Tryit Editor v1.8

Source Code:

<!DOCTYPE html>
<html>
<head>
<script>
function goodbye()
{
alert("Thank you for visiting W3Schools!");
}
</script>
</head>

<body onunload="goodbye()">

<h1>Welcome to my Home Page</h1>
<p>Close this window or press F5 to reload the page.</p>

</body>
</html>

Result:

W3Schools.com - Try it yourself

Edit the code above and click "Submit Code" to see the result.