ES6 Module Loader

ES6 Module Loader polyfill based on http://wiki.ecmascript.org/doku.php?id=harmony:module_loaders by Luke Hoban, Addy Osmani and Guy Bedford.

• Dynamically load ES6 modules in all modern browsers including IE8+
• Supports Traceur for compiling ES6 into ES5 in the browser with source map support
• Use as a base for creating custom spec-compliant module loaders

Not yet suitable for production use while the specification is still subject to change.

Download

• Minified build ~ 11KB
• Unminified ~ 26KB

Getting Started

Include the loader in the page:

  <script src="path/to/es6-module-loader.js"></script>

Use the System (pre-configured Loader):

<script>
  System.baseURL = '/lib';
  System.import('js/test1', function (test1) {
    console.log('js/test1.js loaded', test1);
  });
</script>

where, test1 can contain module syntax:

test1.js:

export function tester() {
  console.log('hello!');
}

Load multiple modules:

System.import(['js/test1', 'js/test2'], function(test1, test2) {
  console.log('test1.js loaded', test1);
  console.log('test2.js loaded', test2);
}, function(err) {
  console.log('loading error');
});

Load a plain JavaScript file from a URL:

System.load('js/libs/jquery-1.7.1.js', function() {
  var $ = System.global.jQuery;
  console.log('jQuery loaded', $);
  $('body').css({'background':'blue'});
});

Integration with Traceur

Include both Traceur and the ES6 module loader in the page:

  <script src="path/to/traceur.js"></script>
  <script src="path/to/es6-module-loader.js"></script>

Load an ES6 module (test.js):

  export class MyClass {
    foo() {
      console.log('es6!');
    }
  }

Import the module:

  <script>
    System.load('test', function(test) {
      new test.MyClass();
    });
  </script>

Creating a Custom Loader

Define a new module Loader instance:

var loader = new Loader({
  global: window,
  strict: false,
  normalize: function (name, referer) {
    return normalized(name, referer.name);
  },
  resolve: function (normalized, options) {
    return '/' + normalized + '.js';
  },
  fetch: function (url, fulfill, reject, options) {
    fulfill(source);
  },
  translate: function (source, options) {
    return compile(source);
  },
  link: function (source, options) {
    return {
      imports: ['some', 'dependencies'],
      execute: function(depA, depB) {
        return new Module({
          some: 'export'
        });
      }
    };
  }
});

The above hooks are all optional, using the default System hooks when not present.

For an overview of working with custom loaders, see Yehuda Katz's essay or the ES6 Module Specification.

Notes and roadmap

Syntax Parsing

The Esprima ES6 Harmony parser is being used to do parsing, loaded only when necessary.

The following module statements are currently supported:

import 'jquery';                        // import a module
import $ from 'jquery';                 // import the default export of a module
import { $ } from 'jquery';             // import a named export of a module
import { $ as jQuery } from 'jquery';   // import a named export to a different name

export var x = 42;                      // export a named variable
export function foo() {};               // export a named function

export default var x = 42;              // export the default export
export default function foo() {};       // export the default export as a function
export default = function foo() {};     // export the default export by assignment

export { encrypt };                     // export an existing variable
export { decrypt as dec };              // export a variable as a new name
export { encrypt as en } from 'crypto'; // export an export from another module
export * from 'crypto';                 // export all exports from another module

NodeJS Support

For use in NodeJS, the Module, Loader and System globals are provided as exports:

  var System = require('es6-module-loader').System;
  
  System.import('some-module', callback);

Tracuer support can also be used in NodeJS, allowing ES6 syntax in NodeJS:

  require('es6-module-loader').traceur = require('traceur');
  var System = require('es6-module-loader').System;

  System.import('es6-file', function(module) {
    module.classMethod();
  });

Custom Esprima Location

To set a custom path to the Esprima Harmony parser, specify the data-esprima-src attribute on the <script> tag used to include the module loader.

Specification Notes

The polyfill is implemented exactly to the specification as closely as possible.

The only feature which is not possible to fully polyfill is the intrinsics functionality and sandboxing of the loader. Custom builtins and full global encapsulation is still provided.

The System normalization and resolution functions are not fully described by the specification, so some assumptions have been made which are listed here https://gist.github.com/guybedford/3712492cf0f629eed761.

To follow the current the specification changes, see https://github.com/ModuleLoader/es6-module-loader/issues?labels=specification&page=1&state=open.

Projects using us

• JSPM Loader is a RequireJS-style loader using our polyfill to load ES6, AMD, CommonJS and global modules

Contributing

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using grunt.

Also, please don't edit files in the "dist" subdirectory as they are generated via grunt. You'll find source code in the "lib" subdirectory!

Release History

• 0.2.4 NodeJS support, relative normalization fixes, IE8 support
• 0.3.0 Traceur support, better error reporting, source maps support, normalization simplifications

License

Copyright (c) 2012 Luke Hoban, Addy Osmani, Guy Bedford
Licensed under the MIT license.