ajax

在《Pragmatic Ajax A Web 2.0 Primer 》中偶然看到对readyStae状态的介绍，感觉这个介绍很实在，摘译如下：
 0: (Uninitialized) the send( ) method has not yet been invoked. 
0的时候send（）方法还没触发
 1: (Loading) the send( ) method has been invoked, request in progress. 
1的时候send方法被调用，请求在发送过程中
 2: (Loaded) the send( ) method has completed, entire response received.
2的时候，请求发送完毕，接收到全部的响应内容
 3: (Interactive) the response is being parsed. 
3的时候，在解析响应内容
 4: (Completed) the response has been parsed, is ready for harvesting. 
4的时候，响应内容接收完毕，客户端可以开始调用。