JS级别联动下拉列表

<form name="form1" method="post" action="index_cx.asp">
<table border="0" align="center" cellpadding="2" cellspacing="1">
                 <tr>
                   <td><div align="right">旅游意向：</div></td>
<script language = "JavaScript">
var onecount;
onecount=0;
subcat = new Array();
//subcat[5] = new Array("abc","1","1");
//  5:类别ID   abc:名称 1:类别 1:ID

subcat[0] = new Array("大洋洲","1","大洋洲");

subcat[1] = new Array("东亚","1","东亚");

subcat[2] = new Array("南亚","1","南亚");

subcat[3] = new Array("东南亚","1","东南亚");

subcat[4] = new Array("地中海及非洲","1","地中海及非洲");

subcat[5] = new Array("欧洲","1","欧洲");

subcat[6] = new Array("港澳地区","1","港澳地区");

subcat[7] = new Array("西南","2","西南");

subcat[8] = new Array("西北","2","西北");

subcat[9] = new Array("华北","2","华北");

subcat[10] = new Array("东北","2","东北");

subcat[11] = new Array("华中","2","华中");

subcat[12] = new Array("华东","2","华东");

subcat[13] = new Array("华南","2","华南");

subcat[14] = new Array("北京周边","2","北京周边");

subcat[15] = new Array("拉丁美洲","1","拉丁美洲");

onecount=16;

function changelocation(locationid)
    {
 document.form1.areaid.options[0]=new Option("-请选择-","");
    document.form1.areaid.length = 1; 

   var locationid=locationid;
    var i;
   for (i=0;i < onecount; i++)
       {
          if (subcat[i][1] == locationid)
           { 
                document.form1.areaid.options[document.form1.areaid.length] = new Option(subcat[i][0], subcat[i][2]);
           }        
        }
        
   }
       </script>
                   <td><select name="rootid" id="rootid" onChange="changelocation(document.form1.rootid.options[document.form1.rootid.selectedIndex].value)">
                       <option  value="" selected>- 请选择 -</option>
                       <option value="1">出境</option>
                       <option value="2">国内</option>
                       <option value="3">省内</option>
                   </select></td>
                   <td>
                 
                   区域 ：</td>
                   <td><select name="areaid" id="areaid">
                       <option  value="" selected>-- 请选择 --</option>
                   </select></td>
                 </tr>
                 <tr>
                   <td colspan="4"><div align="right"></div>                     
                     <div align="right">
                       <input type="submit" name="Submit" value="提交">
</div></td>
                 </tr>
             </table>  
</form>