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Karma plugin for using SystemJS as a module loader.

karma-systemjs works by loading files with System.import() instead of including them with <script/>, as Karma normally does.


Install from npm, along with systemjs, es6-module-loader, and your transpiler:

npm install karma-systemjs systemjs es6-module-loader systemjs-plugin-babel

Make sure all your dependencies, including SystemJS itself, are specified in your SystemJS config.
This is so karma-systemjs can add them to the list of files that karma serves.

// system.conf.js
	paths: {
		'plugin-babel': 'node_modules/systemjs-plugin-babel/plugin-babel.js',
		'systemjs-babel-build': 'node_modules/systemjs-plugin-babel/systemjs-babel-browser.js',
		'systemjs': 'node_modules/systemjs/dist/system.js',
		'system-polyfills': 'node_modules/systemjs/dist/system-polyfills.js',
		'es6-module-loader': 'node_modules/es6-module-loader/dist/es6-module-loader.js'

Dependencies can be specified under paths or map.

// system.conf.js
	map: {
		'plugin-babel': 'node_modules/systemjs-plugin-babel/plugin-babel.js',
		'systemjs-babel-build': 'node_modules/systemjs-plugin-babel/systemjs-babel-browser.js',
		'system-polyfills': 'node_modules/systemjs/dist/system-polyfills.js',
		'es6-module-loader': 'node_modules/es6-module-loader/dist/es6-module-loader.js'

Karma Configuration

Add karma-systemjs to your list of plugins:

plugins: ['karma-systemjs', ...]

Add systemjs to your list of frameworks, (NB. must be included as first framework in list):

frameworks: ['systemjs', ...]

Add SystemJS configuration:

// karma.conf.js
systemjs: {
	// Path to your SystemJS configuration file
	configFile: 'app/system.conf.js',

	// Patterns for files that you want Karma to make available, but not loaded until a module requests them. eg. Third-party libraries.
	serveFiles: [

	// SystemJS configuration specifically for tests, added after your config file.
	// Good for adding test libraries and mock modules
	config: {
		paths: {
			'angular-mocks': 'bower_components/angular-mocks/angular-mocks.js'

karma-systemjs defaults to using Traceur as transpiler.
You can specify another transpiler (eg. plugin-babel or plugin-typescript) by adding it to your SystemJS config:

	transpiler: 'plugin-babel'

The transpiler can also be omitted by setting transpiler to null.

karma-systemjs looks up the paths for es6-module-loader, systemjs, and your transpiler (plugin-babel, traceur, or plugin-typescript) in the paths or map object of your SystemJS configuration.

systemjs: {
	config: {
		paths: {
			'es6-module-loader': 'bower_components/es6-module-loader/dist/es6-module-loader.js'

SystemJS bundles are excluded by default, they can be included by setting the useBundles flag of the systemjs configuration object.

	useBundles: 'true'

I'm getting a "TypeError: 'undefined' is not a function" when using PhantomJS

PhantomJS v1.x doesn't provide the Function.prototype.bind method, which is used by some transpilers.
The best solution is to install phantomjs-polyfill and include it in your SystemJS config.

npm install phantomjs-polyfill

	paths: {
		'phantomjs-polyfill': 'node_modules/phantomjs-polyfill/bind-polyfill.js'

Can I still use this with karma-coverage?

Absolutely, but you'll need to configure karma-coverage to use an instrumenter which supports ES6.

preprocessors: {
	'src/!(*spec).js': ['coverage']

coverageReporter: {
	instrumenters: { isparta : require('isparta') },
	instrumenter: {
		'**/*.js': 'isparta'

I'm getting a "window.chai is undefined" error!

karma-systemjs hijacks every pattern added to files with {included: true}, which may include changes applied by other plugins - such as karma-chai.
The solution is to make sure systemjs is the first item in your frameworks list, so it won't affect the other frameworks.

frameworks: ['systemjs', 'chai']

'src/**/*Spec.js' only matches files in src's subfolders

This appears to be a quirk in minimatch, the glob engine used by both karma and karma-systemjs.
The problem is that the second / is treated as a static part of the pattern. So the shortest path it will match is src//Spec.js.

Simplest solution is to double up your patterns - one for the folder, and another for the subfolder.
['src/*Spec.js', 'src/**/*Spec.js']

What if I need some files to be included through script tags?

You can add patterns for these files to systemjs.includeFiles. Any patterns in this array will be kept at the start of the files list (ie. Before SystemJS and everything else) as is.

My imports aren't getting loaded in sequence!

The initial modules are loaded using Promise.all([System.import(), ...]), which means it's possible for one module to be imported and run before a previous module was run.
This can cause problems if you depend upon this ordering for global modules. eg. angular must be loaded before angular-mocks.

I recommend only importing test suites, not libraries. Libraries should be imported inside your test suites using import or require() statements that would maintain the sequence.
Otherwise you can use systemjs.includeFiles in your Karma config to include globals before any of your tests run.

Alternatively you can set systemjs.strictImportSequence to true, which will chain the System.import() promises together to preserve their sequence.

My tests seem to take a long time to start.

Here's a few hints for speeding up your test runs:

  • Make sure you're only watching files that you care about.
    Instead of specifying just a pattern string, use an object (Karma doco):
    {serveFiles: [{pattern: 'node_modules/**/*.js', watched: false}]}
  • Make sure you're only preprocessing files that you care about.
    eg. If you're using karma-coverage, you'll only want coverage on source code - not node_modules or tests:
    { preprocessors: {'src/!(*spec).js': ['coverage']} }


Breaking Changes

  • v0.13.0: Transpiler is only served, not included, forcing SystemJS to load them.
  • v0.12.0: phantomjs-polyfill is only included if found in SystemJS config.
  • v0.11.0: es6-module-loader and system-polyfills are only included if found in SystemJS config.
  • v0.10.0: Changed require.resolve() static path for babel's browser.js
  • v0.9.0: Arrays in SystemJS config file are overwritten by arrays in karma config, rather than merged. Discussion
  • v0.8.0: MAJOR CHANGE! System.import() is now used to load every file which would normally be {included: true} by Karma, without karma-systemjs.
  • v0.7.0: Takes over setting baseURL to handle SystemJS v0.18.0 restrictions
  • v0.6.0: Deprecated looking up modules in node_modules/ using require.resolve()
  • v0.5.0: Updated to work with SystemJS v0.17.1, which comes with it's own breaking changes.
  • v0.4.0: Looks for babel's browser.js under babel-core instead of babel from require.resolve().
    Better off setting paths.babel in your SystemJS config.