Is JavaScript multithreaded?

Question

Here's my issue - I need to dynamically download several scripts using jQuery.getScript() and execute certain JavaScript code after all the scripts were loaded, so my plan was to do something like this:

function GetScripts(scripts, callback) {   var len = scripts.length   for (var i in scripts)   {     jQuery.getScript(scripts[i], function()      {       len --;       // executing callback function if this is the last script that loaded       if (len == 0)         callback()       })   } } 

This will only work reliably if we assume that script.onload events for each script fire and execute sequentially and synchronously, so there would never be a situation when two or more of the event handlers would pass check for (len == 0) and execute callback method.

So my question - is that assumption correct and if not, what's the way to achieve what I am trying to do?

Answer 1

No, JavaScript is not multi-threaded. It is event driven and your assumption of the events firing sequentially (assuming they load sequentially) is what you will see. Your current implementation appears correct. I believe jQuery's .getScript() injects a new <script> tag, which should also force them to load in the correct order.

Answer 2

Currently JavaScript is not multithreaded, but the things will change in near future. There is a new thing in HTML5 called Worker. It allows you to do some job in background.

But it's currently is not supported by all browsers.