I have no experience with ExtJS, so I can't really compare the two. I've only used the Desktop variant of Qooxdoo.

It's easy to learn, but hard to master. Though there is quite some extensive documentation, you will have to take glances at the qooxdoo sources to fully understand some more advanced stuff. And to track down if something doesn't behave as expected. The source is quite clean and readable though, e.g. the button class: http://goo.gl/Zw6zNI

There's also a simple playground http://goo.gl/QAht5O and an API viewer implemented in qooxdoo itself http://goo.gl/xV5tvn

From the top of my head some random facts:

* Strictly object oriented. Every widget is a class with properties, methods, inheritance, mixins etc. http://goo.gl/AaPb6w

* It makes (or rather you should make) heavy use of data binding. Mostly to link widgets to data stores (being populated/transmitted by some sort of rpc call, the app itself or hardcoded etc), but also to bind widgets to other widgets. http://goo.gl/DxvNWC

* Backend communication comes in several flavors, but most prominent is the JSON-RPC interface. Qooxdoo provides backends for several languages, but it's also rather easy to implement your own. http://goo.gl/IjCT8n

* Communication between objects is done via a simple event chain, i.e. you will use addListener and fireEvent/fireDataEvent a lot. http://goo.gl/Yxfmot

* You can mix your project and have some parts compiled and others loaded from source at runtime. We've been using this to create a metalanguage for forms, which streamlined our application a lot. Basically we don't have to write qooxdoo code anymore to create new forms, but just a xml description of it.

All in all qooxdoo helped us more than it stood in our way. I would use it again.

user:	davenonymous
created:	January 30, 2014
karma:	4