如何判断RadioButtonList1是否被选择

<script type="text/javascript">
 function EmptyCheck()
    {  
          
         var rbltable=document.getElementById("ctl00_ContentPlaceHolder1_RadioButtonList1");  
        var rbs = rbltable.getElementsByTagName("INPUT");   
        var result = false;
 
                 
         for(var i=0;i<rbs.length;i++)
         {
            if (rbs[i].checked==true)
            {
            result=true;
            
            }
            
         }
         
          if ( result == false)
        {
            ymPrompt.errorInfo("请选择模板！",null,null,"警告");
            event.returnValue=false;
            return false;
            
        }    
              
    }
</script>