ExtJS可以用来开发RIA也即富客户端的AJAX应用，是一个用javascript写 的，主要用于创建前端用户界面，是一个与后台技术无关的前端ajax框架。因此，可以把ExtJS用在.Net、Java、Php等各种开发语言开发的应 用中。
ExtJs最开始基于YUI技术，由开发人员Jack Slocum开发，通过参考Java Swing等机制来组织可视化组件，无论从UI界面上CSS样式的应用，到数据解析上的异常处理，都可算是一款不可多得的JavaScript客户端技术 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.
一个简单的例子：
http://extjs.org.cn/node/83