Need to calculate offsetRight in javascript

I need to calculate the offsetRight of a DOM object. I already have some rather simple code for getting the offsetLeft, but there is no javascript offsetRight property. If I add the offsetLeft and offsetWidth, will that work? Or is there a better way?

function getOffsetLeft(obj)
{
    if(obj == null)
        return 0;
    var offsetLeft = 0;
    var tmp = obj;
    while(tmp != null)
    {
        offsetLeft += tmp.offsetLeft;
        tmp = tmp.offsetParent;
    }
    return offsetLeft;
}

function getOffsetRight(obj)
{
    if (obj == null)
        return 0;
    var offsetRight = 0;
    var tmp = obj;
    while (tmp != null)
    {
        offsetRight += tmp.offsetLeft + tmp.offsetWidth;
        tmp = tmp.offsetParent;
    }
    return offsetRight;    
}