v2.4.10

add code of conduct

.jshintignore

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

.npmignore

@@ -1,7 +1,7 @@
 node_modules
 *.log
 *.cache
-lib/6to5/templates
+lib/6to5/transformation/templates
 test
 benchmark
 Makefile

CHANGELOG.md

@@ -1,162 +1,423 @@
-# 1.13.3
+# Changelog
+
+Gaps between patch versions are faulty/broken releases.
+
+## 2.4.10
+
+ * Upgrade `acorn-6to5`.
+
+## 2.4.9
+
+ * Upgrade `acorn-6to5`.
+ * Add optional `protoToAssign` transformer.
+ * Fix missing properties from computed property keys.
+ * Make ES7 comprehensions `let` variables.
+
+## 2.4.8
+
+ * Make `require("6to5/register")` work with browserify - [#370](https://github.com/6to5/6to5/pull/370). Thanks [@hughsk](https://github.com/hughsk)!
+
+## 2.4.7
+
+ * Upgrade `acorn-6to5`.
+
+## 2.4.6
+
+ * Move `coreAliasing` and `undefinedToVoid` transformers down to catch `moduleFormatter` transforms.
+
+## 2.4.5
+
+ * Avoid printing comments if they've already been output.
+
+## 2.4.4
+
+ * Add `module` type to browser build `<script>` handler.
+ * Fix some `MemberExpression` modifying incorrectly setting `property` to a `MemberExpression`.
+
+## 2.4.3
+
+ * Upgrade `acorn-6to5`.
+ * Add support for `FunctionDeclaration`s in `bluebirdCoroutines` and `asyncToGenerators` transformers.
+
+## 2.4.2
+
+ * Upgrade `acorn-6to5`.
+ * Better uids generated for various transformers based on parent node.
+ * Alias flat references in `coreAliasing` transformer.
+
+## 2.4.1
+
+ * Better whitespace handling of parenthesized expressions due to trailing comments.
+ * Fix `yield` inside of comprehensions.
+
+## 2.4.0
+
+ * Use a closure always for classes with a super.
+ * Always use native loops for array comprehensions.
+ * Allow `yield` inside of comprehensions.
+ * Add optional `bluebirdCoroutine` transformer.
+ * Add optional `asyncToGenerator` transformer.
+ * Move `useStrict` transformer to before `_moduleFormatter` causing `"use strict";` to always be placed the very top.
+
+## 2.3.2
+
+ * Add parens on expressions with trailing comments.
+
+## 2.3.1
+
+ * Add `undefinedToVoid` optional transformer.
+ * Use `Object.defineProperty` for computed properties.
+
+## 2.3.0
+
+ * Upgrade `acorn-6to5`.
+ * Support circular references and hoist variable declarations in `system` module formatter.
+ * Add optional transformers, including a new `coreAliasing` transformer that aliases native ES6 static properties to their `core-js` equivalent.
+
+## 2.2.0
+
+ * Make `system` module formatter modules anonymous by default.
+ * Fix duplicate comments being output, breaking code.
+
+## 2.1.0
+
+ * Add `cache` option to register hook.
+ * Update `core-js`.
+ * Fix starting newline not being added on case statements.
+ * Fix destructuring `VariableDeclaration`s not inside `BlockStatement`s and `Program`.
+
+## 2.0.4
+
+ * Avoid being greedy when destructuring array iterables.
+
+## 2.0.3
+
+ * Hoist function declarations in system module formatter for circular references.
+ * Hoist default function declarations in umd and amd module formatters for circular references.
+
+## 2.0.2
+
+ * Inherit comments in `for-of` transformer.
+ * Remove `interopRequire` from `system` module formatter.
+
+## 2.0.1
+
+ * Remap `UpdateExpression` module export binding.
+ * Fix automatic closure on `PrivateDeclaration` in classes.
+
+## 2.0.0
+
+ * Make string literal generation only escapes unicode that it has to.
+ * Internal code generation format options have been exposed.
+ * Change playground method binding operator from `:` to `#` removing ambiguous syntax with terns.
+ * Fix rest parameters in async and generator functions.
+ * Export/import declarations replace by the modules transformer now inherit comments.
+ * Added playground flag to `6to5-node`.
+ * `6to5-node` now behaves the same as `node`.
+ * `6to5-node` now uses `kexec` to become the forked process to correctly propagate signals on unix.
+ * Constants are now block scoped.
+ * Exposed ast transformer.
+ * Merged `commonInterop` and `common` module formatters.
+ * Fix generator comprehensions not inheriting `arguments`, `this` etc.
+ * Object and class mutator shorthand are now enumerable.
+ * Remove regenerator `Generator has already finished` error which isn't spec-compliant.
+ * Expose internal `spec` transformers that nicen up code output.
+ * Add export variable declaration default initializers.
+ * Propagate export declaration reassignments.
+ * Add initializer default to block scoped variable declarations within a loop.
+ * Flow type support.
+ * Make async/await contextual keywords.
+ * Allow `yield`ing of non-objects.
+ * Class declarations now lack an IIFE.
+ * Support falsy and `null` super classes.
+ * Add support for experimental abstract references `private` declarations.
+ * Leave out IIFE for class declarations.
+ * Switched to [core-js](https://github.com/zloirock/core-js) from [es6-symbol](https://github.com/medikoo/es6-symbol) and [es6-shim](https://github.com/paulmillr/es6-shim/) for built-in polyfill.
+ * `amd` and `umd` module formatters now behave the same as `common` with `interopRequire`.
+ * Micro-optimizations to boost performance by 200%.
+ * Rename module formatter methods `import` to `importDeclaration` and `export` to `exportDeclaration`.
+ * Support multiple declarators in export variable declarations.
+ * Freeze tagged template literal object.
+ * Remove inlined `regenerator` fork.
+ * Remove `ParenthesizedExpression`.
+ * Rename `object-spread` helper to `object-without-properties`.
+ * Rename `class-props` helper to `prototype-properties`.
+ * Rename `extends` helper to `inherits`.
+ * Completely rewritten `system` module formatter.
+
+## 1.15.0
+
+ * Don't alias `GeneratorFunction` and check the name which causes minifiers to remove the name and throw an error later on when we check if it's set.
+
+## 1.14.18
+
+ * Fix files only containg comments not being output.
+ * Fix duplicate comments on property key shorthands.
+
+## 1.14.17
+
+ * Add default initializer to let variables within loop bodies.
+ * Fix excessive `break` replacement inside of switches in let scoping.
+
+## 1.14.16
+
+ * Add object getter memos and this shorthand to playground.
+ * Fix while loops in let scoping.
+ * Upgrade `acorn-6to5`.
+
+## 1.14.14
+
+ * Fix template literals escaping.
+
+## 1.14.13
+
+ * Fix let scoping of `while` loops.
+ * Make class methods enumerable.
+
+## 1.14.12
+
+ * Fix duplicate dynamic expressions in call spread.
+
+## 1.14.10
+
+ * Fix let scoping unneccesary override.
+
+## 1.14.6
+
+ * Avoid ensuring a block on non-array node replacements.
+
+## 1.14.5
+
+ * Upgrade `acorn-6to5`.
+ * Fix JSON recursion error for unknown code generator node types.
+ * Ensure that a statement is a block on block/statement types when replacing them with multiple nodes.
+
+## 1.14.4
+
+ * Merge pretzel maps and method binding.
+
+## 1.14.3
+
+ * Add playground pretzel maps.
+
+## 1.14.2
+
+ * Fix `commonInterop` default export handling.
+ * Fix keyworded property key identifiers being turned into computed property key literals.
+
+## 1.14.1
+
+ * Inherit comments from `ClassDeclaration`.
+
+## 1.14.0
+
+ * Add [playground](https://6to5.github.io/playground.html).
+
+## 1.13.13
+
+ * Fix `--debug` in `bin/6to5-node`. Thanks [@timoxley](https://github.com/timoxley).
+
+## 1.13.12
+
+ * Ignore `XJSEmptyExpression`s in `react` transformer output.
+
+## 1.13.11
+
+ * Fix `util.regexify` on falsy values.
+ * Fix `_aliasFunction` with rest parameters.
+ * Export as `module.exports` instead of `exports.default` if there are no other `ExportDeclaration`s in `commonInterop` module formatter.
+ * Add `system` module formatter. Thanks [@douglasduteil](https://github.com/douglasduteil).
+
+## 1.13.10
+
+ * Add support for `AssignmentExpression` destructuring outside of `ExpressionStatement`.
+
+## 1.13.9
+
+ * Fix `VirtualPropertyExpression` visitor keys.
+
+## 1.13.8
+
+ * Only use a single reference in abstract references.
+
+## 1.13.7
+
+ * Upgrade `acorn-6to5`.
+ * Add experimental exponentiation operator support.
+
+## 1.13.6
+
+ * Fix experimental object spread/rest helper.
+
+## 1.13.5
+
+ * Upgrade `acorn-6to5`.
+ * Add experimental support for object spread/rest.
+ * Change `arguments` to array to an additional helper method.
+
+## 1.13.4
+
+ * Fix single spread element returning itself.
+
+## 1.13.3
 
  * Upgrade `acorn-6to5`.
  * Add experimental support for abstract references.
 
-# 1.13.2
+## 1.13.2
 
  * Optimise `Array.from` usage by adding a helper method.
  * Upgrade `acorn-6to5`.
 
-# 1.13.1
+## 1.13.1
 
  * Fix constructor spread optimisation. Thanks [@zloirock](https://github.com/zloirock).
 
-# 1.13.0
+## 1.13.0
 
  * Put experimental ES7 features behind a flag `--experimental` and `experimental` option.
  * Constructor spread performance increase. Thanks [@RReverser](https://github.com/RReverser).
  * Use `self` instead of `window` in the optional 6to5 runtime. Thanks [@RReverser](https://github.com/RReverser).
 
-# 1.12.26
+## 1.12.26
 
  * Support computed property destructuring.
 
-# 1.12.25
+## 1.12.25
 
  * Update `acorn-6to5`, `ast-types`, `es6-shim`, `chokidar`, `estraverse` and `private`.
 
-# 1.12.24
+## 1.12.24
 
  * Collect references that haven't been declared in scope.
 
-# 1.12.23
+## 1.12.23
 
  * Fix generator function export hoisting.
 
-# 1.12.22
+## 1.12.22
 
  * Update `fs-readdir-recursive` and `chokidar`.
  * Support array destructuring on iterables.
  * Make amd module id optional. Thanks [@webpro](https://github.com/webpro).
 
-# 1.12.21
+## 1.12.21
 
  * Fix unneccesary let scoping replacement.
  * Add `commonInterop` module formatter. Thanks [@Naddiseo](https://github.com/Naddiseo).
  * Fix `return` outside of function body bug. Thanks [@brentburg](https://github.com/brentburg).
  * Add more flexible option types.
 
-# 1.12.20
+## 1.12.20
 
  * Append `sourceMappingURL` when using `bin/6to5` and output sourcemaps.
 
-# 1.12.19
+## 1.12.19
 
  * Add `comments` option and `--remove-comments` flag. Thanks [@webpro](htps://github.com/webpro).
  * Embed `regenerator`.
 
-# 1.12.18
+## 1.12.18
 
  * Use `global` reference instead of `window`.
 
-# 1.12.17
+## 1.12.17
 
  * Add `moduleName`, `sourceRoot` and `filenameRelative` options. Thanks [@darvelo](https://github.com/darvelo).
  * Traversal optimisations.
 
-# 1.12.16
+## 1.12.16
 
  * Fix comments not being retained from `MethodDefinition` in classes.
  * Add temporal dead zone in default parameters.
 
-# 1.12.15
+## 1.12.15
 
  * Update `acorn-6to5`.
 
-# 1.12.14
+## 1.12.14
 
  * Fix duplicate let scoping in functions.
  * Make JSX whitespace more React-compliant.
  * Add `_memberExpressionKeywords` transformer that turns keyword identifiers to computed literals.
  * Upgrade `regenerator-6to5`.
 
-# 1.12.13
+## 1.12.13
 
  * Support duplicate constants within different block scopes.
  * Fix for-head duplication testing and replacement.
  * Support `raw` property on tagged template literals.
 
-# 1.12.12
+## 1.12.12
 
  * Make scope tracker more reliable to handle all edgecases.
 
-# 1.12.11
+## 1.12.11
 
  * Block scope classes.
  * Fix generation of integer `Literal`s in `MemberExpression`.
 
-# 1.12.10
+## 1.12.10
 
  * Fix let scoping var hoisting.
 
-# 1.12.9
+## 1.12.9
 
  * Escape unicode characters when generating string `Literal`s.
  * Fix semicolons being output for statements in `ExportDeclaration`.
  * Fix `WithStatement` missing parenthesis.
 
-# 1.12.8
+## 1.12.8
 
  * Temporarily forbid `AssignmentExpression` destructuring outside of `ExpressionStatement`.
 
-# 1.12.7
+## 1.12.7
 
  * Update to latest `acorn-6to5`.
 
-# 1.12.6
+## 1.12.6
 
  * Update to latest `acorn-6to5`.
 
-# 1.12.5
+## 1.12.5
 
  * Fix excessive whitespace trimming resulting in innaccurate sourcemap line.
 
-# 1.12.4
+## 1.12.4
 
  * Add `doc` folder for documentation.
 
-# 1.12.3
+## 1.12.3
 
  * Support generator comprehensions.
  * Use `Array.from` instead of `Array.prototype.slice` in spread transformer.
  * Support spread in `NewExpression`s.
 
-# 1.12.2
+## 1.12.2
 
  * Upgrade `matcha` to `0.6.0` and `browserify` to `6.3.2`.
  * Add own `trimRight` helper instead of relying on the string instance method.
  * Support JSX spreads that aren't the first.
 
-# 1.12.1
+## 1.12.1
 
  * Fix `this` and `arguments` mapping in the `_aliasFunctions` transformer.
 
-# 1.12.0
+## 1.12.0
 
  * Combine `jsx` and `react` transformers to `react`.
  * Update `react` syntax output to React v0.12.
 
-# 1.11.15
+## 1.11.15
 
  * Fix JSX literal whitespace generation.
 
-# 1.11.14
+## 1.11.14
 
  * Avoid using a switch for let-scoping continue and break statements and use an if statement instead.
  * Remove excess whitespace and newlines from JSX literals.
 
-# 1.11.13
+## 1.11.13
 
  * Update regenerator-6to5
  * Add support for most escodegen formatting options

CODE_OF_CONDUCT.md

@@ -0,0 +1,13 @@
+# Contributor Code of Conduct
+
+As contributors and maintainers of this project, we pledge to respect all people who contribute through reporting issues, posting feature requests, updating documentation, submitting pull requests or patches, and other activities.
+
+We are committed to making participation in this project a harassment-free experience for everyone, regardless of level of experience, gender, gender identity and expression, sexual orientation, disability, personal appearance, body size, race, age, or religion.
+
+Examples of unacceptable behavior by participants include the use of sexual language or imagery, derogatory comments or personal attacks, trolling, public or private harassment, insults, or other unprofessional conduct.
+
+Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct. Project maintainers who do not follow the Code of Conduct may be removed from the project team.
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by opening an issue or contacting one or more of the project maintainers.
+
+This Code of Conduct is adapted from the [Contributor Covenant](http://contributor-covenant.org), version 1.0.0, available at [http://contributor-covenant.org/version/1/0/0/](http://contributor-covenant.org/version/1/0/0/)

CONTRIBUTING.md

@@ -1,5 +1,7 @@
 # Contributing
 
+Before contributing, please read the [code of conduct](https://github.com/6to5/6to5/blob/master/CODE_OF_CONDUCT.md).
+
  * **General**
    * No ES6 syntax features or methods, exclusively ES5.
    * Max of five arguments for functions
@@ -9,7 +11,6 @@
    * CamelCase all class names
    * camelBack all variable names
  * **Spacing**
-   * 80 character line max
    * Spaces after all keywords
    * Spaces before all left curly braces
  * **Comments**

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2014 Sebastian McKenzie
+Copyright (c) 2014-2015 Sebastian McKenzie
 
 MIT License
 

Makefile

@@ -16,13 +16,12 @@ bench:
 	node node_modules/matcha/bin/_matcha
 
 lint:
-	$(JSHINT_CMD) lib bin benchmark/index.js
+	$(JSHINT_CMD) --reporter node_modules/jshint-stylish/stylish.js lib bin benchmark/index.js
 
 test-clean:
 	rm -rf test/tmp
 
-test:
-	make lint
+test: lint
 	$(MOCHA_CMD)
 	make test-clean
 
@@ -33,8 +32,7 @@ test-cov:
 test-spec:
 	node $(ISTANBUL_CMD) $(MOCHA_CMD) -- --reporter spec
 
-test-travis:
-	make test-spec
+test-travis: test-spec
 	if test -n "$$CODECLIMATE_REPO_TOKEN"; then codeclimate < coverage/lcov.info; fi
 
 test-browser:

README.md

@@ -3,12 +3,12 @@
 </p>
 
 <p align="center">
-  <a href="https://travis-ci.org/6to5/6to5">
-    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
+  <a href="https://gratipay.com/sebmck">
+    <img alt="Gratipay" src="https://img.shields.io/gratipay/sebmck.svg?style=flat">
   </a>
 
-  <a href="https://ci.appveyor.com/project/sebmck/6to5">
-    <img alt="Appveyor Status" src="http://img.shields.io/appveyor/ci/sebmck/6to5.svg?style=flat&amp;label=appveyor">
+  <a href="https://travis-ci.org/6to5/6to5">
+    <img alt="Travis Status" src="http://img.shields.io/travis/6to5/6to5/master.svg?style=flat&amp;label=travis">
   </a>
 
   <a href="https://codeclimate.com/github/6to5/6to5">
@@ -24,7 +24,11 @@
   </a>
 </p>
 
-**6to5** turns ES6+ code into vanilla ES5, so you can use next generation features **today.**
+<p align="center">
+  <strong>6to5</strong> turns ES6+ code into vanilla ES5, so you can use next generation features <strong>today.</strong>
+</p>
 
-For more information view the [documentation](https://6to5.github.io). For
-support visit the [gitter room](https://gitter.im/6to5/6to5).
+<p align="center">
+  For more information view the <a href="https://6to5.github.io">documentation</a>. For
+  support visit the <a href="https://gitter.im/6to5/6to5">gitter room</a>.
+</p>

benchmark/index.js

@@ -2,9 +2,9 @@ Error.stackTraceLimit = Infinity;
 
 var jsTrans = require("jstransform");
 var traceur = require("traceur");
-var es6tr   = require("es6-transpiler");
+//var es6tr   = require("es6-transpiler");
 var es6now  = require("es6now");
-var esnext  = require("esnext");
+//var esnext  = require("esnext");
 var to5     = require("../lib/6to5");
 
 //var uglify  = require("uglify-js");
@@ -56,12 +56,12 @@ var compilers = {
     }
   },
 
-  esnext: {
+  /*esnext: {
     runtime: readResolve("esnext/node_modules/regenerator/runtime.js") || readResolve("regenerator/runtime.js"),
     compile: function (code) {
       return esnext.compile(code).code;
     }
-  },
+  },*/
 
   es6now: {
     runtime: readResolve("es6now/runtime/ES6.js"),
@@ -70,13 +70,13 @@ var compilers = {
     }
   },
 
-  "es6-transpiler": {
+  /*"es6-transpiler": {
     compile: function (code) {
       var result = es6tr.run({ src: code });
       if (result.errors.length) throw new Error(result.join("; "));
       return result.src;
     }
-  },
+  },*/
 
   jstransform: {
     compile: function (code) {

bin/6to5-node

@@ -5,7 +5,6 @@
  * when found, before invoking the "real" _6to5-node(1) executable.
  */
 
-var spawn = require("child_process").spawn;
 var args  = ["--harmony", __dirname + "/_6to5-node"];
 
 process.argv.slice(2).forEach(function(arg){
@@ -14,18 +13,19 @@ process.argv.slice(2).forEach(function(arg){
   switch (flag) {
     case "-d":
       args.unshift("--debug");
-      args.push("--no-timeouts");
       break;
+
     case "debug":
     case "--debug":
     case "--debug-brk":
       args.unshift(arg);
-      args.push("--no-timeouts");
       break;
+
     case "-gc":
     case "--expose-gc":
       args.unshift("--expose-gc");
       break;
+
     case "--gc-global":
     case "--harmony":
     case "--harmony-proxies":
@@ -37,20 +37,32 @@ process.argv.slice(2).forEach(function(arg){
     case "--trace-deprecation":
       args.unshift(arg);
       break;
+
     default:
-      if (0 == arg.indexOf("--trace")) args.unshift(arg);
-      else args.push(arg);
+      if (arg.indexOf("--trace") === 0) {
+        args.unshift(arg);
+      } else {
+        args.push(arg);
+      }
       break;
   }
 });
 
-var proc = spawn(process.argv[0], args, { stdio: "inherit" });
-proc.on("exit", function (code, signal) {
-  process.on("exit", function (){
-    if (signal) {
-      process.kill(process.pid, signal);
-    } else {
-      process.exit(code);
-    }
+try {
+  var kexec = require("kexec");
+  kexec(process.argv[0], args);
+} catch (err) {
+  if (err.code !== "MODULE_NOT_FOUND") throw err;
+
+  var child_process = require("child_process");
+  var proc = child_process.spawn(process.argv[0], args, { stdio: "inherit" });
+  proc.on("exit", function (code, signal) {
+    process.on("exit", function () {
+      if (signal) {
+        process.kill(process.pid, signal);
+      } else {
+        process.exit(code);
+      }
+    })
   });
-});
+}

bin/6to5-runtime

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

bin/6to5/file.js

@@ -113,16 +113,14 @@ module.exports = function (commander, filenames) {
     walk();
 
     if (commander.watch) {
-      var watcher = chokidar.watch(filenames, {
+      chokidar.watch(filenames, {
         persistent: true,
         ignoreInitial: true
-      });
-
-      _.each(["add", "change", "unlink"], function (type) {
-        watcher.on(type, function (filename) {
+      }).on("all", function (type, filename) {
+        if (type === "add" || type === "change" || type === "unlink" ) {
           console.log(type, filename);
           walk();
-        });
+        }
       });
     }
   };

bin/6to5/index.js

@@ -12,22 +12,33 @@ commander.option("-f, --filename [filename]", "Filename to use when reading from
 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");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
 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("-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("-a, --amd-module-ids", "Insert module id in AMD modules", false);
+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.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 + "]";
+      }
+
       console.log("    - " + key);
     });
 
@@ -88,11 +99,13 @@ if (errors.length) {
 
 exports.opts = {
   sourceMapName: commander.outFile,
-  amdModuleIds:  commander.amdModuleIds,
   experimental:  commander.experimental,
+  playground:    commander.playground,
+  moduleIds:     commander.amdModuleIds || 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

bin/_6to5-node

@@ -1,30 +1,38 @@
 #!/usr/bin/env node
 
-var commander = require("commander");
-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 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");
 
 commander.option("-e, --eval [script]", "Evaluate script");
 commander.option("-p, --print", "Evaluate script and print result");
 commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
 commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
 commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
+commander.option("-g, --playground", "Enable playground support");
+commander.option("-c, --cache", "Cache compiled files and require paths");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
 commander.usage("[options] [ -e script | script.js ] [arguments]");
 commander.parse(process.argv);
 
+if (commander.cache) roadrunner.load();
+
 //
 
 to5.register({
   experimental: commander.experimental,
   extensions:   commander.extensions,
-  ignore:       commander.ignore
+  playground:   commander.playground,
+  ignore:       commander.ignore,
+  cache:        commander.cache && roadrunner.get("6to5")
 });
 
 //
@@ -33,7 +41,8 @@ var _eval = function (code, filename) {
   code = to5.transform(code, {
     filename: filename,
     blacklist: ["useStrict"],
-    experimental: commander.experimental
+    experimental: commander.experimental,
+    playground: commander.playground
   }).code;
   return vm.runInThisContext(code, filename);
 };
@@ -42,21 +51,34 @@ if (commander.eval) {
   var result = _eval(commander.eval, "eval");
   if (commander.print) console.log(result);
 } else {
-  var filenames = commander.args;
+  if (commander.args.length) {
+    // slice all arguments up to the first filename since they're 6to5 args that we handle
+    var args = process.argv.slice(2);
 
-  if (filenames.length) {
-    _.each(filenames, function (filename) {
-      if (!util.isAbsolute(filename)) {
-        filename = path.join(process.cwd(), filename);
+    var i = 0;
+    _.each(args, function (arg, i2) {
+      if (arg[0] !== "-") {
+        i = i2;
+        return false;
       }
-
-      require(require.resolve(filename));
     });
+    args = args.slice(i);
+
+    // make the filename absolute
+    var filename = args[0]
+    if (!util.isAbsolute(filename)) args[0] = path.join(process.cwd(), filename);
+
+    // add back on node and concat the sliced args
+    process.argv = ["node"].concat(args);
+
+    Module.runMain();
   } else {
     replStart();
   }
 }
 
+if (commander.cache) roadrunner.save();
+
 function replStart() {
   repl.start({
     prompt: "> ",

doc/browser.md

@@ -30,7 +30,9 @@ test.test();
 You can build a browser version of the compiler by running the following in the
 6to5 directory:
 
-    $ make build
+```sh
+$ make build
+```
 
 This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
@@ -38,7 +40,9 @@ This will output the files `dist/6to5.js` and `dist/6to5.min.js`.
 
 To test 6to5 in your browser run:
 
-    $ make test-browser
+```sh
+$ make test-browser
+```
 
 And open `test/browser.html` in your browser if it doesn't open automatically.
 

doc/caveats.md

@@ -2,27 +2,40 @@
 
 In order for certain features to work they require certain polyfills. You can
 satisfy **all** 6to5 feature requirements by using the included
-[polyfill](polyfill.md). You may alternatively selectively include what you need:
+[polyfill](polyfill.md).
 
-| Feature                     | Requirements                                                                                                                        |
-| --------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- |
-| Abstract References         | `Symbol`                                                                                                                            |
-| Array destructuring         | `Array.isArray`, `Array.from`                                                                                                       |
-| Async functions, Generators | [experimental option](usage.md#experimental), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
-| Comprehensions              | [experimental option](usage.md#experimental), `Array.isArray`, `Array.from`                                                         |
-| For..Of                     | `Symbol`, `prototype[Symbol.iterator]`                                                                                              |
-| Spread                      | `Array.isArray`, `Array.from`                                                                                                       |
+You may alternatively selectively include what you need:
 
-## Classes
+| Feature                     | Requirements                                                                                                           |
+| --------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
+| Abstract References         | [experimental](experimental.md), `Symbol`                                                                              |
+| Array destructuring         | `Array.from`                                                                                                           |
+| Async functions, Generators | [experimental](experimental.md), [regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) |
+| Comprehensions              | [experimental](experimental.md), `Array.from`                                                                          |
+| For Of                      | `Symbol`, `prototype[Symbol.iterator]`                                                                                 |
+| Modules                     | `Object.assign`*                                                                                                       |
+| Object spread/rest          | [experimental](experimental.md), `Object.assign`                                                                       |
+| Spread                      | `Array.from`                                                                                                           |
 
-Built-in classes such as `Date`, `Array` and `DOM` cannot be subclassed due to
-limitations in ES5 implementations.
+*Only required for exporting a non-function `default` with additional `export`s.
+
+## ES5
+
+Since 6to5 assumes that your code will be ran in an ES5 environment it uses ES5
+functions. So if you're using an environment that has limited or no support for
+ES5 such as lower versions of IE then using the
+[es5-shim](https://github.com/es-shims/es5-shim) along with the
+[6to5 polyfill](polyfill.md) will add support for these methods.
+
+## Internet Explorer
+
+### Classes (10 and below)
 
 If you're inheriting from a class then static properties are inherited from it
 via [\_\_proto\_\_](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/proto),
 this is widely supported but you may run into problems with much older browsers.
 
-**NOTE:** `__proto__` is not supported on IE <= 9 so static properties
+**NOTE:** `__proto__` is not supported in IE <= 10 so static properties
 **will not** be inherited. A possible workaround is to use `super();`:
 
 ```javascript
@@ -38,3 +51,12 @@ class Bar extends Foo {
   }
 }
 ```
+
+## Getters/setters (8 and below)
+
+In IE8 `Object.defineProperty` can only be used on DOM objects. This is
+unfortunate as it's required to set getters and setters. Due to this if
+you plan on supporting IE8 or below then the user of getters and setters
+isn't recommended.
+
+**Reference**: [MDN](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty#Internet_Explorer_8_specific_notes).

doc/differences.md

@@ -1,6 +1,8 @@
 # Differences
 
-## Philosophy
+There are three main points that separate 6to5 from all other transpilers.
+
+### Readable code
 
 The fundamental concept behind 6to5 is that the generated code must be close as
 possible to the original, retaining all the same formatting and readability.
@@ -17,7 +19,7 @@ var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, a
 is generated to the following with 6to5:
 
 ```javascript
-var seattlers = customers.filter(function (c) {
+var seattlers = Array.from(customers).filter(function (c) {
   return c.city == "Seattle";
 }).map(function (c) {
   return {
@@ -47,12 +49,30 @@ var seattlers = (function() {
 }());
 ```
 
-As you can tell, it's not very pretty, unreadable even. Instead of mapping
-directly to a runtime, like other transpilers, 6to5 maps directly to the
-equivalent ES5.
+As you can tell, it's not very pretty. Instead of mapping directly to a
+runtime, like other transpilers, 6to5 maps directly to the equivalent ES5.
 
-I'm not saying 6to5 is for everyone or even suited for everything. Traceur is
-better suited if you'd like a full ES6 environment with polyfills and all.
+Sometimes there are little inline functions that 6to5 needs. These are
+placed at the top of your file much like coffee-script does. If these
+bother you then you can use the [optional runtime](optional-runtime.md).
+We promise that these inline functions will never be significant and will
+always be used as little as possible.
+
+### Static analysis
+
+6to5 uses a lot of static analysis to simplify code as much as possible.
+Not many other transpilers do this, and those that do don't do it nearly
+as much as 6to5. This process is pretty intensive but it leads to higher
+quality code.
+
+### Spec compliancy
+
+6to5 prides itself on
+[spec compliancy](https://kangax.github.io/compat-table/es6/). We have
+excellent support for edgecases, something that many other transpilers
+suffer from, including Traceur. When you use 6to5 you can be confident
+that when you turn it off and use your code in a full ES6 environment
+**it'll just work**.
 
 ## Comparison to other transpilers
 
@@ -63,38 +83,44 @@ better suited if you'd like a full ES6 environment with polyfills and all.
 | Source maps                  | ✓    | ✓       | ✓              | ✓      |        | ✓           |
 | No compiler global pollution | ✓    |         | ✓              | ✓      |        | ✓           |
 | Optional runtime             | ✓    |         | ✓              |        |        | ✓           |
-| Browser support              | ✓    | ✓       |                | ✓      |        |             |
+| Browser compiler             | ✓    | ✓       |                | ✓      |        |             |
 
 ### Language Support
 
-|                              | 6to5  | Traceur | es6-transpiler | esnext | es6now | jstransform |
-| ---------------------------- | ----- | ------- | -------------- | ------ | ------ | ----------- |
-| Abstract references          | ✓     |         |                |        |        |             |
-| Array comprehension          | ✓     | ✓       | ✓              |        |        |             |
-| Arrow functions              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Async functions              | ✓     | ✓       |                | ✓      |        |             |
-| Classes                      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Computed property names      | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Constants                    | ✓     | ✓       | ✓              |        |        |             |
-| Default parameters           | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Destructuring                | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| For-of                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Generators                   | ✓     | ✓       |                | ✓      |        |             |
-| Generator comprehension      | ✓     | ✓       |                |        |        |             |
-| Let scoping                  | ✓     | ✓       | ✓              |        |        |             |
-| Modules                      | ✓     | ✓       |                |        | ✓      |             |
-| Property method assignment   | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Property name shorthand      | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Rest parameters              | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Spread                       | ✓     | ✓       | ✓              | ✓      | ✓      |             |
-| Template literals            | ✓     | ✓       | ✓              | ✓      | ✓      | ✓           |
-| Unicode regex                | ✓     | ✓       | ✓              |        |        |             |
+|                              | 6to5 | Traceur | es6-transpiler | esnext | es6now | jstransform |
+| ---------------------------- | ---- | ------- | -------------- | ------ | ------ | ----------- |
+| Abstract references          | ✓    |         |                |        |        |             |
+| Array comprehension          | ✓    | ✓       | ✓              |        |        |             |
+| Arrow functions              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Async functions              | ✓    | ✓       |                | ✓      |        |             |
+| Async generator functions    | ✓    | ✓       |                |        |        |             |
+| Classes                      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Computed property names      | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Constants                    | ✓    | ✓       | ✓              |        |        |             |
+| Default parameters           | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Destructuring                | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Exponentiation operator      | ✓    | ✓       |                |        |        |             |
+| Flow types                   | ✓    |         |                |        |        | ✓           |
+| For-of                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Generators                   | ✓    | ✓       |                | ✓      |        |             |
+| Generator comprehension      | ✓    | ✓       |                |        |        |             |
+| JSX                          | ✓    |         |                |        |        |             |
+| Let scoping                  | ✓    | ✓       | ✓              |        |        |             |
+| Modules                      | ✓    | ✓       |                |        | ✓      |             |
+| Object rest/spread           | ✓    |         |                |        |        | ✓           |
+| Property method assignment   | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Property name shorthand      | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Rest parameters              | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| React                        | ✓    |         |                |        |        |             |
+| Spread                       | ✓    | ✓       | ✓              | ✓      | ✓      |             |
+| Template literals            | ✓    | ✓       | ✓              | ✓      | ✓      | ✓           |
+| Unicode regex                | ✓    | ✓       | ✓              |        |        |             |
 
 ### [Traceur](https://github.com/google/traceur-compiler)
 
 Traceur requires quite a bulky runtime (~75KB) and produces quite verbose code.
 While this can be trimmed down by selectively building the runtime, it's an
-unneccesary step when a runtime can be eliminated entirely.
+unnecessary step when a large runtime can be eliminated entirely.
 
 ### [es6now](https://github.com/zenparsing/es6now)
 

doc/experimental.md

@@ -0,0 +1,8 @@
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
+
+**WARNING:** These proposals are subject to change so use with
+**extreme caution**.

doc/features.md

@@ -1,6 +1,6 @@
 # Features
 
-## Abstract references ([experimental](usage.md#experimental)) ([spec](https://github.com/zenparsing/es-abstract-refs))
+## Abstract references ([experimental](experimental.md)) ([spec](https://github.com/zenparsing/es-abstract-refs))
 
 ```javascript
 foo::bar;
@@ -8,7 +8,7 @@ foo::bar = baz;
 delete foo::bar;
 ```
 
-## Array comprehension ([experimental](usage.md#experimental))
+## Array comprehensions ([experimental](experimental.md))
 
 ```javascript
 var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
@@ -39,7 +39,7 @@ var bob = {
 };
 ```
 
-## Async functions ([experimental](usage.md#experimental)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
+## Async functions ([experimental](experimental.md)) ([spec](https://github.com/lukehoban/ecmascript-asyncawait))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -49,6 +49,12 @@ async function chainAnimationsAsync(elem, animations) {
 }
 ```
 
+## Async generator functions ([experimental](experimental.md)) ([spec](https://github.com/jhusain/asyncgenerator))
+
+```javascript
+
+```
+
 ## Classes
 
 ```javascript
@@ -130,6 +136,15 @@ var [a] = [];
 a === undefined;
 ```
 
+## Exponentiation operator ([experimental](experimental.md)) ([spec](https://github.com/rwaldron/exponentiation-operator))
+
+```javascript
+var a = 2;
+a **= 2;
+
+var squared = 2 ** 2;
+```
+
 ## For-of
 
 ```javascript
@@ -158,7 +173,7 @@ for (var n of fibonacci()) {
 }
 ```
 
-## Generator comprehension ([experimental](usage.md#experimental))
+## Generator comprehensions ([experimental](experimental.md))
 
 ```javascript
 var nums = [1, 2, 3, 4, 5, 6];
@@ -199,6 +214,13 @@ export default test;
 0o767 === 503; // true
 ```
 
+## Object spread/rest ([experimental](experimental.md)) ([spec](https://github.com/sebmarkbage/ecmascript-rest-spread))
+
+```javascript
+var n = { x, y, ...z };
+var { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
+```
+
 ## Property method assignment
 
 ```javascript
@@ -252,7 +274,6 @@ var x = 5;
 var y = 10;
 console.log(`${x} + ${y} = ${x + y}`); // "5 + 10 = 15"
 ```
-
 ## Unicode regex
 
 ```javascript

doc/index.md

@@ -19,33 +19,40 @@ how you want to use it.
 6to5 will simply compile your ES6+ script to ES5 if you pass it as an argument
 to the command-line tool `6to5`:
 
-    $ 6to5 script.js
+```sh
+$ 6to5 script.js
+```
 
 If you have a file written using ES6+ and you just want to run it, `6to5-node`
 has you covered:
 
-    $ 6to5-node script.js
+```sh
+$ 6to5-node script.js
+```
 
 And it doesn't end here! To see all the ways you can use 6to5, check out the
 [Usage](http://6to5.github.io/usage.html) page.
 
 ## [Features](features.md)
 
- - [Abstract references](features.md#abstract-references) ([experimental](usage.md#experimental))
- - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
- - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
+ - [Abstract references](features.md#abstract-references) ([experimental](experimental.md))
+ - [Array comprehension](features.md#array-comprehension) ([experimental](experimental.md))
+ - [Async functions](features.md#async-functions) ([experimental](experimental.md))
+ - [Async generator functions](features.md#async-generator-functions) ([experimental](experimental.md))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
  - [Constants](features.md#constants)
  - [Default parameters](features.md#default-parameters)
  - [Destructuring](features.md#destructuring)
+ - [Exponentiation operator](features.md#exponentiation-operator) ([experimental](experimental.md))
  - [For-of](features.md#for-of)
  - [Generators](features.md#generators)
- - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](experimental.md))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)
+ - [Object rest/spread](features.md#object-rest-spread) ([experimental](experimental.md))
  - [Property method assignment](features.md#property-method-assignment)
  - [Property name shorthand](features.md#property-name-shorthand)
  - [React/JSX](react.md)

doc/modules.md

@@ -4,7 +4,9 @@
 
 ### CLI
 
-    $ 6to5 --modules common script.js
+```sh
+$ 6to5 --modules common script.js
+```
 
 ### Node
 
@@ -15,11 +17,26 @@ to5.transform('import "foo";', { modules: "common" });
 
 ## Formats
 
-### Common (Default)
+ * [AMD](#amd)
+ * [Common (Default)](#common-default)
+ * [Ignore](#ignore)
+ * [System](#system)
+ * [UMD](#umd)
+
+### Common
+
+```sh
+$ 6to5 --modules common
+```
 
 **In**
 
 ```javascript
+export default test;
+
+export {test};
+export var test = 5;
+
 import "foo";
 
 import foo from "foo";
@@ -27,32 +44,38 @@ import * as foo from "foo";
 
 import {bar} from "foo";
 import {foo as bar} from "foo";
-
-export {test};
-export var test = 5;
-
-export default test;
 ```
 
 **Out**
 
 ```javascript
+"use strict";
+
+var _interopRequire = function (obj) {
+  return obj && (obj["default"] || obj);
+};
+
+exports = module.exports = test;
+
+exports.test = test;
+var test = exports.test = 5;
+
 require("foo");
 
-var foo = require("foo").default;
+var foo = _interopRequire(require("foo"));
+
 var foo = require("foo");
 
 var bar = require("foo").bar;
 var bar = require("foo").foo;
-
-exports.test = test;
-var test = 5; exports.test = test;
-
-exports.default = test;
 ```
 
 ### AMD
 
+```sh
+$ 6to5 --modules amd
+```
+
 **In**
 
 ```javascript
@@ -67,9 +90,14 @@ export function bar() {
 
 ```javascript
 define(["exports", "foo"], function (exports, _foo) {
-  exports.bar = bar;
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -85,6 +113,10 @@ define("filename", ["exports", "foo"], function (exports, _foo) {})
 
 ### UMD
 
+```sh
+$ 6to5 --modules umd
+```
+
 **In**
 
 ```javascript
@@ -104,10 +136,15 @@ export function bar() {
   } else if (typeof exports !== "undefined") {
     factory(exports, require("foo"));
   }
-})(function (exports) {
-  exports.bar = bar;
+})(function (exports, _foo) {
+  "use strict";
 
-  var foo = _foo.default;
+  var _interopRequire = function (obj) {
+    return obj && (obj["default"] || obj);
+  };
+
+  exports.bar = bar;
+  var foo = _interopRequire(_foo);
 
   function bar() {
     return foo("foobar");
@@ -117,6 +154,10 @@ export function bar() {
 
 ### Ignore
 
+```sh
+$ 6to5 --modules ignore
+```
+
 **In**
 
 ```javascript
@@ -135,11 +176,52 @@ function bar() {
 }
 ```
 
+### System
+
+```sh
+$ 6to5 --modules system
+```
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+System.register("bar", ["foo"], function (_export) {
+  "use strict";
+
+  var __moduleName = "bar";
+
+  var foo;
+  function bar() {
+    return foo("foobar");
+  }
+  return {
+    setters: [function (m) {
+      foo = m.default;
+    }],
+    execute: function () {
+      _export("bar", bar);
+    }
+  };
+});
+```
+
 ## Custom
 
 You can alternatively specify module names instead of one of the built-in types.
 
-    $ 6to5 --modules custom-module-formatter
+```sh
+$ 6to5 --modules custom-module-formatter
+```
 
 **node_modules/custom-module-formatter/index.js**
 
@@ -155,7 +237,7 @@ ModuleFormatter.prototype.transform = function (ast) {
   // feel free to modify this however
 };
 
-ModuleFormatter.prototype.import = function (node, nodes) {
+ModuleFormatter.prototype.importDeclaration = function (node, nodes) {
   // node is an ImportDeclaration
 };
 
@@ -164,7 +246,7 @@ ModuleFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   // node is an ImportDeclaration
 };
 
-ModuleFormatter.prototype.export = function (node, nodes) {
+ModuleFormatter.prototype.exportDeclaration = function (node, nodes) {
   // node is an ExportDeclaration
 };
 

doc/optional-runtime.md

@@ -18,7 +18,9 @@ Simply use the following option if you're using the [Node API](usage.md#node):
 
 or the following flag if you're using the [CLI](usage.md#cli):
 
-    $ 6to5 --runtime
+```ssh
+$ 6to5 --runtime
+```
 
 Then just include the runtime before your generated code.
 
@@ -26,7 +28,9 @@ Then just include the runtime before your generated code.
 
 You can get the runtime via either:
 
-    $ 6to5-runtime
+```sh
+$ 6to5-runtime
+```
 
 or
 
@@ -45,7 +49,9 @@ argument:
 require("6to5").runtime("myCustomNamespace");
 ```
 
-    $ 6to5-runtime myCustomNamespace
+```sh
+$ 6to5-runtime myCustomNamespace
+```
 
 See [Options - runtime](usage.md#options) for documentation on changing the
 reference in generated code.

doc/playground.md

@@ -0,0 +1,140 @@
+# Playground
+
+Playground is a proving ground for **possible** ES7 proposals.
+
+**NOTE: These features are in no way endorsed by Ecma International and are not a part of ES6. They might become a part of ECMAScript in the future.**
+
+## Usage
+
+    $ 6to5 --playground
+
+```javascript
+to5.transform("code", { playground: true });
+```
+
+**NOTE:** Enabling `playground` also enables [experimental support](experimental.md).
+
+## Features
+
+ * [Memoization operator](#memoization-operator)
+ * [Method binding](#method-binding)
+ * [Method binding function shorthand](#method-binding-function-shorthand)
+ * [Object getter memoization](#object-getter-memoization)
+ * [This shorthand](#this-shorthand)
+
+### Memoization assignment operator
+
+The memoization assignment operator allows you to lazily set an object property.
+It checks whether there's a property defined on the object and if there isn't then
+the right hand value is set.
+
+This means that `obj.x` in the following `var x = { x: undefined }; obj.x ?= 2;`
+will still be `undefined` because it's already been defined on the object.
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+obj.x; // 2
+
+obj = { x: 1 };
+obj.x ?= 2;
+obj.x; // 1
+
+obj = { x: undefined }
+obj.x ?= 2;
+obj.x; // undefined
+```
+
+```javascript
+var obj = {};
+obj.x ?= 2;
+```
+
+equivalent to
+
+```javascript
+var obj = {};
+if (!Object.prototype.hasOwnProperty.call(obj, "x")) obj.x = 2;
+```
+
+### Method binding
+
+```javascript
+var fn = obj#method;
+var fn = obj#method("foob");
+```
+
+equivalent to
+
+```javascript
+var fn = obj.method.bind(obj);
+var fn = obj.method.bind(obj, "foob");
+```
+
+### Method binding function shorthand
+
+```javascript
+["foo", "bar"].map(#toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(#toFixed(2)); // ["1.12", "23.53", "3.00"]
+```
+
+equivalent to
+
+```javascript
+["foo", "bar"].map(function (val) { return val.toUpperCase(); });
+[1.1234, 23.53245, 3].map(function (val) { return val.toFixed(2); });
+```
+
+### Object getter memoization
+
+```javascript
+var foo = {
+  memo bar() {
+    return complex();
+  }
+};
+
+class Foo {
+  memo bar() {
+    return complex();
+  }
+}
+```
+
+equivalent to
+
+```javascript
+var foo = {
+  get bar() {
+    return Object.defineProperty(this, "bar", {
+      value: complex(),
+      enumerable: true,
+      configurable: true,
+      writable: true
+    }).bar;
+  }
+};
+
+class Foo {
+  get bar() {
+    return Object.defineProperty(this, "bar", {
+      value: complex(),
+      enumerable: true,
+      configurable: true,
+      writable: true
+    }).bar;
+  }
+}
+```
+
+### This shorthand
+
+```javascript
+@foo
+```
+
+equivalent to
+
+```javascirpt
+this.foo
+```

doc/plugins.md

@@ -1,17 +1,33 @@
 # Plugins
 
- - [Broccoli](https://github.com/very-geek/broccoli-6to5-transpiler)
- - [Browserify](https://github.com/6to5/6to5-browserify)
- - [Brunch](https://github.com/es128/6to5-brunch)
- - [Duo](https://github.com/bdo-labs/duo6to5)
- - [Connect](https://github.com/6to5/6to5-connect)
- - [Gobble](https://github.com/gobblejs/gobble-6to5)
- - [Gulp](https://github.com/sindresorhus/gulp-6to5)
- - [Grunt](https://github.com/sindresorhus/grunt-6to5)
- - [Jade](https://github.com/Apoxx/jade-6to5)
+## Build systems
+
+ - [Broccoli](https://github.com/6to5/broccoli-6to5-transpiler)
+ - [Browserify](https://github.com/6to5/6to5ify)
+ - [Brunch](https://github.com/6to5/6to5-brunch)
+ - [Duo](https://github.com/6to5/duo6to5)
+ - [Gobble](https://github.com/6to5/gobble-6to5)
+ - [Gulp](https://github.com/6to5/gulp-6to5)
+ - [Grunt](https://github.com/6to5/grunt-6to5)
+ - [Sprockets](https://github.com/josh/sprockets-es6) or via [Browserify](https://github.com/6to5/6to5-rails)
+ - [webpack](https://github.com/6to5/6to5-loader)
+
+## Integrations
+
+ - [Isparta](https://github.com/douglasduteil/isparta) - Code coverage with `karma` and `instanbul` using 6to5
+ - [JSXHint](https://github.com/STRML/JSXHint) - A wrapper around JSHint to allow linting of JSX files
+
+## Bridges
+
+ - [Ruby](https://github.com/6to5/6to5-ruby)
+
+## Testing
+
  - [Jest](https://github.com/6to5/6to5-jest)
- - [JSXHint](https://github.com/STRML/JSXHint) (A wrapper around JSHint to allow linting of JSX files)
- - [Karma](https://github.com/shuhei/karma-6to5-preprocessor)
+ - [Karma](https://github.com/6to5/karma-6to5-preprocessor)
  - [Mocha](https://github.com/6to5/6to5-mocha)
- - [Rails](https://github.com/josh/sprockets-es6) or via [browserify-rails](https://github.com/6to5/6to5-rails)
- - [webpack](https://github.com/Couto/6to5-loader)
+
+## Misc
+
+ - [Connect](https://github.com/6to5/6to5-connect)
+ - [Jade](https://github.com/6to5/jade-6to5)

doc/polyfill.md

@@ -1,16 +1,15 @@
 # Polyfill
 
-6to5 includes a polyfill that includes the
-[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and the
-[es6-shim](https://github.com/paulmillr/es6-shim) and
-[es6-symbol](https://github.com/medikoo/es6-symbol) polyfills.
+6to5 includes a polyfill that includes a custom
+[regenerator runtime](https://github.com/facebook/regenerator/blob/master/runtime.js) and
+[core.js](https://github.com/zloirock/core-js).
 
 This will emulate a full ES6 environment. This polyfill is automatically loaded
-when using [6to5-node](usage.md#node).
+when using [6to5-node](usage.md#node) and [6to5/register](usage.md#register-hook).
 
 ## Usage
 
-### Node
+### Node/Browserify
 
 You need to include the polyfill require at the top the **entry point** to your
 application.
@@ -19,9 +18,17 @@ application.
 require("6to5/polyfill");
 ```
 
+Fortunately, this is automatically loaded when using:
+
+```javascript
+require("6to5/register");
+```
+
 ### Browser
 
 Available from the `browser-polyfill.js` file within the 6to5 directory of an
 npm release. This needs to be included **before** all your compiled 6to5 code.
 You can either prepend it to your compiled code or include it in a `<script>`
 before it.
+
+**NOTE:** Do not `require` this via browserify etc, use `6to5/polyfill`.

doc/react.md

@@ -12,5 +12,6 @@ To disable this behaviour add `react` to your blacklist:
 to5.transform("code", { blacklist: ["react"] });
 ```
 
-
-    $ 6to5 --blacklist react
+```sh
+$ 6to5 --blacklist react
+```

doc/usage.md

@@ -4,47 +4,67 @@
 
 Compile the file `script.js` and output it to stdout.
 
-    $ 6to5 script.js
+```sh
+$ 6to5 script.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js`.
 
-    $ 6to5 script.js --out-file script-compiled.js
+```sh
+$ 6to5 script.js --out-file script-compiled.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js` and save a
 source map to `script-compiled.js.map`.
 
-    $ 6to5 script.js --source-maps --out-file script-compiled.js
+```sh
+$ 6to5 script.js --source-maps --out-file script-compiled.js
+```
 
 Compile the file `script.js` and output it to `script-compiled.js` with a source
 map embedded in a comment at the bottom.
 
-    $ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```sh
+$ 6to5 script.js --source-maps-inline --out-file script-compiled.js
+```
 
 Compile the entire `src` directory and output it to the `lib` directory.
 
-    $ 6to5 src --out-dir lib
+```sh
+$ 6to5 src --out-dir lib
+```
 
 Compile the entire `src` directory and output it to the one concatenated file.
 
-    $ 6to5 src --out-file script-compiled.js
+```sh
+$ 6to5 src --out-file script-compiled.js
+```
 
 Pipe a file in via stdin and output it to `script-compiled.js`
 
-    $ 6to5 --out-file script-compiled.js < script.js
+```sh
+$ 6to5 --out-file script-compiled.js < script.js
+```
 
 ### Node
 
 Launch a repl.
 
-    $ 6to5-node
+```sh
+$ 6to5-node
+```
 
 Evaluate code.
 
-    $ 6to5-node -e "class Test { }"
+```sh
+$ 6to5-node -e "class Test { }"
+```
 
 Compile and run `test.js`.
 
-    $ 6to5-node test
+```sh
+$ 6to5-node test
+```
 
 ## Node
 
@@ -75,6 +95,15 @@ to5.transformFile("filename.js", options, function (err, result) {
 });
 ```
 
+### to5.transform.fromAst(ast, [code], [opts])
+
+```javascript
+var result = to5.transform.fromAst(ast, "var a = 2;", opts);
+result.code;
+result.map;
+result.ast;
+```
+
 #### Options
 
 ```javascript
@@ -123,23 +152,57 @@ to5.transformFile("filename.js", options, function (err, result) {
   // Default: `sourceRoot` option.
   moduleRoot: "my-app",
 
-  // If truthy, insert an explicit id for each defined AMD module.
-  // By default, AMD modules are anonymous.
+  // If truthy, insert an explicit id for each defined AMD/System module.
+  // By default, AMD/System modules are anonymous.
   // Default: false
-  amdModuleIds: true,
+  moduleIds: true,
 
   // Optionally replace all 6to5 helper declarations with a referenece to this
   // variable. If set to `true` then the default namespace is used "to5Runtime".
   // Default: false
   runtime: true,
 
-  // Output comments in generated output
-  // Default: true
-  comments: false,
-
   // Enable support for experimental ES7 features
   // Default: false
-  experimental: true
+  experimental: true,
+
+  // Set this to `false` if you don't want the transformed AST in the returned
+  // result
+  // Default: true
+  ast: true,
+
+  // Set this to `false` if you don't want the transformed code in the returned
+  // result
+  // Default: true
+  code: true,
+
+  format: {
+    // Output comments in generated output
+    // Default: true
+    comments: true,
+
+    // Do not include superfluous whitespace characters and line terminators
+    // Default: false
+    compact: false,
+
+    indent: {
+      // Preserve parentheses in new expressions that have no arguments
+      // Default: true
+      parentheses: true,
+
+      // Adjust the indentation of multiline comments to keep asterisks vertically aligned
+      // Default: true
+      adjustMultilineComment: true,
+
+      // Indent string
+      // Default: "  "
+      style: "  ",
+
+      // Base indent level
+      // Default: 0
+      base: 0
+    }
+  }
 }
 ```
 
@@ -147,7 +210,10 @@ to5.transformFile("filename.js", options, function (err, result) {
 
 All subsequent files required by node with the extensions `.es6` and `.js` will
 be transformed by 6to5. The polyfill specified in [Polyfill](polyfill.md) is
-also required.
+also required; but this is automatically loaded when using:
+
+Source maps are automatically configured so if any errors a thrown then line
+number info is mapped and you'll get the correct source location.
 
 ```javascript
 require("6to5/register");
@@ -164,6 +230,8 @@ require("6to5/register")({
 });
 ```
 
+**NOTE:** Using 6to5-node or `require("6to5/register")`, 6to5 will check what features are available in the current environment and blacklists them if they're supported.
+
 #### Options
 
 ```javascript
@@ -182,15 +250,10 @@ require("6to5/register")({
 
   // This will remove the currently hooked extensions of .es6 and .js so you'll
   // have to add them back if you want them to be used again.
-  extensions: [".js", ".es6"]
+  extensions: [".js", ".es6"],
+
+  // Enables `roadrunner` cache that will save to a `.roadrunner.json` file in your cwd
+  // Do not check this into git as it's user-specific
+  cache: true
 });
 ```
-
-## Experimental
-
-6to5 also has experimental support for ES7 proposals. You can enable this with
-the `experimental: true` option when using the [Node API](#node) or
-`--experimental` when using the [CLI](#cli).
-
-**WARNING:** These proposals are subject to change so use with
-**extreme caution**.

lib/6to5/browser.js

@@ -34,7 +34,7 @@ transform.load = function (url, callback, opts, hold) {
 
 var runScripts = function () {
   var scripts = [];
-  var types   = ["text/ecmascript-6", "text/6to5"];
+  var types   = ["text/ecmascript-6", "text/6to5", "module"];
   var index   = 0;
 
   var exec = function () {
@@ -60,8 +60,9 @@ var runScripts = function () {
     }
   };
 
-  var _scripts = global.document.getElementsByTagName("script");
-  for (var i in _scripts) {
+  var _scripts = global.document .getElementsByTagName("script");
+
+  for (var i = 0; i < _scripts.length; ++i) {
     var _script = _scripts[i];
     if (types.indexOf(_script.type) >= 0) scripts.push(_script);
   }

lib/6to5/file.js

@@ -10,31 +10,51 @@ var t         = require("./types");
 var _         = require("lodash");
 
 function File(opts) {
-  this.opts            = File.normaliseOptions(opts);
-  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
-
-  this.declarations = {};
-  this.uids         = {};
-  this.ast          = {};
+  this.dynamicImports = [];
+  this.opts           = File.normaliseOptions(opts);
+  this.transformers   = this.getTransformers();
+  this.uids           = {};
+  this.ast            = {};
 }
 
-File.declarations = ["extends", "class-props", "slice", "apply-constructor",
-                     "tagged-template-literal", "interop-require", "to-array"];
+File.helpers = [
+  "inherits",
+  "defaults",
+  "prototype-properties",
+  "apply-constructor",
+  "tagged-template-literal",
+  "interop-require",
+  "to-array",
+  "sliced-to-array",
+  "object-without-properties",
+  "has-own",
+  "slice",
+  "define-property",
+  "async-to-generator"
+];
+
+File.excludeHelpersFromRuntime = [
+  "async-to-generator"
+];
 
 File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
     experimental: false,
+    playground:   false,
     whitespace:   true,
+    moduleIds:    opts.amdModuleIds || false,
     blacklist:    [],
     whitelist:    [],
     sourceMap:    false,
+    optional:     [],
     comments:     true,
     filename:     "unknown",
     modules:      "common",
     runtime:      false,
-    code:         true
+    code:         true,
+    ast:          true
   });
 
   // normalise windows path separators to unix
@@ -64,19 +84,52 @@ File.normaliseOptions = function (opts) {
     opts.runtime = "to5Runtime";
   }
 
+  if (opts.playground) {
+    opts.experimental = true;
+  }
+
   transform._ensureTransformerNames("blacklist", opts.blacklist);
   transform._ensureTransformerNames("whitelist", opts.whitelist);
+  transform._ensureTransformerNames("optional", opts.optional);
 
   return opts;
 };
 
-File.prototype.toArray = function (node) {
+File.prototype.getTransformers = function () {
+  var file = this;
+  var transformers = [];
+  var secondPassTransformers = [];
+
+  _.each(transform.transformers, function (transformer) {
+    if (transformer.canRun(file)) {
+      transformers.push(transformer);
+
+      if (transformer.secondPass) {
+        secondPassTransformers.push(transformer);
+      }
+
+      if (transformer.manipulateOptions) {
+        transformer.manipulateOptions(file.opts, file);
+      }
+    }
+  });
+
+  return transformers.concat(secondPassTransformers);
+};
+
+File.prototype.toArray = function (node, i) {
   if (t.isArrayExpression(node)) {
     return node;
   } else if (t.isIdentifier(node) && node.name === "arguments") {
-    return t.callExpression(t.memberExpression(this.addDeclaration("slice"), t.identifier("call")), [node]);
+    return t.callExpression(t.memberExpression(this.addHelper("slice"), t.identifier("call")), [node]);
   } else {
-    return t.callExpression(this.addDeclaration("to-array"), [node]);
+    var declarationName = "to-array";
+    var args = [node];
+    if (i) {
+      args.push(t.literal(i));
+      declarationName = "sliced-to-array";
+    }
+    return t.callExpression(this.addHelper(declarationName), args);
   }
 };
 
@@ -89,7 +142,7 @@ File.prototype.getModuleFormatter = function (type) {
   }
 
   if (!ModuleFormatter) {
-    throw new ReferenceError("unknown module formatter type " + type);
+    throw new ReferenceError("Unknown module formatter type " + JSON.stringify(type));
   }
 
   return new ModuleFormatter(this);
@@ -107,28 +160,38 @@ File.prototype.parseShebang = function (code) {
   return code;
 };
 
-File.prototype.addDeclaration = function (name) {
-  if (!_.contains(File.declarations, name)) {
+File.prototype.addImport = function (id, source) {
+  var specifiers = [t.importSpecifier(t.identifier("default"), id)];
+  var declar = t.importDeclaration(specifiers, t.literal(source));
+  declar._blockHoist = 3;
+  this.dynamicImports.push(declar);
+};
+
+File.prototype.addHelper = function (name) {
+  if (!_.contains(File.helpers, name)) {
     throw new ReferenceError("unknown declaration " + name);
   }
 
-  var declar = this.declarations[name];
-  if (declar) return declar.uid;
+  var program = this.ast.program;
+
+  var declar = program._declarations && program._declarations[name];
+  if (declar) return declar.id;
 
   var ref;
   var runtimeNamespace = this.opts.runtime;
-  if (runtimeNamespace) {
+  if (runtimeNamespace && !_.contains(File.excludeHelpersFromRuntime, name)) {
     name = t.identifier(t.toIdentifier(name));
     return t.memberExpression(t.identifier(runtimeNamespace), name);
   } else {
     ref = util.template(name);
   }
 
-  var uid = t.identifier(this.generateUid(name));
-  this.declarations[name] = {
-    uid: uid,
-    node: ref
-  };
+  var uid = this.generateUidIdentifier(name);
+  this.scope.push({
+    key: name,
+    id: uid,
+    init: ref
+  });
   return uid;
 };
 
@@ -141,14 +204,16 @@ File.prototype.errorWithNode = function (node, msg, Error) {
   return err;
 };
 
-File.prototype.parse = function (code) {
+File.prototype.addCode = function (code) {
   code = (code || "") + "";
+  this.code = code;
+  return this.parseShebang(code);
+};
 
+File.prototype.parse = function (code) {
   var self = this;
 
-  this.code = code;
-
-  code = this.parseShebang(code);
+  code = this.addCode(code);
 
   return util.parse(this.opts, code, function (tree) {
     self.transform(tree);
@@ -157,29 +222,43 @@ File.prototype.parse = function (code) {
 };
 
 File.prototype.transform = function (ast) {
-  this.ast = ast;
-  this.scope = new Scope(ast.program);
-
   var self = this;
 
-  _.each(transform.transformers, function (transformer) {
+  this.ast = ast;
+  this.scope = new Scope(ast.program);
+  this.moduleFormatter = this.getModuleFormatter(this.opts.modules);
+
+  var astRun = function (key) {
+    _.each(self.transformers, function (transformer) {
+      transformer.astRun(self, key);
+    });
+  };
+
+  astRun("enter");
+
+  _.each(this.transformers, function (transformer) {
     transformer.transform(self);
   });
+
+  astRun("exit");
 };
 
 File.prototype.generate = function () {
   var opts = this.opts;
   var ast  = this.ast;
 
-  if (!opts.code) {
-    return {
-      code: "",
-      map:  null,
-      ast:  ast
-    };
-  }
+  var result = {
+    code: "",
+    map: null,
+    ast: null
+  };
 
-  var result = generate(ast, opts, this.code);
+  if (opts.ast) result.ast = ast;
+  if (!opts.code) return result;
+
+  var _result = generate(ast, opts, this.code);
+  result.code = _result.code;
+  result.map  = _result.map;
 
   if (this.shebang) {
     // add back shebang
@@ -190,8 +269,6 @@ File.prototype.generate = function () {
     result.code += "\n" + util.sourceMapToComment(result.map);
   }
 
-  result.ast = result;
-
   return result;
 };
 

lib/6to5/generation/buffer.js

@@ -35,7 +35,7 @@ Buffer.prototype.dedent = function () {
 };
 
 Buffer.prototype.semicolon = function () {
-  if (this.format.semicolons) this.push(";");
+  this.push(";");
 };
 
 Buffer.prototype.ensureSemicolon = function () {
@@ -66,9 +66,7 @@ Buffer.prototype.removeLast = function (cha) {
 };
 
 Buffer.prototype.newline = function (i, removeLast) {
-  if (!this.buf) return;
   if (this.format.compact) return;
-  if (this.endsWith("{\n")) return;
 
   if (_.isBoolean(i)) {
     removeLast = i;
@@ -76,6 +74,7 @@ Buffer.prototype.newline = function (i, removeLast) {
   }
 
   if (_.isNumber(i)) {
+    if (this.endsWith("{\n")) i--;
     if (this.endsWith(util.repeat(i, "\n"))) return;
 
     var self = this;
@@ -88,7 +87,10 @@ Buffer.prototype.newline = function (i, 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._push("\n");
 };
 

lib/6to5/generation/generator.js

@@ -37,7 +37,6 @@ _.each(Buffer.prototype, function (fn, key) {
 CodeGenerator.normaliseOptions = function (opts) {
   return _.merge({
     parentheses: true,
-    semicolons: true,
     comments: opts.comments == null || opts.comments,
     compact: false,
     indent: {
@@ -53,10 +52,12 @@ CodeGenerator.generators = {
   comprehensions:   require("./generators/comprehensions"),
   expressions:      require("./generators/expressions"),
   statements:       require("./generators/statements"),
+  playground:       require("./generators/playground"),
   classes:          require("./generators/classes"),
   methods:          require("./generators/methods"),
   modules:          require("./generators/modules"),
   types:            require("./generators/types"),
+  flow:             require("./generators/flow"),
   base:             require("./generators/base"),
   jsx:              require("./generators/jsx")
 };
@@ -70,6 +71,12 @@ CodeGenerator.prototype.generate = function () {
 
   this.print(ast);
 
+  var comments = [];
+  _.each(ast.comments, function (comment) {
+    if (!comment._displayed) comments.push(comment);
+  });
+  this._printComments(comments);
+
   return {
     map:  this.map.get(),
     code: this.buffer.get()
@@ -108,6 +115,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
   if (!node) return "";
 
   var self = this;
+
   opts = opts || {};
 
   var newline = function (leading) {
@@ -131,12 +139,21 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
       var needs = n.needsWhitespaceAfter;
       if (leading) needs = n.needsWhitespaceBefore;
       lines += needs(node, parent);
+
+      // generated nodes can't add starting file whitespace
+      if (!self.buffer.get()) lines = 0;
     }
 
     self.newline(lines);
   };
 
   if (this[node.type]) {
+    var needsCommentParens = t.isExpression(node) && node.leadingComments && node.leadingComments.length;
+    var needsParens        = needsCommentParens || n.needsParens(node, parent);
+
+    if (needsParens) this.push("(");
+    if (needsCommentParens) this.indent();
+
     this.printLeadingComments(node, parent);
 
     newline(true);
@@ -144,13 +161,12 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
     if (opts.before) opts.before();
     this.map.mark(node, "start");
 
-    // only compute if this node needs parens if our parent has been changed
-    // since acorn would've wrapped us in a ParanthesizedExpression
-    var needsParens = parent !== node._parent && n.needsParens(node, parent);
-    if (needsParens) this.push("(");
-
     this[node.type](node, this.buildPrint(node), parent);
 
+    if (needsCommentParens) {
+      this.newline();
+      this.dedent();
+    }
     if (needsParens) this.push(")");
 
     this.map.mark(node, "end");
@@ -160,7 +176,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     this.printTrailingComments(node, parent);
   } else {
-    throw new ReferenceError("unknown node " + node.type + " " + JSON.stringify(node));
+    throw new ReferenceError("unknown node of type " + JSON.stringify(node.type) + " with constructor " + JSON.stringify(node && node.constructor.name));
   }
 };
 
@@ -258,6 +274,21 @@ CodeGenerator.prototype._printComments = function (comments) {
   var self = this;
 
   _.each(comments, function (comment) {
+    var skip = false;
+
+    // find the original comment in the ast and set it as displayed
+    _.each(self.ast.comments, function (origComment) {
+      if (origComment.start === comment.start) {
+        // comment has already been output
+        if (origComment._displayed) skip = true;
+
+        origComment._displayed = true;
+        return false;
+      }
+    });
+
+    if (skip) return;
+
     // whitespace before
     self.newline(self.whitespace.getNewlinesBefore(comment));
 

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

@@ -18,12 +18,6 @@ exports.UnaryExpression = function (node, print) {
   print(node.argument);
 };
 
-exports.ParenthesizedExpression = function (node, print) {
-  this.push("(");
-  print(node.expression);
-  this.push(")");
-};
-
 exports.UpdateExpression = function (node, print) {
   if (node.prefix) {
     this.push(node.operator);
@@ -98,8 +92,15 @@ exports.AssignmentExpression = function (node, print) {
   print(node.right);
 };
 
+var SCIENTIFIC_NOTATION = /e/i;
+
 exports.MemberExpression = function (node, print) {
-  print(node.object);
+  var obj = node.object;
+  print(obj);
+
+  if (!node.computed && t.isMemberExpression(node.property)) {
+    throw new TypeError("Got a MemberExpression for MemberExpression property");
+  }
 
   if (node.computed) {
     this.push("[");
@@ -107,7 +108,7 @@ exports.MemberExpression = function (node, print) {
     this.push("]");
   } else {
     // 5..toFixed(2);
-    if (t.isLiteral(node.object) && util.isInteger(node.object.value)) {
+    if (t.isLiteral(obj) && util.isInteger(obj.value) && !SCIENTIFIC_NOTATION.test(obj.value.toString())) {
       this.push(".");
     }
 

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

@@ -0,0 +1,3 @@
+exports.ClassProperty = function () {
+  throw new Error("not implemented");
+};

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

@@ -1,7 +1,14 @@
 var t = require("../../types");
 var _ = require("lodash");
 
-exports.ImportSpecifier =
+exports.ImportSpecifier = function (node, print) {
+  if (node.id && node.id.name === "default") {
+    print(node.name);
+  } else {
+    return exports.ExportSpecifier.apply(this, arguments);
+  }
+};
+
 exports.ExportSpecifier = function (node, print) {
   print(node.id);
   if (node.name) {
@@ -62,7 +69,9 @@ exports.ImportDeclaration = function (node, print) {
         self.push(", ");
       }
 
-      if (!spec.default && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
+      var isDefault = spec.id && spec.id.name === "default";
+
+      if (!isDefault && spec.type !== "ImportBatchSpecifier" && !foundImportSpecifier) {
         foundImportSpecifier = true;
         self.push("{ ");
       }

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

@@ -0,0 +1,7 @@
+var _ = require("lodash");
+
+_.each(["BindMemberExpression", "BindFunctionExpression"], function (type) {
+  exports[type] = function () {
+    throw new ReferenceError("Trying to render non-standard playground node " + JSON.stringify(type));
+  };
+});

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

@@ -146,7 +146,7 @@ exports.SwitchCase = function (node, print) {
     this.push("default:");
   }
 
-  this.space();
+  this.newline();
   print.sequence(node.consequent, { indent: true });
 };
 
@@ -164,6 +164,12 @@ exports.VariableDeclaration = function (node, print, parent) {
   }
 };
 
+exports.PrivateDeclaration = function (node, print) {
+  this.push("private ");
+  print.join(node.declarations, { separator: ", " });
+  this.semicolon();
+};
+
 exports.VariableDeclarator = function (node, print) {
   if (node.init) {
     print(node.id);

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

@@ -4,7 +4,8 @@ exports.Identifier = function (node) {
   this.push(node.name);
 };
 
-exports.SpreadElement = function (node, print) {
+exports.SpreadElement =
+exports.SpreadProperty = function (node, print) {
   this.push("...");
   print(node.argument);
 };
@@ -83,8 +84,8 @@ exports.Literal = function (node) {
   if (type === "string") {
     val = JSON.stringify(val);
 
-    // escape unicode characters
-    val = val.replace(/[\u007f-\uffff]/g, function (c) {
+    // escape illegal js but valid json unicode characters
+    val = val.replace(/[\u000A\u000D\u2028\u2029]/g, function (c) {
       return "\\u" + ("0000" + c.charCodeAt(0).toString(16)).slice(-4);
     });
 

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

@@ -92,13 +92,6 @@ exports.YieldExpression = function (node, parent) {
          t.isYieldExpression(parent);
 };
 
-exports.Literal = function (node, parent) {
-  // (1).valueOf()
-  if (_.isNumber(node.value) && t.isMemberExpression(parent) && parent.object === node) {
-    return true;
-  }
-};
-
 exports.ClassExpression = function (node, parent) {
   return t.isExpressionStatement(parent);
 };

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

@@ -9,6 +9,10 @@ exports.before = {
       }
     },
 
+    SpreadProperty: function (node, parent) {
+      return exports.before.nodes.Property(node, parent);
+    },
+
     SwitchCase: function (node, parent) {
       if (parent.cases[0] === node) {
         return 1;
@@ -24,7 +28,13 @@ exports.before = {
 };
 
 exports.after = {
-  nodes: {},
+  nodes: {
+    AssignmentExpression: function (node) {
+      if (t.isFunction(node.right)) {
+        return 1;
+      }
+    }
+  },
 
   list: {
     VariableDeclaration: function (node) {
@@ -45,6 +55,8 @@ _.each({
   Function: 1,
   Class: 1,
   For: 1,
+  ArrayExpression: { after: 1 },
+  ObjectExpression: { after: 1 },
   SwitchStatement: 1,
   IfStatement: { before: 1 },
   CallExpression: { after: 1 },

lib/6to5/generation/whitespace.js

@@ -38,7 +38,11 @@ Whitespace.prototype.getNewlinesAfter = function (node) {
     }
   });
 
-  return this.getNewlinesBetween(startToken, endToken);
+  if (endToken.type.type === "eof") {
+    return 1;
+  } else {
+    return this.getNewlinesBetween(startToken, endToken);
+  }
 };
 
 Whitespace.prototype.getNewlinesBetween = function (startToken, endToken) {

lib/6to5/index.js

@@ -3,7 +3,9 @@ var util      = require("./util");
 var fs        = require("fs");
 var _         = require("lodash");
 
-exports.runtime = require("./runtime");
+exports.types = require("./types");
+
+exports.runtime = require("./runtime-generator");
 
 exports.register = function (opts) {
   var register = require("./register");

lib/6to5/patch.js

@@ -1,28 +1,47 @@
 var t = require("./types");
 var _ = require("lodash");
 
+// estraverse
+
+var estraverse = require("estraverse");
+_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+
+// regenerator/recast/ast-types
+
 var types = require("ast-types");
 var def   = types.Type.def;
+var or    = types.Type.or;
 
-// Program wrapper
-def("File")
-  .bases("Node")
-  .build("program")
-  .field("program", def("Program"));
-
-// Non-standard Acorn type
-def("ParenthesizedExpression")
-  .bases("Expression")
-  .build("expression")
-  .field("expression", def("Expression"));
-
-// Same as ImportNamespaceSpecifier but `id` is `name`
+// Acorn - Same as ImportNamespaceSpecifier but `id` is `name`
 def("ImportBatchSpecifier")
   .bases("Specifier")
   .build("name")
   .field("name", def("Identifier"));
 
-types.finalize();
+// Abstract references
+def("VirtualPropertyExpression")
+  .bases("Expression")
+  .build("object", "property")
+  .field("object", def("Expression"))
+  .field("property", or(def("Identifier"), def("Expression")));
 
-var estraverse = require("estraverse");
-_.extend(estraverse.VisitorKeys, t.VISITOR_KEYS);
+def("PrivateDeclaration")
+  .bases("Declaration")
+  .build("declarations")
+  .field("declarations", [def("Identifier")]);
+
+// Playground
+def("BindMemberExpression")
+  .bases("Expression")
+  .build("object", "property", "arguments")
+  .field("object", def("Expression"))
+  .field("property", or(def("Identifier"), def("Expression")))
+  .field("arguments", [def("Expression")]);
+
+def("BindFunctionExpression")
+  .bases("Expression")
+  .build("callee", "arguments")
+  .field("callee", def("Expression"))
+  .field("arguments", [def("Expression")]);
+
+types.finalize();

lib/6to5/polyfill.js

@@ -1,37 +1,2 @@
-/* jshint newcap: false */
-
-var ensureSymbol = function (key) {
-  Symbol[key] = Symbol[key] || Symbol();
-};
-
-var ensureProto = function (Constructor, key, val) {
-  var proto = Constructor.prototype;
-  proto[key] = proto[key] || val;
-};
-
-//
-
-if (typeof Symbol === "undefined") {
-  require("es6-symbol/implement");
-}
-
-require("es6-shim");
-require("./transformation/transformers/es6-generators/runtime");
-
-// Abstract references
-
-ensureSymbol("referenceGet");
-ensureSymbol("referenceSet");
-ensureSymbol("referenceDelete");
-
-ensureProto(Function, Symbol.referenceGet, function () { return this; });
-
-ensureProto(Map, Symbol.referenceGet, Map.prototype.get);
-ensureProto(Map, Symbol.referenceSet, Map.prototype.set);
-ensureProto(Map, Symbol.referenceDelete, Map.prototype.delete);
-
-if (global.WeakMap) {
-  ensureProto(WeakMap, Symbol.referenceGet, WeakMap.prototype.get);
-  ensureProto(WeakMap, Symbol.referenceSet, WeakMap.prototype.set);
-  ensureProto(WeakMap, Symbol.referenceDelete, WeakMap.prototype.delete);
-}
+require("core-js/shim");
+require("regenerator/runtime");

lib/6to5/register-browser.js

@@ -0,0 +1,4 @@
+// Required to safely use 6to5/register within a browserify codebase.
+module.exports = function () {};
+
+require("./polyfill");

lib/6to5/register.js

@@ -1,8 +1,10 @@
 require("./polyfill");
 
 var sourceMapSupport = require("source-map-support");
+var roadrunner       = require("roadrunner");
 var util             = require("./util");
 var to5              = require("./index");
+var fs               = require("fs");
 var _                = require("lodash");
 
 sourceMapSupport.install({
@@ -37,15 +39,22 @@ var blacklistTest = function (transformer, code) {
 };
 
 blacklistTest("arrayComprehension", "var foo = [for (foo of bar) foo * foo];");
-//blacklistTest("generatorComprehension", "");
+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", "const foo = 0;");
+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() {}");
+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() {} }");
@@ -61,22 +70,41 @@ var transformOpts = {};
 var ignoreRegex   = /node_modules/;
 var onlyRegex;
 var whitelist     = [];
+var cache;
 var exts          = {};
 var maps          = {};
 var old           = require.extensions[".js"];
 
+var mtime = function (filename) {
+  return +fs.statSync(filename).mtime;
+};
+
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, _.extend({
+  var result;
+
+  if (cache) {
+    var cached = cache[filename];
+    if (cached && cached.mtime === mtime(filename)) {
+      result = cached;
+    }
+  }
+
+  result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
-    modules:   "commonInterop"
+    ast:       false
   }, transformOpts));
 
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
+
   maps[filename] = result.map;
 
   m._compile(result.code, filename);
@@ -108,5 +136,13 @@ module.exports = function (opts) {
 
   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");
+  }
+
   _.extend(transformOpts, opts);
 };

lib/6to5/runtime-generator.js

@@ -18,7 +18,11 @@ module.exports = function (namespace) {
     )
   ]));
 
-  _.each(File.declarations, function (name) {
+  _.each(File.helpers, function (name) {
+    if (_.contains(File.excludeHelpersFromRuntime, name)) {
+      return false;
+    }
+
     var key = t.identifier(t.toIdentifier(name));
     body.push(t.expressionStatement(
       t.assignmentExpression("=", t.memberExpression(namespace, key), util.template(name))

lib/6to5/templates/arguments-slice-assign-arg.js

@@ -1 +0,0 @@
-var VARIABLE_NAME = SLICE_KEY.call(arguments, SLICE_ARG);

lib/6to5/templates/arguments-slice-assign.js

@@ -1 +0,0 @@
-var VARIABLE_NAME = SLICE_KEY.call(arguments);

lib/6to5/templates/arguments-slice.js

@@ -1 +0,0 @@
-SLICE_KEY.call(arguments);

lib/6to5/templates/array-expression-comprehension-filter.js

@@ -1,5 +0,0 @@
-ARRAY.filter(function (KEY) {
-  return FILTER;
-}).map(function (KEY) {
-  return STATEMENT;
-});

lib/6to5/templates/array-expression-comprehension-map.js

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

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

@@ -1,2 +0,0 @@
-SUPER_NAME.apply(this, arguments);
-

lib/6to5/templates/class.js

@@ -1,7 +0,0 @@
-(function () {
-  var CLASS_NAME = function () {
-
-  };
-
-  return CLASS_NAME;
-})()

lib/6to5/templates/exports-assign-key.js

@@ -1 +0,0 @@
-exports.VARIABLE_NAME = OBJECT.KEY;

lib/6to5/templates/exports-default.js

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

lib/6to5/templates/function-return-obj.js

@@ -1,3 +0,0 @@
-(function (KEY) {
-  return KEY;
-})(OBJECT)

lib/6to5/templates/object-define-properties-closure.js

@@ -1,4 +0,0 @@
-(function (KEY) {
-  CONTENT;
-  return KEY;
-})(OBJECT);

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

@@ -1,4 +0,0 @@
-(function (strings, raw) {
-  return Object.defineProperties(strings, { raw: { value: raw } });
-});
-

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

@@ -0,0 +1,205 @@
+module.exports = DefaultFormatter;
+
+var traverse = require("../../traverse");
+var util     = require("../../util");
+var t        = require("../../types");
+var _        = require("lodash");
+
+function DefaultFormatter(file) {
+  this.file = file;
+
+  this.localExports = this.getLocalExports();
+  this.remapAssignments();
+}
+
+DefaultFormatter.prototype.getLocalExports = function () {
+  var localExports = {};
+
+  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));
+      }
+    }
+  });
+
+  return localExports;
+};
+
+DefaultFormatter.prototype.remapExportAssignment = function (node) {
+  return t.assignmentExpression(
+    "=",
+    node.left,
+    t.assignmentExpression(
+      node.operator,
+      t.memberExpression(t.identifier("exports"), node.left),
+      node.right
+    )
+  );
+};
+
+DefaultFormatter.prototype.remapAssignments = function () {
+  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);
+      }
+    }
+  });
+};
+
+DefaultFormatter.prototype.getModuleName = function () {
+  var opts = this.file.opts;
+  var filenameRelative = opts.filenameRelative;
+  var moduleName = "";
+
+  if (opts.moduleRoot) {
+    moduleName = opts.moduleRoot + "/";
+  }
+
+  if (!opts.filenameRelative) {
+    return moduleName + opts.filename.replace(/^\//, "");
+  }
+
+  if (opts.sourceRoot) {
+    // remove sourceRoot from filename
+    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
+    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
+  }
+
+  // remove extension
+  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
+
+  moduleName += filenameRelative;
+
+  return moduleName;
+};
+
+DefaultFormatter.prototype._pushStatement = function (ref, nodes) {
+  if (t.isClass(ref) || t.isFunction(ref)) {
+    if (ref.id) {
+      nodes.push(t.toStatement(ref));
+      ref = ref.id;
+    }
+  }
+
+  return ref;
+};
+
+DefaultFormatter.prototype._hoistExport = function (declar, assign, priority) {
+  if (t.isFunctionDeclaration(declar)) {
+    assign._blockHoist = priority || 2;
+  }
+
+  return assign;
+};
+
+DefaultFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
+  var inherits = false;
+  if (node.specifiers.length === 1) inherits = node;
+
+  if (node.source) {
+    if (t.isExportBatchSpecifier(specifier)) {
+      // export * from "foo";
+      nodes.push(this._exportsWildcard(getRef(), node));
+    } else {
+      // export { foo } from "test";
+      nodes.push(this._exportsAssign(
+        t.getSpecifierName(specifier),
+        t.memberExpression(getRef(), specifier.id),
+        node
+      ));
+    }
+  } else {
+    // export { foo };
+    nodes.push(this._exportsAssign(t.getSpecifierName(specifier), specifier.id, node));
+  }
+};
+
+DefaultFormatter.prototype._exportsWildcard = function (objectIdentifier) {
+  return util.template("exports-wildcard", {
+    OBJECT: objectIdentifier
+  }, true);
+};
+
+DefaultFormatter.prototype._exportsAssign = function (id, init) {
+  return util.template("exports-assign", {
+    VALUE: init,
+    KEY:   id
+  }, true);
+};
+
+DefaultFormatter.prototype.exportDeclaration = function (node, nodes) {
+  var declar = node.declaration;
+
+  var id = declar.id;
+
+  if (node.default) {
+    id = t.identifier("default");
+  }
+
+  var assign;
+
+  if (t.isVariableDeclaration(declar)) {
+    for (var i in declar.declarations) {
+      var decl = declar.declarations[i];
+
+      decl.init = this._exportsAssign(decl.id, decl.init, node).expression;
+
+      var newDeclar = t.variableDeclaration(declar.kind, [decl]);
+      if (i === "0") t.inherits(newDeclar, declar);
+      nodes.push(newDeclar);
+    }
+  } else {
+    var ref = declar;
+
+    if (t.isFunctionDeclaration(declar) || t.isClassDeclaration(declar)) {
+      ref = declar.id;
+      nodes.push(declar);
+    }
+
+    assign = this._exportsAssign(id, ref, node);
+
+    nodes.push(assign);
+
+    this._hoistExport(declar, assign);
+  }
+};

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

@@ -1,16 +1,28 @@
 module.exports = AMDFormatter;
 
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-var _                 = require("lodash");
+var DefaultFormatter = require("./_default");
+var util             = require("../../util");
+var t                = require("../../types");
+var _                = require("lodash");
 
-function AMDFormatter(file) {
-  this.file = file;
+function AMDFormatter() {
+  DefaultFormatter.apply(this, arguments);
   this.ids  = {};
 }
 
-util.inherits(AMDFormatter, CommonJSFormatter);
+util.inherits(AMDFormatter, DefaultFormatter);
+
+AMDFormatter.prototype.buildDependencyLiterals = function () {
+  var names = [];
+  for (var name in this.ids) {
+    names.push(t.literal(name));
+  }
+  return names;
+};
+
+/**
+ * Wrap the entire body in a `define` wrapper.
+ */
 
 AMDFormatter.prototype.transform = function (ast) {
   var program = ast.program;
@@ -18,10 +30,7 @@ AMDFormatter.prototype.transform = function (ast) {
 
   // build an array of module names
 
-  var names = [t.literal("exports")];
-  _.each(this.ids, function (id, name) {
-    names.push(t.literal(name));
-  });
+  var names = [t.literal("exports")].concat(this.buildDependencyLiterals());
   names = t.arrayExpression(names);
 
   // build up define container
@@ -40,35 +49,17 @@ AMDFormatter.prototype.transform = function (ast) {
   program.body = [t.expressionStatement(call)];
 };
 
-AMDFormatter.prototype.getModuleName = function () {
-  var opts = this.file.opts;
-  var filenameRelative = opts.filenameRelative;
-  var moduleName = "";
+/**
+ * Get the AMD module name that we'll prepend to the wrapper
+ * to define this module
+ */
 
-  if (!opts.amdModuleIds) {
+AMDFormatter.prototype.getModuleName = function () {
+  if (this.file.opts.moduleIds) {
+    return DefaultFormatter.prototype.getModuleName.apply(this, arguments);
+  } else {
     return null;
   }
-
-  if (opts.moduleRoot) {
-    moduleName = opts.moduleRoot + "/";
-  }
-
-  if (!opts.filenameRelative) {
-    return moduleName + opts.filename.replace(/^\//, "");
-  }
-
-  if (opts.sourceRoot) {
-    // remove sourceRoot from filename
-    var sourceRootRegEx = new RegExp("^" + opts.sourceRoot + "\/?");
-    filenameRelative = filenameRelative.replace(sourceRootRegEx, "");
-  }
-
-  // remove extension
-  filenameRelative = filenameRelative.replace(/\.(.*?)$/, "");
-
-  moduleName += filenameRelative;
-
-  return moduleName;
 };
 
 AMDFormatter.prototype._push = function (node) {
@@ -82,27 +73,22 @@ AMDFormatter.prototype._push = function (node) {
   }
 };
 
-AMDFormatter.prototype.import = function (node) {
+AMDFormatter.prototype.importDeclaration = function (node) {
   this._push(node);
 };
 
 AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var key = t.getSpecifierName(specifier);
-  var id  = specifier.id;
-
-  // import foo from "foo";
-  if (specifier.default) {
-    id = t.identifier("default");
-  }
-
-  var ref;
+  var ref = this._push(node);
 
   if (t.isImportBatchSpecifier(specifier)) {
     // import * as bar from "foo";
-    ref = this._push(node);
-  } else {
+  } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
     // import foo from "foo";
-    ref = t.memberExpression(this._push(node), id, false);
+    ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
+  } else {
+    // import {foo} from "foo";
+    ref = t.memberExpression(ref, specifier.id, false);
   }
 
   nodes.push(t.variableDeclaration("var", [

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

@@ -1,28 +0,0 @@
-module.exports = CommonJSInteropFormatter;
-
-var CommonJSFormatter = require("./common");
-var util              = require("../../util");
-var t                 = require("../../types");
-
-function CommonJSInteropFormatter(file) {
-  this.file = file;
-}
-
-util.inherits(CommonJSInteropFormatter, CommonJSFormatter);
-
-CommonJSInteropFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  // import foo from "foo";
-   if (specifier.default) {
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(variableName,
-        t.callExpression(this.file.addDeclaration("interop-require"), [util.template("require", {
-          MODULE_NAME: node.source.raw
-        })])
-      )
-    ]));
-  } else {
-    CommonJSFormatter.prototype.importSpecifier.apply(this, arguments);
-  }
-};

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

@@ -1,132 +1,97 @@
 module.exports = CommonJSFormatter;
 
-var util = require("../../util");
-var t    = require("../../types");
+var DefaultFormatter = require("./_default");
+var traverse         = require("../../traverse");
+var util             = require("../../util");
+var t                = require("../../types");
 
 function CommonJSFormatter(file) {
-  this.file = 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;
 }
 
-CommonJSFormatter.prototype.import = function (node, nodes) {
-  // import "foo";
-  nodes.push(util.template("require", {
-    //inherits: node,
-
-    MODULE_NAME: node.source.raw
-  }, true));
-};
+util.inherits(CommonJSFormatter, DefaultFormatter);
 
 CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var variableName = t.getSpecifierName(specifier);
 
   // import foo from "foo";
-  if (specifier.default) {
-    specifier.id = t.identifier("default");
+  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
+        })])
+      )
+    ]));
+  } else {
+    // import foo from "foo";
+
+    var templateName = "require-assign";
+
+    // import * as bar from "foo";
+    if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
+
+    nodes.push(util.template(templateName, {
+      VARIABLE_NAME: variableName,
+      MODULE_NAME:   node.source,
+      KEY:           specifier.id
+    }));
   }
-
-  var templateName = "require-assign";
-
-  // import * as bar from "foo";
-  if (specifier.type !== "ImportBatchSpecifier") templateName += "-key";
-
-  nodes.push(util.template(templateName, {
-    //inherits: node.specifiers.length === 1 && node,
-
-    VARIABLE_NAME: variableName,
-    MODULE_NAME:   node.source.raw,
-    KEY:           specifier.id
-  }));
 };
 
-CommonJSFormatter.prototype.export = function (node, nodes) {
-  var declar = node.declaration;
+CommonJSFormatter.prototype.importDeclaration = function (node, nodes) {
+  // import "foo";
+  nodes.push(util.template("require", {
+    MODULE_NAME: node.source
+  }, true));
+};
 
+CommonJSFormatter.prototype.exportDeclaration = function (node, nodes) {
   if (node.default) {
-    var ref = declar;
-
-    if (t.isClass(ref) || t.isFunction(ref)) {
-      if (ref.id) {
-        nodes.push(t.toStatement(ref));
-        ref = ref.id;
-      }
-    }
-
-    nodes.push(util.template("exports-default", {
-      //inherits: node,
-
-      VALUE: ref
-    }, true));
-  } else {
+    var declar = node.declaration;
     var assign;
 
-    if (t.isVariableDeclaration(declar)) {
-      var decl = declar.declarations[0];
+    // module.exports = VALUE;
+    var templateName = "exports-default-module";
 
-      if (decl.init) {
-        decl.init = util.template("exports-assign", {
-          //inherits: node,
+    // exports = module.exports = VALUE;
+    if (this.hasNonDefaultExports) templateName = "exports-default-module-override";
 
-          VALUE: decl.init,
-          KEY:   decl.id
-        });
-      }
-
-      nodes.push(declar);
-    } else {
-      assign = util.template("exports-assign", {
-        //inherits: node,
-
-        VALUE: declar.id,
-        KEY:   declar.id
+    if (t.isFunction(declar) || !this.hasNonDefaultExports) {
+      assign = util.template(templateName, {
+        VALUE: this._pushStatement(declar, nodes)
       }, true);
 
-      nodes.push(t.toStatement(declar));
-      nodes.push(assign);
-
-      if (t.isFunctionDeclaration(declar)) {
-        assign._blockHoist = true;
-      }
-    }
-  }
-};
-
-CommonJSFormatter.prototype._exportSpecifier = function (getRef, specifier, node, nodes) {
-  var variableName = t.getSpecifierName(specifier);
-
-  var inherits = false;
-  if (node.specifiers.length === 1) inherits = node;
-
-  if (node.source) {
-    if (t.isExportBatchSpecifier(specifier)) {
-      // export * from "foo";
-      nodes.push(util.template("exports-wildcard", {
-        //inherits: inherits,
-
-        OBJECT: getRef()
-      }, true));
+      // hoist to the top if this default is a function
+      nodes.push(this._hoistExport(declar, assign, 3));
+      return;
     } else {
-      // export { foo } from "test";
-      nodes.push(util.template("exports-assign-key", {
-        //inherits: inherits,
+      // 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 = Object.assign(exports["default"], exports)
+      //
 
-        VARIABLE_NAME: variableName.name,
-        OBJECT:        getRef(),
-        KEY:           specifier.id
-      }, true));
+      assign = util.template("common-export-default-assign", true);
+      assign._blockHoist = 0;
+
+      nodes.push(assign);
     }
-  } else {
-    // export { foo };
-    nodes.push(util.template("exports-assign", {
-      //inherits: inherits,
-
-      VALUE: specifier.id,
-      KEY:   variableName
-    }, true));
   }
+
+  DefaultFormatter.prototype.exportDeclaration.apply(this, arguments);
 };
 
 CommonJSFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
-  return this._exportSpecifier(function () {
+  this._exportSpecifier(function () {
     return t.callExpression(t.identifier("require"), [node.source]);
   }, specifier, node, nodes);
 };

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

@@ -6,19 +6,13 @@ function IgnoreFormatter() {
 
 }
 
-IgnoreFormatter.prototype.import = function () {
-
-};
-
-IgnoreFormatter.prototype.importSpecifier = function () {
-
-};
-
-IgnoreFormatter.prototype.export = function (node, nodes) {
+IgnoreFormatter.prototype.exportDeclaration = function (node, nodes) {
   var declar = t.toStatement(node.declaration, true);
   if (declar) nodes.push(t.inherits(declar, node));
 };
 
+IgnoreFormatter.prototype.importDeclaration =
+IgnoreFormatter.prototype.importSpecifier =
 IgnoreFormatter.prototype.exportSpecifier = function () {
 
 };

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

@@ -0,0 +1,174 @@
+module.exports = SystemFormatter;
+
+var AMDFormatter = require("./amd");
+var traverse     = require("../../traverse");
+var util         = require("../../util");
+var t            = require("../../types");
+var _            = require("lodash");
+
+function SystemFormatter(file) {
+  this.exportIdentifier  = file.generateUidIdentifier("export");
+  this.noInteropRequire = true;
+
+  AMDFormatter.apply(this, arguments);
+}
+
+util.inherits(SystemFormatter, AMDFormatter);
+
+SystemFormatter.prototype._addImportSource = function (node, exportNode) {
+  node._importSource = exportNode.source && exportNode.source.value;
+  return node;
+};
+
+SystemFormatter.prototype._exportsWildcard = function (objectIdentifier, node) {
+  var leftIdentifier = this.file.generateUidIdentifier("key");
+  var valIdentifier  = t.memberExpression(objectIdentifier, leftIdentifier, true);
+
+  var left = t.variableDeclaration("var", [
+    t.variableDeclarator(leftIdentifier)
+  ]);
+
+  var right = objectIdentifier;
+
+  var block = t.blockStatement([
+    this.buildExportCall(leftIdentifier, valIdentifier)
+  ]);
+
+  return this._addImportSource(t.forInStatement(left, right, block), node);
+};
+
+SystemFormatter.prototype._exportsAssign = function (id, init, node) {
+  var call = this.buildExportCall(t.literal(id.name), init, true);
+  return this._addImportSource(call, node);
+};
+
+SystemFormatter.prototype.remapExportAssignment = function (node) {
+  return this.buildExportCall(t.literal(node.left.name), node);
+};
+
+SystemFormatter.prototype.buildExportCall = function (id, init, isStatement) {
+  var call = t.callExpression(this.exportIdentifier, [id, init]);
+  if (isStatement) {
+    return t.expressionStatement(call);
+  } else {
+    return call;
+  }
+};
+
+SystemFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
+  AMDFormatter.prototype.importSpecifier.apply(this, arguments);
+  this._addImportSource(_.last(nodes), node);
+};
+
+SystemFormatter.prototype.buildRunnerSetters = function (block, hoistDeclarators) {
+  return t.arrayExpression(_.map(this.ids, function (uid, source) {
+    var nodes = [];
+
+    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);
+          }
+
+          this.remove();
+        }
+      }
+    });
+
+    return t.functionExpression(null, [uid], t.blockStatement(nodes));
+  }));
+};
+
+SystemFormatter.prototype.transform = function (ast) {
+  var program = ast.program;
+
+  var hoistDeclarators = [];
+  var moduleName = this.getModuleName();
+  var moduleNameLiteral = t.literal(moduleName);
+
+  var block = t.blockStatement(program.body);
+
+  var runner = util.template("system", {
+    MODULE_NAME: moduleNameLiteral,
+    MODULE_DEPENDENCIES: t.arrayExpression(this.buildDependencyLiterals()),
+    EXPORT_IDENTIFIER: this.exportIdentifier,
+    SETTERS: this.buildRunnerSetters(block, hoistDeclarators),
+    EXECUTE: t.functionExpression(null, [], block)
+  }, true);
+
+  var handlerBody = runner.expression.arguments[2].body.body;
+  if (!moduleName) runner.expression.arguments.shift();
+
+  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();
+      }
+
+      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;
+    handlerBody.unshift(hoistDeclar);
+  }
+
+  // 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();
+      }
+    }
+  });
+
+  handlerBody.push(returnStatement);
+
+  program.body = [runner];
+};

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

@@ -18,9 +18,9 @@ UMDFormatter.prototype.transform = function (ast) {
   // build an array of module names
 
   var names = [];
-  _.each(this.ids, function (id, name) {
+  for (var name in this.ids) {
     names.push(t.literal(name));
-  });
+  }
 
   // factory
 

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

@@ -0,0 +1,37 @@
+(function (fn) {
+  return function () {
+    var gen = fn.apply(this, arguments);
+
+    return new Promise(function (resolve, reject) {
+      function step(getNext) {
+        var next;
+
+        try {
+          next = getNext();
+        } catch(e) {
+          reject(e);
+          return;
+        }
+
+        if (next.done) {
+          resolve(next.value);
+          return;
+        }
+
+        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();
+      });
+    });
+  }
+})

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

@@ -0,0 +1,3 @@
+if (SUPER_NAME) {
+  SUPER_NAME.apply(this, arguments);
+}

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

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

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

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

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

@@ -0,0 +1,8 @@
+(function (obj, defaults) {
+  for (var key in defaults) {
+    if (obj[key] === undefined) {
+      obj[key] = defaults[key];
+    }
+  }
+  return obj;
+})

lib/6to5/transformation/templates/define-property.js

@@ -0,0 +1,8 @@
+(function (obj, key, value) {
+  return Object.defineProperty(obj, key, {
+    value: value,
+    enumerable: true,
+    configurable: true,
+    writable: true
+  });
+});

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

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

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

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

lib/6to5/transformation/templates/has-own.js

@@ -0,0 +1 @@
+Object.prototype.hasOwnProperty;

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

@@ -1,5 +1,5 @@
 (function (child, parent) {
-  child.prototype = Object.create(parent.prototype, {
+  child.prototype = Object.create(parent && parent.prototype, {
     constructor: {
       value: child,
       enumerable: false,
@@ -7,5 +7,5 @@
       configurable: true
     }
   });
-  child.__proto__ = parent;
+  if (parent) child.__proto__ = parent;
 })

lib/6to5/transformation/templates/object-without-properties.js

@@ -0,0 +1,9 @@
+(function (obj, keys) {
+  var target = {};
+  for (var i in obj) {
+    if (keys.indexOf(i) >= 0) continue;
+    if (!Object.prototype.hasOwnProperty.call(obj, i)) continue;
+    target[i] = obj[i];
+  }
+  return target;
+})

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

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