ExtJS是一种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。功能丰富，无人能出其右。无论是界面之美，还是功能之强，ext的表格控件都高居榜首。单选行，多选行，高亮显示选中的行，推拽改变列宽度，按列排序，这些基本功能咱们就不提了。
自动生成行号，支持checkbox全选，动态选择显示哪些列，支持本地以及远程分页，可以对单元格按照自己的想法进行渲染，这些也算可以想到的功能。再加上可编辑grid，添加新行，删除一或多行，提示多行数据，推拽改变grid大小，grid之间拖拽一或多行，甚至可以在tree和grid之间进行拖拽，啊，这些功能实在太神奇了。更令人惊叹的是，这些功能竟然都在ext表格控件里实现了。
其实从ext3开始就支持各种方式的统计，且有控件支持excel导出。
ExtJS 主要用来开发RIA富客户端的AJAX应用，主要用于创建前端用户界面，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 JackSlocum开发，通过参考JavaSwing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。
Ext JS 4.0.1发行说明：
Performance Improvements
A large part of our focus for this first patch release has been on making sure that the framework’s performance is as good as it should be. Receiving so many reports from our community’s real world usage has been immensely valuable here and has opened up insights into how we can better optimize for your usage patterns.
Firstly we looked at grid performance. While in the majority of cases the grid in 4.0.0 is significantly faster than in 3.x, there were some cases where it was not performing as well as we would like. For example, performance with a large number of rows is excellent, but adding a large number of columns slowed things down.
Thanks to your help we’ve been able to improve the grid’s performance under these circumstances by a significant margin — often yielding a 300% improvement over 4.0.0. This affects several grid configurations and shows the most noticeable improvement in render time.
There are further optimizations lined up for the grid in the next release, but grids aren’t the only subject of our attention. We’ve also optimized several edge cases involving form layouts — again offering enormous speed improvements in some configurations.
We’ve improved performance with small optimizations across much of the framework but this is all driven by your reports and feedback on the forums and other venues. We’re thrilled at the level of engagement the community has with Ext JS and I hope we’re living up to your expectations with these patch releases.
Bug Fixes
As well as the performance improvements, Ext JS 4.0.1 also brings with it a number of bug fixes for issues that were highlighted in 4.0.0. The 920.html">Release Notes contains a full list of the bugs that were addressed in this release. We also further improved the documentation for a number of classes and updated guides based on your feedback.
We expect to make a Ext JS 4.0.2 release available in the next week or two with further improvements and performance optimizations. As part of our updated release policy this will again be available to everyone. Thanks again for all of your invaluable feedback since Ext JS 4 final was released, we couldn’t do this without you.
下载地址：http://www.sencha.com/products/extjs/download/