问题：XMLHttpRequest-处理服务器连接丢失

Question

How do I handle the scenario where I making a synchronous request to the server using XMLHttpRequest and the server is not available?

xmlhttp.open("POST","Page.aspx",false);
xmlhttp.send(null);

Right now this scenario results into a JavaScript error: "The system cannot locate the resource specified"

Answer 1

Ok I resolved it by using try...catch around xmlhttprequest.send

:

xmlhttp.open("POST","Page.aspx",false);              
       try
       {
       xmlhttp.send(null);
       }
       catch(e)
       {
            alert('there was a problem communicating with the server');
       }       

Answer 2

尝试超时属性。

xmlHTTP.TimeOut= 2000 

Answer 3

You don't check for properly returned status. By the code you gave you are doing a GET request. To properly check the status of your request, you must create an event handler for the onreadystatechange event and then inside it check if the readyState property is equal 4 and then inside the method if the status is 200.

You can find a detailed explanation here : Ajax Tutorial by Mozilla

 
xmlhttp.onreadystatechange=function()

xmlhttp.open("GET","Page.aspx",false);
{
  if (xmlhttp.readyState==4) 
  {
     if (xmlhttp.status==200)
     {
       //Ajax handling logic
     }
  }
}
xmlhttp.send(null);