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5.0.1 • Public • Published


👩‍🏭 worker-plugin

Automatically bundle & compile Web Workers within Webpack.


Automatically compiles modules loaded in Web Workers:

const worker = new Worker('./foo.js', { type: 'module' });
                          gets bundled using webpack

The best part? That worker constructor works just fine without bundling turned on, but when bundled the result is supported in all browsers that support Web Workers - all the way back to IE 10!

Workers with fully dynamic URLs, Blob URLs, data URLs or with no { type:'module' } option are left unchanged.

Compatibility Note: Webpack 5 now includes worker bundling. It uses a slightly different syntax:
new Worker(new URL("./my_worker.js", import.meta.url))


npm install -D worker-plugin

Then drop it into your webpack.config.js:

+ const WorkerPlugin = require('worker-plugin');

module.exports = {
  plugins: [
+    new WorkerPlugin()

Note: If you're planning on having more than one worker, you'll need to make sure output.filename is set to something dynamic, e.g. "[name].bundle.js" otherwise the generated filenames will overwrite one another.


worker.js: (our worker module)

// This is a module worker, so we can use imports (in the browser too!)
import { calculatePi } from './some-other-module';

addEventListener('message', event => {

main.js: (our demo, on the main thread)

const piWorker = new Worker('./worker.js', { type: 'module' });
piWorker.onmessage = event => {
  console.log('pi: ' +;

Note: in order to ensure WorkerPlugin bundles your worker, make sure you're passing a string URL/filename to the Worker constructor. WorkerPlugin cannot bundle workers with dynamic/variable filenames, Blob or data URLs - it will leave them unmodified and print a warning during your build.


In most cases, no options are necessary to use WorkerPlugin.

globalObject (string | false)

WorkerPlugin will print a warning if your Webpack configuration has output.globalObject set to window, since doing so breaks Hot Module Replacement in web workers.

If you're not using HMR and want to disable this warning, pass globalObject:false:

new WorkerPlugin({
  // disable warnings about "window" breaking HMR:
  globalObject: false

To configure the value of output.globalObject for WorkerPlugin's internal Webpack Compiler, set globalObject to any String:

new WorkerPlugin({
  // use "self" as the global object when receiving hot updates.
  globalObject: 'self' // <-- this is the default value

plugins (array)

By default, WorkerPlugin doesn't run any of your configured Webpack plugins when bundling worker code - this avoids running things like html-webpack-plugin twice. For cases where it's necessary to apply a plugin to Worker code, use the plugins option.

Here you can specify the names of plugins to "copy" from your existing Webpack configuration, or provide specific plugins to apply only to worker code:

module.exports = {
  plugins: [
    // an example of a plugin already being used:
    new SomeExistingPlugin({ <...> }),

    new WorkerPlugin({
      plugins: [
        // A string here will copy the named plugin from your configuration:
        // Or you can specify a plugin directly, only applied to Worker code:
        new SomePluginToApplyOnlyToWorkers({ <...> })

sharedWorker (boolean)

If set to true, this option enables the bundling of SharedWorker:

const shared = new SharedWorker('./my-shared-worker.js', { type: 'module' });

worker (boolean)

If set to false, this option disables the bundling of [Worker]. Intended to be used with { sharedWorker: true } to allow bundling of [SharedWorker] only without also bundling [Worker].

preserveTypeModule (boolean)

workerType (string)

Normally, WorkerPlugin will transform new Worker('./a.js', { type: 'module' }) to completely remove the type option, outputting something like new Worker('a.worker.js'). This allows the plugin to compile Module Workers to Classic Workers, which are supported in all browsers.

To instead retain {type:'module'} in bundled output, set the preserveTypeModule option to true:

  plugins: [
    new WorkerPlugin({
      preserveTypeModule: true

Similarly, if you need to have WorkerPlugin output a specific type value, use the workerType option to specify it:

  plugins: [
    new WorkerPlugin({
      workerType: 'foo'  // note: this isn't a thing!


At its core, worker-plugin provides two features: parsing and handling of new Worker(), and standalone bundling of modules for use in a different JavaScript context.

If all you want is to compile separate bundles for a module, worker-plugin/loader provides the bundling functionality of worker-plugin as a standalone Webpack loader. This is useful for generating bundles for use in iframes, Service Workers or Worklets. Applying worker-plugin/loader to an import will bundle that module and return its URL:

import workerUrl from 'worker-plugin/loader!./my-worker';

console.log(workerUrl); // "/0.worker.js"


Two options are available:

Option Type Description
name string Controls the name of the generated chunk.
The name is used to generate a URL according to output.chunkFilename.
esModule boolean Export the URL from an ES Module (export default url).
The default is CommonJS (module.exports = url).

Options can be supplied inline:

import url from 'worker-plugin/loader?name=foo&esModule!./foo';

... or by setting up a loader alias:

// webpack.config.js to enable this:
// import url from 'worker!./foo';
  resolveLoader: {
    alias: {
      worker: 'worker-plugin/loader?esModule'



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