Move a WebAssembly module into its own thread
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


Build Status npm version npm downloads MIT Donate

Move a WebAssembly module into its own thread

wasm-worker only supports browser environments, since it uses Web Workers. For use in a NodeJS environment, Web Workers must be polyfilled using a library like node-webworker.


You can install wasm-worker using npm:

npm install --save wasm-worker

If you aren't using npm in your project, you can include wasmWorker using UMD build in the dist folder with <script> tag.


Once you have installed wasm-worker, supposing a CommonJS environment, you can import and use it in this way:

import wasmWorker from 'wasm-worker';

// supposing an "add.wasm" module that exports a single function "add"
  .then(module => {
    return module.exports.add(1, 2);
  .then(sum => {
    console.log('1 + 2 = ' + sum);
  .catch(ex => {
    // ex is a string that represents the exception

// you can also run js functions inside the worker
// to access importObject for example
  .then(module => {
      // module,
      // importObject,
    }) => {
      // here is sync
      const sum = instance.exports.add(...params);
      return '1 + 2 = ' + sum;
    }, [1, 2]);
  .then(result => {


type JsCallback = (context: {
  module: WebAssembly.Module,
  instance: WebAssembly.Instance,
  importObject: importObject,
  params: any,
}) => any;

type WasmWorkerModule = {
  exports: {
    [export: string]: (...any: Array<any>) => Promise<any>
  // run a js function inside the worker and provides it the given params
  // ⚠️ Caveat: the function you pass cannot rely on its surrounding scope, since it is executed in an isolated context.
  // Please use the "params" parameter to provide some values to the callback
  run: (callback: JsCallback, params?: any) => Promise<any>

type Options = {
  // the first 3 properties are used to create the Web Worker
  name: string,
  type: 'classic' | 'module',
  credentials: 'omit' | 'same-origin' | 'include',
  // the getImportObject function is used to get the options to instantiate the WebAssembly Module
  // ⚠️ Caveat: the function you pass cannot rely on its surrounding scope, since it is executed in an isolated context.
  getImportObject: () => importObject,

wasmWorker(url: string, options?: Options): Promise<WasmWorkerModule> // browser only
wasmWorker(bufferSource: TypedArray | ArrayBuffer, options?: Options): Promise<WasmWorkerModule>

Browser support

wasm-worker uses fetch, Worker and obviously WebAssembly APIs, they are broadly supported by major browser engines but you would like to polyfill them to support old versions.

if (!window.fetch || !window.Worker || !window.WebAssembly) {
} else {


If your app has a Content-Security-Policy, wasm-worker require worker-src data: and script-src data: in your config.


This project is inspired by greenlet.

Change Log

This project adheres to Semantic Versioning.
Every release, along with the migration instructions, is documented on the Github Releases page.


Matteo Basso

Copyright and License

Copyright (c) 2018, Matteo Basso.

wasm-worker source code is licensed under the MIT License.