Are two elements overlapping each other?

function isOverlapping(elm1, elm2) {
  var pos_elm1 = AJS.absolutePosition(elm1);
  var pos_elm2 = AJS.absolutePosition(elm2);
  var top1 = pos_elm1.y;
  var left1 = pos_elm1.x;
  var right1 = left1 + elm1.offsetWidth;
  var bottom1 = top1 + elm1.offsetHeight;
  var top2 = pos_elm2.y;
  var left2 = pos_elm2.x;
  var right2 = left2 + elm2.offsetWidth;
  var bottom2 = top2 + elm2.offsetHeight;
  var getSign = function(v) {
    if(v > 0) return "+";
    else if(v < 0) return "-";
    else return 0;
  }

  if ((getSign(top1 - bottom2) != getSign(bottom1 - top2)) &&
      (getSign(left1 - right2) != getSign(right1 - left2)))
    return true; 
  return false;
}

function absolutePosition(elm) {
  var posObj = {'x': elm.offsetLeft, 'y': elm.offsetTop};
  if(elm.offsetParent) {
    var temp_pos = absolutePosition(elm.offsetParent);
    posObj.x += temp_pos.x;
    posObj.y += temp_pos.y;
  }
  return posObj;
}