JS获取单选框的值

<script language="javascript" type="text/javascript">
function test()
{

       var radioValue= "";

       var frm=document.getElementById('category');

       for(var i=0;i<frm.radioName.length;i++)
{
           if(frm.radioName[i].checked==true)
{
              radioValue= frm.radioName[i].value;
              break;
           }
       }

       alert("单选框的值为:"+radioValue);
}
</script>