js得到RadioButtonList的值

function getRadio()
     {
         var opts = document.all("rbListColumnType");
         if (opts)
         {
             for (var i = 0; i < opts.length; i++)
             {
                 if (opts[i].checked)
                 {
                     alert(i);
                     break;
                 }
             }
         }
     }