JS 移动选定的列表项

function moveOptions(direction)
{
    var sel = document.getElementById('menus_navlist');
    if (sel.selectedIndex == -1)
    {
        return;
    }

    len = sel.length
    for (i = 0; i < len; i++)
    {
        if (sel.options[i].selected)
        {
            if (i == 0 && direction == 'up')
            {
                return;
            }

            newOpt = sel.options[i].cloneNode(true);

            sel.removeChild(sel.options[i]);
            tarOpt = (direction == "up") ? sel.options[i-1] : sel.options[i+1]
            sel.insertBefore(newOpt, tarOpt);
            newOpt.selected = true;
            break;
        }
    }
}