handle ajax error when a user clicks refresh

There are several suggested approaches for detecting this:

• Several have suggested the use of a beforeunload handler to set a boolean flag so that the error handler can know that the page is being unloaded (See list of related/duplicated posts below). This is great, except that mobile Safari on iOS doesn't support the beforeunload event.

• Sachindra suggested an approach where instead of firing the error function immediately, it got delayed a second in a setTimeout(..., 1000). That way, there is a good chance the page has actually disappeared by the time the error handler gets called. "Good chance" that is. I bet if I have a huge page with e.g. many <input>s, it could take more than 1 sec to unload, and then perhaps the error handler would fire anyway.

I therefore suggest a combination of reliably detecting beforeunload support and if beforeunload is not supported (cough iPad/iPhone cough) revert to Sachindra's delay trick.

See the full solution with beforeunload detection and all in this jsfiddle.

It looks like the situation is a little better for jQuery 2.x than for 1.x, but 2.x also seems a little flakey, and so I still find this suggestion prudent.

P.S: There were also suggestions involving testing some fields in the XHR / jqXHR object. (Here and here). I have not come accross a combination that could distinguish between user navigation and restarting the webserver during a long-running AJAX call, and I have therefore not found this approach useful to me.

This is really also an answer to these related/duplicated Stack Overflow questions:

• jQuery AJAX fires error callback on window unload?
• $.ajax calls success handler when request fails because of browser reloading
• How best to handle errors during jquery ajax calls caused by user clicking on links
• Detecting that a jQuery.ajax call failed because the page is reloading?

and these posts outside of Stack Overflow:

• What's the proper way to deal with AJAX error because of page reload?
• How to Distinguish a User-Aborted AJAX Call from an Error | I like stuff.

[this is an edit from the previous answer, which had outstanding questions that I have since resolved]

jQuery throws the error event when the user navigates away from the page either by refreshing, clicking a link, or changing the URL in the browser. You can detect these types of errors by by implementing an error handler for the ajax call, and inspecting the xmlHttpRequest object:

$.ajax({    /* ajax options omitted */    error: function (xmlHttpRequest, textStatus, errorThrown) {         if(xmlHttpRequest.readyState == 0 || xmlHttpRequest.status == 0)               return;  // it's not really an error         else              // Do normal error handling});

var isPageBeingRefreshed = false;window.onbeforeunload = function() {    isPageBeingRefreshed = true;};$.ajax({    error: function (xhr, type, errorThrown) {        if (!xhr.getAllResponseHeaders()) {            xhr.abort();            if (isPageBeingRefreshed) {                return; // not an error            }        }    }});