SystemJS build tool
JavaScript HTML Shell

SystemJS Build Tool Build Status Support

SystemJS Builder 0.16 release notes

Note for SystemJS 0.19 support use SystemJS Builder 0.15

Provides a single-file build for SystemJS of mixed-dependency module trees.

Builds ES6 into ES5, CommonJS, AMD and globals into a single file in a way that supports the CSP SystemJS loader as well as circular references.



import $ from "./jquery.js";
export var hello = 'es6';


define(function() {
  return 'this is jquery';

Will build the module app into a bundle containing both app and jquery defined through System.register calls.

Circular references and bindings in ES6, CommonJS and AMD all behave exactly as they should, including maintaining execution order.


API Reference



npm install systemjs-builder

Basic Use

Ensure that the transpiler is installed separately (npm install babel-core here).

var path = require("path");
var Builder = require('systemjs-builder');

// optional constructor options
// sets the baseURL and loads the configuration file
var builder = new Builder('path/to/baseURL', 'path/to/system/config-file.js');

.bundle('local/module.js', 'outfile.js')
.then(function() {
  console.log('Build complete');
.catch(function(err) {
  console.log('Build error');

Setting Configuration

Configuration can be injected via builder.config:

  map: {
    'a': 'b.js'

To load custom configuration files use builder.loadConfig:

// `builder.loadConfig` will load config from a file containing `System.config({...})`
.then(function() {
  // ready to build

Multiple config calls can be run, which will combine into the loader configuration.

Resetting Configuration

To reset the loader state and configuration use builder.reset().

When config was passed into the new Builder(baseURL, configFile) constructor, the config will be reset to this exact configFile state.

Self-Executing (SFX) Bundles

To make a bundle that is independent of the SystemJS loader entirely, we can make SFX bundles:

builder.buildStatic('myModule.js', 'outfile.js', options);

This bundle file can then be included with a <script> tag, and no other dependencies would need to be included in the page. You'll likely want your module to export a global variable when loaded from a script tag, and this can be configured via globalName. For example

builder.buildStatic('src/NavBar.js', 'dist/NavBarStaticBuild.js', {
  globalName: 'NavBar'

will cause the output of your module to be assigned to a global variable named NavBar. If you're making a static bundle, while excluding certain dependencies, those dependencies will of course need to have already been loaded on your page, with their own global variables exported. You can match these global variables up with your needed dependencies with globalDeps. For example

builder.buildStatic('src/NavBar.js - react', 'dist/NavBarStaticBuild.js', {
  globalName: 'NavBar',
  globalDeps: {
    'react': 'React'

will create a static build of NavBar—without React—which, when loaded via a script tag, exports an eponymous global variable, and assumes the existence of a React global variable, which will be used for the react dependency.

This would support users with a setup of

<script src='path/to/react.min.js'></script>
<script src='path/to/NavBarStaticBuild.js'></script>

Note that another way of excluding react would be with externals.

builder.buildStatic('src/NavBar.js', 'dist/NavBarStaticBuild.js', {
  externals: ['react'],
  globalName: 'NavBar',
  globalDeps: {
    'react': 'React'

This would also exclude react but, if react defined any dependencies which NavBar also defined, those dependencies would be included in the build.

Of course the above explanations involving globalDeps and globalName only apply to when your end user loads the static file from a script tag. Since the output is (by default, see below) UMD, a script loader like SystemJS or requireJS would process it as configured, or via AMD respectively.

By default, the Traceur or Babel runtime are automatically included in the SFX bundle if needed. To exclude the Babel or Traceur runtime set the runtime build option to false:

builder.buildStatic('myModule.js', 'outfile.js', { runtime: false });

SFX Format

SFX bundles can also be output as a custom module format - amd, cjs or es6 for consumption in different environments.

This is handled via the format (previously sfxFormat) option:

builder.buildStatic('myModule.js', 'outfile.js', { format: 'cjs' });

The first module used as input (myModule.js here) will then have its exports output as the CommonJS exports of the whole SFX bundle itself when run in a CommonJS environment.

Adapter Modules

To have globals like jQuery not included, and included in a separate script tag, set up an adapter module something like:


module.exports = window.jQuery;

Minification & Source Maps

As well as an options.config parameter, it is also possible to specify minification and source maps options:

builder.bundle('myModule.js', 'outfile.js', { minify: true, sourceMaps: true, config: cfg });

Compile time with source maps can also be improved with the lowResSourceMaps option, where the mapping granularity is per-line instead of per-character:

builder.bundle('myModule.js', 'outfile.js', { sourceMaps: true, lowResSourceMaps: true });

Minification Options

  • mangle, defaults to true.
  • globalDefs, object allowing for global definition assignments for dead code removal.
builder.bundle('myModule.js', 'outfile.js', { minify: true, mangle: false, globalDefs: { DEBUG: false } });

SourceMap Options

  • sourceMaps, Either boolean value (enable/disable) or string value 'inline' which will inline the SourceMap data as Base64 data URI right in the generated output file (never use in production). (Default is false)
  • sourceMapContents, Boolean value that determines if original sources shall be directly included in the SourceMap. Using inline source contents generates truely self contained SourceMaps which will not need to load the external original source files during debugging. (Default is false; when using sourceMaps='inline' it defaults true)

In-Memory Builds

Leave out the outFile option to run an in-memory build:

builder.bundle('myModule.js', { minify: true }).then(function(output) {
  output.source;    // generated bundle source
  output.sourceMap; // generated bundle source map
  output.modules;   // array of module names defined in the bundle

The output object above is provided for all builds, including when outFile is set.

output.modules can be used to directly populate SystemJS bundles configuration.

Ignore Resources

If loading resources that shouldn't even be traced as part of the build (say an external import), these can be configured with:

  meta: {
    'resource/to/ignore.js': {
      build: false

Overriding Fetch

The framework fetch function can be overridden in order to provide the source for a file manually. This is useful if you want to pre-process the source of a file before using the builder.

var mySource = 'import * from foo; var foo = "bar";'; // get source as a string
builder.bundle('foo.js', {
  fetch: function (load, fetch) {
    if ('foo.js') !== -1) {
      return mySource;
    } else {
      // fall back to the normal fetch method
      return fetch(load);

The load variable describes the file that is trying to be loaded. This is called once for every file that is trying to be fetched, including dependencies.

The fetch function should return a string.

Bundle Arithmetic

Both and builder.buildStatic support bundle arithmetic expressions. This allows for the easy construction of custom bundles.

There is also a builder.trace for building direct trace tree objects, which can be directly passed into builder.bundle or builder.buildStatic.

Example - Arithmetic Expressions

In this example we build all our application code in app/ excluding the tree app/corelibs:

var Builder = require('systemjs-builder');

var builder = new Builder({
  baseURL: '...',
  map: {
  } // etc. config

builder.bundle('app/* - app/corelibs.js', 'output-file.js', { minify: true, sourceMaps: true });

Example - Common Bundles

To build the dependencies in common between two modules, use the & operator:

builder.bundle('app/page1.js & app/page2.js', 'common.js');

We can then exclude this common bundle in future builds:

builder.bundle('app/componentA.js - common.js', { minify: true, sourceMaps: true });

Example - Third-Party Dependency Bundles

Build a bundle of all dependencies of the app/ package excluding anything from app/ itself.

For this we can use the [module] syntax which represents a single module instead of all its dependencies as well:

builder.bundle('app/**/* - [app/**/*]', 'dependencies.js', { minify: true, sourceMaps: true });

The above means take the tree of app and all its dependencies, and subtract just the modules in app, thus leaving us with just the tree of dependencies of the app package.

Example - Multiple Common Bundles

Parentheses are supported, so the following would bundle everything in common with page1 and page2, and also everything in common between page3 and page4:

builder.bundle('(app/page1.js & app/page2.js) + (app/page3.js & app/page4.js)', 'common.js');

Example - Direct Trace API

Instead of using the arithmetic syntax, we can construct the trace ourselves.

In this example we build app/first and app/second into two separate bundles, while creating a separate shared bundle:

var Builder = require('systemjs-builder');

var builder = new Builder({
  // ...

Promise.all([builder.trace('app/first.js'), builder.trace('app/second.js')])
.then(function(trees) {
  var commonTree = builder.intersectTrees(trees[0], trees[1]);
  return Promise.all([
    builder.bundle(commonTree, 'shared-bundle.js'),
    builder.bundle(builder.subtractTrees(trees[0], commonTree), 'first-bundle.js'),
    builder.bundle(builder.subtractTrees(trees[1], commonTree), 'second-bundle.js')