npm i -D worker-loader

Inlined

App.js

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

Config

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) {});

|Name|Type|Default|Description| |:--:|:--:|:-----:|:----------| |name|{String}|[hash].worker.js|Set a custom name for the output script| |inline|{Boolean}|false|Inline the worker as a BLOB| |fallback|{Boolean}|false|Require a fallback for non-worker supporting environments| |publicPath|{String}|null|Override the path from which worker scripts are downloaded| |crossOrigin|{Boolean}|false|Use an inline BLOB worker to trigger an importScripts call for the publicPath|

name

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. When using name alone [hash] is omitted.

webpack.config.js*

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

inline

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 }
}

fallback

Require a fallback for non-worker supporting environments

webpack.config.js

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

publicPath

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/' }
}

crossOrigin

Results in the use of an intermediate BLOB worker that will allow loading the worker code hosted on another origin. This is useful if you want to host your javascript and worker code on a CDN and only makes sense if you have configured a publicPath (either globally, using publicPath: true, or local to this loader) that is an http:// or https:// url.

webpack.config.js

{
  loader: 'worker-loader'
  options: {
    publicPath: 'https://cdn.mysite.fast/',
    crossOrigin: true,
  }
}

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))

Integrating with ES2015 Modules

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))

Integrating with TypeScript

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) => {});

Cross-Origin Policy

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/' }
}