DEPRECATED for v5: https://webpack.js.org/guides/web-workers/
Web Worker loader for webpack 4.
Note that this is specific to webpack 4. To use Web Workers in webpack 5, see https://webpack.js.org/guides/web-workers/.
To begin, you'll need to install worker-loader:
$ npm install worker-loader --save-devApp.js
import Worker from "worker-loader!./Worker.js";webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.js$/,
use: { loader: "worker-loader" },
},
],
},
};App.js
import Worker from "./file.worker.js";
const worker = new Worker();
worker.postMessage({ a: 1 });
worker.onmessage = function (event) {};
worker.addEventListener("message", function (event) {});And run webpack via your preferred method.
| Name | Type | Default | Description |
|---|---|---|---|
worker |
{String|Object} |
Worker |
Allows to set web worker constructor name and options |
publicPath |
{String|Function} |
based on output.publicPath |
specifies the public URL address of the output files when referenced in a browser |
filename |
{String|Function} |
based on output.filename |
The filename of entry chunks for web workers |
chunkFilename |
{String} |
based on output.chunkFilename |
The filename of non-entry chunks for web workers |
inline |
'no-fallback'|'fallback' |
undefined |
Allow to inline the worker as a BLOB |
esModule |
{Boolean} |
true |
Use ES modules syntax |
Type: String|Object
Default: Worker
Set the worker type.
Allows to set web worker constructor name.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
worker: "SharedWorker",
},
},
],
},
};Allow to set web worker constructor name and options.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
worker: {
type: "SharedWorker",
options: {
type: "classic",
credentials: "omit",
name: "my-custom-worker-name",
},
},
},
},
],
},
};Type: String|Function
Default: based on output.publicPath
The publicPath specifies the public URL address of the output files when referenced in a browser.
If not specified, the same public path used for other webpack assets is used.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
publicPath: "/scripts/workers/",
},
},
],
},
};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/`;
},
},
},
],
},
};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.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
filename: "[name].[contenthash].worker.js",
},
},
],
},
};webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
filename: (pathData) => {
if (
/\.worker\.(c|m)?js$/i.test(pathData.chunk.entryModule.resource)
) {
return "[name].custom.worker.js";
}
return "[name].js";
},
},
},
],
},
};Type: String
Default: based on output.chunkFilename, adding worker suffix, for example - output.chunkFilename: '[id].js' value of this option will be [id].worker.js
The filename of non-entry chunks for web workers.
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
chunkFilename: "[id].[contenthash].worker.js",
},
},
],
},
};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$/i,
loader: "worker-loader",
options: {
inline: "fallback",
},
},
],
},
};Type: Boolean
Default: true
By default, worker-loader generates JS modules that use the ES modules syntax.
You can enable a CommonJS modules syntax using:
webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
loader: "worker-loader",
options: {
esModule: false,
},
},
],
},
};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$/i,
loader: "worker-loader",
options: {
esModule: false,
},
},
],
},
};You can even use ES6+ features if you have the babel-loader configured.
index.js
import Worker from "./my.worker.js";
const worker = new Worker();
let result;
worker.onmessage = (event) => {
if (!result) {
result = document.createElement("div");
result.setAttribute("id", "result");
document.body.append(result);
}
result.innerText = JSON.stringify(event.data);
};
const button = document.getElementById("button");
button.addEventListener("click", () => {
worker.postMessage({ postMessage: true });
});my.worker.js
onmessage = function (event) {
const workerResult = event.data;
workerResult.onmessage = true;
postMessage(workerResult);
};webpack.config.js
module.exports = {
module: {
rules: [
{
test: /\.worker\.(c|m)?js$/i,
use: [
{
loader: "worker-loader",
},
{
loader: "babel-loader",
options: {
presets: ["@babel/preset-env"],
},
},
],
},
],
},
};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) => {});Alternatively, you can omit the worker-loader! prefix passed to import statement by using the following notation.
This is useful for executing the code using a non-WebPack runtime environment
(such as Jest with workerloader-jest-transformer).
typings/worker-loader.d.ts
declare module "*.worker.ts" {
// 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 MyWorker from "./my.worker.ts";
const worker = new MyWorker();
worker.postMessage({ a: 1 });
worker.onmessage = (event) => {};
worker.addEventListener("message", (event) => {});webpack.config.js
module.exports = {
module: {
rules: [
// Place this *before* the `ts-loader`.
{
test: /\.worker\.ts$/,
loader: "worker-loader",
},
{
test: /\.ts$/,
loader: "ts-loader",
},
],
},
resolve: {
extensions: [".ts", ".js"],
},
};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/" },
},
],
},
};Please take a moment to read our contributing guidelines if you haven't yet done so.