worker-loader

What is worker-loader?

The worker-loader npm package is a webpack loader that allows you to create web workers from your JavaScript files. It simplifies the process of offloading tasks to background threads, which can help improve the performance of your web applications by handling CPU-intensive operations without blocking the main thread.

What are worker-loader's main functionalities?

Basic Web Worker Setup

This feature allows you to set up a basic web worker using worker-loader. The code demonstrates how to import a worker script, create a new worker instance, send a message to the worker, and handle messages received from the worker.

const Worker = require('worker-loader!./worker.js');
const worker = new Worker();
worker.postMessage({ message: 'Hello, Worker!' });
worker.onmessage = function(event) {
  console.log('Received from worker:', event.data);
};

Handling Multiple Workers

This feature demonstrates how to handle multiple web workers simultaneously. The code shows how to import and create instances of different worker scripts, send tasks to each worker, and handle their responses independently.

const Worker1 = require('worker-loader!./worker1.js');
const Worker2 = require('worker-loader!./worker2.js');
const worker1 = new Worker1();
const worker2 = new Worker2();
worker1.postMessage({ task: 'Task 1' });
worker2.postMessage({ task: 'Task 2' });
worker1.onmessage = function(event) {
  console.log('Worker 1 completed:', event.data);
};
worker2.onmessage = function(event) {
  console.log('Worker 2 completed:', event.data);
};

Using Web Workers with TypeScript

This feature illustrates how to use worker-loader with TypeScript. The code demonstrates importing a TypeScript worker script, creating a worker instance, sending a message to the worker, and handling the response.

import Worker from 'worker-loader!./worker.ts';
const worker = new Worker();
worker.postMessage({ message: 'Hello, TypeScript Worker!' });
worker.onmessage = function(event) {
  console.log('Received from TypeScript worker:', event.data);
};

Other packages similar to worker-loader

comlink

Comlink is a library that simplifies the use of Web Workers by providing a proxy-based API. It allows you to call functions in the worker as if they were local functions, making the communication between the main thread and the worker more intuitive. Compared to worker-loader, Comlink offers a higher-level abstraction for worker communication.

threads

Threads is a library that provides a simple and modern API for using Web Workers. It supports both JavaScript and TypeScript and offers features like thread pools and message channels. Threads focuses on ease of use and performance, making it a good alternative to worker-loader for more complex worker management.

greenlet

Greenlet is a lightweight library that allows you to run functions in a Web Worker with minimal overhead. It provides a simple API for offloading functions to a worker and returning the results as promises. Greenlet is a good choice for projects that need a minimalistic solution for using Web Workers compared to the more feature-rich worker-loader.

README

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. 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/' }
}

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 default 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 from "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

Changelog

2.0.0 (2018-05-27)

Updates

• refactor(index): remove Tapable.apply calls (#121)
• docs: use ES6 import in TypeScript README example (#140) …
• docs(README): add note about omitted hashes (options.name) (#131)
• fix(package): homepage URL typo (#130)

Breaking Changes

Drops support for Webpack versions < 3.0.0

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