Ask HN: What is your favorite Javascript UI framework out there ?

Jquery by a mile, for all the reasons others have mentioned + I'm also using jqueryUI which supports the newish Theming framework and is a great way to bring a consistant Ui feel to your app. the online theme generator is very slick and is designer friendly too.

ExtJS is my personal favourite - amazing collection of ready-to-go components, very good doco, a strong community, loads of extensions etc. The performance is also very good.

There have been some issues regarding licensing with some OS purists feeling that Ext 'tricked' its early adopters. Personally I couldn't care less. I treat it as a commercial product for which i'm more than happy to pay $300.

Since the OP is asking for UI frameworks I assume you're both referring to JQueryUI.

A UI framework is only as good as the widgets it ships with and looks to me like JQueryUI is a bit light on in this regard. Certainly a good framework for adding a few simple UI elements like accordions etc. Not as useful for projects requiring more complex elements like grids, treeviews, layout managers etc.

If you don't limit yourself to a strictly JS UI library, you can try NOLOH (http://www.noloh.com). NOLOH stands for Not One Line of HTML and allows you to work on a single language on the server-side without ever having to deal with the client. Unlike SproutCore, or Cappuccino, which are fat-clients, NOLOH is lightweight and on-demand. This means that your application loads instantly (noloh.com is a noloh app), and there's never any unnecessary code loaded on the client at any time, either on the server, or client. Best of all this is done automatically for you completely transparent to the developer.

Furthermore, all the native widgets & core for that matter are completely skinnable, extendable, and modifiable as you can see from the vast visual differences and feel in the numerous NOLOH applications.

NOLOH also allows you to easily use most 3rd party JavaScript widgets & components out of the box, without a single line of modification to the 3rd party library. You can see how easy that is at http://github.com/noloh, take SyntaxHighlighter for example. If you have large set of legacy HTML, no worries, NOLOH allows you to work with that and seamlessly communicate with the server check out a demonstration here: http://www.youtube.com/phpframework#p/c/C102458C2FFD8ACF/5/i...

Also, unlike Sproutcore or Cappuccino, the client is only used for rendering and not a store of your business logic. So all your valuable application logic is completely protected from prying eyes.

For all that are wary about NOLOH, give it a watch at http://youtube.com/phpframework to see simple and efficient it really is. We've been around since 2005 (though only available to the public since last year) and have a growing set of articles & videos. In the coming month we'll have more demos than you'll know what to do with.

Disclaimer: I'm a co-founder of NOLOH.

[edited for clarity]

You don't have to write any of your backend in Javascript w/ SproutCore or Cappuccino.

My favorite by far is Cappuccino. It designed almost exactly like Cocoa, which is a fantastic framework for writing apps with UIs. It comes with a ton of components that are already designed for you. You can completely skip the cost of a graphic designer (you still have understand interaction design).