How to detect elements overlapping (overlaying) using JavaScript?

Question

How to detect overlap HTML elements, using JavaScript?

I have an item list (

). It slides up and down using JavaScript. When it slides down, de

Answer 1

function isObjOnObj(a,b){
    var al = a.left;
    var ar = a.left+a.width;
    var bl = b.left;
    var br = b.left+b.width;

    var at = a.top;
    var ab = a.top+a.height;
    var bt = b.top;
    var bb = b.top+b.height;

    if(bl>ar || br<al){return false;}//overlap not possible
    if(bt>ab || bb<at){return false;}//overlap not possible

    if(bl>al && bl<ar){return true;}
    if(br>al && br<ar){return true;}

    if(bt>at && bt<ab){return true;}
    if(bb>at && bb<ab){return true;}

    return false;
}

Answer 2

This feels like collision detection, and there's a solution just posted. Instead, I would suggest working out how many list items would be needed for a menu to overlap (i.e. 10), and hide the div when those menus (with 10 li) are selected.

Answer 3

Why not just raise the z-index of your UL to be above the div at the bottom?

add:

#wrap {
    z-index  : 2;
    position : relative;
}