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pseudo-worker Build Status Coverage Status

A tiny and mostly spec-compliant WebWorker polyfill, designed for browsers that don't support WebWorkers, or for browsers that don't support certain features of WebWorkers (e.g. IndexedDB in Safari).

This runs on the main thread, so you don't get any of the multithreading benefits of WebWorkers. However, it should be "good enough" for the less-compliant browsers.

The bundle size is very small: 1kB after uglify+gzip!


npm install pseudo-worker


var PseudoWorker = require('pseudo-worker');
var worker = new PseudoWorker('script.js');

Or as a polyfill:

// now window.Worker is polyfilled in older browsers 

Instead of Browserify/Webpack, you can also use it directly as a script tag:

<script src=""></script>

Then it's available as window.PseudoWorker. Or for the polyfill:

<script src=""></script>

Supported APIS

  • onmessage
  • onerror
  • addEventListener
  • removeEventListener
  • postMessage

Note: inside the worker, you must use the self variable instead of the implicit global object. I.e. do this:

self.onmessage = ...

Not this:

onmessage = ...

Supported browsers

The full list of browsers that are tested in CI are in .zuul.yml. But basically:

  • Chrome
  • Firefox
  • Safari 7+
  • IE 8+
  • iOS 7.0+
  • Android 4.0+

Node.js is not supported. Check out node-webworker instead.

Testing the library


npm install

Then to test in Node (using an XHR shim):

npm test

Or to test manually in your browser of choice:

npm run test-local

Or to test in a browser using SauceLabs:

npm run test-browser

Or to test in PhantomJS:

npm run test-phantom

Or to test with coverage reports:

npm run coverage