Worker Loader

This loader registers the script as Web Worker

npm i -D worker-loader

App.js

import Worker from 'worker-loader!./Worker.js';

webpack.config.js

{
  module: {
    rules: [
      {
        test: /\.worker\.js$/,
        use: { loader: 'worker-loader' }
      }
    ]
  }
}

App.js

import Worker from './file.worker.js';

const worker = new Worker();

worker.postMessage({ a: 1 });
worker.onmessage = function (event) {};

worker.addEventListener("message", function (event) {});

To set a custom name for the output script, use the name parameter. The name may contain the string [hash], which will be replaced with a content dependent hash for caching purposes

webpack.config.js*

{
  loader: 'worker-loader',
  options: { name: 'WorkerName.[hash].js' }
}

You can also inline the worker as a BLOB with the inline parameter

webpack.config.js

{
  loader: 'worker-loader',
  options: { inline: true }
}

ℹ️ Inline mode will also create chunks for browsers without support for inline workers, to disable this behavior just set fallback parameter as false

webpack.config.js

{
  loader: 'worker-loader'
  options: { inline: true, fallback: false }
}

Require a fallback for non-worker supporting environments

webpack.config.js

{
  loader: 'worker-loader'
  options: { fallback: false }
}

Overrides the path from which worker scripts are downloaded. If not specified, the same public path used for other webpack assets is used

webpack.config.js

{
  loader: 'worker-loader'
  options: { publicPath: '/scripts/workers/' }
}

The worker file can import dependencies just like any other file

Worker.js

const _ = require('lodash')

const obj = { foo: 'foo' }

_.has(obj, 'foo')

// Post data to parent thread
self.postMessage({ foo: 'foo' })

// Respond to message from parent thread
self.addEventListener('message', (event) => console.log(event))  

ℹ️ You can even use ES2015 Modules if you have the babel-loader configured.

Worker.js

import _ from 'lodash'

const obj = { foo: 'foo' }

_.has(obj, 'foo')

// Post data to parent thread
self.postMessage({ foo: 'foo' })

// Respond to message from parent thread
self.addEventListener('message', (event) => console.log(event))

To integrate with TypeScript, you will need to define a custom module for the exports of your worker

typings/custom.d.ts

declare module "worker-loader!*" {
  class WebpackWorker extends Worker {
    constructor();
  }

  export = WebpackWorker;
}

Worker.ts

const ctx: Worker = self as any;

// Post data to parent thread
ctx.postMessage({ foo: "foo" });

// Respond to message from parent thread
ctx.addEventListener("message", (event) => console.log(event));

App.ts

import Worker = require("worker-loader!./Worker");

const worker = new Worker();

worker.postMessage({ a: 1 });
worker.onmessage = (event) => {};

worker.addEventListener("message", (event) => {});

WebWorkers are restricted by a same-origin policy, so if your webpack assets are not being served from the same origin as your application, their download may be blocked by your browser. This scenario can commonly occur if you are hosting your assets under a CDN domain. Even downloads from the webpack-dev-server could be blocked. There are two workarounds

Firstly, you can inline the worker as a blob instead of downloading it as an external script via the inline parameter

App.js

import Worker from './file.worker.js';

webpack.config.js

{
  loader: 'worker-loader'
  options: { inline: true }
}

Secondly, you may override the base download URL for your worker script via the publicPath option

App.js

// This will cause the worker to be downloaded from `/workers/file.worker.js`
import Worker from './file.worker.js';

webpack.config.js

{
  loader: 'worker-loader'
  options: { publicPath: '/workers/' }
}

Bogdan Chadkin

Juho Vepsäläinen

Joshua Wiens

Michael Ciniawsky

Alexander Krasnoyarov