$(window).unload wait for AJAX call to finish before leaving a webpage

Well, you can set async: false on your AJAX call to make the browser wait for the request to finish before doing anything else, but note that this will 'hang' the browser for the duration of the request.

$.ajax({
    type: 'POST',
    async: false,
    url: '/clientarea/utils/record-time',
    data: 'teid=' + teid + '&t=' + t
});

From the manual:

^{By default, all requests are sent asynchronous (i.e. this is set to true by default). If you need synchronous requests, set this option to false. Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active.}

⚠ WARNING: This answer was posted in 2010 and is now outdated - the XHR specification highlights the following statement:

Synchronous XMLHttpRequest outside of workers is in the process of being removed from the web platform as it has detrimental effects to the end user’s experience. (This is a long process that takes many years.) Developers must not pass false for the async argument when current global object is a Window object. User agents are strongly encouraged to warn about such usage in developer tools and may experiment with throwing an "InvalidAccessError" DOMException when it occurs.

DevTools in Chrome has recently started warning about it, so this change (which has been coming for some years) could be imminent.

The best solution is to use navigator.sendBeacon. It is brand new functionality which is starting to get implemented in new releases of browsers. The function is available in browsers newer than Chrome 39 and Firefox 31. It is not supported by Internet Explorer and Safari at the time of writing. To make sure your request gets send in the browsers that don't support the new functionality yet, you can use this solution:

var navigator.sendBeacon = navigator.sendBeacon || function (url, data) {
  var client = new XMLHttpRequest();
  client.open("POST", url, false); // third parameter indicates sync xhr
  client.setRequestHeader("Content-Type", "text/plain;charset=UTF-8");
  client.send(data);
};

Hope this helps!

for me, yours is not a good idea for the browser to wait before closing...
simply because what if I really want to close it?...

if a page bother a user, it's not good...

my suggestion is, in the page, you wait for 2 minutes (if 2 minutes is the requirements), then send an ajax that the user has done his 2 minutes...

you can then check it on the server side if one has his 2 minutes or not...

How about setting a cookie in the unload handler? The server should see it on the subsequent requests.

<script>
    $(window).unload(function(){document.cookie='left_on='+(new Date())})
</script>