x
<html><body onbeforeunload="return myFunction()"><h1>HTML DOM Events</h1><h2>The beforeunload Event</h2><p>This example assigns an "onbeforeunload" event to a body element.</p><p>Close this window, press F5 or click on the link below to invoke the onbeforeunload event.</p><a href="https://www.w3schools.com">Click here to go to w3schools.com</a> <script>function myFunction() { return "Write something clever here...";}</script></body></html>