JAVAScript 实现的城市联动菜单

<script>
/*
作者：fibona(熊祥众)
写作日期：2005年12月
实现功能；实现一个静态的城市与省区选择的联动菜单
这主要讲述的是一个联动选择的实现原理，可以通过此原理实现动态的联动选择
*/
</script>

<script language="JavaScript">
function validate(theform)
{
//alert(document.all.city.value);
if (document.all.city.value == "")
{
alert("城市值非空");
return false;
}else{
return true;
}
}
</script>
<form method="post" name="form1" action="#" enctype="multipart/form-data" onSubmit="return validate(this)">
<tr>
<td bgcolor="#F8F8F8" width="20%">选择城市:</td>
<td bgcolor="#FFFFFF"><select name="city"onChange=changelocation(this.value)>
<option value="" selected>>>>>请选择<<<<</option>
<OPTION value='1' >北京</OPTION><OPTION value='2' >上海</OPTION><OPTION value='3' >湖南 </OPTION>
</select></td>
</tr>
<tr>
<td bgcolor="#F8F8F8" width="20%">选择市或者城区:</td>
<td bgcolor="#FFFFFF"> <select name="area">
<SCRIPT language=JavaScript>
var onecount;
onecount=0;
subcat = new Array();
subcat[0] = new Array(1,'东城');
subcat[1] = new Array(1,'西城');
subcat[2] = new Array(1,'丰台');
subcat[3] = new Array(1,'海淀');
subcat[4] = new Array(1,'通州');
subcat[5] = new Array(1,'其它区');
subcat[6] = new Array(2,'奉贤');
subcat[7] = new Array(2,'南汇');
subcat[8] = new Array(2,'青浦');
subcat[9] = new Array(2,'松江');
subcat[10] = new Array(2,'徐汇');
subcat[11] = new Array(2,'浦东');
subcat[12] = new Array(3,'长沙');
subcat[13] = new Array(3,'永州');
subcat[14] = new Array(3,'衡阳');
onecount=15;
function changelocation(locationid)
{

document.all.area.length = 0;
var locationid=locationid;
var i,flag=0;
for (i=0;i < onecount; i++)
{
if (subcat[i][0] == locationid)
{
document.all.area.options[document.all.area.length] = new Option(subcat[i][1]);
flag=1;
}
}
if (flag==0)
{document.all.options.options[document.all.area.length] = new Option('>>>>选择市或者区<<<<');
}
}</SCRIPT>
<option value="" selected>>>>>选择市或者区<<<<</option>
</select></td>
</tr>
<input type="submit" name="topicsubmit" value="提交" tabindex="5">
</form>