Problem using onbeforeunload in JQuery or Javascript

Good Day All

i am opening a Popup and i want to bind the "onbeforeunload" to the popup that if someone clicks on the close button in the window or close button in the page , the event should fire a javascript function that is on the page that opened the popup.

 function ProcessPayment(Downloadurl)
        {
         
           
            var url = "http://XXXX.com/cccc_ccccc/2938dc870cd394?tc_id=210&tc_45f=50.0&sig=fc5cbfe44230";
            var popupWindow = window;

   popupWindow.onbeforeunload = function () {
                if (Downloadurl != "") {
                    $.fileDownload(Downloadurl)
                  .done(function () { alert('File download a success!'); })
                  .fail(function () { alert('File download failed!'); });
                }
                else {
                    alert("No URL found");
                }
            }

            //open the Popup window
            popupWindow.open(url, 'popUpWindow', 'height=400,width=500,left=10,top=10,resizable=no,scrollbars=yes,toolbar=no,menubar=no,location=no,directories=no,status=yes')
             //bind the event so that when a user close the windown , we download the file 
         
            

when i try this nothing happens the event does not get work and no error in the browsers console

Thanks

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