Question

We use jQuery’s global ajaxError() handler to alert the user of any AJAX failures:

$(document).ajaxError(function() {  
    $("There was a network or server error. Please try again later.").dialog({  
        title: "Error",  
        modal: true,  
        resizable: false,  
        buttons: { 'Ok': function() { (this).dialog("close"); } }  
    });  
});  

Unfortunately, this global error handler also fires if the user leaves the page before it finishes loading. Here are the steps to reproduce the error:

1. User visits Page A, which includes elements that load via AJAX.
2. AJAX elements on Page A begin loading.
3. User clicks link to visit Page B before AJAX elements on Page A have finished loading.
4. The error dialog box appears briefly before the browser redirects to Page B.

Any idea how we can get ajaxError() not to trigger when the error is directly caused by the user visiting a new page?

UPDATE: Here’s my code now, after incorporating the suggestions in the comments:

// I added a 3 second delay to our error dialog, enough time
// for the user to leave for a new page:
$(document).ajaxError(function() {
    setTimeout(my_error_handler, 3000);
});

// Warn user before leaving page if AJAX is still loading.
// Not sure I'll keep this:
$(document).ajaxStart(function() {
    ajaxing = true;
});

$(document).ajaxStop(function() {
    ajaxing = false;
});

window.onbeforeunload = function() {
    if (typeof(ajaxing) != 'undefined' && ajaxing) {
        return "Page elements are still loading!";
    }
};

Answer 1

Well yes, if the user navigates to another page, the xhr will abort, which is, in effect, an unsuccessful communication. A solution would be to register a listener for the onbeforeunload event, and unbind ajaxError there, basically saying: the user is about to leave the page, so i do not wish to be informed of the ajax errors that might follow.

Some sites, though, like GMail, do the other way around: if you try to navigate away from the page while there are still some ajax requests pending, it gives you an prompt that says you’ve got some processes still running, and lets the user decide whether to stay on the site until the request has finished, or to go ahead and navigate away.