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Lazy web workers only work when someone is watching - in the UI thread!
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Lazy web workers only work when someone is watching - in the UI thread!


IE<10 doesn't support web workers. By using a lazy-worker, you can code to the web workers spec even on IE.

Can I use this?

Since lazy-worker only overwrites the global Worker object if it doesn't already exist, lazy-worker can be used both in browsers that have native web worker support and those that don't. The global Worker object can be manually overridden by calling lazyWorker.exportWorker(). Alternatively, the lazyWorker.Worker constructor can be used directly to create lazy workers.

Browser Support

  • Chrome 21+
  • Firefox 14+
  • Safari 5+
  • Opera 12+
  • Internet Explorer 9+

Running the Unit Tests

The test.html file needs to be hosted by a server and not open from the local file system. If you have ruby, run ruby -r webrick -e "s = => 9090, :DocumentRoot => Dir.pwd); trap('INT') { s.shutdown }; s.start" in the top level directory and open http://localhost:9090/test/test.html.

Alternatively, the tests can be run using the grunt build tool command grunt qunit.

Current Web Worker Functionality

  • Creating workers
    • Both the Worker constructor and any lazy-worker instances will have a lazy property set to true
  • Sending messages
    • Only the onmessage function is supported. lazy-worker might support the addEventListener method in the future.
  • Loading scripts within workers using the importScripts function
  • Error handling within workers using the onerror function
  • Nested workers


// In main.js
Worker.lazy; // true
var worker = new Worker('my-worker.js');
worker.lazy; // true

worker.onmessage = function(msg) {

worker.onerror = function(err) {
  console.log('Error: ', err.type, err.message);

  foo: 'foo'
// In my-worker.js

self.onmessage = function(msg) {
  var foo = + 'bar';

    foo: foo
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