For modern browsers (IE 10+, FF, Safari, Chrome): It looks like you would have to use the facade pattern to build a consistent interface and do a lot of fiddling using this info.
I'm looking for a simple modern way to determine the x, y coordinates of where a user clicked in a div and use those coordinates to position a pie menu as determined in this SO Question.
No libraries unless used to show concept.
Reference
What is the difference between screenX/Y, clientX/Y and pageX/Y?
Here is a google hit that shows 3 different event properties