二级联动(javascript Array)

<script language="javascript" type="text/javascript">
<!--
var arrSubRelatingType = new Array(); //关联交易子类
    <%                          
        VOList relating_type = (VOList)request.getAttribute("typenameListrelating");                                 
        for(int i = 0; i < relating_type.count(); i++)
        {    
    %>
            arrSubRelatingType[<%=i%>] = new Array();
            arrSubRelatingType[<%=i%>][0]='<%=relating_type.get(i).getString("type_id")%>';        
            arrSubRelatingType[<%=i%>][1]='<%=relating_type.get(i).getString("type_name")%>';    
            arrSubRelatingType[<%=i%>][2]='<%=relating_type.get(i).getString("group_id")%>';                        
    <%     
        }    
    %>

    // 增加一个名为 trim 的函数作为 String 构造函数的原型对象的一个方法
        String.prototype.trim = function()
        {
            // 用正则表达式将前后空格
            // 用空字符串替代。
            return this.replace(/(^\s*)|(\s*$)/g, "");
        }
         //二级联动
        function linkage(selBigID,selSmallID,tip,arrSmallClass)
        {
            var objL = document.getElementById(selBigID);
            var obj = document.getElementById(selSmallID);
            obj.length = 0;
            if(tip.trim()=="") tip="－请选择－";  
            
            if(objL.selectedIndex == 0)
            {                
                obj.options[0] = new Option(tip, ""); 
                return;
            }            
            
            var len = 0;
            var bigClassId = objL.options[objL.selectedIndex].value;  
            var tip2 = "－无子类－";
            for(var i=0; i<arrSmallClass.length; i++)
            {
                //alert(bigClassId +' --- '+ arrSmallClass[i][2]);
                if(arrSmallClass[i][2] == bigClassId)
                {
                    tip2 = tip;
                    obj.options[++len] = new Option(arrSmallClass[i][1], arrSmallClass[i][0]);
                }
            }         
            obj.options[0] = new Option(tip2, "");   
           }
   //-->
  </script>

============================================
 <td height="35" align="right">关联交易大类别：</td>
      <td height="35">
          <select id="drpBig_relating_type" name="drpBig_relating_type" Onchange="javascript:linkage(this.id,'drpSmall_relating_type','',arrSubRelatingType);">
             <option value="">－请选择－</option>        
             <exp:options name="drpBig_relating_type" list="groupnameListrelating" idfield="group_id" namefield="group_name" default="<%=this.value("val_big_relating","")%>" />     
          </select>
      </td>
      <td height="35" align="right">关联交易子类别：</td>
      <td height="35">
      <select id="drpSmall_relating_type" name="drpSmall_relating_type">
           <option value="">－请选择－</option>
         <exp:options name="drpSmall_relating_type" list="typenameListrelatingSub" idfield="type_id" namefield="type_name" default="<%=this.value("val_small_relating","")%>"/>
      </select>
      </td>