Ext JS

Ext JS is a javascript api for desktop looks and feels for a web application.It follows the concept of oops as wells as lots of good design pattern is integrated with it.It heavily depends on JSON for data to and forth between the server and the client.
The beautiful advantage of Ext Js is it faster than other javascript libraries as it caches the data and also it uses JSON String for Ajax type data transfer.As JSON takes less memory from its counterpart XML data transfer.I have spoken the good part of Ext JS,but let me tell about its sad part its a licenced based api.But can be used free if you are not making any profit from your apps where you are using Ext Js.Also Ext JS can be integrated with JSF for developing ajax based custom components.