ExtJS可以用來開發RIA也即富客戶端的AJAX應用，是一個用javascript寫 的，主要用于創建前端用戶界面，是一個與后臺技術無關的前端ajax框架。因此，可以把ExtJS用在.Net、Java、Php等各種開發語言開發的應 用中。
ExtJs最開始基于YUI技術，由開發人員Jack Slocum開發，通過參考Java Swing等機制來組織可視化組件，無論從UI界面上CSS樣式的應用，到數據解析上的異常處理，都可算是一款不可多得的JavaScript客戶端技術 的精品。
ExtJS: http://www.spket.com/demos/js.html spket插件(eclipse)
· Start Aptana and navigate the application menu to: Help → Software Updates → Find and Install… → Search for new features to install → New remote site…
· Name: “Spket”, Url: “http://www.spket.com/update/”
· Restart Eclipse
· Watch this Spket IDE Tutorial to see how to easily add Ext code assist (you can point it at the latest /src/ext.jsb to keep code assist up to date with the latest Ext version). The steps are basically:
o Window → Preferences → Spket → JavaScript Profiles → New
o Enter “ExtJS” and click OK
o Select “ExtJS” and click “Add Library”, then choose “ExtJS” from the dropdown
o Select “ExtJS” and click “Add File”, then choose the “ext.jsb” file in your “./ext-2.x/source” directory
o Set the new ExtJS profile as the default by selecting it an clicking the “Default” button on the right-hand side of the “JavaScript Profiles” dialog.
o Restart Eclipse
o Create a new JS file and type: Ext. and you should get the Ext Code completion options.
一個簡單的例子：
http://extjs.org.cn/node/83