How to center align pop up div using Javascript

Question

How to align a pop up division to center of monitor/screen using javascript?

I tried using screen.width and screen.height to get center. But the division gets aligne

Answer 1

I also had this vertical centering problem on any webpage that required scrolling.

Switching to position: fixed solved it, so:

position:fixed;
top:50%;
left:50%;
margin:-50px 0 0 -100px; /* [-(height/2)px 0 0 -(width/2)px] */

This worked in firefox, google chrome, safari (pc) and IE9.

Unfortunately, I wanted it to appear in front of an pdf file - the pop up did appear in front using Firefox, Chrome but went behind in IE9 and Safari....