开发人员使用Javascr ipt的一个主要原因就是可以避免回发过程中带来的页面刷新。例如我们可以根据用户的需要使用Treeview控件来展开和折叠相应的数据节点。当你展开一个节点时，该Treeview控件将会利用Javascr ipt读取服务器上的子节点信息，然后平滑无刷新地插入这些新节点。如果没有使用Javascr ipt的话，Treeview控件将会因为页面的回发而重新构建。不但用户会发现因页面刷新而带来的延迟，而且页面极有可能回复到原来的状态，即丢失前面所展开的那些子节点信息。对于服务器端来说，因为每次回发的过程中都要处理大量的视图状态（View State）信息，这也会严重影响程序的整体执行性能。在ASP.NET 2.0中，引入了一个称为"客户端回调"的功能，利用这个内建的解决方案我们可以轻松实现客户端脚本和服务器端代码间的交互，从而避免了页面因回发带来的频繁刷新。-The use of Javascr ipt developers is a major cause of hair to avoid the process of bringing back the page to refresh. For example we can use according to the Treeview control necessary to expand and collapse the corresponding data node. When you expand a node, the Treeview control server will use Javascr ipt to read information on the child nodes, then no smooth set to insert the new node. If you are not using Javascr ipt, then, Treeview control will return because the page and rebuild hair. Users will find that not only refresh the page because of the delay brought about, but the page is very likely reply to the original status, namely, the loss of those who started in front of the sub-node information. For server-side, the hair back every time because the process must deal with many view status (View State) information, which will seriously affect the performance of the overall implementation process. In ASP.NET 2.0, the introduction of a group called the "Client Callback" feature, use