<!DOCTYPE html> <html> <head> <title>BeforeUnload Event Example</title> <script type="text/javascript" src="EventUtil.js"></script> </head> <body> <div id="myDiv">Try to navigate away from this page.</div> <script type="text/javascript"> EventUtil.addHandler(window, "beforeunload", function(event){ event = EventUtil.getEvent(event); var message = "I'm really going to miss you if you go."; event.returnValue = message; return message; }); </script> </body> </html>