Last week at work, I encountered a very peculiar problem in Internet Explorer. There were several IE-related bugs reported in a certain part of the service. However, I couldn’t reproduce them and I expected these bugs had been fixed during other updates in the code..

..until it suddenly happened. All the tested versions of IE’s (6, 7, 8) started reporting either error “failed” or “unexpected error”, pointing to jQuery’s code. And there worst part was that error occurred occasionally, although nothing was changed.

In this case, there’s jQuery 1.3.2 in use. Error message didn’t help and the line it was pointing to, belonged to a internal / helper function into jQuery.

At first, errors disappeared after some fixes I expected to resolve the situation. But, like I mentioned earlier: these errors were occasional.

I didn’t have anything that could have helped me at least a little on tracking this problem (later I found not even unit tests would’ve solved this – although it’s not an argument why I didn’t have unit testing for javascript). So, my only choice was trying to isolate the problem function by function, line by line.

Ultimately I found that all the errors were caused by event handler bindings made with function $.fn.live(). I couldn’t blame the selectors being too unprecise, although I reduced the amount of troublemakers by fine-tuning them. In addition, I found that wrapping them in setTimeout() with small delay would have possibly fixed the problem. Also, IE6 had the most problems, while IE7 started to feel stable.

Most likely there was something going on with perfomance. However, after all this I wasn’t in a mood to expect these problems were completely solved. So I ended up binding event handlers with $.fn.bind() whenever something was dynamically added. It meant more lines of code, but it also meant that no errors were occurred ever again.

The point of this article can be put in one sentence: if you receive an error with message “failed” or “unexpected error” from jQuery and this happens only in Internet Explorer, comment out every possible live() binding and try again.