php+js 二級聯動

<?
require dirname(__FILE__).'/include/common.inc.php';
global $db;
$area=$db->select("select * from cms_area where parentid=0");
?>
<form id="myform" name="myform" action="" method="post">
<select name="areaid" id="areaid" onchange="getarea2(document.myform.areaid.options[document.myform.areaid.selectedIndex].value);">
<option value="-1">-請選擇-</option>
<? foreach($area as $r){?>
<option value="<?=$r[areaid]?>"><?=$r['name']?></option>
<? }?>
</select>
<select name="areaid2" id="areaid2">
<option value="-1">-商圈-</option>
</select>
</form>
<script>
function getarea2(pid)
{

    var area=new Array();
    var num=0;
    var data=new Array();
<?php
$area=getarea();
$rownum=count($area);
for($i=0;$i<$rownum;$i++){
   echo "data[".$i."] = new Array('".$area[$i]["name"]."',".$area[$i]["areaid"].",".$area[$i]["parentid"].")\n"; //用數組 _option 的元素建立二維數組,第一列是city的text,第二列是city自身Id,第三列是city的父級Id.
}

?>

   document.getElementById('areaid2').length=0;

    for(i=0;i<data.length;i++)
    {
          if (data[i][2] == pid)   
             {     
                document.getElementById('areaid2').options[document.getElementById('areaid2').length] = new Option(data[i][0], data[i][1]);   
             }
        }
    
}
</script>
<?
function getarea()
{
global $db;

$area=$db->select("select * from cms_area where parentid in (select areaid from cms_area where parentid=0)");
return $area;
}
?>