Question

I’ve used jquery’s offset().top, but when running it 4000 times in a loop the browsers freezes for a few seconds. Is there a faster way to get this?

This is happening on the iPAD the desktop is faster.

for (counter=1; counter<4000; counter++)
{
   yPos = Math.round($("#star_"+counter).offset().top);

Answer 1

.offset().top always returns an integer, so rounding it is unnecessary. Furthermore, you can cache the jQuery object for efficiency:

$box = $('#box');
// start your loop here
    yPos = $box.offset().top;
// end loop

UPDATE

Assign a class to each star so you don’t have to keep creating new jQuery objects:

$('.stars').each(function(i,el) { 
    var yPos = this.offsetTop; 
});

http://api.jquery.com/each

https://developer.mozilla.org/en-US/docs/DOM/element.scrollTop