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<html><body><h1>HTML DOM Events</h1><h2>The beforeunload Event</h2><p>Use the HTML DOM to assign an "onbeforeunload" event to the window object.</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>window.onbeforeunload = function(event) { event.returnValue = "Write something clever here..";};</script></body></html>