js取ASP.NET服务器控件RadioButtonList选中的值

<script type="text/javascript">
    
    //取得RadioButtonList客户端id 如服务器端控件RadioButtonList的服务器端ID为：rblTest
    var radioButtonListClientID="<%= rblTest.ClientID %>"
    
    //根据RadioButtonList控件的客户端id取被选中的值
    //oId 为控件的客户端id
    //返回null时为没有选中
    function GetRadioButtonListSelectValue(oId) {
        var returnValue=null;
        var oRadioButtonList=document.getElementById(oId);
        var oRadioButtonLists=oRadioButtonList.getElementsByTagName('input');
        for(var i=0;i<oRadioButtonLists.length;i++) {
            if(oRadioButtonLists[i].type == "radio") {
                if(oRadioButtonLists[i].checked) {
                    returnValue = oRadioButtonLists[i].value;
                    break;
                }
            }
        }
        return returnValue;
    }
</script>