<!DOCTYPE html>
<html>
<body onbeforeprint="myFunction()">
<h1>Try to print this document</h1>
<p><b>Tip:</b> Keyboard shortcuts, such as Ctrl+P sets the page to print.</p>
<p><b>Note:</b> The onbeforeprint event is only supported in Internet Explorer and Firefox. </p>
<script>
function myFunction() {
alert("You are about to print this document!");
}
</script>
</body>
</html>