<!DOCTYPE html>
<html>
<body>
<div onmousedown="WhichButton(event)">Click this text with one of your mouse buttons to return a number.
<p>
0 = The left mouse button<br>
1 = The middle mouse button<br>
2 = The right mouse button
</p>
<p><strong>Note:</strong> Internet Explorer 8, and earlier, returns another result:</p>
<p>
1 = The left mouse button<br>
4 = The middle mouse button<br>
2 = The right mouse button
</p>
</div>
<script>
function WhichButton(event) {
alert("You pressed button: " + event.button)
}
</script>
</body>
</html>