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

worker loader module for webpack

Getting Started

To begin, you'll need to install worker-loader:

$ npm install worker-loader --save-dev

Inlined

App.js

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

Config

webpack.config.js

module.exports = {
  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) {});

And run webpack via your preferred method.

Options

Name	Type	Default	Description
worker	{String|Object}	Worker	Allows to set web worker constructor name and options
publicPath	{String|Function}	based on output.publicPath	specifies the public URL address of the output files when referenced in a browser
filename	{String|Function}	based on output.filename	The filename of entry chunks for web workers
chunkFilename	{String}	based on output.chunkFilename	The filename of non-entry chunks for web workers
inline	'no-fallback'|'fallback'	undefined	Allow to inline the worker as a BLOB
esModule	{Boolean}	true	Use ES modules syntax

worker

Type: String|Object Default: Worker

Set the worker type.

String

Allows to set web worker constructor name.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          worker: "SharedWorker",
        },
      },
    ],
  },
};

Object

Allow to set web worker constructor name and options.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          worker: {
            type: "SharedWorker",
            options: {
              type: "classic",
              credentials: "omit",
              name: "my-custom-worker-name",
            },
          },
        },
      },
    ],
  },
};

publicPath

Type: String|Function Default: based on output.publicPath

The publicPath specifies the public URL address of the output files when referenced in a browser. If not specified, the same public path used for other webpack assets is used.

String

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          publicPath: "/scripts/workers/",
        },
      },
    ],
  },
};

Function

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          publicPath: (pathData, assetInfo) => {
            return `/scripts/${pathData.hash}/workers/`;
          },
        },
      },
    ],
  },
};

filename

Type: String|Function Default: based on output.filename, adding worker suffix, for example - output.filename: '[name].js' value of this option will be [name].worker.js

The filename of entry chunks for web workers.

String

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          filename: "[name].[contenthash].worker.js",
        },
      },
    ],
  },
};

Function

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          filename: (pathData) => {
            if (
              /\.worker\.(c|m)?js$/i.test(pathData.chunk.entryModule.resource)
            ) {
              return "[name].custom.worker.js";
            }

            return "[name].js";
          },
        },
      },
    ],
  },
};

chunkFilename

Type: String Default: based on output.chunkFilename, adding worker suffix, for example - output.chunkFilename: '[id].js' value of this option will be [id].worker.js

The filename of non-entry chunks for web workers.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          chunkFilename: "[id].[contenthash].worker.js",
        },
      },
    ],
  },
};

inline

Type: 'fallback' | 'no-fallback' Default: undefined

Allow to inline the worker as a BLOB.

Inline mode with the fallback value will create file for browsers without support web workers, to disable this behavior just use no-fallback value.

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          inline: "fallback",
        },
      },
    ],
  },
};

esModule

Type: Boolean Default: true

By default, worker-loader generates JS modules that use the ES modules syntax.

You can enable a CommonJS modules syntax using:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          esModule: false,
        },
      },
    ],
  },
};

Examples

Basic

The worker file can import dependencies just like any other file:

index.js

import Worker from "./my.worker.js";

var worker = new Worker();

var result;

worker.onmessage = function (event) {
  if (!result) {
    result = document.createElement("div");
    result.setAttribute("id", "result");

    document.body.append(result);
  }

  result.innerText = JSON.stringify(event.data);
};

const button = document.getElementById("button");

button.addEventListener("click", function () {
  worker.postMessage({ postMessage: true });
});

my.worker.js

onmessage = function (event) {
  var workerResult = event.data;

  workerResult.onmessage = true;

  postMessage(workerResult);
};

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        loader: "worker-loader",
        options: {
          esModule: false,
        },
      },
    ],
  },
};

Integrating with ES6+ features

You can even use ES6+ features if you have the babel-loader configured.

index.js

import Worker from "./my.worker.js";

const worker = new Worker();

let result;

worker.onmessage = (event) => {
  if (!result) {
    result = document.createElement("div");
    result.setAttribute("id", "result");

    document.body.append(result);
  }

  result.innerText = JSON.stringify(event.data);
};

const button = document.getElementById("button");

button.addEventListener("click", () => {
  worker.postMessage({ postMessage: true });
});

my.worker.js

onmessage = function (event) {
  const workerResult = event.data;

  workerResult.onmessage = true;

  postMessage(workerResult);
};

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.worker\.(c|m)?js$/i,
        use: [
          {
            loader: "worker-loader",
          },
          {
            loader: "babel-loader",
            options: {
              presets: ["@babel/preset-env"],
            },
          },
        ],
      },
    ],
  },
};

Integrating with TypeScript

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

typings/worker-loader.d.ts

declare module "worker-loader!*" {
  // You need to change `Worker`, if you specified a different value for the `workerType` option
  class WebpackWorker extends Worker {
    constructor();
  }

  // Uncomment this if you set the `esModule` option to `false`
  // export = WebpackWorker;
  export default WebpackWorker;
}

my.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));

index.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

module.exports = {
  module: {
    rules: [
      {
        loader: "worker-loader",
        options: { inline: "fallback" },
      },
    ],
  },
};

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

module.exports = {
  module: {
    rules: [
      {
        loader: "worker-loader",
        options: { publicPath: "/workers/" },
      },
    ],
  },
};

Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

CONTRIBUTING

License

MIT

Changelog

3.0.8 (2021-02-11)

Bug Fixes

• make inline workers work from inside workers (#307) (2abd129)