We (my team and our clients) are experimenting serious memory leaks

while using the Ajax methods (as expected, just in IE6).

Demo page (runs jQuery 1.1.1):

http://blog.scriptia.net/temp/jquery-ajax-leaks/ajax-leaks.html.

Leaks seriously.

After some investigation, I've found

http://alex.dojotoolkit.org/?p=528, a post by Alex Russell where he

writes:

"As with DOM event handlers, IE gets easily confused about what it can

and cannot clean up when you make XMLHTTP requests. The naive way of

listening for the "finished" state in an asynchronous request is to

attach a function to the XMLHTTP object's onreadystatechange slot and

determine inside the handler if the desired state has been reached.

The problem though is the same as with DOM event handlers; since the

XMLHTTP object in IE is an ActiveX control, IEs reference counting

mechanism goes walkabout when presented with an event handler that is

assigned from the JavaScript context. The contexts (closures)

referenced by the event handler get leaked. Oops.

After much testing, we figured out a pattern that prevents this kind

of leakage. Instead of attaching a method to be called back to, Dojo's

IO system starts a timer to watch for state changes on in-flight

network requests. When a change is detected, we dispatch the correct

event handler from outside the XMLHTTP object's event system. Since we

never set a closure reference between the ActiveX object and the

JavaScript context, we never leak it. Of course, once there are no

more operations "in the air", we cancel the timer that watches for

state changes to prevent further resource usage."

So, I've applied his method to jQuery. No leaks. See

http://blog.scriptia.net/temp/jquery-ajax-leaks/ajax-fixed.html

I'm attaching a patch which:

1. Uses a timer instead of onreadystatechange

2. Nullifies both xml and xml2

Hope this helps in resolving the issue.