<!DOCTYPE html>
<html>
<head>
<script>
function closeIt()
{
return "Any string value here forces a dialog box to \n" +
"appear before closing the window.";
}
window.onbeforeunload = closeIt;
</script>
</head>
<body>
<a href="https://www.jb51.net">Click here to navigate to
www.jb51.net</a>
</body>
</html>