javascript - How to detect timeout on an AJAX (XmlHttpRequest) call in the browser?

Question

I'm looking on the web, but documentation is hard to come by. We all know the basic AJAX call using the browser's built-in XMLHttpRequest object (assume a modern browser here):

var xmlHttp = new XMLHttpRequest();  // Assumes native object

xmlHttp.open("GET", "http://www.example.com", false);

xmlHttp.send("");

var statusCode = xmlHttp.status;
// Process it, and I'd love to know if the request timed out

So, is there a way that I can detect that the AJAX call timed out by inspecting the XMLHttpRequest object in the browser? Would I be advised to do something like window.setTimeout(function() { xmlHttp.abort() }, 30000);?

Thanks!

-Mike

Answer 1

Some of the modern browsers (2012) do this without having to rely on setTimeout: it's included in the XMLHttpRequest. See answer https://stackoverflow.com/a/4958782/698168:

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function () {
    if (xhr.readyState == 4) {
        alert("ready state = 4");
    }
};

xhr.open("POST", "http://www.service.org/myService.svc/Method", true);
xhr.setRequestHeader("Content-type", "application/json; charset=utf-8");
xhr.timeout = 4000;
xhr.ontimeout = function () { alert("Timed out!!!"); }
xhr.send(json);