Question

I need to execute an action of a controller when a user leave a page (close, refresh, go to link, etc.). The action code is like:

public ActionResult WindowUnload(int token)
    {
        MyObjects[token].Dispose();
        return Content("Disposed");
    }

On window download I do Ajax request to the action:

$(window).unload(function ()
{
    $.ajax({
        type: "POST",
        url: "@Url.Action("WindowUnload")",
        data: {token: "@ViewData["Token"]"},
        cache: false,
        async: true
    });
    //alert("Disposing.");
})

The above ajax request does not come to my controller, i.e., the action is not executed.
To make the code above to work I have to uncomment the alert line, but I don’t want to fire alert on a user.

If I change async option to false (alert is commented), then it sometimes works. For example, if I refresh the page several times too fast then the action will not be executed for every unload.

Any suggestions how to execute the action on every unload without alert?
Note, I don’t need to return anything from action to the page.

Updated: answers summary

It is not possible reliably to do request on unload, since it is not proper or expected behavior on unload. So it is better to redesign the application and avoid doing HTTP request on window unload.
If it is not avoidable, then there are common solutions (described in the question):

1. Call ajax synchronously, i.e., async: false.
   • Pros: works in most cases.
   • Pros: silent
   • Cons: does not work in some cases, e.g, when a user refreshes the windows several times too fast (observed in Firefox)
2. Use alert on success or after ajax call
   • Pros: seems to work in all cases.
   • Cons: is not silent and fires pop up alert.

Answer 1

This wont work and even if you are able to somehow make it work it will give you lots of headaches later on, because this is not how the browser/HTTP is supposed to be used. When the page is unloading (in browser) the browser will call the unload event and then unload the page (you cannot make it wait, not even my making sync ajax calls) and in case the call was going on and the browser after executing the code unload the page, the call will also get cancelled and thats why you see the call on server sometimes and sometimes it doesn’t work. If you could tell use why you want to do this we could suggest you a better approach.