Alert Message in Window.Close in Jquery

Alert Message in Window.Close in  Jquery

window.onbeforeunload = function(){
    alert('You are closing the window');
}

Unload fires every time the current page is unloaded, that includes clicking on links, so you have to remove the event for them:
Code:
$(function () {
  $("btnSubmit").click(function {
    window.onbeforeunload = null;
  });
});