最近在做一個小功能的時候遇到這樣一個問題：
頁面中用ajax調用一個ws接口，有時候ws接口總是超時，我就在頁面ajax添加timeout
屬性，代碼如下：
$.ajax({
2 async:false,
3 cache:false,
4 timeout:5000,
5 url:"someurl.htm",
6 success:function(msg){ alert(msg); }
7 });
加上timeout屬性后調試，發現當接口超時5秒后，頁面並未斷開請求，是timeout沒生效嗎？
查看了下timeout參數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：
該請求在客戶端被阻塞，就有可能在ajax sent方法被調用之前超時。按照其定義，timeout參數，應該只是請求超時，不涉及響應。 此處，服務器被阻塞，請求卻是成功了，服務器響應中。。。。。
超過設定的timeout就會執行error，單后台還在運行，只是客戶端不再做相應
修改代碼，證實一下，是否超時5秒，會執行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 });
結果卻沒有alert；在網上早了一圈，結果發現async這個參數的問題，
當async設置為false，同步的時候，timeout是不生效的。