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worker-loader

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Worker Loader

This loader registers the script as Web Worker

Install

npm i -D worker-loader

Usage

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) {});

Options

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

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

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/' }
}

Examples

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/' }
}

Maintainers


Bogdan Chadkin

Juho Vepsäläinen

Joshua Wiens

Michael Ciniawsky

Alexander Krasnoyarov