In the Ajax-based commenting system at my site, when a user clicks a button to show any recently posted comments, part of the information that's returned from the Ajax call (in JSON form) is an array of objects that describes any recently edited or deleted comments that are already on the page. The Ajax callback function walks through this array and uses the ID attributes of modified comments to find them on the page and update their HTML accordingly.

Here's the code that performs this function:

for (var i = 0; i < delarray.length; i++) {

var dnum = $('#'+delarray[i].id).find('.cnum a:first-child').html();

$('#'+delarray[i].id).html(delarray[i].c).find('.cnum a:first-child').html(dnum);

}

The problem is that in version 1.3 and 1.3.1, this code executes <em>much</em> more slowly than it did in version 1.2.6, causing script timeout alerts in both IE6 and 7, and in Firefox. (In Safari it seems fine.)

The pages where the problem shows up contain a lot of comments, 500+ in many cases. But version 1.2.6 was imperceptibly fast, whereas 1.3.1 takes many seconds to get through the same loop, even if it only executes a few times.

Here's a page where you can see this slowdown, with the unminified version 1.3.1 installed on it; scroll to the bottom and click the 'new comments' button right above the comment submission form. In IE 6 or 7, you should have a long wait followed by the "script running too slowly" alert.

http://littlegreenfootballs.com/weblog/weblogx.php?entry=32524