javascript overlay not covering full page when div expands the page height

Question

I realize there's already been several questions like this, but I think my case is a little different.
I have an div that I am absolutely positioning and floating on top of the page, and I'm setting an overlay behind it to grey out the rest of the page. I have it working okay until you scroll up and down the page.

The problem is, when the div appears, it is still populating with ajax data. So the height and width of the bg overlay has already been set, but once all the data loads into the floating div, it sometimes pushing the page down so the height increases. So, I can't calculate the height and width of the window or document because the floating div might not be fully loaded yet, and once it does, it pushes the screen down further, causing the bg overlay to not cover the whole page.

So for example, in the code it's going something like:

loadBoxContent = function(){
..DO AJAX HERE..
..PUT CONTENT INTO FLOATING DIV..
$('#floatDiv').show()
$('#darkOverlay').height($(window).height());

}

I verified this by adding an alert, so that by the time I've clicked the alert, the bg overlay was able to calculate the true page size, and it looks fine. Sorry, if this sounds confusing but hopefully you get what I'm trying to achieve. I'm assuming this isn't too difficult, but I haven't been able to figure it out. Any help would be appreciated, I'm using jquery.

Thanks

Answer 1

Overlay ;)

** update, setting position of all corners to 0 instead of using width/height 100% **

$("<div/>")
 .css({
    position:"fixed", // ze trick 
    background:"#000",
    opacity:.5,
    top:0,
    bottom: 0,
    left:0,
    right: 0,
    zIndex: 2999 // everything you want on top, gets higher z-index
  })
 .appendTo("body");

Or put the above css settings in a css stylesheet (opacity needs cross browser hacks).

$("#dark-overlay").show();