I have recently been doing quite a bit of development with both ExtJS and jQuery and I thought I would share my experiences with both of them. One thing to keep in mind is that I’m not going to say whether one is really good or bad - they’re both excellent libraries and your choice for any given project might simply come down to personal preference. That said, the rest of this will be my opinion on the two.
I’ve recently been developing a web-based application (a RIA one might say) and, after initially trying to get it working right in jQuery, I decided to have a go at using ExtJS, a JavaScript library I’ve been meaning to try for a while. Basically, it is a JavaScript library that includes a ton of things for building web application other libraries don’t - not surprising considering it started life as an add-on to YUI. Here is my initial impressions of it, most of which are direct comparisons to jQuery.
Version 1.2 of the jQuery JavaScript library has been released. There seems to have been quite a few subtle alterations to the selector and AJAX systems so if you’ve done some development with jQuery and want to upgrade then you should read How To Upgrade on the jQuery wiki. I myself shall be looking into this in the near future.