */
+function getLookupIndex(i, base, max) {
+  i += base;
+
+  if (i >= max)
+    i -= max;
+
+  return i;
+}
 
 function Whitespace(tokens, comments) {
   this.tokens = _.sortBy(tokens.concat(comments), "start");
-  this.used   = [];
+  this.used   = {};
+
+  // Profiling this code shows that while generator passes over it, indexes
+  // returned by `getNewlinesBefore` and `getNewlinesAfter` are always increasing.
+
+  // We use this implementation detail for an optimization: instead of always
+  // starting to look from `this.tokens[0]`, we will start `for` loops from the
+  // previous successful match. We will enumerate all tokens—but the common
+  // case will be much faster.
+
+  this._lastFoundIndex = 0;
 }
 
 Whitespace.prototype.getNewlinesBefore = function (node) {
@@ -13,13 +43,17 @@ Whitespace.prototype.getNewlinesBefore = function (node) {
   var tokens = this.tokens;
   var token;
 
-  for (var i = 0; i < tokens.length; i++) {
+  for (var j = 0; j < tokens.length; j++) {
+    // optimize for forward traversal by shifting for loop index
+    var i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
     token = tokens[i];
 
     // this is the token this node starts with
     if (node.start === token.start) {
       startToken = tokens[i - 1];
       endToken = token;
+
+      this._lastFoundIndex = i;
       break;
     }
   }
@@ -33,13 +67,17 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
   var tokens = this.tokens;
   var token;
 
-  for (var i = 0; i < tokens.length; i++) {
+  for (var j = 0; j < tokens.length; j++) {
+    // optimize for forward traversal by shifting for loop index
+    var i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
     token = tokens[i];
 
     // this is the token this node ends with
     if (node.end === token.end) {
       startToken = token;
       endToken = tokens[i + 1];
+
+      this._lastFoundIndex = i;
       break;
     }
   }
@@ -60,12 +98,11 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {
   var start = startToken ? startToken.loc.end.line : 1;
   var end   = endToken.loc.start.line;
-
   var lines = 0;
 
   for (var line = start; line < end; line++) {
-    if (!_.contains(this.used, line)) {
-      this.used.push(line);
+    if (typeof this.used[line] === "undefined") {
+      this.used[line] = true;
       lines++;
     }
   }

lib/6to5/helpers/clone.js

@@ -0,0 +1,12 @@
+"use strict";
+
+module.exports = function cloneDeep(obj) {
+  var obj2 = {};
+  if (!obj) return obj2;
+
+  for (var key in obj) {
+    obj2[key] = obj[key];
+  }
+
+  return obj2;
+};

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

@@ -0,0 +1,79 @@
+// syntax highlighting based on https://github.com/dominictarr/ansi-highlight by the fantastic Dominic Tarr
+
+var supportsColor = require("supports-color");
+var tokenize      = require("js-tokenizer");
+var chalk         = require("chalk");
+var util          = require("../util");
+
+var defs = {
+  string1:  "red",
+  string2:  "red",
+  punct:    ["white", "bold"],
+  curly:    "green",
+  parens:   ["blue", "bold"],
+  square:   ["yellow"],
+  name:     "white",
+  keyword:  ["cyan"],
+  number:   "magenta",
+  regexp:   "magenta",
+  comment1: "grey",
+  comment2: "grey"
+};
+
+var highlight = function (text) {
+  var colorize = function (str, col) {
+    if (!col) return str;
+
+    if (Array.isArray(col)) {
+      col.forEach(function (col) {
+        str = chalk[col](str);
+      });
+    } else {
+      str = chalk[col](str);
+    }
+    return str;
+  };
+
+  return tokenize(text, true).map(function (str) {
+    var type = tokenize.type(str);
+    return colorize(str, defs[type]);
+  }).join("");
+};
+
+module.exports = function (lines, lineNumber, colNumber) {
+  colNumber = Math.max(colNumber, 0);
+
+  if (supportsColor) {
+    lines = highlight(lines);
+  }
+
+  lines = lines.split("\n");
+
+  var start = Math.max(lineNumber - 3, 0);
+  var end   = Math.min(lines.length, lineNumber + 3);
+  var width = (end + "").length;
+
+  if (!lineNumber && !colNumber) {
+    start = 0;
+    end = lines.length;
+  }
+
+  return "\n" + lines.slice(start, end).map(function (line, i) {
+    var curr = i + start + 1;
+
+    var gutter = curr === lineNumber ? "> " : "  ";
+
+    var sep = curr + util.repeat(width + 1);
+    gutter += sep + "| ";
+
+    var str = gutter + line;
+
+    if (colNumber && curr === lineNumber) {
+      str += "\n";
+      str += util.repeat(gutter.length - 2);
+      str += "|" + util.repeat(colNumber) + "^";
+    }
+
+    return str;
+  }).join("\n");
+};

lib/6to5/helpers/object.js

@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = function () {
+  return Object.create(null);
+};

lib/6to5/helpers/to-fast-properties.js

@@ -0,0 +1,17 @@
+"use strict";
+
+/**
+ * A trick from Bluebird to force V8 to use fast properties for an object.
+ * Read more: http://stackoverflow.com/questions/24987896/
+ *
+ * Use %HasFastProperties(obj) and --allow-natives-syntax to check whether
+ * a particular object already has fast properties.
+ */
+
+module.exports = function toFastProperties(obj) {
+  /*jshint -W027*/
+  function f() {}
+  f.prototype = obj;
+  return f;
+  eval(obj);
+};

lib/6to5/index.js

@@ -1,3 +1,5 @@
+"use strict";
+
 var transform = require("./transformation/transform");
 var util      = require("./util");
 var fs        = require("fs");
@@ -7,8 +9,6 @@ exports.version = require("../../package").version;
 
 exports.types = require("./types");
 
-exports.runtime = require("./runtime-generator");
-
 exports.register = function (opts) {
   var register = require("./register");
   if (opts != null) register(opts);

lib/6to5/patch.js

@@ -1,22 +1,31 @@
+"use strict";
+
 var t = require("./types");
 var _ = require("lodash");
 
+require("./types/node");
+
 // estraverse
 
 var estraverse = require("estraverse");
 _.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
 
-// regenerator/recast/ast-types
+// regenerator-6to5/ast-types
 
 var types = require("ast-types");
 var def   = types.Type.def;
 var or    = types.Type.or;
 
+def("File")
+  .bases("Node")
+  .build("program")
+  .field("program", def("Program"));
+
 def("AssignmentPattern")
-    .bases("Pattern")
-    .build("left", "right")
-    .field("left", def("Pattern"))
-    .field("right", def("Expression"));
+  .bases("Pattern")
+  .build("left", "right")
+  .field("left", def("Pattern"))
+  .field("right", def("Expression"));
 
 // Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
@@ -24,6 +33,11 @@ def("ImportBatchSpecifier")
   .build("name")
   .field("name", def("Identifier"));
 
+def("RestElement")
+  .bases("Node")
+  .build("argument")
+  .field("argument", def("Pattern"));
+
 // Abstract references
 def("VirtualPropertyExpression")
   .bases("Expression")

lib/6to5/polyfill.js

@@ -1,2 +1,9 @@
+"use strict";
+
+if (global._6to5Polyfill) {
+  throw new Error("only one instance of 6to5/polyfill is allowed");
+}
+global._6to5Polyfill = true;
+
 require("core-js/shim");
-require("regenerator/runtime");
+require("regenerator-6to5/runtime");

lib/6to5/register-browser.js

@@ -1,3 +1,5 @@
+"use strict";
+
 // required to safely use 6to5/register within a browserify codebase
 
 module.exports = function () {};

lib/6to5/register-cache.js

@@ -0,0 +1,36 @@
+"use strict";
+
+var path = require("path");
+var os   = require("os");
+var fs   = require("fs");
+
+var FILENAME = path.join(os.tmpdir(), "6to5.json");
+var data = {};
+
+exports.save = function () {
+  fs.writeFileSync(FILENAME, JSON.stringify(data, null, "  "));
+};
+
+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 () {
+    process.removeListener("SIGINT", sigint);
+    exports.save();
+    process.kill(process.pid, "SIGINT");
+  };
+
+  process.on("SIGINT", sigint);
+};
+
+exports.get = function () {
+  return data;
+};

lib/6to5/register.js

@@ -1,7 +1,9 @@
+"use strict";
+
 require("./polyfill");
 
 var sourceMapSupport = require("source-map-support");
-var roadrunner       = require("roadrunner");
+var registerCache    = require("./register-cache");
 var util             = require("./util");
 var to5              = require("./index");
 var fs               = require("fs");
@@ -23,46 +25,8 @@ sourceMapSupport.install({
 
 //
 
-var blacklist  = [];
-
-var blacklistTest = function (transformer, code) {
-  try {
-    if (_.isFunction(code)) {
-      code();
-    } else {
-      new Function(code);
-    }
-    blacklist.push(transformer);
-  } catch (err) {
-    if (err.name !== "SyntaxError") throw err;
-  }
-};
-
-blacklistTest("arrayComprehension", "var foo = [for (foo of bar) foo * foo];");
-blacklistTest("generatorComprehension", "var foo = (for (foo of bar) foo * foo)");
-blacklistTest("arrowFunctions", "var foo = x => x * x;");
-blacklistTest("classes", "class Foo {}");
-blacklistTest("computedPropertyNames", "var foo = { [foo]: bar };");
-blacklistTest("constants", function () {
-  try {
-    new Function("const foo = 'foo';\nfoo = 'wow';");
-  } catch (err) {
-    return; // constants are supported
-  }
-  throw new SyntaxError;
-});
-blacklistTest("defaultParamaters", "var foo = function (bar = 0) {};");
-blacklistTest("destructuring", "var { x, y } = { x: 0, y: 0 };");
-blacklistTest("forOf", "for (var foo of bar) {}");
-blacklistTest("generators", "function* foo() {}\nasync function bar() {}"); // generators/async functions delegated to same transformer
-blacklistTest("letScoping", "let foo = 0;");
-blacklistTest("modules", 'import foo from "from";');
-blacklistTest("propertyMethodAssignment", "{ get foo() {} }");
-blacklistTest("propertyNameShorthand", "var foo = { x, y };");
-blacklistTest("restParameters", "function foo(...bar) {}");
-blacklistTest("spread", "foo(...bar);");
-blacklistTest("templateLiterals", "var foo = `foo`;");
-blacklistTest("unicodeRegex", function () { new RegExp("foo", "u"); });
+registerCache.load();
+var cache = registerCache.get();
 
 //
 
@@ -70,7 +34,6 @@ var transformOpts = {};
 var ignoreRegex   = /node_modules/;
 var onlyRegex;
 var whitelist     = [];
-var cache;
 var exts          = {};
 var maps          = {};
 var old           = require.extensions[".js"];
@@ -95,7 +58,6 @@ var loader = function (m, filename) {
 
   result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
-    blacklist: blacklist,
     sourceMap: true,
     ast:       false
   }, transformOpts));
@@ -128,21 +90,18 @@ hookExtensions(util.canCompile.EXTENSIONS);
 module.exports = function (opts) {
   // normalise options
   opts = opts || {};
-  if (_.isRegExp(opts)) opts = { ignore: opts };
-  if (opts.ignoreRegex != null) opts.ignore = opts.ignoreRegex;
 
   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) cache = opts.cache;
   if (opts.cache === false) cache = null;
-  if (opts.cache === true) {
-    roadrunner.load();
-    roadrunner.setup();
-    cache = roadrunner.get("6to5");
-  }
+
+  delete opts.extensions;
+  delete opts.ignore;
+  delete opts.cache;
+  delete opts.only;
 
   _.extend(transformOpts, opts);
 };

lib/6to5/runtime-generator.js

@@ -1,33 +0,0 @@
-var generator = require("./generation/generator");
-var util      = require("./util");
-var File      = require("./file");
-var t         = require("./types");
-var _         = require("lodash");
-
-module.exports = function (namespace) {
-  namespace = t.identifier(t.toIdentifier(namespace || "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([]))
-    )
-  ]));
-
-  _.each(File.helpers, function (name) {
-    if (_.contains(File.excludeHelpersFromRuntime, name)) {
-      return;
-    }
-
-    var key = t.identifier(t.toIdentifier(name));
-    body.push(t.expressionStatement(
-      t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))
-    ));
-  });
-
-  return generator(tree).code;
-};

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

@@ -0,0 +1,46 @@
+"use strict";
+
+var explode = require("./explode-assignable-expression");
+var t       = require("../../types");
+
+module.exports = function (exports, opts) {
+  var isAssignment = function (node) {
+    return node.operator === opts.operator + "=";
+  };
+
+  var buildAssignment = function (left, right) {
+    return t.assignmentExpression("=", left, right);
+  };
+
+  exports.ExpressionStatement = function (node, parent, scope, context, file) {
+    // hit the `AssignmentExpression` one below
+    if (file.isConsequenceExpressionStatement(node)) return;
+
+    var expr = node.expression;
+    if (!isAssignment(expr)) return;
+
+    var nodes    = [];
+    var exploded = explode(expr.left, nodes, file, scope, true);
+
+    nodes.push(t.expressionStatement(
+      buildAssignment(exploded.ref, opts.build(exploded.uid, expr.right))
+    ));
+
+    return nodes;
+  };
+
+  exports.AssignmentExpression = function (node, parent, scope, context, file) {
+    if (!isAssignment(node)) return;
+
+    var nodes    = [];
+    var exploded = explode(node.left, nodes, file, scope);
+    nodes.push(buildAssignment(exploded.ref, opts.build(exploded.uid, node.right)));
+
+    return t.toSequenceExpression(nodes, scope);
+  };
+
+  exports.BinaryExpression = function (node) {
+    if (node.operator !== opts.operator) return;
+    return opts.build(node.left, node.right);
+  };
+};

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

@@ -0,0 +1,25 @@
+"use strict";
+
+var t = require("../../types");
+
+module.exports = function build(node, buildBody) {
+  var self = node.blocks.shift();
+  if (!self) return;
+
+  var child = build(node, buildBody);
+  if (!child) {
+    // last item
+    child = buildBody();
+
+    // add a filter as this is our final stop
+    if (node.filter) {
+      child = t.ifStatement(node.filter, t.blockStatement([child]));
+    }
+  }
+
+  return t.forOfStatement(
+    t.variableDeclaration("let", [t.variableDeclarator(self.left)]),
+    self.right,
+    t.blockStatement([child])
+  );
+};

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

@@ -0,0 +1,47 @@
+"use strict";
+
+var explode = require("./explode-assignable-expression");
+var t       = require("../../types");
+
+module.exports = function (exports, opts) {
+  var buildAssignment = function (left, right) {
+    return t.assignmentExpression("=", left, right);
+  };
+
+  exports.ExpressionStatement = function (node, parent, scope, context, file) {
+    // hit the `AssignmentExpression` one below
+    if (file.isConsequenceExpressionStatement(node)) return;
+
+    var expr = node.expression;
+    if (!opts.is(expr, file)) return;
+
+    var nodes = [];
+
+    var exploded = explode(expr.left, nodes, file, scope);
+
+    nodes.push(t.ifStatement(
+      opts.build(exploded.uid, file),
+      t.expressionStatement(buildAssignment(exploded.ref, expr.right))
+    ));
+
+    return nodes;
+  };
+
+  exports.AssignmentExpression = function (node, parent, scope, context, file) {
+    if (!opts.is(node, file)) return;
+
+    var nodes    = [];
+    var exploded = explode(node.left, nodes, file, scope);
+
+    nodes.push(t.logicalExpression(
+      "&&",
+      opts.build(exploded.uid, file),
+      buildAssignment(exploded.ref, node.right)
+    ));
+
+    // todo: duplicate expression node
+    nodes.push(exploded.ref);
+
+    return t.toSequenceExpression(nodes, scope);
+  };
+};

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

@@ -0,0 +1,73 @@
+"use strict";
+
+var t = require("../../types");
+
+var getObjRef = function (node, nodes, file, scope) {
+  var ref;
+  if (t.isIdentifier(node)) {
+    if (scope.has(node.name, true)) {
+      // this variable is declared in scope so we can be 100% sure
+      // that evaluating it multiple times wont trigger a getter
+      // or something else
+      return node;
+    } else {
+      // could possibly trigger a getter so we need to only evaluate
+      // it once
+      ref = node;
+    }
+  } else if (t.isMemberExpression(node)) {
+    ref = node.object;
+
+    if (t.isIdentifier(ref) && scope.has(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
+      return ref;
+    }
+  } else {
+    throw new Error("We can't explode this node type " + node.type);
+  }
+
+  var temp = scope.generateUidBasedOnNode(ref);
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(temp, ref)
+  ]));
+  return temp;
+};
+
+var getPropRef = function (node, nodes, file, scope) {
+  var prop = node.property;
+  var key = t.toComputedKey(node, prop);
+  if (t.isLiteral(key)) return key;
+
+  var temp = scope.generateUidBasedOnNode(prop);
+  nodes.push(t.variableDeclaration("var", [
+    t.variableDeclarator(temp, prop)
+  ]));
+  return temp;
+};
+
+module.exports = function (node, nodes, file, scope, allowedSingleIdent) {
+  var obj;
+  if (t.isIdentifier(node) && allowedSingleIdent) {
+    obj = node;
+  } else {
+    obj = getObjRef(node, nodes, file, scope);
+  }
+
+  var ref, uid;
+
+  if (t.isIdentifier(node)) {
+    ref = node;
+    uid = obj;
+  } else {
+    var prop = getPropRef(node, nodes, file, scope);
+    var computed = node.computed || t.isLiteral(prop);
+    uid = ref = t.memberExpression(obj, prop, computed);
+  }
+
+  return {
+    uid: uid,
+    ref: ref
+  };
+};

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

@@ -0,0 +1,51 @@
+"use strict";
+
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+
+var visitor = {
+  enter: function (node, parent, scope, context, state) {
+    // check if this node is an identifier that matches the same as our function id
+    if (!t.isIdentifier(node, { name: state.id })) return;
+
+    // check if this node is the one referenced
+    if (!t.isReferenced(node, parent)) return;
+
+    // check that we don't have a local variable declared as that removes the need
+    // for the wrapper
+    var localDeclar = scope.get(state.id, true);
+    if (localDeclar !== state.outerDeclar) return;
+
+    state.selfReference = true;
+    context.stop();
+  }
+};
+
+exports.property = function (node, file, scope) {
+  var key = t.toComputedKey(node, node.key);
+  if (!t.isLiteral(key)) return node; // we can't set a function id with this
+
+  var id = t.toIdentifier(key.value);
+  key = t.identifier(id);
+
+  var state = {
+    id: id,
+    selfReference: false,
+    outerDeclar: scope.get(id, true),
+  };
+
+  traverse(node, visitor, scope, state);
+
+  if (state.selfReference) {
+    // todo: support generators
+    node.value = util.template("property-method-assignment-wrapper", {
+      FUNCTION: node.value,
+      FUNCTION_ID: key,
+      FUNCTION_KEY: scope.generateUidIdentifier(id),
+      WRAPPER_KEY: scope.generateUidIdentifier(id + "Wrapper")
+    });
+  } else {
+    node.value.id = key;
+  }
+};

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

@@ -0,0 +1,35 @@
+"use strict";
+
+var traverse = require("../../traverse");
+var t        = require("../../types");
+
+var visitor = {
+  enter: function (node, parent, scope, context) {
+    if (t.isFunction(node)) context.skip();
+
+    if (t.isAwaitExpression(node)) {
+      node.type = "YieldExpression";
+    }
+  }
+};
+
+module.exports = function (node, callId, scope) {
+  node.async = false;
+  node.generator = true;
+
+  traverse(node, visitor, scope);
+
+  var call = t.callExpression(callId, [node]);
+  var id = node.id;
+  delete node.id;
+
+  if (t.isFunctionDeclaration(node)) {
+    var declar = t.variableDeclaration("let", [
+      t.variableDeclarator(id, call)
+    ]);
+    declar._blockHoist = true;
+    return declar;
+  } else {
+    return call;
+  }
+};

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

@@ -0,0 +1,251 @@
+"use strict";
+
+module.exports = ReplaceSupers;
+
+var traverse = require("../../traverse");
+var t        = require("../../types");
+
+/**
+ * Description
+ *
+ * @param {Object} opts
+ */
+
+function ReplaceSupers(opts) {
+  this.topLevelThisReference = null;
+  this.methodNode            = opts.methodNode;
+  this.className             = opts.className;
+  this.superName             = opts.superName;
+  this.isLoose               = opts.isLoose;
+  this.scope                 = opts.scope;
+  this.file                  = opts.file;
+}
+
+/**
+ * Gets a node representing the super class value of the named property.
+ *
+ * @example
+ *
+ *   _get(Object.getPrototypeOf(CLASS.prototype), "METHOD", this)
+ *
+ * @param {Node} property
+ * @param {boolean} isStatic
+ * @param {boolean} isComputed
+ *
+ * @returns {Node}
+ */
+
+ReplaceSupers.prototype.superProperty = function (property, isStatic, 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"))
+        ]
+      ),
+      isComputed ? property : t.literal(property.name),
+      thisExpression
+    ]
+  );
+};
+
+/**
+ * Description
+ *
+ * @param {Object} node
+ * @param {Object} id
+ * @param {Object} parent
+ * @returns {Object}
+ */
+
+ReplaceSupers.prototype.looseSuperProperty = function (methodNode, id, parent) {
+  var methodName = methodNode.key;
+  var superName  = this.superName || t.identifier("Function");
+
+  if (parent.property === id) {
+    return;
+  } else if (t.isCallExpression(parent, { callee: id })) {
+    // super(); -> ClassName.prototype.MethodName.call(this);
+    parent.arguments.unshift(t.thisExpression());
+
+    if (methodName.name === "constructor") {
+      // constructor() { super(); }
+      return t.memberExpression(superName, t.identifier("call"));
+    } else {
+      id = superName;
+
+      // foo() { super(); }
+      if (!methodNode.static) {
+        id = t.memberExpression(id, t.identifier("prototype"));
+      }
+
+      id = t.memberExpression(id, methodName, methodNode.computed);
+      return t.memberExpression(id, t.identifier("call"));
+    }
+  } else if (t.isMemberExpression(parent) && !methodNode.static) {
+    // super.test -> ClassName.prototype.test
+    return t.memberExpression(superName, t.identifier("prototype"));
+  } else {
+    return superName;
+  }
+};
+
+/**
+ * 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
+ *
+ * @param {Function} getThisReference
+ * @param {Object} node
+ * @param {Object} parent
+ */
+
+ReplaceSupers.prototype.looseHandle = function (getThisReference, node, parent) {
+  if (t.isIdentifier(node, { name: "super" })) {
+    return this.looseSuperProperty(this.methodNode, 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);
+    t.appendToMemberExpression(callee, t.identifier("call"));
+    node.arguments.unshift(getThisReference());
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Function} getThisReference
+ * @param {Object} node
+ * @param {Object} parent
+ */
+
+ReplaceSupers.prototype.specHandle = function (getThisReference, node, parent) {
+  var methodNode = this.methodNode;
+  var property;
+  var computed;
+  var args;
+
+  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)) {
+    var callee = node.callee;
+    if (t.isIdentifier(callee, { name: "super" })) {
+      // super(); -> _get(Object.getPrototypeOf(ClassName), "MethodName", this).call(this);
+      property = methodNode.key;
+      computed = methodNode.computed;
+      args = node.arguments;
+
+      // 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") {
+        var methodName = methodNode.key.name || "METHOD_NAME";
+        throw this.file.errorWithNode(node, "Direct super call is illegal in non-constructor, use super." + methodName + "() instead");
+      }
+    } else {
+      if (!t.isMemberExpression(callee)) return;
+      if (callee.object.name !== "super") return;
+
+      // 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;
+
+    // super.name; -> _get(Object.getPrototypeOf(ClassName.prototype), "name", this);
+    property = node.property;
+    computed = node.computed;
+  }
+
+  if (!property) return;
+
+  var thisReference = getThisReference();
+  var superProperty = this.superProperty(property, methodNode.static, computed, thisReference);
+  if (args) {
+    if (args.length === 1 && t.isSpreadElement(args[0])) {
+      // super(...arguments);
+      return t.callExpression(
+        t.memberExpression(superProperty, t.identifier("apply")),
+        [thisReference, args[0].argument]
+      );
+    } else {
+      return t.callExpression(
+        t.memberExpression(superProperty, t.identifier("call")),
+        [thisReference].concat(args)
+      );
+    }
+  } else {
+    return superProperty;
+  }
+};

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

@@ -1,13 +1,15 @@
+"use strict";
+
 var t = require("../../types");
 
-exports._has = function (node) {
+exports.has = function (node) {
   var first = node.body[0];
   return t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" });
 };
 
-exports._wrap = function (node, callback) {
+exports.wrap = function (node, callback) {
   var useStrictNode;
-  if (exports._has(node)) {
+  if (exports.has(node)) {
     useStrictNode = node.body.shift();
   }
 
@@ -17,11 +19,3 @@ exports._wrap = function (node, callback) {
     node.body.unshift(useStrictNode);
   }
 };
-
-exports.ast = {
-  exit: function (ast) {
-    if (!exports._has(ast.program)) {
-      ast.program.body.unshift(t.expressionStatement(t.literal("use strict")));
-    }
-  }
-};

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

@@ -1,81 +1,135 @@
+"use strict";
+
 module.exports = DefaultFormatter;
 
 var traverse = require("../../traverse");
+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.localExports = this.getLocalExports();
-  this.localImports = this.getLocalImports();
+  this.hasNonDefaultExports = false;
+
+  this.hasLocalExports = false;
+  this.hasLocalImports = false;
+
+  this.localImportOccurences = object();
+  this.localExports = object();
+  this.localImports = object();
+
+  this.getLocalExports();
+  this.getLocalImports();
 
   this.remapAssignments();
-
-  //this.checkCollisions();
 }
 
-DefaultFormatter.prototype.getLocalExports = function () {
-  var localExports = {};
+DefaultFormatter.prototype.doDefaultExportInterop = function (node) {
+  return node.default && !this.noInteropRequire && !this.hasNonDefaultExports;
+};
 
-  traverse(this.file.ast, {
-    enter: function (node) {
-      var declar = node && node.declaration;
-      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
-        _.extend(localExports, t.getIds(declar, true));
+DefaultFormatter.prototype.bumpImportOccurences = function (node) {
+  var source = node.source.value;
+  var occurs = this.localImportOccurences;
+  occurs[source] = occurs[source] || 0;
+  occurs[source] += node.specifiers.length;
+};
+
+var exportsVisitor = {
+  enter: function (node, parent, scope, context, 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));
+      }
+
+      if (!node.default) {
+        formatter.hasNonDefaultExports = true;
+      }
+
+      if (node.source) {
+        formatter.bumpImportOccurences(node);
       }
     }
-  });
+  }
+};
 
-  return localExports;
+DefaultFormatter.prototype.getLocalExports = function () {
+  traverse(this.file.ast, exportsVisitor, this.file.scope, this);
+};
+
+var importsVisitor = {
+  enter: function (node, parent, scope, context, formatter) {
+    if (t.isImportDeclaration(node)) {
+      formatter.hasLocalImports = true;
+      _.extend(formatter.localImports, t.getIds(node, true));
+      formatter.bumpImportOccurences(node);
+    }
+  }
 };
 
 DefaultFormatter.prototype.getLocalImports = function () {
-  var localImports = {};
-
-  traverse(this.file.ast, {
-    enter: function (node) {
-      if (t.isImportDeclaration(node)) {
-        _.extend(localImports, t.getIds(node, true));
-      }
-    }
-  });
-
-  return localImports;
+  traverse(this.file.ast, importsVisitor, this.file.scope, this);
 };
 
-DefaultFormatter.prototype.checkCollisions = function () {
-  // todo: all check export collissions
+var remapVisitor = {
+  enter: function (node, parent, scope, context, formatter) {
+    if (t.isUpdateExpression(node) && formatter.isLocalReference(node.argument, scope)) {
+      context.skip();
 
-  var localImports = this.localImports;
-  var file = this.file;
+      // expand to long file assignment expression
+      var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
 
-  var isLocalReference = function (node) {
-    return t.isIdentifier(node) && _.has(localImports, node.name) && localImports[node.name] !== node;
-  };
+      // remap this assignment expression
+      var remapped = formatter.remapExportAssignment(assign);
 
-  var check = function (node) {
-    if (isLocalReference(node)) {
-      throw file.errorWithNode(node, "Illegal assignment of module import");
-    }
-  };
-
-  traverse(file.ast, {
-    enter: function (node) {
-      if (t.isAssignmentExpression(node)) {
-
-        var left = node.left;
-        if (t.isMemberExpression(left)) {
-          while (left.object) left = left.object;
-        }
-
-        check(left);
-      } else if (t.isDeclaration(node)) {
-        _.each(t.getIds(node, true), check);
+      // we don't need to change the result
+      if (t.isExpressionStatement(parent) || node.prefix) {
+        return remapped;
       }
+
+      var nodes = [];
+      nodes.push(remapped);
+
+      var operator;
+      if (node.operator === "--") {
+        operator = "+";
+      } else { // "++"
+        operator = "-";
+      }
+      nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
+
+      return t.sequenceExpression(nodes);
     }
-  });
+
+    if (t.isAssignmentExpression(node) && formatter.isLocalReference(node.left, scope)) {
+      context.skip();
+      return formatter.remapExportAssignment(node);
+    }
+  }
+};
+
+DefaultFormatter.prototype.remapAssignments = function () {
+  if (this.hasLocalImports) {
+    traverse(this.file.ast, remapVisitor, this.file.scope, this);
+  }
+};
+
+DefaultFormatter.prototype.isLocalReference = function (node) {
+  var localImports = this.localImports;
+  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) {
@@ -90,51 +144,10 @@ DefaultFormatter.prototype.remapExportAssignment = function (node) {
   );
 };
 
-DefaultFormatter.prototype.remapAssignments = function () {
+DefaultFormatter.prototype.isLocalReference = function (node, scope) {
   var localExports = this.localExports;
-  var self = this;
-
-  var isLocalReference = function (node, scope) {
-    var name = node.name;
-    return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
-  };
-
-  traverse(this.file.ast, {
-    enter: function (node, parent, scope) {
-      if (t.isUpdateExpression(node) && isLocalReference(node.argument, scope)) {
-        this.skip();
-
-        // expand to long file assignment expression
-        var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
-
-        // remap this assignment expression
-        var remapped = self.remapExportAssignment(assign);
-
-        // we don't need to change the result
-        if (t.isExpressionStatement(parent) || node.prefix) {
-          return remapped;
-        }
-
-        var nodes = [];
-        nodes.push(remapped);
-
-        var operator;
-        if (node.operator === "--") {
-          operator = "+";
-        } else { // "++"
-          operator = "-";
-        }
-        nodes.push(t.binaryExpression(operator, node.argument, t.literal(1)));
-
-        return t.sequenceExpression(nodes);
-      }
-
-      if (t.isAssignmentExpression(node) && isLocalReference(node.left, scope)) {
-        this.skip();
-        return self.remapExportAssignment(node);
-      }
-    }
-  });
+  var name = node.name;
+  return t.isIdentifier(node) && localExports[name] && localExports[name] === scope.get(name, true);
 };
 
 DefaultFormatter.prototype.getModuleName = function () {
@@ -188,25 +201,37 @@ DefaultFormatter.prototype._hoistExport = function (declar, assign, priority) {
   return assign;
 };
 
-DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
+DefaultFormatter.prototype.getExternalReference = function (node, nodes) {
+  var ids = this.ids;
+  var id = node.source.value;
+
+  if (ids[id]) {
+    return ids[id];
+  } else {
+    return this.ids[id] = this._getExternalReference(node, nodes);
+  }
+};
+
+DefaultFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
   var inherits = false;
   if (node.specifiers.length === 1) inherits = node;
 
   if (node.source) {
+    var ref = this.getExternalReference(node, nodes);
+
     if (t.isExportBatchSpecifier(specifier)) {
       // export * from "foo";
-      nodes.push(this._exportsWildcard(getRef(), node));
+      nodes.push(this.buildExportsWildcard(ref, node));
     } else {
-      var ref;
       if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
         // importing a default so we need to normalise it
-        ref = t.callExpression(this.file.addHelper("interop-require"), [getRef()]);
+        ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
       } else {
-        ref = t.memberExpression(getRef(), specifier.id);
+        ref = t.memberExpression(ref, t.getSpecifierId(specifier));
       }
 
       // export { foo } from "test";
-      nodes.push(this._exportsAssign(
+      nodes.push(this.buildExportsAssignment(
         t.getSpecifierName(specifier),
         ref,
         node
@@ -214,18 +239,18 @@ DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node,
     }
   } else {
     // export { foo };
-    nodes.push(this._exportsAssign(t.getSpecifierName(specifier), specifier.id, node));
+    nodes.push(this.buildExportsAssignment(t.getSpecifierName(specifier), specifier.id, node));
   }
 };
 
-DefaultFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+DefaultFormatter.prototype.buildExportsWildcard = function (objectIdentifier) {
   return t.expressionStatement(t.callExpression(this.file.addHelper("defaults"), [
     t.identifier("exports"),
     t.callExpression(this.file.addHelper("interop-require-wildcard"), [objectIdentifier])
   ]));
 };
 
-DefaultFormatter.prototype._exportsAssign = function (id, init) {
+DefaultFormatter.prototype.buildExportsAssignment = function (id, init) {
   return util.template("exports-assign", {
     VALUE: init,
     KEY:   id
@@ -244,13 +269,13 @@ DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
   var assign;
 
   if (t.isVariableDeclaration(declar)) {
-    for (var i in declar.declarations) {
+    for (var i = 0; i < declar.declarations.length; i++) {
       var decl = declar.declarations[i];
 
-      decl.init = this._exportsAssign(decl.id, decl.init, node).expression;
+      decl.init = this.buildExportsAssignment(decl.id, decl.init, node).expression;
 
       var newDeclar = t.variableDeclaration(declar.kind, [decl]);
-      if (i === "0") t.inherits(newDeclar, declar);
+      if (i === 0) t.inherits(newDeclar, declar);
       nodes.push(newDeclar);
     }
   } else {
@@ -261,7 +286,7 @@ DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
       nodes.push(declar);
     }
 
-    assign = this._exportsAssign(id, ref, node);
+    assign = this.buildExportsAssignment(id, ref, node);
 
     nodes.push(assign);
 

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

@@ -1,8 +1,10 @@
+"use strict";
+
 var util = require("../../util");
 
 module.exports = function (Parent) {
   var Constructor = function () {
-    this.noInteropExport = true;
+    this.noInteropRequire = true;
     Parent.apply(this, arguments);
   };
 

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

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

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

@@ -1,3 +1,5 @@
+"use strict";
+
 module.exports = AMDFormatter;
 
 var DefaultFormatter = require("./_default");
@@ -8,7 +10,6 @@ var _                = require("lodash");
 
 function AMDFormatter() {
   CommonFormatter.apply(this, arguments);
-  this.ids = {};
 }
 
 util.inherits(AMDFormatter, DefaultFormatter);
@@ -66,33 +67,30 @@ AMDFormatter.prototype.getModuleName = function () {
   }
 };
 
-AMDFormatter.prototype._push = function (node) {
-  var id  = node.source.value;
-  var ids = this.ids;
-
-  if (ids[id]) {
-    return ids[id];
-  } else {
-    return this.ids[id] = this.file.generateUidIdentifier(id);
-  }
+AMDFormatter.prototype._getExternalReference = function (node) {
+  return this.file.generateUidIdentifier(node.source.value);
 };
 
 AMDFormatter.prototype.importDeclaration = function (node) {
-  this._push(node);
+  this.getExternalReference(node);
 };
 
 AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var key = t.getSpecifierName(specifier);
-  var ref = this._push(node);
+  var ref = this.getExternalReference(node);
 
-  if (t.isImportBatchSpecifier(specifier)) {
+  if (_.contains(this.file.dynamicImported, node)) {
+    // Prevent unnecessary renaming of dynamic imports.
+    this.ids[node.source.value] = key;
+    return;
+  } else if (t.isImportBatchSpecifier(specifier)) {
     // import * as bar from "foo";
   } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
     // import foo from "foo";
     ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
   } else {
     // import {foo} from "foo";
-    ref = t.memberExpression(ref, specifier.id, false);
+    ref = t.memberExpression(ref, t.getSpecifierId(specifier), false);
   }
 
   nodes.push(t.variableDeclaration("var", [
@@ -101,16 +99,9 @@ AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
 };
 
 AMDFormatter.prototype.exportDeclaration = function (node) {
-  if (node.default && !this.noInteropExport) {
+  if (this.doDefaultExportInterop(node)) {
     this.passModuleArg = true;
   }
 
   CommonFormatter.prototype.exportDeclaration.apply(this, arguments);
 };
-
-AMDFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  var self = this;
-  return this._exportSpecifier(function () {
-    return self._push(node);
-  }, specifier, node, nodes);
-};

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

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

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

@@ -1,20 +1,18 @@
+"use strict";
+
 module.exports = CommonJSFormatter;
 
 var DefaultFormatter = require("./_default");
-var traverse         = require("../../traverse");
 var util             = require("../../util");
 var t                = require("../../types");
+var _                = require("lodash");
 
 function CommonJSFormatter(file) {
   DefaultFormatter.apply(this, arguments);
 
-  var hasNonDefaultExports = false;
-  traverse(file.ast, {
-    enter: function (node) {
-      if (t.isExportDeclaration(node) && !node.default) hasNonDefaultExports = true;
-    }
-  });
-  this.hasNonDefaultExports = hasNonDefaultExports;
+  if (this.hasNonDefaultExports) {
+    file.ast.program.body.push(util.template("exports-module-declaration", true));
+  }
 }
 
 util.inherits(CommonJSFormatter, DefaultFormatter);
@@ -22,15 +20,14 @@ util.inherits(CommonJSFormatter, DefaultFormatter);
 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var variableName = t.getSpecifierName(specifier);
 
+  var ref = this.getExternalReference(node, nodes);
+
   // import foo from "foo";
   if (t.isSpecifierDefault(specifier)) {
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(variableName,
-        t.callExpression(this.file.addHelper("interop-require"), [util.template("require", {
-          MODULE_NAME: node.source
-        })])
-      )
-    ]));
+    if (!_.contains(this.file.dynamicImported, node)) {
+      ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
+    }
+    nodes.push(t.variableDeclaration("var", [t.variableDeclarator(variableName, ref)]));
   } else {
     if (specifier.type === "ImportBatchSpecifier") {
       // import * as bar from "foo";
@@ -38,17 +35,18 @@ CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes)
         t.variableDeclarator(
           variableName,
           t.callExpression(this.file.addHelper("interop-require-wildcard"), [
-            t.callExpression(t.identifier("require"), [node.source])
+            ref
           ])
         )
       ]));
     } else {
-      // import foo from "foo";
-      nodes.push(util.template("require-assign-key", {
-        VARIABLE_NAME: variableName,
-        MODULE_NAME:   node.source,
-        KEY:           specifier.id
-      }));
+      // import { foo } from "foo";
+      nodes.push(t.variableDeclaration("var", [
+        t.variableDeclarator(
+          variableName,
+          t.memberExpression(ref, t.getSpecifierId(specifier))
+        )
+      ]));
     }
   }
 };
@@ -61,45 +59,35 @@ CommonJSFormatter.prototype.importDeclaration = function (node, nodes) {
 };
 
 CommonJSFormatter.prototype.exportDeclaration = function (node, nodes) {
-  if (node.default && !this.noInteropRequire && !this.noInteropExport) {
+  if (this.doDefaultExportInterop(node)) {
     var declar = node.declaration;
-    var assign;
+    var assign = util.template("exports-default-assign", {
+      VALUE: this._pushStatement(declar, nodes)
+    }, true);
 
-    // module.exports = VALUE;
-    var templateName = "exports-default-module";
-
-    // exports = module.exports = VALUE;
-    if (this.hasNonDefaultExports) templateName = "exports-default-module-override";
-
-    if (t.isFunctionDeclaration(declar) || !this.hasNonDefaultExports) {
-      assign = util.template(templateName, {
-        VALUE: this._pushStatement(declar, nodes)
-      }, true);
-
-      // hoist to the top if this default is a function
-      nodes.push(this._hoistExport(declar, assign, 3));
-      return;
-    } else {
-      // this export isn't a function so we can't hoist it to the top so we need to set it
-      // at the very end of the file with something like:
-      //
-      //   module.exports = _extends(exports["default"], exports)
-      //
-
-      assign = util.template("common-export-default-assign", {
-        EXTENDS_HELPER: this.file.addHelper("extends")
-      }, true);
-      assign._blockHoist = 0;
-
-      nodes.push(assign);
+    if (t.isFunctionDeclaration(declar)) {
+      // we can hoist this assignment to the top of the file
+      assign._blockHoist = 3;
     }
+
+    nodes.push(assign);
+    return;
   }
 
   DefaultFormatter.prototype.exportDeclaration.apply(this, arguments);
 };
 
-CommonJSFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  this._exportSpecifier(function () {
-    return t.callExpression(t.identifier("require"), [node.source]);
-  }, specifier, node, nodes);
+CommonJSFormatter.prototype._getExternalReference = function (node, nodes) {
+  var source = node.source.value;
+  var call = t.callExpression(t.identifier("require"), [node.source]);
+
+  if (this.localImportOccurences[source] > 1) {
+    var uid = this.file.generateUidIdentifier(source);
+    nodes.push(t.variableDeclaration("var", [
+      t.variableDeclarator(uid, call)
+    ]));
+    return uid;
+  } else {
+    return call;
+  }
 };

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

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

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

@@ -0,0 +1,10 @@
+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")
+};

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

@@ -1,17 +1,20 @@
+"use strict";
+
 module.exports = SystemFormatter;
 
-var AMDFormatter = require("./amd");
-var useStrict    = require("../transformers/use-strict");
-var traverse     = require("../../traverse");
-var util         = require("../../util");
-var t            = require("../../types");
-var _            = require("lodash");
+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");
 
 function SystemFormatter(file) {
-  this.exportIdentifier  = file.generateUidIdentifier("export");
+  this.exportIdentifier = file.generateUidIdentifier("export");
   this.noInteropRequire = true;
 
-  AMDFormatter.apply(this, arguments);
+  DefaultFormatter.apply(this, arguments);
 }
 
 util.inherits(SystemFormatter, AMDFormatter);
@@ -21,7 +24,7 @@ SystemFormatter.prototype._addImportSource = function (node, exportNode) {
   return node;
 };
 
-SystemFormatter.prototype._exportsWildcard = function (objectIdentifier, node) {
+SystemFormatter.prototype.buildExportsWildcard = function (objectIdentifier, node) {
   var leftIdentifier = this.file.generateUidIdentifier("key");
   var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
 
@@ -38,7 +41,7 @@ SystemFormatter.prototype._exportsWildcard = function (objectIdentifier, node) {
   return this._addImportSource(t.forInStatement(left, right, block), node);
 };
 
-SystemFormatter.prototype._exportsAssign = function (id, init, node) {
+SystemFormatter.prototype.buildExportsAssignment = function (id, init, node) {
   var call = this.buildExportCall(t.literal(id.name), init, true);
   return this._addImportSource(call, node);
 };
@@ -61,31 +64,95 @@ SystemFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   this._addImportSource(_.last(nodes), node);
 };
 
+var runnerSettersVisitor = {
+  enter: function (node, parent, scope, context, state) {
+    if (node._importSource === state.source) {
+      if (t.isVariableDeclaration(node)) {
+        _.each(node.declarations, function (declar) {
+          state.hoistDeclarators.push(t.variableDeclarator(declar.id));
+          state.nodes.push(t.expressionStatement(
+            t.assignmentExpression("=", declar.id, declar.init)
+          ));
+        });
+      } else {
+        state.nodes.push(node);
+      }
+
+      context.remove();
+    }
+  }
+};
+
 SystemFormatter.prototype.buildRunnerSetters = function (block, hoistDeclarators) {
+  var scope = this.file.scope;
+
   return t.arrayExpression(_.map(this.ids, function (uid, source) {
-    var nodes = [];
+    var state = {
+      source:           source,
+      nodes:            [],
+      hoistDeclarators: hoistDeclarators
+    };
 
-    traverse(block, {
-      enter: function (node) {
-        if (node._importSource === source) {
-          if (t.isVariableDeclaration(node)) {
-            _.each(node.declarations, function (declar) {
-              hoistDeclarators.push(t.variableDeclarator(declar.id));
-              nodes.push(t.expressionStatement(
-                t.assignmentExpression("=", declar.id, declar.init)
-              ));
-            });
-          } else {
-            nodes.push(node);
-          }
+    traverse(block, runnerSettersVisitor, scope, state);
 
-          this.remove();
+    return t.functionExpression(null, [uid], t.blockStatement(state.nodes));
+  }));
+};
+
+var hoistVariablesVisitor = {
+  enter: function (node, parent, scope, context, hoistDeclarators) {
+    if (t.isFunction(node)) {
+      // nothing inside is accessible
+      return context.skip();
+    }
+
+    if (t.isVariableDeclaration(node)) {
+      if (node.kind !== "var" && !t.isProgram(parent)) { // let, const
+        // can't be accessed
+        return;
+      }
+
+      // ignore block hoisted nodes as these can be left in
+      if (node._blockHoist) return;
+
+      var nodes = [];
+
+      for (var i = 0; i < node.declarations.length; i++) {
+        var declar = node.declarations[i];
+        hoistDeclarators.push(t.variableDeclarator(declar.id));
+        if (declar.init) {
+          // no initializer so we can just hoist it as-is
+          var assign = t.expressionStatement(t.assignmentExpression("=", declar.id, declar.init));
+          nodes.push(assign);
         }
       }
-    });
 
-    return t.functionExpression(null, [uid], t.blockStatement(nodes));
-  }));
+      // for (var i in test)
+      // for (var i = 0;;)
+      if (t.isFor(parent)) {
+        if (parent.left === node) {
+          return node.declarations[0].id;
+        }
+
+        if (parent.init === node) {
+          return t.toSequenceExpression(nodes, scope);
+        }
+      }
+
+      return nodes;
+    }
+  }
+};
+
+var hoistFunctionsVisitor = {
+  enter: function (node, parent, scope, context, handlerBody) {
+    if (t.isFunction(node)) context.skip();
+
+    if (t.isFunctionDeclaration(node) || node._blockHoist) {
+      handlerBody.push(node);
+      context.remove();
+    }
+  }
 };
 
 SystemFormatter.prototype.transform = function (ast) {
@@ -111,46 +178,8 @@ SystemFormatter.prototype.transform = function (ast) {
   var returnStatement = handlerBody.pop();
 
   // hoist up all variable declarations
-  traverse(block, {
-    enter: function (node, parent, scope) {
-      if (t.isFunction(node)) {
-        // nothing inside is accessible
-        return this.skip();
-      }
+  traverse(block, hoistVariablesVisitor, this.file.scope, hoistDeclarators);
 
-      if (t.isVariableDeclaration(node)) {
-        if (node.kind !== "var" && !t.isProgram(parent)) { // let, const
-          // can't be accessed
-          return;
-        }
-
-        var nodes = [];
-
-        _.each(node.declarations, function (declar) {
-          hoistDeclarators.push(t.variableDeclarator(declar.id));
-          if (declar.init) {
-            // no initializer so we can just hoist it as-is
-            var assign = t.expressionStatement(t.assignmentExpression("=", declar.id, declar.init));
-            nodes.push(assign);
-          }
-        });
-
-        // for (var i in test)
-        // for (var i = 0;;)
-        if (t.isFor(parent)) {
-          if (parent.left === node) {
-            return node.declarations[0].id;
-          }
-
-          if (parent.init === node) {
-            return t.toSequenceExpression(nodes, scope);
-          }
-        }
-
-        return nodes;
-      }
-    }
-  });
   if (hoistDeclarators.length) {
     var hoistDeclar = t.variableDeclaration("var", hoistDeclarators);
     hoistDeclar._blockHoist = true;
@@ -158,20 +187,11 @@ SystemFormatter.prototype.transform = function (ast) {
   }
 
   // hoist up function declarations for circular references
-  traverse(block, {
-    enter: function (node) {
-      if (t.isFunction(node)) this.skip();
-
-      if (t.isFunctionDeclaration(node) || node._blockHoist) {
-        handlerBody.push(node);
-        this.remove();
-      }
-    }
-  });
+  traverse(block, hoistFunctionsVisitor, this.file.scope, handlerBody);
 
   handlerBody.push(returnStatement);
 
-  if (useStrict._has(block)) {
+  if (useStrict.has(block)) {
     handlerBody.unshift(block.body.shift());
   }
 

lib/6to5/transformation/modules/umd-strict

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

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

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

lib/6to5/transformation/templates/array-comprehension-for-each.js

@@ -1,3 +0,0 @@
-ARRAY.forEach(function (KEY) {
-
-});

lib/6to5/transformation/templates/async-to-generator.js

@@ -3,35 +3,26 @@
     var gen = fn.apply(this, arguments);
 
     return new Promise(function (resolve, reject) {
-      function step(getNext) {
-        var next;
+      var callNext = step.bind(gen.next);
+      var callThrow = step.bind(gen.throw);
 
+      function step(arg) {
         try {
-          next = getNext();
-        } catch(e) {
-          reject(e);
+          var info = this(arg);
+          var value = info.value;
+        } catch (error) {
+          reject(error);
           return;
         }
 
-        if (next.done) {
-          resolve(next.value);
-          return;
+        if (info.done) {
+          resolve(value);
+        } else {
+          Promise.resolve(value).then(callNext, callThrow);
         }
-
-        Promise.resolve(next.value).then(function (v) {
-          step(function () {
-            return gen.next(v);
-          });
-        }, function (e) {
-          step(function () {
-            return gen["throw"](e);
-          });
-        });
       }
 
-      step(function () {
-        return gen.next();
-      });
+      callNext();
     });
-  }
+  };
 })

lib/6to5/transformation/templates/common-export-default-assign.js

@@ -1 +0,0 @@
-module.exports = EXTENDS_HELPER(exports["default"], exports);

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

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

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

@@ -0,0 +1 @@
+exports.__esModule = true;

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

@@ -2,7 +2,9 @@
   for (var i = 1; i < arguments.length; i++) {
     var source = arguments[i];
     for (var key in source) {
-      target[key] = source[key];
+      if (Object.prototype.hasOwnProperty.call(source, key)) {
+        target[key] = source[key];
+      }
     }
   }
   return target;

lib/6to5/transformation/templates/interop-require-wildcard.js

@@ -1,3 +1,3 @@
 (function (obj) {
-  return obj && obj.constructor === Object ? obj : { default: obj };
+  return obj && obj.__esModule ? obj : { default: obj };
 })

lib/6to5/transformation/templates/interop-require.js

@@ -1,3 +1,3 @@
 (function (obj) {
-  return obj && (obj["default"] || obj);
+  return obj && obj.__esModule ? obj.default : obj;
 })

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

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

lib/6to5/transformation/templates/tagged-template-literal.js

@@ -3,4 +3,3 @@
       raw: { value: Object.freeze(raw) }
   }));
 });
-

lib/6to5/transformation/transform.js

@@ -1,6 +1,9 @@
+"use strict";
+
 module.exports = transform;
 
 var Transformer = require("./transformer");
+var object      = require("../helpers/object");
 var File        = require("../file");
 var util        = require("../util");
 var _           = require("lodash");
@@ -19,84 +22,52 @@ transform.fromAst = function (ast, code, opts) {
   return file.generate();
 };
 
-transform._ensureTransformerNames = function (type, keys) {
-  for (var i in keys) {
-    var key = keys[i];
-    if (!_.has(transform.transformers, key)) {
-      throw new ReferenceError("unknown transformer " + key + " specified in " + type);
+transform._ensureTransformerNames = function (type, rawKeys) {
+  var keys = [];
+
+  for (var i = 0; i < rawKeys.length; i++) {
+    var key = rawKeys[i];
+
+    var deprecatedKey = transform.deprecatedTransformerMap[key];
+    if (deprecatedKey) {
+      // deprecated key, remap it to the new one
+      console.error(
+        "The transformer " + key + " has been renamed to " + deprecatedKey +
+        " in v3.0.0 - backwards compatibilty will be removed 4.0.0"
+      );
+      rawKeys.push(deprecatedKey);
+    } else if (transform.transformers[key]) {
+      // valid key
+      keys.push(key);
+    } else if (transform.namespaces[key]) {
+      // namespace, append all transformers within this namespace
+      keys = keys.concat(transform.namespaces[key]);
+    } else {
+      // invalid key
+      throw new ReferenceError(
+        "Unknown transformer " + key + " specified in " + type + " - " +
+        "transformer key names have been changed in 3.0.0 see " +
+        "the changelog for more info " +
+        "https://github.com/6to5/6to5/blob/master/CHANGELOG.md#300"
+      );
     }
   }
+
+  return keys;
 };
 
-transform.transformers = {};
+transform.transformers = object();
+transform.namespaces   = object();
 
-transform.moduleFormatters = {
-  commonStrict: require("./modules/common-strict"),
-  umdStrict:    require("./modules/umd-strict"),
-  amdStrict:    require("./modules/amd-strict"),
-  common:       require("./modules/common"),
-  system:       require("./modules/system"),
-  ignore:       require("./modules/ignore"),
-  amd:          require("./modules/amd"),
-  umd:          require("./modules/umd")
-};
+transform.deprecatedTransformerMap = require("./transformers/deprecated");
+transform.moduleFormatters = require("./modules");
 
-_.each({
-  specNoForInOfAssignment:   require("./transformers/spec-no-for-in-of-assignment"),
-  specSetters:               require("./transformers/spec-setters"),
+var rawTransformers = require("./transformers");
 
-  // playground
-  methodBinding:             require("./transformers/playground-method-binding"),
-  memoizationOperator:       require("./transformers/playground-memoization-operator"),
-  objectGetterMemoization:   require("./transformers/playground-object-getter-memoization"),
+_.each(rawTransformers, function (transformer, key) {
+  var namespace = key.split(".")[0];
+  transform.namespaces[namespace] = transform.namespaces[namespace] || [];
+  transform.namespaces[namespace].push(key);
 
-  asyncToGenerator:          require("./transformers/optional-async-to-generator"),
-  bluebirdCoroutines:        require("./transformers/optional-bluebird-coroutines"),
-
-  react:                     require("./transformers/react"),
-  modules:                   require("./transformers/es6-modules"),
-  propertyNameShorthand:     require("./transformers/es6-property-name-shorthand"),
-  arrayComprehension:        require("./transformers/es7-array-comprehension"),
-  generatorComprehension:    require("./transformers/es7-generator-comprehension"),
-  arrowFunctions:            require("./transformers/es6-arrow-functions"),
-  classes:                   require("./transformers/es6-classes"),
-
-  objectSpread:              require("./transformers/es7-object-spread"),
-  exponentiationOperator:    require("./transformers/es7-exponentiation-operator"),
-  spread:                    require("./transformers/es6-spread"),
-  templateLiterals:          require("./transformers/es6-template-literals"),
-  propertyMethodAssignment:  require("./transformers/es6-property-method-assignment"),
-  computedPropertyNames:     require("./transformers/es6-computed-property-names"),
-  destructuring:             require("./transformers/es6-destructuring"),
-  defaultParameters:         require("./transformers/es6-default-parameters"),
-  forOf:                     require("./transformers/es6-for-of"),
-  unicodeRegex:              require("./transformers/es6-unicode-regex"),
-  abstractReferences:        require("./transformers/es7-abstract-references"),
-
-  constants:                 require("./transformers/es6-constants"),
-  letScoping:                require("./transformers/es6-let-scoping"),
-
-  _blockHoist:               require("./transformers/_block-hoist"),
-
-  generators:                require("./transformers/es6-generators"),
-  restParameters:            require("./transformers/es6-rest-parameters"),
-
-  protoToAssign:             require("./transformers/optional-proto-to-assign"),
-
-  _declarations:             require("./transformers/_declarations"),
-
-  // wrap up
-  useStrict:                 require("./transformers/use-strict"),
-  _aliasFunctions:           require("./transformers/_alias-functions"),
-  _moduleFormatter:          require("./transformers/_module-formatter"),
-
-  typeofSymbol:              require("./transformers/optional-typeof-symbol"),
-  coreAliasing:              require("./transformers/optional-core-aliasing"),
-  undefinedToVoid:           require("./transformers/optional-undefined-to-void"),
-
-  // spec
-  specPropertyLiterals:         require("./transformers/spec-property-literals"),
-  specMemberExpressionLiterals: require("./transformers/spec-member-expression-literals")
-}, function (transformer, key) {
   transform.transformers[key] = new Transformer(key, transformer);
 });

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

@@ -0,0 +1,69 @@
+module.exports = TransformerPass;
+
+var traverse = require("../traverse");
+var _        = require("lodash");
+
+/**
+ * This class is responsible for traversing over the provided `File`s
+ * AST and running it's parent transformers handlers over it.
+ */
+
+function TransformerPass(file, transformer) {
+  this.transformer = transformer;
+  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;
+  if (key[0] === "_") return true;
+
+  var blacklist = opts.blacklist;
+  if (blacklist.length && _.contains(blacklist, key)) return false;
+
+  var whitelist = opts.whitelist;
+  if (whitelist.length && !_.contains(whitelist, key)) return false;
+
+  if (transformer.optional && !_.contains(opts.optional, key)) return false;
+
+  if (transformer.experimental && !opts.experimental) 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.transform = function () {
+  var file = this.file;
+
+  this.astRun("before");
+
+  var state = { file: file, handlers: this.handlers, pass: this };
+  traverse(file.ast, transformVisitor, file.scope, state);
+
+  this.astRun("after");
+};

lib/6to5/transformation/transformer.js

@@ -1,15 +1,23 @@
+"use strict";
+
 module.exports = Transformer;
 
-var traverse = require("../traverse");
-var t        = require("../types");
-var _        = require("lodash");
+var TransformerPass = require("./transformer-pass");
+var t               = require("../types");
+var _               = require("lodash");
+
+/**
+ * This is the class responsible for normalising a transformers handlers
+ * as well as constructing a `TransformerPass` that is repsonsible for
+ * actually running the transformer over the provided `File`.
+ */
 
 function Transformer(key, transformer, opts) {
   this.manipulateOptions = transformer.manipulateOptions;
   this.experimental      = !!transformer.experimental;
   this.secondPass        = !!transformer.secondPass;
-  this.transformer       = this.normalise(transformer);
   this.optional          = !!transformer.optional;
+  this.handlers          = this.normalise(transformer);
   this.opts              = opts || {};
   this.key               = key;
 }
@@ -32,6 +40,9 @@ Transformer.prototype.normalise = function (transformer) {
 
     if (!_.isObject(fns)) return;
 
+    if (!fns.enter) fns.enter = _.noop;
+    if (!fns.exit) fns.exit = _.noop;
+
     transformer[type] = fns;
 
     var aliases = t.FLIPPED_ALIAS_KEYS[type];
@@ -45,54 +56,6 @@ Transformer.prototype.normalise = function (transformer) {
   return transformer;
 };
 
-Transformer.prototype.astRun = function (file, key) {
-  var transformer = this.transformer;
-
-  if (transformer.ast && transformer.ast[key]) {
-    transformer.ast[key](file.ast, file);
-  }
-};
-
-Transformer.prototype.transform = function (file) {
-  var transformer = this.transformer;
-
-  var build = function (exit) {
-    return function (node, parent, scope) {
-      var fns = transformer[node.type];
-      if (!fns) return;
-
-      var fn = fns.enter;
-      if (exit) fn = fns.exit;
-      if (!fn) return;
-
-      return fn.call(this, node, parent, file, scope);
-    };
-  };
-
-  this.astRun(file, "before");
-
-  traverse(file.ast, {
-    enter: build(),
-    exit:  build(true)
-  });
-
-  this.astRun(file, "after");
-};
-
-Transformer.prototype.canRun = function (file) {
-  var opts = file.opts;
-  var key  = this.key;
-  if (key[0] === "_") return true;
-
-  var blacklist = opts.blacklist;
-  if (blacklist.length && _.contains(blacklist, key)) return false;
-
-  var whitelist = opts.whitelist;
-  if (whitelist.length && !_.contains(whitelist, key)) return false;
-
-  if (this.optional && !_.contains(opts.optional, key)) return false;
-
-  if (this.experimental && !opts.experimental) return false;
-
-  return true;
+Transformer.prototype.buildPass = function (file) {
+  return new TransformerPass(file, this);
 };

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

@@ -1,86 +0,0 @@
-var traverse = require("../../traverse");
-var t        = require("../../types");
-
-var go = function (getBody, node, file, scope) {
-  var argumentsId;
-  var thisId;
-
-  var getArgumentsId = function () {
-    return argumentsId = argumentsId || file.generateUidIdentifier("arguments", scope);
-  };
-
-  var getThisId = function () {
-    return thisId = thisId || file.generateUidIdentifier("this", scope);
-  };
-
-  // traverse the function and find all alias functions so we can alias
-  // `arguments` and `this` if necessary
-  traverse(node, {
-    enter: function (node) {
-      if (!node._aliasFunction) {
-        if (t.isFunction(node)) {
-          // stop traversal of this node as it'll be hit again by this transformer
-          return this.skip();
-        } else {
-          return;
-        }
-      }
-
-      // traverse all child nodes of this function and find `arguments` and `this`
-      traverse(node, {
-        enter: function (node, parent) {
-          if (t.isFunction(node) && !node._aliasFunction) {
-            return this.skip();
-          }
-
-          if (node._ignoreAliasFunctions) return this.skip();
-
-          var getId;
-
-          if (t.isIdentifier(node) && node.name === "arguments") {
-            getId = getArgumentsId;
-          } else if (t.isThisExpression(node)) {
-            getId = getThisId;
-          } else {
-            return;
-          }
-
-          if (t.isReferenced(node, parent)) return getId();
-        }
-      });
-
-      return this.skip();
-    }
-  });
-
-  var body;
-
-  var pushDeclaration = function (id, init) {
-    body = body || getBody();
-    body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(id, init)
-    ]));
-  };
-
-  if (argumentsId) {
-    pushDeclaration(argumentsId, t.identifier("arguments"));
-  }
-
-  if (thisId) {
-    pushDeclaration(thisId, t.thisExpression());
-  }
-};
-
-exports.Program = function (node, parent, file, scope) {
-  go(function () {
-    return node.body;
-  }, node, file, scope);
-};
-
-exports.FunctionDeclaration =
-exports.FunctionExpression = function (node, parent, file, scope) {
-  go(function () {
-    t.ensureBlock(node);
-    return node.body.body;
-  }, node, file, scope);
-};

lib/6to5/transformation/transformers/_module-formatter.js

@@ -1,11 +0,0 @@
-var transform = require("../transform");
-
-exports.ast = {
-  exit: function (ast, file) {
-    if (!transform.transformers.modules.canRun(file)) return;
-
-    if (file.moduleFormatter.transform) {
-      file.moduleFormatter.transform(ast);
-    }
-  }
-};

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

@@ -0,0 +1,38 @@
+{
+  "specNoForInOfAssignment": "validation.noForInOfAssignment",
+  "specSetters": "validation.setters",
+  "specBlockScopedFunctions": "spec.blockScopedFunctions",
+  "malletOperator": "playground.malletOperator",
+  "methodBinding": "playground.methodBinding",
+  "memoizationOperator": "playground.memoizationOperator",
+  "objectGetterMemoization": "playground.objectGetterMemoization",
+  "modules": "es6.modules",
+  "propertyNameShorthand": "es6.properties.shorthand",
+  "arrayComprehension": "es7.comprehensions",
+  "generatorComprehension": "es7.comprehensions",
+  "arrowFunctions": "es6.arrowFunctions",
+  "classes": "es6.classes",
+  "objectSpread": "es7.objectSpread",
+  "exponentiationOperator": "es7.exponentiationOperator",
+  "spread": "es6.spread",
+  "templateLiterals": "es6.templateLiterals",
+  "propertyMethodAssignment": "es6.properties.shorthand",
+  "computedPropertyNames": "es6.properties.computed",
+  "defaultParameters": "es6.parameters.default",
+  "restParameters": "es6.parameters.rest",
+  "destructuring": "es6.destructuring",
+  "forOf": "es6.forOf",
+  "unicodeRegex": "es6.unicodeRegex",
+  "abstractReferences": "es7.abstractReferences",
+  "constants": "es6.constants",
+  "letScoping": "es6.letScoping",
+  "blockScopingTDZ": "es6.blockScopingTDZ",
+  "generators": "regenerator",
+  "protoToAssign": "spec.protoToAssign",
+  "typeofSymbol": "spec.typeofSymbol",
+  "coreAliasing": "selfContained",
+  "undefinedToVoid": "spec.undefinedToVoid",
+  "undeclaredVariableCheck": "validation.undeclaredVariableCheck",
+  "specPropertyLiterals": "minification.propertyLiterals",
+  "specMemberExpressionLiterals": "minification.memberExpressionLiterals"
+}

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

@@ -0,0 +1,26 @@
+"use strict";
+
+var util = require("../../../util");
+var t    = require("../../../types");
+
+exports.ObjectExpression = function (node) {
+  var mutatorMap = {};
+  var hasAny = false;
+
+  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);
+      return false;
+    } else {
+      return true;
+    }
+  });
+
+  if (!hasAny) return;
+
+  return t.callExpression(
+    t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
+    [node, util.buildDefineProperties(mutatorMap)]
+  );
+};

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

@@ -1,436 +0,0 @@
-var propertyMethodAssignment = require("./es6-property-method-assignment");
-var traverse                 = require("../../traverse");
-var util                     = require("../../util");
-var t                        = require("../../types");
-
-exports.ClassDeclaration = function (node, parent, file, scope) {
-  return new Class(node, file, scope, true).run();
-};
-
-exports.ClassExpression = function (node, parent, file, scope) {
-  if (!node.id) {
-    if (t.isProperty(parent) && parent.value === node && !parent.computed && t.isIdentifier(parent.key)) {
-      // var o = { foo: class {} };
-      node.id = parent.key;
-    }
-
-    if (t.isVariableDeclarator(parent)) {
-      node.id = parent.id;
-    }
-  }
-
-  return new Class(node, file, scope, false).run();
-};
-
-/**
- * Description
- *
- * @param {Node} node
- * @param {File} file
- * @param {Scope} scope
- * @param {Boolean} closure
- */
-
-function Class(node, file, scope, isStatement) {
-  this.isStatement = isStatement;
-  this.scope       = scope;
-  this.node        = node;
-  this.file        = file;
-
-  this.hasInstanceMutators = false;
-  this.hasStaticMutators   = false;
-
-  this.instanceMutatorMap = {};
-  this.staticMutatorMap   = {};
-  this.hasConstructor     = false;
-  this.className          = node.id || file.generateUidIdentifier("class", scope);
-  this.superName          = node.superClass;
-  this.isLoose            = file.isLoose("classes");
-}
-
-/**
- * Description
- *
- * @returns {Array}
- */
-
-Class.prototype.run = function () {
-  var superName = this.superName;
-  var className = this.className;
-  var file      = this.file;
-
-  //
-
-  var body = this.body = [];
-
-  var constructor;
-  if (this.node.id) {
-    constructor = t.functionDeclaration(className, [], t.blockStatement([]));
-    body.push(constructor);
-  } else {
-    constructor = t.functionExpression(null, [], t.blockStatement([]));
-    body.push(t.variableDeclaration("var", [
-      t.variableDeclarator(className, constructor)
-    ]));
-  }
-  this.constructor = constructor;
-
-  var closureParams = [];
-  var closureArgs = [];
-
-  //
-
-  if (superName) {
-    closureArgs.push(superName);
-
-    if (!t.isIdentifier(superName)) {
-      var superRef = this.scope.generateUidBasedOnNode(superName, this.file);
-      superName = superRef;
-    }
-
-    closureParams.push(superName);
-
-    this.superName = superName;
-    body.push(t.expressionStatement(t.callExpression(file.addHelper("inherits"), [className, superName])));
-  }
-
-  this.buildBody();
-
-  t.inheritsComments(body[0], this.node);
-
-  var init;
-
-  if (body.length === 1) {
-    // only a constructor so no need for a closure container
-    init = t.toExpression(constructor);
-  } else {
-    body.push(t.returnStatement(className));
-    init = t.callExpression(
-      t.functionExpression(null, closureParams, t.blockStatement(body)),
-      closureArgs
-    );
-  }
-
-  if (this.isStatement) {
-    return t.variableDeclaration("let", [
-      t.variableDeclarator(className, init)
-    ]);
-  } else {
-    return init;
-  }
-};
-
-/**
- * Description
- */
-
-Class.prototype.buildBody = function () {
-  var constructor = this.constructor;
-  var className   = this.className;
-  var superName   = this.superName;
-  var classBody   = this.node.body.body;
-  var body        = this.body;
-
-  for (var i in classBody) {
-    var node = classBody[i];
-    if (t.isMethodDefinition(node)) {
-      this.replaceInstanceSuperReferences(node);
-
-      if (node.key.name === "constructor") {
-        this.pushConstructor(node);
-      } else {
-        this.pushMethod(node);
-      }
-    } else if (t.isPrivateDeclaration(node)) {
-      this.closure = true;
-      body.unshift(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, {
-      CLASS_NAME: className,
-      SUPER_NAME: this.superName
-    }, true));
-  }
-
-  var instanceProps;
-  var staticProps;
-
-  if (this.hasInstanceMutators) {
-    instanceProps = util.buildDefineProperties(this.instanceMutatorMap);
-  }
-
-  if (this.hasStaticMutators) {
-    staticProps = util.buildDefineProperties(this.staticMutatorMap);
-  }
-
-  if (instanceProps || staticProps) {
-    staticProps = staticProps || t.literal(null);
-
-    var args = [className, staticProps];
-    if (instanceProps) args.push(instanceProps);
-
-    body.push(t.expressionStatement(
-      t.callExpression(this.file.addHelper("prototype-properties"), args)
-    ));
-  }
-};
-
-/**
- * Push a method to it's respective mutatorMap.
- *
- * @param {Node} node MethodDefinition
- */
-
-Class.prototype.pushMethod = function (node) {
-  var methodName = node.key;
-
-  var kind = node.kind;
-
-  if (kind === "") {
-    propertyMethodAssignment._namedMethod(node, this.file, this.scope);
-
-    if (this.isLoose) {
-      // use assignments instead of define properties for loose classes
-
-      var className = this.className;
-      if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
-      methodName = t.memberExpression(className, methodName, node.computed);
-
-      var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
-      t.inheritsComments(expr, node);
-      this.body.push(expr);
-      return;
-    }
-
-    kind = "value";
-  }
-
-  var mutatorMap = this.instanceMutatorMap;
-  if (node.static) {
-    this.hasStaticMutators = true;
-    mutatorMap = this.staticMutatorMap;
-  } else {
-    this.hasInstanceMutators = true;
-  }
-
-  util.pushMutatorMap(mutatorMap, methodName, kind, node.computed, node);
-};
-
-/**
- * Gets a node representing the super class value of the named property.
- *
- * @example
- *
- *   _get(Object.getPrototypeOf(CLASS.prototype), "METHOD", this)
- *
- * @param {Node} property
- * @param {boolean} isStatic
- * @param {boolean} isComputed
- *
- * @returns {Node}
- */
-
-Class.prototype.superProperty = function (property, isStatic, 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"))
-        ]
-      ),
-      isComputed ? property : t.literal(property.name),
-      thisExpression
-    ]
-  );
-};
-
-/**
- * Description
- *
- * @param {Object} node
- * @param {Object} id
- * @param {Object} parent
- * @returns {Object}
- */
-
-Class.prototype.looseSuperProperty = function (methodNode, id, parent) {
-  var methodName = methodNode.key;
-  var superName  = this.superName || t.identifier("Function");
-
-  if (parent.property === id) {
-    return;
-  } else if (t.isCallExpression(parent, { callee: id })) {
-    // super(); -> ClassName.prototype.MethodName.call(this);
-    parent.arguments.unshift(t.thisExpression());
-
-    if (methodName.name === "constructor") {
-      // constructor() { super(); }
-      return t.memberExpression(superName, t.identifier("call"));
-    } else {
-      id = superName;
-
-      // foo() { super(); }
-      if (!methodNode.static) {
-        id = t.memberExpression(id, t.identifier("prototype"));
-      }
-
-      id = t.memberExpression(id, methodName, methodNode.computed);
-      return t.memberExpression(id, t.identifier("call"));
-    }
-  } else if (t.isMemberExpression(parent) && !methodNode.static) {
-    // super.test -> ClassName.prototype.test
-    return t.memberExpression(superName, t.identifier("prototype"));
-  } else {
-    return superName;
-  }
-};
-
-/**
- * Replace all `super` references with a reference to our `superClass`.
- *
- * @param {Node} methodNode MethodDefinition
- */
-
-Class.prototype.replaceInstanceSuperReferences = function (methodNode) {
-  var method = methodNode.value;
-  var self   = this;
-
-  var topLevelThisReference;
-
-  traverseLevel(method, true);
-
-  if (topLevelThisReference) {
-    method.body.body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(topLevelThisReference, t.thisExpression())
-    ]));
-  }
-
-  function traverseLevel(node, topLevel) {
-    traverse(node, {
-      enter: function (node, parent) {
-        if (t.isFunction(node) && !t.isArrowFunctionExpression(node)) {
-          // we need to call traverseLevel again so we're context aware
-          traverseLevel(node, false);
-          return this.skip();
-        }
-
-        var getThisReference = function () {
-          if (topLevel) {
-            // top level so `this` is the instance
-            return t.thisExpression();
-          } else {
-            // not in the top level so we need to create a reference
-            return topLevelThisReference = topLevelThisReference || self.file.generateUidIdentifier("this");
-          }
-        };
-
-        var callback = specHandle;
-        if (self.isLoose) callback = looseHandle;
-        return callback(getThisReference, node, parent);
-      }
-    });
-  }
-
-  function looseHandle(getThisReference, node, parent) {
-    if (t.isIdentifier(node, { name: "super" })) {
-      return self.looseSuperProperty(methodNode, 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);
-      t.appendToMemberExpression(callee, t.identifier("call"));
-      node.arguments.unshift(getThisReference());
-    }
-  }
-
-  function specHandle(getThisReference, node, parent) {
-    var property;
-    var computed;
-    var args;
-
-    if (t.isIdentifier(node, { name: "super" })) {
-      if (!(t.isMemberExpression(parent) && !parent.computed && parent.property === node)) {
-        throw self.file.errorWithNode(node, "illegal use of bare super");
-      }
-    } else if (t.isCallExpression(node)) {
-      var callee = node.callee;
-      if (t.isIdentifier(callee, { name: "super" })) {
-        // super(); -> _get(Object.getPrototypeOf(ClassName), "MethodName", this).call(this);
-        property = methodNode.key;
-        computed = methodNode.computed;
-        args = node.arguments;
-      } else {
-        if (!t.isMemberExpression(callee)) return;
-        if (callee.object.name !== "super") return;
-
-        // 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;
-
-      // super.name; -> _get(Object.getPrototypeOf(ClassName.prototype), "name", this);
-      property = node.property;
-      computed = node.computed;
-    }
-
-    if (!property) return;
-
-    var thisReference = getThisReference();
-    var superProperty = self.superProperty(property, methodNode.static, computed, thisReference);
-    if (args) {
-      if (args.length === 1 && t.isSpreadElement(args[0])) {
-        // super(...arguments);
-        return t.callExpression(
-          t.memberExpression(superProperty, t.identifier("apply")),
-          [thisReference, args[0].argument]
-        );
-      } else {
-        return t.callExpression(
-          t.memberExpression(superProperty, t.identifier("call")),
-          [thisReference].concat(args)
-        );
-      }
-    } else {
-      return superProperty;
-    }
-  }
-};
-
-/**
- * Replace the constructor body of our class.
- *
- * @param {Node} method MethodDefinition
- */
-
-Class.prototype.pushConstructor = function (method) {
-  if (method.kind) {
-    throw this.file.errorWithNode(method, "illegal kind for constructor method");
-  }
-
-  var construct = this.constructor;
-  var fn        = method.value;
-
-  this.hasConstructor = true;
-
-  t.inherits(construct, fn);
-  t.inheritsComments(construct, method);
-
-  construct._ignoreUserWhitespace = true;
-  construct.defaults              = fn.defaults;
-  construct.params                = fn.params;
-  construct.body                  = fn.body;
-  construct.rest                  = fn.rest;
-};

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

@@ -1,82 +0,0 @@
-var traverse = require("../../traverse");
-var t        = require("../../types");
-var _        = require("lodash");
-
-exports.Program =
-exports.BlockStatement =
-exports.ForInStatement =
-exports.ForOfStatement =
-exports.ForStatement = function (node, parent, file) {
-  var hasConstants = false;
-  var constants = {};
-
-  /**
-   * Check the results of `util.getIds` as `names` generated from a
-   * node against it's parent.
-   */
-
-  var check = function (parent, names, scope) {
-    for (var name in names) {
-      var nameNode = names[name];
-      if (!_.has(constants, name)) continue;
-      if (parent && t.isBlockStatement(parent) && parent !== constants[name]) continue;
-
-      if (scope) {
-        var defined = scope.get(name);
-        if (defined && defined === nameNode) continue;
-      }
-
-      throw file.errorWithNode(nameNode, name + " is read-only");
-    }
-  };
-
-  var getIds = function (node) {
-    return t.getIds(node, true, ["MemberExpression"]);
-  };
-
-  /**
-   * Collect all constants in this scope.
-   */
-
-  _.each(node.body, function (child, parent) {
-    if (t.isExportDeclaration(child)) {
-      child = child.declaration;
-    }
-
-    if (t.isVariableDeclaration(child, { kind: "const" })) {
-      for (var i in child.declarations) {
-        var declar = child.declarations[i];
-
-        var ids = getIds(declar);
-        for (var name in ids) {
-          var nameNode = ids[name];
-
-          var names = {};
-          names[name] = nameNode;
-          check(parent, names);
-
-          constants[name] = parent;
-          hasConstants = true;
-        }
-
-        declar._ignoreConstant = true;
-      }
-
-      child._ignoreConstant = true;
-      child.kind = "let";
-    }
-  });
-
-  if (!hasConstants) return;
-
-  traverse(node, {
-    enter: function (child, parent, scope) {
-      if (child._ignoreConstant) return;
-      if (t.isVariableDeclaration(child)) return;
-
-      if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-        check(parent, getIds(child), scope);
-      }
-    }
-  });
-};

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

@@ -1,91 +0,0 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
-
-exports.Function = function (node, parent, file, scope) {
-  if (!node.defaults || !node.defaults.length) return;
-  t.ensureBlock(node);
-
-  var ids = node.params.map(function (param) {
-    return t.getIds(param);
-  });
-
-  var iife = false;
-  var i;
-  var def;
-
-  var checkTDZ = function (ids) {
-    var check = function (node, parent) {
-      if (!t.isIdentifier(node) || !t.isReferenced(node, parent)) return;
-
-      if (ids.indexOf(node.name) >= 0) {
-        throw file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
-      }
-
-      if (scope.has(node.name, true)) {
-        iife = true;
-      }
-    };
-
-    check(def, node);
-    traverse(def, { enter: check });
-  };
-
-  for (i in node.defaults) {
-    def = node.defaults[i];
-    if (!def) continue;
-
-    var param = node.params[i];
-
-    // temporal dead zone check - here we prevent accessing of params that
-    // are to the right - ie. uninitialized parameters
-    var rightIds = ids.slice(i);
-    for (i in rightIds) {
-      checkTDZ(rightIds[i]);
-    }
-
-    // we're accessing a variable that's already defined within this function
-    var has = scope.get(param.name, true);
-    if (has && node.params.indexOf(has) < 0) {
-      iife = true;
-    }
-  }
-
-  var body = [];
-
-  var argsIdentifier = t.identifier("arguments");
-  argsIdentifier._ignoreAliasFunctions = true;
-
-  var lastNonDefaultParam = 0;
-
-  for (i in node.defaults) {
-    def = node.defaults[i];
-    if (!def) {
-      lastNonDefaultParam = +i + 1;
-      continue;
-    }
-
-    body.push(util.template("default-parameter", {
-      VARIABLE_NAME: node.params[i],
-      DEFAULT_VALUE: def,
-      ARGUMENT_KEY:  t.literal(+i),
-      ARGUMENTS:     argsIdentifier
-    }, true));
-  }
-
-  // we need to cut off all trailing default parameters
-  node.params = node.params.slice(0, lastNonDefaultParam);
-
-  if (iife) {
-    var container = t.functionExpression(null, [], node.body, node.generator);
-    container._aliasFunction = true;
-
-    body.push(t.returnStatement(t.callExpression(container, [])));
-
-    node.body = t.blockStatement(body);
-  } else {
-    node.body.body = body.concat(node.body.body);
-  }
-
-  node.defaults = [];
-};

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

@@ -1,497 +0,0 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
-var _        = require("lodash");
-
-var isLet = function (node, parent) {
-  if (!t.isVariableDeclaration(node)) return false;
-  if (node._let) return true;
-  if (node.kind !== "let") return false;
-
-  // https://github.com/6to5/6to5/issues/255
-  if (!t.isFor(parent) || t.isFor(parent) && parent.left !== node) {
-    _.each(node.declarations, function (declar) {
-      declar.init = declar.init || t.identifier("undefined");
-    });
-  }
-
-  node._let = true;
-  node.kind = "var";
-  return true;
-};
-
-var isVar = function (node, parent) {
-  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node, parent);
-};
-
-var standardiseLets = function (declars) {
-  for (var i in declars) {
-    delete declars[i]._let;
-  }
-};
-
-exports.VariableDeclaration = function (node, parent) {
-  isLet(node, parent);
-};
-
-exports.Loop = function (node, parent, file, scope) {
-  var init = node.left || node.init;
-  if (isLet(init, node)) {
-    t.ensureBlock(node);
-    node.body._letDeclars = [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, file, scope);
-  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);
-  }
-};
-
-exports.BlockStatement = function (block, parent, file, scope) {
-  if (!t.isLoop(parent)) {
-    var letScoping = new LetScoping(false, block, parent, file, scope);
-    letScoping.run();
-  }
-};
-
-/**
- * Description
- *
- * @param {Boolean|Node} loopParent
- * @param {Node} block
- * @param {Node} parent
- * @param {File} file
- * @param {Scope} scope
- */
-
-function LetScoping(loopParent, block, parent, file, scope) {
-  this.loopParent = loopParent;
-  this.parent     = parent;
-  this.scope      = scope;
-  this.block      = block;
-  this.file       = file;
-
-  this.letReferences = {};
-  this.body          = [];
-}
-
-/**
- * Start the ball rolling.
- */
-
-LetScoping.prototype.run = function () {
-  var block = this.block;
-
-  if (block._letDone) return;
-  block._letDone = true;
-
-  this.info = this.getInfo();
-
-  // remap all let references that exist in upper scopes to their uid
-  this.remap();
-
-  // this is a block within a `Function` so we can safely leave it be
-  if (t.isFunction(this.parent)) return this.noClosure();
-
-  // this block has no let references so let's clean up
-  if (!this.info.keys.length) return this.noClosure();
-
-  // returns whether or not there are any outside let references within any
-  // functions
-  var referencesInClosure = this.getLetReferences();
-
-  // no need for a closure so let's clean up
-  if (!referencesInClosure) return this.noClosure();
-
-  // if we're inside of a for loop then we search to see if there are any
-  // `break`s, `continue`s, `return`s etc
-  this.has = this.checkLoop();
-
-  // hoist var references to retain scope
-  this.hoistVarDeclarations();
-
-  // set let references to plain var references
-  standardiseLets(this.info.declarators);
-
-  // turn letReferences into an array
-  var letReferences = _.values(this.letReferences);
-
-  // build the closure that we're going to wrap the block with
-  var fn = t.functionExpression(null, letReferences, t.blockStatement(block.body));
-  fn._aliasFunction = true;
-
-  // replace the current block body with the one we're going to build
-  block.body = this.body;
-
-  // change upper scope references with their uid if they have one
-  var params = this.getParams(letReferences);
-
-  // build a call and a unique id that we can assign the return value to
-  var call = t.callExpression(fn, params);
-  var ret  = this.file.generateUidIdentifier("ret", this.scope);
-
-  var hasYield = traverse.hasType(fn.body, "YieldExpression", t.FUNCTION_TYPES);
-  if (hasYield) {
-    fn.generator = true;
-    call = t.yieldExpression(call, true);
-  }
-
-  this.build(ret, call);
-};
-
-/**
- * There are no let references accessed within a closure so we can just turn the
- * lets into vars.
- */
-
-LetScoping.prototype.noClosure = function () {
-  standardiseLets(this.info.declarators);
-};
-
-/**
- * Traverse through block and replace all references that exist in a higher
- * scope to their uids.
- */
-
-LetScoping.prototype.remap = function () {
-  var replacements = this.info.duplicates;
-  var block        = this.block;
-
-  if (!this.info.hasDuplicates) return;
-
-  var replace = function (node, parent, scope) {
-    if (!t.isIdentifier(node)) return;
-    if (!t.isReferenced(node, parent)) return;
-    if (scope && scope.hasOwn(node.name)) return;
-    node.name = replacements[node.name] || node.name;
-  };
-
-  var traverseReplace = function (node, parent) {
-    replace(node, parent);
-    traverse(node, { enter: replace });
-  };
-
-  var loopParent = this.loopParent;
-  if (loopParent) {
-    traverseReplace(loopParent.right, loopParent);
-    traverseReplace(loopParent.test, loopParent);
-    traverseReplace(loopParent.update, loopParent);
-  }
-
-  traverse(block, { enter: replace });
-};
-
-/**
- * Description
- *
- * @returns {Object}
- */
-
-LetScoping.prototype.getInfo = function () {
-  var block = this.block;
-  var scope = this.scope;
-  var file  = this.file;
-
-  var opts = {
-    // array of `Identifier` names of let variables that appear lexically out of
-    // this scope but should be accessible - eg. `ForOfStatement`.left
-    outsideKeys: [],
-
-    // array of let `VariableDeclarator`s that are a part of this block
-    declarators: block._letDeclars || [],
-
-    // object of duplicate ids and their aliases - if there's an `Identifier`
-    // name that's used in an upper scope we generate a unique id and replace
-    // all references with it
-    duplicates:  {},
-
-    hasDuplicates: false,
-
-    // array of `Identifier` names of let variables that are accessible within
-    // the current block
-    keys:        []
-  };
-
-  var duplicates = function (id, key) {
-    var has = scope.parentGet(key);
-
-    if (has && has !== id) {
-      // there's a variable with this exact name in an upper scope so we need
-      // to generate a new name
-      opts.duplicates[key] = id.name = file.generateUid(key, scope);
-      opts.hasDuplicates = true;
-    }
-  };
-
-  var i;
-  var declar;
-
-  for (i in opts.declarators) {
-    declar = opts.declarators[i];
-    opts.declarators.push(declar);
-
-    var keys = t.getIds(declar, true);
-    _.each(keys, duplicates);
-    keys = Object.keys(keys);
-
-    opts.outsideKeys = opts.outsideKeys.concat(keys);
-    opts.keys = opts.keys.concat(keys);
-  }
-
-  for (i in block.body) {
-    declar = block.body[i];
-    if (!isLet(declar, block)) continue;
-
-    var declars = t.getIds(declar, true);
-    for (var key in declars) {
-      duplicates(declars[key], key);
-      opts.keys.push(key);
-    }
-  }
-
-  return opts;
-};
-
-/**
- * If we're inside of a loop then traverse it and check if it has one of
- * the following node types `ReturnStatement`, `BreakStatement`,
- * `ContinueStatement` and replace it with a return value that we can track
- * later on.
- *
- * @returns {Object}
- */
-
-LetScoping.prototype.checkLoop = function () {
-  var has = {
-    hasContinue: false,
-    hasReturn:   false,
-    hasBreak:    false,
-  };
-
-  traverse(this.block, {
-    enter: function (node, parent) {
-      var replace;
-
-      if (t.isFunction(node) || t.isLoop(node)) {
-        return this.skip();
-      }
-
-      if (node && !node.label) {
-        if (t.isBreakStatement(node)) {
-          if (t.isSwitchCase(parent)) return;
-
-          has.hasBreak = true;
-          replace = t.returnStatement(t.literal("break"));
-        } else if (t.isContinueStatement(node)) {
-          has.hasContinue = true;
-          replace = t.returnStatement(t.literal("continue"));
-        }
-      }
-
-      if (t.isReturnStatement(node)) {
-        has.hasReturn = true;
-        replace = t.returnStatement(t.objectExpression([
-          t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
-        ]));
-      }
-
-      if (replace) return t.inherits(replace, node);
-    }
-  });
-
-  return has;
-};
-
-/**
- * Hoist all var declarations in this block to before it so they retain scope
- * once we wrap everything in a closure.
- */
-
-LetScoping.prototype.hoistVarDeclarations = function () {
-  var self = this;
-  traverse(this.block, {
-    enter: function (node, parent) {
-      if (t.isForStatement(node)) {
-        if (isVar(node.init, node)) {
-          node.init = t.sequenceExpression(self.pushDeclar(node.init));
-        }
-      } else if (t.isFor(node)) {
-        if (isVar(node.left, node)) {
-          node.left = node.left.declarations[0].id;
-        }
-      } else if (isVar(node, parent)) {
-        return self.pushDeclar(node).map(t.expressionStatement);
-      } else if (t.isFunction(node)) {
-        return this.skip();
-      }
-    }
-  });
-};
-
-/**
- * Build up a parameter list that we'll call our closure wrapper with, replacing
- * all duplicate ids with their uid.
- *
- * @param {Array} params
- * @returns {Array}
- */
-
-LetScoping.prototype.getParams = function (params) {
-  var info = this.info;
-  params = _.cloneDeep(params);
-  _.each(params, function (param) {
-    param.name = info.duplicates[param.name] || param.name;
-  });
-  return params;
-};
-
-/**
- * Get all let references within this block. Stopping whenever we reach another
- * block.
- */
-
-LetScoping.prototype.getLetReferences = function () {
-  var closurify = false;
-  var self = this;
-
-  // traverse through this block, stopping on functions and checking if they
-  // contain any outside let references
-  traverse(this.block, {
-    enter: function (node, parent, scope) {
-      if (t.isFunction(node)) {
-        traverse(node, {
-          enter: function (node, parent) {
-            // not an identifier so we have no use
-            if (!t.isIdentifier(node)) return;
-
-            // not a direct reference
-            if (!t.isReferenced(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;
-
-            closurify = true;
-
-            // this key doesn't appear just outside our scope
-            if (!_.contains(self.info.outsideKeys, node.name)) return;
-
-            // push this badboy
-            self.letReferences[node.name] = node;
-          }
-        });
-
-        return this.skip();
-      }
-    }
-  });
-
-  return closurify;
-};
-
-/**
- * Turn a `VariableDeclaration` into an array of `AssignmentExpressions` with
- * their declarations hoisted to before the closure wrapper.
- *
- * @param {Node} node VariableDeclaration
- * @returns {Array}
- */
-
-LetScoping.prototype.pushDeclar = function (node) {
-  this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
-    return t.variableDeclarator(declar.id);
-  })));
-
-  var replace = [];
-
-  for (var i in node.declarations) {
-    var declar = node.declarations[i];
-    if (!declar.init) continue;
-
-    var expr = t.assignmentExpression("=", declar.id, declar.init);
-    replace.push(t.inherits(expr, declar));
-  }
-
-  return replace;
-};
-
-/**
- * Push the closure to the body.
- *
- * @param {Node} ret Identifier
- * @param {Node} call CallExpression
- */
-
-LetScoping.prototype.build = function (ret, call) {
-  var has = this.has;
-  if (has.hasReturn || has.hasBreak || has.hasContinue) {
-    this.buildHas(ret, call);
-  } else {
-    this.body.push(t.expressionStatement(call));
-  }
-};
-
-/**
- * Description
- *
- * @param {Node} ret Identifier
- * @param {Node} call CallExpression
- */
-
-LetScoping.prototype.buildHas = function (ret, call) {
-  var body = this.body;
-
-  body.push(t.variableDeclaration("var", [
-    t.variableDeclarator(ret, call)
-  ]));
-
-  var loopParent = this.loopParent;
-  var retCheck;
-  var has = this.has;
-  var cases = [];
-
-  if (has.hasReturn) {
-    // typeof ret === "object"
-    retCheck = util.template("let-scoping-return", {
-      RETURN: ret
-    });
-  }
-
-  if (has.hasBreak || has.hasContinue) {
-    // ensure that the parent has a label as we're building a switch and we
-    // need to be able to access it
-    var label = loopParent.label = loopParent.label || this.file.generateUidIdentifier("loop", this.scope);
-
-    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)]));
-    }
-
-    if (has.hasReturn) {
-      cases.push(t.switchCase(null, [retCheck]));
-    }
-
-    if (cases.length === 1) {
-      var single = cases[0];
-      body.push(t.ifStatement(
-        t.binaryExpression("===", ret, single.test),
-        single.consequent[0]
-      ));
-    } else {
-      body.push(t.switchStatement(ret, cases));
-    }
-  } else {
-    if (has.hasReturn) body.push(retCheck);
-  }
-};

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

@@ -1,73 +0,0 @@
-var traverse = require("../../traverse");
-var util     = require("../../util");
-var t        = require("../../types");
-
-exports._namedMethod = function (node, file, scope) {
-  var key = t.toComputedKey(node, node.key);
-  if (!t.isLiteral(key)) return node; // we can't set a function id with this
-
-  var id = t.toIdentifier(key.value);
-  key = t.identifier(id);
-
-  var selfReference = false;
-  var outerDeclar = scope.get(id, true);
-
-  traverse(node, {
-    enter: function (node, parent, scope) {
-      // check if this node is an identifier that matches the same as our function id
-      if (!t.isIdentifier(node, { name: id })) return;
-
-      // check if this node is the one referenced
-      if (!t.isReferenced(node, parent)) return;
-
-      // check that we don't have a local variable declared as that removes the need
-      // for the wrapper
-      var localDeclar = scope.get(id, true);
-      if (localDeclar !== outerDeclar) return;
-
-      selfReference = true;
-      this.stop();
-    }
-  }, scope);
-
-  if (selfReference) {
-    node.value = util.template("property-method-assignment-wrapper", {
-      FUNCTION: node.value,
-      FUNCTION_ID: key,
-      FUNCTION_KEY: file.generateUidIdentifier(id, scope),
-      WRAPPER_KEY: file.generateUidIdentifier(id + "Wrapper", scope)
-    });
-  } else {
-    node.value.id = key;
-  }
-};
-
-exports.Property = function (node, parent, file, scope) {
-  if (!node.method) return;
-
-  node.method = false;
-
-  exports._namedMethod(node, file, scope);
-};
-
-exports.ObjectExpression = function (node) {
-  var mutatorMap = {};
-  var hasAny = false;
-
-  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);
-      return false;
-    } else {
-      return true;
-    }
-  });
-
-  if (!hasAny) return;
-
-  return t.callExpression(
-    t.memberExpression(t.identifier("Object"), t.identifier("defineProperties")),
-    [node, util.buildDefineProperties(mutatorMap)]
-  );
-};

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

@@ -1,8 +0,0 @@
-var t = require("../../types");
-var _ = require("lodash");
-
-exports.Property = function (node) {
-  if (!node.shorthand) return;
-  node.shorthand = false;
-  node.key = t.removeComments(_.clone(node.key));
-};

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

@@ -1,36 +0,0 @@
-var util = require("../../util");
-var t    = require("../../types");
-
-exports.Function = function (node, parent, file) {
-  if (!node.rest) return;
-
-  var rest = node.rest;
-  delete node.rest;
-
-  t.ensureBlock(node);
-
-  var argsId = t.identifier("arguments");
-  argsId._ignoreAliasFunctions = true;
-
-  var start = t.literal(node.params.length);
-  var key = file.generateUidIdentifier("key");
-
-  var arrKey = key;
-  if (node.params.length) {
-    arrKey = t.binaryExpression("-", arrKey, start);
-  }
-
-  node.body.body.unshift(
-    t.variableDeclaration("var", [
-      t.variableDeclarator(rest, t.arrayExpression([]))
-    ]),
-
-    util.template("rest", {
-      ARGUMENTS: argsId,
-      ARRAY_KEY: arrKey,
-      START: start,
-      ARRAY: rest,
-      KEY: key
-    })
-  );
-};

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

@@ -1,4 +1,6 @@
-var t = require("../../types");
+"use strict";
+
+var t = require("../../../types");
 
 exports.ArrowFunctionExpression = function (node) {
   t.ensureBlock(node);

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

@@ -0,0 +1,50 @@
+"use strict";
+
+var traverse = require("../../../traverse");
+var t        = require("../../../types");
+
+var visitor = {
+  enter: function (node, parent, scope, context, 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;
+
+    var declaredLoc  = declared.loc;
+    var referenceLoc = node.loc;
+
+    if (!declaredLoc || !referenceLoc) return;
+
+    // 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");
+    }
+  }
+};
+
+exports.optional = true;
+
+exports.Loop =
+exports.Program =
+exports.BlockStatement = function (node, parent, scope, context, file) {
+  var letRefs = node._letReferences;
+  if (!letRefs) return;
+
+  var state = {
+    letRefs: letRefs,
+    file:    file
+  };
+
+  traverse(node, visitor, scope, state);
+};

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

@@ -0,0 +1,491 @@
+"use strict";
+
+var traverse = require("../../../traverse");
+var object   = require("../../../helpers/object");
+var util     = require("../../../util");
+var t        = require("../../../types");
+var _        = require("lodash");
+
+var isLet = function (node, parent) {
+  if (!t.isVariableDeclaration(node)) return false;
+  if (node._let) return true;
+  if (node.kind !== "let") return false;
+
+  // https://github.com/6to5/6to5/issues/255
+  if (!t.isFor(parent) || t.isFor(parent) && parent.left !== node) {
+    for (var i = 0; i < node.declarations.length; i++) {
+      var declar = node.declarations[i];
+      declar.init = declar.init || t.identifier("undefined");
+    }
+  }
+
+  node._let = true;
+  node.kind = "var";
+  return true;
+};
+
+var isVar = function (node, parent) {
+  return t.isVariableDeclaration(node, { kind: "var" }) && !isLet(node, parent);
+};
+
+var standardiseLets = function (declars) {
+  for (var i = 0; i < declars.length; i++) {
+    delete declars[i]._let;
+  }
+};
+
+exports.VariableDeclaration = function (node, parent) {
+  isLet(node, parent);
+};
+
+exports.Loop = function (node, parent, scope, context, 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);
+  }
+};
+
+exports.Program =
+exports.BlockStatement = function (block, parent, scope, context, file) {
+  if (!t.isLoop(parent)) {
+    var letScoping = new LetScoping(false, block, parent, scope, file);
+    letScoping.run();
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Boolean|Node} loopParent
+ * @param {Node} block
+ * @param {Node} parent
+ * @param {Scope} scope
+ * @param {File} file
+ */
+
+function LetScoping(loopParent, block, parent, scope, file) {
+  this.loopParent = loopParent;
+  this.parent     = parent;
+  this.scope      = scope;
+  this.block      = block;
+  this.file       = file;
+
+  this.outsideLetReferences = object();
+  this.hasLetReferences     = false;
+  this.letReferences        = block._letReferences = object();
+  this.body                 = [];
+}
+
+/**
+ * Start the ball rolling.
+ */
+
+LetScoping.prototype.run = function () {
+  var block = this.block;
+  if (block._letDone) return;
+  block._letDone = true;
+
+  var needsClosure = this.getLetReferences();
+
+  // this is a block within a `Function/Program` so we can safely leave it be
+  if (t.isFunction(this.parent) || t.isProgram(this.block)) return;
+
+  // we can skip everything
+  if (!this.hasLetReferences) return;
+
+  if (needsClosure) {
+    this.needsClosure();
+  } else {
+    this.remap();
+  }
+};
+
+function replace(node, parent, scope, context, 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) {
+    node.name = remap.uid;
+  } else {
+    // scope already has it's own declaration that doesn't
+    // match the one we have a stored replacement for
+    if (context) context.skip();
+  }
+}
+
+var replaceVisitor = {
+  enter: replace
+};
+
+function traverseReplace(node, parent, scope, remaps) {
+  replace(node, parent, scope, null, remaps);
+  traverse(node, replaceVisitor, scope, remaps);
+}
+
+/**
+ * Description
+ */
+
+LetScoping.prototype.remap = function () {
+  var hasRemaps = false;
+  var letRefs   = this.letReferences;
+  var scope     = this.scope;
+
+  // alright, so since we aren't wrapping this block in a closure
+  // we have to check if any of our let variables collide with
+  // those in upper scopes and then if they do, generate a uid
+  // for them and replace all references with it
+  var remaps = object();
+
+  for (var key in letRefs) {
+    // just an Identifier node we collected in `getLetReferences`
+    // this is the defining identifier of a declaration
+    var ref = letRefs[key];
+
+    if (scope.parentHas(key)) {
+      var uid = scope.generateUidIdentifier(ref.name).name;
+      ref.name = uid;
+
+      hasRemaps = true;
+      remaps[key] = remaps[uid] = {
+        node: ref,
+        uid: uid
+      };
+    }
+  }
+
+  if (!hasRemaps) return;
+
+  //
+
+  var loopParent = this.loopParent;
+  if (loopParent) {
+    traverseReplace(loopParent.right, loopParent, scope, remaps);
+    traverseReplace(loopParent.test, loopParent, scope, remaps);
+    traverseReplace(loopParent.update, loopParent, scope, remaps);
+  }
+
+  traverse(this.block, replaceVisitor, scope, remaps);
+};
+
+/**
+ * Description
+ */
+
+LetScoping.prototype.needsClosure = function () {
+  var block = this.block;
+
+  // if we're inside of a for loop then we search to see if there are any
+  // `break`s, `continue`s, `return`s etc
+  this.has = this.checkLoop();
+
+  // hoist var references to retain scope
+  this.hoistVarDeclarations();
+
+  // turn outsideLetReferences into an array
+  var params = _.values(this.outsideLetReferences);
+
+  // build the closure that we're going to wrap the block with
+  var fn = t.functionExpression(null, params, t.blockStatement(block.body));
+  fn._aliasFunction = true;
+
+  // replace the current block body with the one we're going to build
+  block.body = this.body;
+
+  // build a call and a unique id that we can assign the return value to
+  var call = t.callExpression(fn, params);
+  var ret  = this.scope.generateUidIdentifier("ret");
+
+  // handle generators
+  var hasYield = traverse.hasType(fn.body, this.scope, "YieldExpression", t.FUNCTION_TYPES);
+  if (hasYield) {
+    fn.generator = true;
+    call = t.yieldExpression(call, true);
+  }
+
+  // handlers async functions
+  var hasAsync = traverse.hasType(fn.body, this.scope, "AwaitExpression", t.FUNCTION_TYPES);
+  if (hasAsync) {
+    fn.async = true;
+    call = t.awaitExpression(call, true);
+  }
+
+  this.build(ret, call);
+};
+
+var letReferenceFunctionVisitor = {
+  enter: function (node, parent, scope, context, 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;
+
+    // not a part of our scope
+    if (!state.letReferences[node.name]) return;
+
+    state.closurify = true;
+  }
+};
+
+var letReferenceBlockVisitor = {
+  enter: function (node, parent, scope, context, state) {
+    if (t.isFunction(node)) {
+      traverse(node, letReferenceFunctionVisitor, scope, state);
+      return context.skip();
+    }
+  }
+};
+
+/**
+ * Description
+ */
+
+LetScoping.prototype.getLetReferences = function () {
+  var block = this.block;
+
+  var declarators = block._letDeclarators || [];
+  var declar;
+
+  //
+  for (var i = 0; i < declarators.length; i++) {
+    declar = declarators[i];
+    _.extend(this.outsideLetReferences, t.getIds(declar, true));
+  }
+
+  //
+  if (block.body) {
+    for (i = 0; i < block.body.length; i++) {
+      declar = block.body[i];
+      if (isLet(declar, block)) {
+        declarators = declarators.concat(declar.declarations);
+      }
+    }
+  }
+
+  //
+  for (i = 0; i < declarators.length; i++) {
+    declar = declarators[i];
+    var keys = t.getIds(declar, true);
+    _.extend(this.letReferences, keys);
+    this.hasLetReferences = true;
+  }
+
+  // no let references so we can just quit
+  if (!this.hasLetReferences) return;
+
+  // set let references to plain var references
+  standardiseLets(declarators);
+
+  var state = {
+    letReferences: this.letReferences,
+    closurify:     false
+  };
+
+  // traverse through this block, stopping on functions and checking if they
+  // contain any local let references
+  traverse(this.block, letReferenceBlockVisitor, this.scope, state);
+
+  return state.closurify;
+};
+
+var loopVisitor = {
+  enter: function (node, parent, scope, context, state) {
+    var replace;
+
+    if (t.isFunction(node) || t.isLoop(node)) {
+      return context.skip();
+    }
+
+    if (node && !node.label && state.isLoop) {
+      if (t.isBreakStatement(node)) {
+        if (t.isSwitchCase(parent)) return;
+
+        state.hasBreak = true;
+        replace = t.returnStatement(t.literal("break"));
+      } else if (t.isContinueStatement(node)) {
+        state.hasContinue = true;
+        replace = t.returnStatement(t.literal("continue"));
+      }
+    }
+
+    if (t.isReturnStatement(node)) {
+      state.hasReturn = true;
+      replace = t.returnStatement(t.objectExpression([
+        t.property("init", t.identifier("v"), node.argument || t.identifier("undefined"))
+      ]));
+    }
+
+    if (replace) return t.inherits(replace, node);
+  }
+};
+
+/**
+ * If we're inside of a loop then traverse it and check if it has one of
+ * the following node types `ReturnStatement`, `BreakStatement`,
+ * `ContinueStatement` and replace it with a return value that we can track
+ * later on.
+ *
+ * @returns {Object}
+ */
+
+LetScoping.prototype.checkLoop = function () {
+  var state = {
+    hasContinue: false,
+    hasReturn:   false,
+    hasBreak:    false,
+    isLoop:      !!this.loopParent
+  };
+
+  traverse(this.block, loopVisitor, this.scope, state);
+  return state;
+};
+
+var hoistVarDeclarationsVisitor = {
+  enter: function (node, parent, scope, context, self) {
+    if (t.isForStatement(node)) {
+      if (isVar(node.init, node)) {
+        node.init = t.sequenceExpression(self.pushDeclar(node.init));
+      }
+    } else if (t.isFor(node)) {
+      if (isVar(node.left, node)) {
+        node.left = node.left.declarations[0].id;
+      }
+    } else if (isVar(node, parent)) {
+      return self.pushDeclar(node).map(t.expressionStatement);
+    } else if (t.isFunction(node)) {
+      return context.skip();
+    }
+  }
+};
+
+/**
+ * Hoist all var declarations in this block to before it so they retain scope
+ * once we wrap everything in a closure.
+ */
+
+LetScoping.prototype.hoistVarDeclarations = function () {
+  traverse(this.block, hoistVarDeclarationsVisitor, this.scope, this);
+};
+
+/**
+ * Turn a `VariableDeclaration` into an array of `AssignmentExpressions` with
+ * their declarations hoisted to before the closure wrapper.
+ *
+ * @param {Node} node VariableDeclaration
+ * @returns {Array}
+ */
+
+LetScoping.prototype.pushDeclar = function (node) {
+  this.body.push(t.variableDeclaration(node.kind, node.declarations.map(function (declar) {
+    return t.variableDeclarator(declar.id);
+  })));
+
+  var replace = [];
+
+  for (var i = 0; i < node.declarations.length; i++) {
+    var declar = node.declarations[i];
+    if (!declar.init) continue;
+
+    var expr = t.assignmentExpression("=", declar.id, declar.init);
+    replace.push(t.inherits(expr, declar));
+  }
+
+  return replace;
+};
+
+/**
+ * Push the closure to the body.
+ *
+ * @param {Node} ret Identifier
+ * @param {Node} call CallExpression
+ */
+
+LetScoping.prototype.build = function (ret, call) {
+  var has = this.has;
+  if (has.hasReturn || has.hasBreak || has.hasContinue) {
+    this.buildHas(ret, call);
+  } else {
+    this.body.push(t.expressionStatement(call));
+  }
+};
+
+/**
+ * Description
+ *
+ * @param {Node} ret Identifier
+ * @param {Node} call CallExpression
+ */
+
+LetScoping.prototype.buildHas = function (ret, call) {
+  var body = this.body;
+
+  body.push(t.variableDeclaration("var", [
+    t.variableDeclarator(ret, call)
+  ]));
+
+  var loopParent = this.loopParent;
+  var retCheck;
+  var has = this.has;
+  var cases = [];
+
+  if (has.hasReturn) {
+    // typeof ret === "object"
+    retCheck = util.template("let-scoping-return", {
+      RETURN: ret
+    });
+  }
+
+  if (has.hasBreak || has.hasContinue) {
+    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)]));
+    }
+
+    if (has.hasReturn) {
+      cases.push(t.switchCase(null, [retCheck]));
+    }
+
+    if (cases.length === 1) {
+      var single = cases[0];
+      body.push(t.ifStatement(
+        t.binaryExpression("===", ret, single.test),
+        single.consequent[0]
+      ));
+    } else {
+      body.push(t.switchStatement(ret, cases));
+    }
+  } else {
+    if (has.hasReturn) body.push(retCheck);
+  }
+};

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

@@ -0,0 +1,258 @@
+"use strict";
+
+var ReplaceSupers = require("../../helpers/replace-supers");
+var nameMethod    = require("../../helpers/name-method");
+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.ClassExpression = function (node, parent, scope, context, file) {
+  if (!node.id) {
+    if (t.isProperty(parent) && parent.value === node && !parent.computed && t.isIdentifier(parent.key)) {
+      // var o = { foo: class {} };
+      node.id = parent.key;
+    }
+
+    if (t.isVariableDeclarator(parent) && t.isIdentifier(parent.id)) {
+      // var foo = class {};
+      node.id = parent.id;
+    }
+  }
+
+  return new Class(node, file, scope, false).run();
+};
+
+/**
+ * Description
+ *
+ * @param {Node} node
+ * @param {File} file
+ * @param {Scope} scope
+ * @param {Boolean} closure
+ */
+
+function Class(node, file, scope, isStatement) {
+  this.isStatement = isStatement;
+  this.scope       = scope;
+  this.node        = node;
+  this.file        = file;
+
+  this.hasInstanceMutators = false;
+  this.hasStaticMutators   = false;
+
+  this.instanceMutatorMap = {};
+  this.staticMutatorMap   = {};
+  this.hasConstructor     = false;
+  this.className          = node.id || scope.generateUidIdentifier("class");
+  this.superName          = node.superClass;
+  this.isLoose            = file.isLoose("es6.classes");
+}
+
+/**
+ * Description
+ *
+ * @returns {Array}
+ */
+
+Class.prototype.run = function () {
+  var superName = this.superName;
+  var className = this.className;
+  var file      = this.file;
+
+  //
+
+  var body = this.body = [];
+
+  var constructor;
+  if (this.node.id) {
+    constructor = t.functionDeclaration(className, [], t.blockStatement([]));
+    body.push(constructor);
+  } else {
+    constructor = t.functionExpression(null, [], t.blockStatement([]));
+    body.push(t.variableDeclaration("var", [
+      t.variableDeclarator(className, constructor)
+    ]));
+  }
+  this.constructor = constructor;
+
+  var closureParams = [];
+  var closureArgs = [];
+
+  //
+
+  if (superName) {
+    closureArgs.push(superName);
+
+    if (!t.isIdentifier(superName)) {
+      var superRef = this.scope.generateUidBasedOnNode(superName, this.file);
+      superName = superRef;
+    }
+
+    closureParams.push(superName);
+
+    this.superName = superName;
+    body.push(t.expressionStatement(t.callExpression(file.addHelper("inherits"), [className, superName])));
+  }
+
+  this.buildBody();
+
+  t.inheritsComments(body[0], this.node);
+
+  var init;
+
+  if (body.length === 1) {
+    // only a constructor so no need for a closure container
+    init = t.toExpression(constructor);
+  } else {
+    body.push(t.returnStatement(className));
+    init = t.callExpression(
+      t.functionExpression(null, closureParams, t.blockStatement(body)),
+      closureArgs
+    );
+  }
+
+  if (this.isStatement) {
+    return t.variableDeclaration("let", [
+      t.variableDeclarator(className, init)
+    ]);
+  } else {
+    return init;
+  }
+};
+
+/**
+ * Description
+ */
+
+Class.prototype.buildBody = function () {
+  var constructor = this.constructor;
+  var className   = this.className;
+  var superName   = this.superName;
+  var classBody   = this.node.body.body;
+  var body        = this.body;
+
+  for (var i = 0; i < classBody.length; i++) {
+    var node = classBody[i];
+    if (t.isMethodDefinition(node)) {
+      var replaceSupers = new ReplaceSupers({
+        methodNode: node,
+        className:  this.className,
+        superName:  this.superName,
+        isLoose:    this.isLoose,
+        scope:      this.scope,
+        file:       this.file
+      });
+      replaceSupers.replace();
+
+      if (node.key.name === "constructor") {
+        this.pushConstructor(node);
+      } else {
+        this.pushMethod(node);
+      }
+    } else if (t.isPrivateDeclaration(node)) {
+      this.closure = true;
+      body.unshift(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, {
+      CLASS_NAME: className,
+      SUPER_NAME: this.superName
+    }, true));
+  }
+
+  var instanceProps;
+  var staticProps;
+
+  if (this.hasInstanceMutators) {
+    instanceProps = util.buildDefineProperties(this.instanceMutatorMap);
+  }
+
+  if (this.hasStaticMutators) {
+    staticProps = util.buildDefineProperties(this.staticMutatorMap);
+  }
+
+  if (instanceProps || staticProps) {
+    staticProps = staticProps || t.literal(null);
+
+    var args = [className, staticProps];
+    if (instanceProps) args.push(instanceProps);
+
+    body.push(t.expressionStatement(
+      t.callExpression(this.file.addHelper("prototype-properties"), args)
+    ));
+  }
+};
+
+/**
+ * Push a method to it's respective mutatorMap.
+ *
+ * @param {Node} node MethodDefinition
+ */
+
+Class.prototype.pushMethod = function (node) {
+  var methodName = node.key;
+
+  var kind = node.kind;
+
+  if (kind === "") {
+    nameMethod.property(node, this.file, this.scope);
+
+    if (this.isLoose) {
+      // use assignments instead of define properties for loose classes
+
+      var className = this.className;
+      if (!node.static) className = t.memberExpression(className, t.identifier("prototype"));
+      methodName = t.memberExpression(className, methodName, node.computed);
+
+      var expr = t.expressionStatement(t.assignmentExpression("=", methodName, node.value));
+      t.inheritsComments(expr, node);
+      this.body.push(expr);
+      return;
+    }
+
+    kind = "value";
+  }
+
+  var mutatorMap = this.instanceMutatorMap;
+  if (node.static) {
+    this.hasStaticMutators = true;
+    mutatorMap = this.staticMutatorMap;
+  } else {
+    this.hasInstanceMutators = true;
+  }
+
+  util.pushMutatorMap(mutatorMap, methodName, kind, node.computed, node);
+};
+
+/**
+ * Replace the constructor body of our class.
+ *
+ * @param {Node} method MethodDefinition
+ */
+
+Class.prototype.pushConstructor = function (method) {
+  if (method.kind) {
+    throw this.file.errorWithNode(method, "illegal kind for constructor method");
+  }
+
+  var construct = this.constructor;
+  var fn        = method.value;
+
+  this.hasConstructor = true;
+
+  t.inherits(construct, fn);
+  t.inheritsComments(construct, method);
+
+  construct._ignoreUserWhitespace = true;
+  construct.params                = fn.params;
+  construct.body                  = fn.body;
+};

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

@@ -0,0 +1,41 @@
+"use strict";
+
+var traverse = require("../../../traverse");
+var t        = require("../../../types");
+
+var visitor = {
+  enter: function (node, parent, scope, context, state) {
+    if (t.isDeclaration(node) || t.isAssignmentExpression(node)) {
+      var ids = t.getIds(node, true);
+
+      for (var key in ids) {
+        var id = ids[key];
+
+        var constant = state.constants[key];
+
+        // no constant exists
+        if (!constant) continue;
+
+        // 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;
+
+        throw state.file.errorWithNode(id, key + " is read-only");
+      }
+    } else if (t.isScope(node)) {
+      context.skip();
+    }
+  }
+};
+
+exports.Scope = function (node, parent, scope, context, file) {
+  traverse(node, visitor, scope, {
+    constants: scope.getAllOfKind("const"),
+    file:      file
+  });
+};
+
+exports.VariableDeclaration = function (node) {
+  if (node.kind === "const") node.kind = "let";
+};

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

@@ -1,18 +1,34 @@
+"use strict";
+
 // TODO: Clean up
 
-var t = require("../../types");
+var t = require("../../../types");
 
 var buildVariableAssign = function (opts, id, init) {
   var op = opts.operator;
   if (t.isMemberExpression(id)) op = "=";
 
+  var node;
+
   if (op) {
-    return t.expressionStatement(t.assignmentExpression("=", id, init));
+    node = t.expressionStatement(t.assignmentExpression(op, id, init));
   } else {
-    return t.variableDeclaration(opts.kind, [
+    node = t.variableDeclaration(opts.kind, [
       t.variableDeclarator(id, init)
     ]);
   }
+
+  node._blockHoist = opts.blockHoist;
+
+  return node;
+};
+
+var buildVariableDeclar = function (opts, id, init) {
+  var declar = t.variableDeclaration("var", [
+    t.variableDeclarator(id, init)
+  ]);
+  declar._blockHoist = opts.blockHoist;
+  return declar;
 };
 
 var push = function (opts, nodes, elem, parentId) {
@@ -46,27 +62,27 @@ var pushAssignmentPattern = function (opts, nodes, pattern, parentId) {
 };
 
 var pushObjectPattern = function (opts, nodes, pattern, parentId) {
-  for (var i in pattern.properties) {
+  for (var i = 0; i < pattern.properties.length; i++) {
     var prop = pattern.properties[i];
     if (t.isSpreadProperty(prop)) {
-        // get all the keys that appear in this object before the current spread
-        var keys = [];
-        for (var i2 in pattern.properties) {
-          var prop2 = pattern.properties[i2];
+      // 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;
+        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);
+        var key = prop2.key;
+        if (t.isIdentifier(key)) {
+          key = t.literal(prop2.key.name);
         }
-        keys = t.arrayExpression(keys);
+        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));
+      var value = t.callExpression(opts.file.addHelper("object-without-properties"), [parentId, keys]);
+      nodes.push(buildVariableAssign(opts, prop.argument, value));
     } else {
       if (t.isLiteral(prop.key)) prop.computed = true;
 
@@ -87,23 +103,21 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
 
   var i;
 
-  var hasSpreadElement = false;
-  for (i in pattern.elements) {
-    if (t.isSpreadElement(pattern.elements[i])) {
-      hasSpreadElement = true;
+  var hasRest = false;
+  for (i = 0; i < pattern.elements.length; i++) {
+    if (t.isRestElement(pattern.elements[i])) {
+      hasRest = true;
       break;
     }
   }
 
-  var toArray = opts.file.toArray(parentId, !hasSpreadElement && pattern.elements.length);
+  var toArray = opts.file.toArray(parentId, !hasRest && pattern.elements.length);
 
   var _parentId = opts.scope.generateUidBasedOnNode(parentId, opts.file);
-  nodes.push(t.variableDeclaration("var", [
-    t.variableDeclarator(_parentId, toArray)
-  ]));
+  nodes.push(buildVariableDeclar(opts, _parentId, toArray));
   parentId = _parentId;
 
-  for (i in pattern.elements) {
+  for (i = 0; i < pattern.elements.length; i++) {
     var elem = pattern.elements[i];
     if (!elem) continue;
 
@@ -111,7 +125,7 @@ var pushArrayPattern = function (opts, nodes, pattern, parentId) {
 
     var newPatternId;
 
-    if (t.isSpreadElement(elem)) {
+    if (t.isRestElement(elem)) {
       newPatternId = opts.file.toArray(parentId);
 
       if (i > 0) {
@@ -131,16 +145,11 @@ var pushPattern = function (opts) {
   var nodes = opts.nodes;
   var pattern = opts.pattern;
   var parentId = opts.id;
-  var file = opts.file;
   var scope = opts.scope;
 
   if (!t.isArrayExpression(parentId) && !t.isMemberExpression(parentId) && !t.isIdentifier(parentId)) {
-    var key = scope.generateUidBasedOnNode(parentId, file);
-
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(key, parentId)
-    ]));
-
+    var key = scope.generateUidBasedOnNode(parentId);
+    nodes.push(buildVariableDeclar(opts, key, parentId));
     parentId = key;
   }
 
@@ -148,14 +157,14 @@ var pushPattern = function (opts) {
 };
 
 exports.ForInStatement =
-exports.ForOfStatement = function (node, parent, file, scope) {
+exports.ForOfStatement = function (node, parent, scope, context, file) {
   var declar = node.left;
   if (!t.isVariableDeclaration(declar)) return;
 
   var pattern = declar.declarations[0].id;
   if (!t.isPattern(pattern)) return;
 
-  var key = file.generateUidIdentifier("ref", scope);
+  var key = scope.generateUidIdentifier("ref");
   node.left = t.variableDeclaration(declar.kind, [
     t.variableDeclarator(key, null)
   ]);
@@ -174,24 +183,25 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   block.body = nodes.concat(block.body);
 };
 
-exports.Function = function (node, parent, file, scope) {
+exports.Function = function (node, parent, scope, context, file) {
   var nodes = [];
 
   var hasDestructuring = false;
 
-  node.params = node.params.map(function (pattern) {
+  node.params = node.params.map(function (pattern, i) {
     if (!t.isPattern(pattern)) return pattern;
 
     hasDestructuring = true;
-    var parentId = file.generateUidIdentifier("ref", scope);
+    var parentId = scope.generateUidIdentifier("ref");
 
     pushPattern({
-      kind:    "var",
-      nodes:   nodes,
-      pattern: pattern,
-      id:      parentId,
-      file:    file,
-      scope:   scope
+      blockHoist: node.params.length - i,
+      pattern:    pattern,
+      nodes:      nodes,
+      scope:      scope,
+      file:       file,
+      kind:       "var",
+      id:         parentId
     });
 
     return parentId;
@@ -205,11 +215,11 @@ exports.Function = function (node, parent, file, scope) {
   block.body = nodes.concat(block.body);
 };
 
-exports.CatchClause = function (node, parent, file, scope) {
+exports.CatchClause = function (node, parent, scope, context, file) {
   var pattern = node.param;
   if (!t.isPattern(pattern)) return;
 
-  var ref = file.generateUidIdentifier("ref", scope);
+  var ref = scope.generateUidIdentifier("ref");
   node.param = ref;
 
   var nodes = [];
@@ -223,15 +233,15 @@ exports.CatchClause = function (node, parent, file, scope) {
   node.body.body = nodes.concat(node.body.body);
 };
 
-exports.ExpressionStatement = function (node, parent, file, scope) {
+exports.ExpressionStatement = function (node, parent, scope, context, file) {
   var expr = node.expression;
   if (expr.type !== "AssignmentExpression") return;
-
   if (!t.isPattern(expr.left)) return;
+  if (file.isConsequenceExpressionStatement(node)) return;
 
   var nodes = [];
 
-  var ref = file.generateUidIdentifier("ref", scope);
+  var ref = scope.generateUidIdentifier("ref");
   nodes.push(t.variableDeclaration("var", [
     t.variableDeclarator(ref, expr.right)
   ]));
@@ -245,14 +255,12 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
   return nodes;
 };
 
-exports.AssignmentExpression = function (node, parent, file, scope) {
-  if (parent.type === "ExpressionStatement") return;
+exports.AssignmentExpression = function (node, parent, scope, context, file) {
   if (!t.isPattern(node.left)) return;
 
-  var tempName = file.generateUid("temp", scope);
-  var ref = t.identifier(tempName);
+  var ref = scope.generateUidIdentifier("temp");
   scope.push({
-    key: tempName,
+    key: ref.name,
     id: ref
   });
 
@@ -270,7 +278,7 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
   return t.toSequenceExpression(nodes, scope);
 };
 
-exports.VariableDeclaration = function (node, parent, file, scope) {
+exports.VariableDeclaration = function (node, parent, scope, context, file) {
   if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
 
   var nodes = [];
@@ -278,7 +286,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   var declar;
 
   var hasPattern = false;
-  for (i in node.declarations) {
+  for (i = 0; i < node.declarations.length; i++) {
     declar = node.declarations[i];
     if (t.isPattern(declar.id)) {
       hasPattern = true;
@@ -287,18 +295,18 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   }
   if (!hasPattern) return;
 
-  for (i in node.declarations) {
+  for (i = 0; i < node.declarations.length; i++) {
     declar = node.declarations[i];
 
     var patternId = declar.init;
     var pattern   = declar.id;
     var opts = {
-      kind:    node.kind,
-      nodes:   nodes,
       pattern: pattern,
-      id:      patternId,
+      nodes:   nodes,
+      scope:   scope,
+      kind:    node.kind,
       file:    file,
-      scope:   scope
+      id:      patternId,
     };
 
     if (t.isPattern(pattern) && patternId) {
@@ -317,7 +325,7 @@ exports.VariableDeclaration = function (node, parent, file, scope) {
   if (!t.isProgram(parent) && !t.isBlockStatement(parent)) {
     declar = null;
 
-    for (i in nodes) {
+    for (i = 0; i < nodes.length; i++) {
       node = nodes[i];
       declar = declar || t.variableDeclaration(node.kind, []);
 

lib/6to5/transformation/transformers/es6/for-of.js

@@ -1,11 +1,13 @@
-var util = require("../../util");
-var t    = require("../../types");
+"use strict";
 
-exports.ForOfStatement = function (node, parent, file, scope) {
+var util = require("../../../util");
+var t    = require("../../../types");
+
+exports.ForOfStatement = function (node, parent, scope, context, file) {
   var callback = spec;
-  if (file.isLoose("forOf")) callback = loose;
+  if (file.isLoose("es6.forOf")) callback = loose;
 
-  var build  = callback(node, parent, file, scope);
+  var build  = callback(node, parent, scope, context, file);
   var declar = build.declar;
   var loop   = build.loop;
   var block  = loop.body;
@@ -17,7 +19,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   t.ensureBlock(node);
 
   // add the value declaration to the new loop body
-  if (declar){
+  if (declar) {
     if (build.shouldUnshift) {
       block.body.unshift(declar);
     } else {
@@ -28,10 +30,13 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   // push the rest of the original loop body onto our new body
   block.body = block.body.concat(node.body.body);
 
+  // todo: find out why this is necessary? #538
+  loop._scopeInfo = node._scopeInfo;
+
   return loop;
 };
 
-var loose = function (node, parent, file, scope) {
+var loose = function (node, parent, scope, context, file) {
   var left = node.left;
   var declar, id;
 
@@ -49,10 +54,10 @@ var loose = function (node, parent, file, scope) {
   }
 
   var loop = util.template("for-of-loose", {
-    LOOP_OBJECT:  file.generateUidIdentifier("iterator", scope),
-    IS_ARRAY:     file.generateUidIdentifier("isArray", scope),
+    LOOP_OBJECT:  scope.generateUidIdentifier("iterator"),
+    IS_ARRAY:     scope.generateUidIdentifier("isArray"),
     OBJECT:       node.right,
-    INDEX:        file.generateUidIdentifier("i", scope),
+    INDEX:        scope.generateUidIdentifier("i"),
     ID:           id
   });
 
@@ -63,11 +68,11 @@ var loose = function (node, parent, file, scope) {
   };
 };
 
-var spec = function (node, parent, file, scope) {
+var spec = function (node, parent, scope, context, file) {
   var left = node.left;
   var declar;
 
-  var stepKey   = file.generateUidIdentifier("step", scope);
+  var stepKey   = scope.generateUidIdentifier("step");
   var stepValue = t.memberExpression(stepKey, t.identifier("value"));
 
   if (t.isIdentifier(left) || t.isPattern(left)) {
@@ -83,7 +88,7 @@ var spec = function (node, parent, file, scope) {
   }
 
   var loop = util.template("for-of", {
-    ITERATOR_KEY: file.generateUidIdentifier("iterator", scope),
+    ITERATOR_KEY: scope.generateUidIdentifier("iterator"),
     STEP_KEY:     stepKey,
     OBJECT:       node.right
   });

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

@@ -1,16 +1,12 @@
-var t = require("../../types");
+"use strict";
 
-exports.ast = {
-  before: function (ast, file) {
-    ast.program.body = file.dynamicImports.concat(ast.program.body);
-  }
-};
+var t = require("../../../types");
 
-exports.ImportDeclaration = function (node, parent, file) {
+exports.ImportDeclaration = function (node, parent, scope, context, file) {
   var nodes = [];
 
   if (node.specifiers.length) {
-    for (var i in node.specifiers) {
+    for (var i = 0; i < node.specifiers.length; i++) {
       file.moduleFormatter.importSpecifier(node.specifiers[i], node, nodes, parent);
     }
   } else {
@@ -18,16 +14,16 @@ exports.ImportDeclaration = function (node, parent, file) {
   }
 
   if (nodes.length === 1) {
-    // inherit `_blockHoist`
-    // this for `_blockHoist` in File.prototype.addImport
+    // inherit `_blockHoist` - this is for `_blockHoist` in File.prototype.addImport
     nodes[0]._blockHoist = node._blockHoist;
   }
 
   return nodes;
 };
 
-exports.ExportDeclaration = function (node, parent, file) {
+exports.ExportDeclaration = function (node, parent, scope, context, file) {
   var nodes = [];
+  var i;
 
   if (node.declaration) {
     // make sure variable exports have an initialiser
@@ -38,11 +34,17 @@ exports.ExportDeclaration = function (node, parent, file) {
     }
 
     file.moduleFormatter.exportDeclaration(node, nodes, parent);
-  } else {
-    for (var i in node.specifiers) {
+  } else if (node.specifiers) {
+    for (i = 0; i < node.specifiers.length; i++) {
       file.moduleFormatter.exportSpecifier(node.specifiers[i], node, nodes, parent);
     }
   }
 
+  if (node._blockHoist) {
+    for (i = 0; i < nodes.length; i++) {
+      nodes[i]._blockHoist = node._blockHoist;
+    }
+  }
+
   return nodes;
 };