ajax readystate

ajax 在请求时一共有0-4五种状态，

Holds the status of the XMLHttpRequest. Changes from 0 to 4: 
0: request not initialized 
1: server connection established
2: request received 
3: processing request 
4: request finished and response is ready

用原生javascript处理ajax：

xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
  }

jquery用suceess, error, complete, beforesend等方法对应xhr的状态，但却没有对应readystate等于3时的函数，

在stackoverflow看到一解决办法，不知可行否

var xhr = $.ajax({ ... });
xhr.onreadystatechange = function() { alert(xhr.readyState); };