Friday, December 7, 2012

Inlining HTML5 WebWorker source content

I have been playing with HTML5 WebWorkers in an attempt to solve a performance problem and came up with a simple way to inline the WebWorker's source code. The Basics of Web Workers tutorial demonstrates inlining via script tags marked as 'type="javascript/worker"' however this means placing the WebWorker source within the HTML page. I use AMD for my module loading and would like to avoid this approach. With that in mind I came up with the following :

    var webWorkerFunc = function() {
        onmessage = function(e) {


    var content = webWorkerFunc.toString();
    content = content.substring("function () {".length+1);
    content = content.substring(0, content.lastIndexOf("}"));

    var URL = window.URL || window.webkitURL;    var blob = new Blob([content]);
    var blobURL = URL.createObjectURL(blob);
    var webWorker = new Worker(blobURL);
    webWorker.onmessage = function(e) {


This approach is similar to the one described in the HTML5 Rocks tutorial except that the Function.toString() is used to obtain the WebWorker source code. The function wrapper is stripped and the result passed into the Blob constructor.


  1. Hi Richard,

    Thanks for the snippet. I think you left out a var for onmessage on line 2.


  2. Jon, its actually correct. This is the onmessage handler that gets called when a message is sent via webworker.postMessage. It has to be a global within the WebWorker.