systemjs

What is systemjs?

SystemJS is a dynamic module loader that can load ES modules, AMD, CommonJS, and global scripts in the browser and Node.js. It provides a way to load modules asynchronously and supports various module formats, making it a versatile tool for managing dependencies and module loading in JavaScript applications.

What are systemjs's main functionalities?

Loading ES Modules

SystemJS can dynamically import ES modules. The code sample demonstrates how to load an ES module asynchronously and handle the loaded module.

System.import('/path/to/module.js').then(function(module) {
  console.log(module);
});

Loading CommonJS Modules

SystemJS can also load CommonJS modules. The code sample shows how to load a CommonJS module asynchronously.

System.import('/path/to/commonjs-module.js').then(function(module) {
  console.log(module);
});

Loading AMD Modules

SystemJS supports loading AMD modules. The code sample demonstrates how to load an AMD module asynchronously.

System.import('/path/to/amd-module.js').then(function(module) {
  console.log(module);
});

Loading Global Scripts

SystemJS can load global scripts that do not export any modules. The code sample shows how to load a global script asynchronously.

System.import('/path/to/global-script.js').then(function() {
  console.log('Global script loaded');
});

Configuring SystemJS

SystemJS allows configuration for module loading. The code sample demonstrates how to configure the base URL, paths, and module mappings.

System.config({
  baseURL: '/base/url',
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  map: {
    'jquery': 'npm:jquery@3.5.1/dist/jquery.js'
  }
});

Other packages similar to systemjs

requirejs

RequireJS is a JavaScript file and module loader. It is optimized for in-browser use, but it can be used in other JavaScript environments, such as Rhino and Node. Compared to SystemJS, RequireJS primarily focuses on AMD modules and does not support as many module formats.

webpack

Webpack is a module bundler that takes modules with dependencies and generates static assets representing those modules. Unlike SystemJS, which is a dynamic module loader, Webpack bundles modules at build time, which can result in better performance for production applications.

browserify

Browserify allows you to use Node.js-style require() to organize your browser code and load modules. It transforms Node.js modules into a format that can be used in the browser. Compared to SystemJS, Browserify focuses on CommonJS modules and does not support as many module formats.

es-module-loader

ES Module Loader is a polyfill for the ES Module Loader specification. It provides a way to load ES modules in environments that do not natively support them. Compared to SystemJS, ES Module Loader is more focused on ES modules and does not support other module formats.

README

SystemJS

Universal dynamic module loader - loads ES6 modules, AMD, CommonJS and global scripts in the browser and NodeJS.

Designed as a collection of extensions to the ES6 module loader which can also be applied individually.

• Loads any module format.
• Provides comprehensive and exact replications of AMD, CommonJS and ES6 circular reference handling.
• Loads ES6 modules compiled into the System.register form for production, maintaining full circular references support.
• Supports RequireJS-style map, paths, bundles, shim and plugins.
• Tracks package versions, and resolves semver-compatibile requests through package version syntax - package@x.y.z, package^@x.y.z.
• Loader plugins allow loading assets through the module naming system such as CSS, JSON or images.

Designed to work with the ES6 Module Loader polyfill (9KB) for a combined total footprint of 16KB minified and gzipped. In future, with native implementations, the ES6 Module Loader polyfill should no longer be necessary. As jQuery provides for the DOM, this library can smooth over inconsistiencies and missing practical functionality provided by the native System loader.

Runs in IE8+ and NodeJS.

For discussion, see the Google Group.

Documentation

• Loader Configuration
• Map Configuration
• Meta Configuration
• Module Format Support
• Relative Dynamic Loading
• Versions Extension
• Production Workflows
• Creating Plugins
• Creating a Custom Module Format

Getting Started

Setup

Download es6-module-loader.js and traceur.js and locate them in the same folder as system.js from this repo.

We then include dist/system.js with a script tag in the page.

es6-module-loader.js will then be included from the same folder automatically and Traceur is dynamically included from traceur.js when loading an ES6 module only.

Alternatively, es6-module-loader.js or traceur.js can be included before system.js with a script tag in the page.

Simple Application Structure

The standard application structure would be something like the following:

index.html:

<script src="system.js"></script>
<script>
  // Identical to writing System.baseURL = ...
  System.config({

    // set all requires to "lib" for library code
    baseURL: '/lib/',
    
    // set "app" as an exception for our application code
    paths: {
      'app/*': '/app/*.js'
    }
  });

  System.import('app/app')
</script>

app/app.js:

  // relative require for within the package
  require('./local-dep');    // -> /app/local-dep.js

  // library resource
  var $ = require('jquery'); // -> /lib/jquery.js

  // format detected automatically
  console.log('loaded CommonJS');

Module format detection happens in the order System.register, ES6, AMD, then CommonJS and falls back to global modules.

Named defines are also supported, with the return value for a module containing named defines being its last named define.

Note that when running locally, ensure you are running from a local server or a browser with local XHR requests enabled. If not you will get an error message.

For Chrome on Mac, you can run it with: /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --allow-file-access-from-files &> /dev/null &

In Firefox this requires navigating to about:config, entering security.fileuri.strict_origin_policy in the filter box and toggling the option to false.

Loading ES6

app/es6-file.js:

  export class q {
    constructor() {
      this.es6 = 'yay';
    }
  }

  <script>
    System.import('app/es6-file').then(function(m) {
      console.log(new m.q().es6); // yay
    });
  </script>

ES6 modules define named exports, provided as getters on a special immutable Module object.

To build for production, see the System.register build workflow.

For further infomation on ES6 module loading, see the ES6 Module Loader polyfill documentation.

For further details about SystemJS module format support, see the wiki page.

Plugins

Plugins handle alternative loading scenarios, including loading assets such as CSS or images, and providing custom transpilation scenarios.

Supported Plugins:

• CSS System.import('my/file.css!')
• Image System.import('some/image.png!image')
• JSON System.import('some/data.json!').then(function(json){})
• Text System.import('some/text.txt!text').then(function(text) {})

Additional Community Plugins:

• JSX System.import('template.jsx!')
• Markdown System.import('app/some/project/README.md!').then(function(html) {})
• WebFont System.import('google Port Lligat Slab, Droid Sans !font')

Additional plugin submissions to the above are welcome.

Read the guide here on creating plugins.

NodeJS Usage

To load modules in NodeJS, install SystemJS with:

  npm install systemjs

We can then load modules equivalently to in the browser:

var System = require('systemjs');

// loads './app.js' from the current directory
System.import('./app').then(function(m) {
  console.log(m);
});

Running the tests

To install the dependencies correctly, run bower install from the root of the repo, then open test/test.html in a browser with a local server or file access flags enabled.

License

MIT