How can i find out the size of a cell with javascript

Question

I have a popup that pops up right underneathe a so it looks like the (don\'t ask why). on 1024 *760 its the same width as the tab

Answer 1

var element = document.getElementById('whatever');
//or however you want to get the element
var width;
if (typeof element.clip !== "undefined") { width = element.clip.width; } 
else {
    if (element.style.pixelWidth) { width = element.style.pixelWidth; } 
    else { width = element.offsetWidth; } 
}