es6-module-transpiler

ES6 Module Transpiler

ES6 Module Transpiler is an experimental compiler that allows you to write your JavaScript using a subset of the current ES6 module syntax, and compile it into AMD or CommonJS modules.

WARNING: The ES6 module syntax is still undergoing a lot of churn, and will likely change before final approval.

ES6 Module Transpiler will track ES6 syntax, and not attempt to maintain backwards compatibility with syntax that ultimately did not succeed as part of ES6.

This compiler provides a way to experiment with ES6 syntax in real world scenarios to see how the syntax holds up. It also provides a nicer, more declarative way to write AMD (or CommonJS) modules.

See the CHANGELOG for the latest updates.

Usage

Build tools

The easiest way to use the transpiler is from an existing build tool. There several plugins developed for different build tools:

• Grunt: grunt-es6-module-transpiler, maintained by @joefiorini (not yet compatible with v0.5.x)
• Gulp: gulp-es6-module-transpiler, maintained by @ryanseddon (not yet compatible with v0.5.x)
• Brunch: es6-module-transpiler-brunch, maintained by @gcollazo (CommonJS only) (not yet compatible with v0.5.x)
• Broccoli: broccoli-es6-concatenator, maintained by @joliss (not yet compatible with v0.5.x)
• Mimosa: mimosa-es6-module-transpiler, maintained by @dbashford (not yet compatible with v0.5.x)
• AMD Formatter: es6-module-transpiler-amd-formatter, maintained by @caridy (compatible with v0.5.x+ only)

Executable

The transpiler can be used directly from the command line:

$ npm install -g es6-module-transpiler
$ compile-modules convert < foo.js

Here is the basic usage:

compile-modules convert -I lib -o out FILE [FILE…]

Library

You can also use the transpiler as a library:

var transpiler = require('es6-module-transpiler');
var Container = transpiler.Container;
var FileResolver = transpiler.FileResolver;
var BundleFormatter = transpiler.formatters.bundle;

var container = new Container({
  resolvers: [new FileResolver(['lib/'])],
  formatter: new BundleFormatter()
});

container.getModule('index');
container.write('out/mylib.js');

Supported ES6 Module Syntax

Again, this syntax is in flux and is closely tracking the module work being done by TC39.

Named Exports

There are two types of exports. Named exports like the following:

// foobar.js
var foo = 'foo', bar = 'bar';

export { foo, bar };

This module has two named exports, foo and bar.

You can also write this form as:

// foobar.js
export var foo = 'foo';
export var bar = 'bar';

Either way, another module can then import your exports like so:

import { foo, bar } from 'foobar';

console.log(foo);  // 'foo'

Default Exports

You can also export a default export. For example, an ES6ified jQuery might look like this:

// jquery.js
var jQuery = function() {};

jQuery.prototype = {
  // ...
};

export default jQuery;

Then, an app that uses jQuery could import it with:

import $ from 'jquery';

The default export of the "jquery" module is now aliased to $.

A default export makes the most sense as a module's "main" export, like the jQuery object in jQuery. You can use default and named exports in parallel.

Other Syntax

module

Whereas the import keyword imports specific identifiers from a module, the module keyword creates an object that contains all of a module's exports:

module foobar from "foobar";
console.log(foobar.foo);  // "foo"

In ES6, this created object is read-only, so don't treat it like a mutable namespace! NOTE: This syntax especially may be removed or modified before ES6 is finalized!

import "foo";

A "bare import" that doesn't import any identifiers is useful for executing side effects in a module. For example:

// alerter.js
alert("alert! alert!");

// alertee.js
import "alerter";  // will pop up alert box

Compiled Output

Default Exports

This is super important:

Default exports bind to an identifier on the module called default!

Internally, the transpiler will use this default identifer when importing, but any outside consumer needs to be aware that it should use the default key and not the module itself. For example, a CommonJS consumer should look like this:

var $ = require('jquery')['default'];

Installation

Add this project to your application's package.json by running this:

$ npm install --save es6-module-transpiler

Or install it globally:

$ npm install -g es6-module-transpiler

Acknowledgements

Thanks to Yehuda Katz for js_module_transpiler, the library on which this one is based. Thanks to Dave Herman for his work on ES6 modules. Thanks to Erik Bryn for providing the initial push to write this library. Thanks to Domenic Denicola & Thomas Boyt for their efforts to make this project even better. And finally thanks to the JavaScript community at Square for helping to write and release this library.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Any contributors to the master es6-module-transpiler repository must sign the Individual Contributor License Agreement (CLA). It's a short form that covers our bases and makes sure you're eligible to contribute.

When you have a change you'd like to see in the master repository, send a pull request. Before we merge your request, we'll make sure you're in the list of people who have signed a CLA.

Thanks, and enjoy living in the ES6 future!

Changelog

v0.6.2 <span class="release-date">(2014-08-20)</span>

• Prevent all instances of export reassignment, not just those at the top level.