JavaScript - Get Element's Position

/**
 * @purpose            : Get the (x,y) coordinate of a DOM element
 * @param  object elem : a DOM element or null
 * @return object      : an associative array, where indicies "x"
 *                       and "y" hold their respective coordinates
 * @note               : function is recursive
 */
function getXYpos(elem) {
   if (!elem) {
      return {"x":0,"y":0};
   }
   var xy={"x":elem.offsetLeft,"y":elem.offsetTop}
   var par=getXYpos(elem.offsetParent);
   for (var key in par) {
      xy[key]+=par[key];
   }
   return xy;
}