js兑现两级联动代码 _JavaScript

js实现两级联动代码

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>New Document </title>
<script language="JavaScript" type="text/javascript">

var city=[
 ["北京","天津","上海","重庆"],
 ["南京","苏州","南通","常州"],
 ["福州","福安","龙岩","南平"],
 ["广州","潮阳","潮州","澄海"],
 ["兰州","白银","定西","敦煌"]
 ];
function getCity(){
 var sltProvince=document.getElementById("province");
 var sltCity=document.getElementById("city");
 var provinceCity=city[sltProvince.selectedIndex-1];
 sltCity.length=1;
 for(var i=0;i<provinceCity.length;i++){
 sltCity[i+1]=new Option(provinceCity[i],provinceCity[i]);
 }
}

 </script>
 </head>
 <body>

 <form action="somepage.asp" name=theForm">
 <select name="province" id="province" onChange="getCity()">
  <option value="0">请选择所在省份</option>
  <option value="直辖市">直辖市</option>
  <option value="江苏省">江苏省</option>
  <option value="福建省">福建省</option>
  <option value="广东省">广东省</option>
  <option value="甘肃省">甘肃省</option>
 </select>
 <select id="city" name="city">
  <option value="0">请选择所在城市</option>
 </select>
 </form>
 </body>
 </html>

?在网上找的这段代码，本来想把它拓展到三级联动，但是没有做出来，有人会的话能否贡献下代码，万分感谢！