最近在做一个小功能的时候遇到这样一个问题：
页面中用ajax调用一个ws接口，有时候ws接口总是超时，我就在页面ajax添加timeout
属性，代码如下：
$.ajax({
2 async:false,
3 cache:false,
4 timeout:5000,
5 url:"someurl.htm",
6 success:function(msg){ alert(msg); }
7 });
加上timeout属性后调试，发现当接口超时5秒后，页面并未断开请求，是timeout没生效吗？
查看了下timeout参数api：
Set a timeout (in milliseconds) for the request. This will override any global timeout set with $.ajaxSetup(). The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent. In jQuery 1.4.x and below, the XMLHttpRequest object will be in an invalid state if the request times out; accessing any object members may throw an exception. In Firefox 3.0+ only, script and JSONP requests cannot be cancelled by a timeout; the script will run even if it arrives after the timeout period.
The timeout period starts at the point the $.ajax call is made; if several other requests are in progress and the browser has no connections available, it is possible for a request to time out before it can be sent。
我理解的意思是：
该请求在客户端被阻塞，就有可能在ajax sent方法被调用之前超时。按照其定义，timeout参数，应该只是请求超时，不涉及响应。 此处，服务器被阻塞，请求却是成功了，服务器响应中。。。。。
超过设定的timeout就会执行error，单后台还在运行，只是客户端不再做相应
修改代码，证实一下，是否超时5秒，会执行timeout方法：
$.ajax({ 2 async:false, 3 cache:false, 4 timeout:5000, 5 url:"someurl.htm", 6 error:function(jqXHR, textStatus, errorThrown){ 7 alert(textStatus); 8 }, 9 success:function(msg){ alert(msg); } 10 });
结果却没有alert；在网上早了一圈，结果发现async这个参数的问题，
当async设置为false，同步的时候，timeout是不生效的。