Geting the position of the mouse pointer in JavaScript (Works in IE7)

The following function will return the position of the mouse pointer based on the event. It actually works in IE7.

function getPosition(e) {
    e = e || window.event;
    var cursor = {x:0, y:0};
    if (e.pageX || e.pageY) {
        cursor.x = e.pageX;
        cursor.y = e.pageY;
    } 
    else {
        var de = document.documentElement;
        var b = document.body;
        cursor.x = e.clientX + 
            (de.scrollLeft || b.scrollLeft) - (de.clientLeft || 0);
        cursor.y = e.clientY + 
            (de.scrollTop || b.scrollTop) - (de.clientTop || 0);
    }
    return cursor;
}

Example usage

popupMenu.style.left = getPosition(event).x;
popupMenu.style.top = getPosition(event).y;