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