function clean(o)
{
       var oc = o.childNodes;
       for(var i = 0; i < oc.length; ++ i )
       {
              o.removeChild(oc[i]);
        }
}

是无效的，请用:

function clean(o)
{
       while(o.childNodes[0])
      {
             o.removeChild(o.childNodes[0]);
       }
}