jQuery asynchronous function call, no AJAX request

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stockoverflow This post by John Resig (of jQuery) explains a bit about how JavaScript handles its single thread.  http://ejohn.org/blog/how-javascript-timers-work/

This article also explains: "One thing to remember when executing functions asynchronously in JavaScript, is all other JavaScript execution in the page halts until a function call is completed. This is how all the current browsers execute JavaScript, and can cause real performance issues if you are trying to call too many things asynchronously at the same time. A long running function will actually "lock up" the browser for the user. The same is true for synchronous function calls too."

All that said, it's possible you could simulate an asynchronous function call yourself by breaking whatever loop you are doing into a smaller chunk and using setTimeout().

For instance this function:

1. // Sync
   
2. (function() {
   
3.   for(var x = 0; x < 100000; ++x) {console.log(x)}
   
4. })()
   
5. 
   
6. // ASync
   
7. var x = 0;
   
8. setTimeout(function() {
   
9.    console.log(x++);
   
10.    if(x < 100000) setTimeout(arguments.callee, 1);
    
11. } ,1)

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You might want web workers!
Edit: I'm surprised how many people jumped to "its not possible" so I will elaborate. Web Workers are part of the HTML 5 spec. They allow you to spawn threads to run scripts in the background without blocking the UI. They must be external js files, are invoked by
var worker = new Worker('my_task.js');and are communicated to via events.

workers don't access the DOM because the DOM is not multi-thread safe. So the worker should run hardcore calculations and let the caller manipulate the DOM.       

From: stockoverflow