传统的HTML页面中连动下拉框采用了两种方法：
1）直接将下拉框中的内容hardcode于html的javascript中，调用javascript函数循环写入下拉框中。这种方法不适用于下拉框内容经常改变的情况。因为数据源和javascript程序写死在同一页面。
<html>
<head>
<title>List</title>
<meta http-equiv="Content-Type" content="text/html; c
harset=gb2312">
<script LANGUAGE="javascript">
<!--
var onecount;
onecount=0;
subcat = new Array();
subcat[0] = new Array("徐汇区","01","001");
subcat[1] = new Array("嘉定区","01","002");
subcat[2] = new Array("黄浦区","01","003");
subcat[3] = new Array("南昌市","02","004");
subcat[4] = new Array("九江市","02","005");
subcat[5] = new Array("上饶市","02","006");
onecount=6;
function changelocation(locationid)
{
document.myform.smalllocation.length = 0;
var locationid=locationid;
var i;
document.myform.smalllocation.options[0] = new Option('====所有地区====','');
for (i=0;i <onecount; i++)
{
if (subcat[i][1] == locationid)
{
document.myform.smalllocation.options[document.myform.smalllocation.length]
= new Option(subcat[i][0], subcat[i][2]);
}
}
}
//-->
</script>
</head>
<body>
<form name="myform" method="post">
<select name="biglocation"
onChange="changelocation(document.myform.biglocation.options[document.myform.biglocation.selectedIndex].value)">
<option value="01" selected>上海</option>
<option value="02">江西</option>
</select>
<select name="smalllocation">
<option selected value="">==所有地区==</option>
</select>
</form>
<script LANGUAGE="javascript">
<!--
changelocation(document.myform.biglocation.options[document.myform.biglocation.selectedIndex].value);
//-->
</script>
</body>
</html>
2）javascript 直接读取数据库，取数据库中的记录写入javascript中，然后和第一种方法一样，调用javascript函数循环写入下拉框中。此方法将数据源与javascript分开，但,公开数据库的连接，从安全角度说，没有多少实用价值。
我的方法是将下拉框中的数据放在XML文件中，用javascript读XML文件，取得下拉框中的内容。
HTML 文件如下：
<!-- myfile.html -->
<html>
<head>
<script language="JavaScript" for="window" event="onload">
var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
var i=0;
var j=0;
var subclass_name="";
loadXML();
function loadXML(){
xmlDoc.async="false";
xmlDoc.load("account.xml");
xmlObj=xmlDoc.documentElement;
nodes = xmlDoc.documentElement.childNodes;
document.frm.mainclass.options.length = 0;
document.frm.subclass.options.length = 0;
for (i=0;i<xmlObj.childNodes.length;i++){
labels=xmlObj.childNodes(i).getAttribute("display_name");
values=xmlObj.childNodes(i).text;
document.frm.mainclass.add(document.createElement("OPTION"));
document.frm.mainclass.options[i].text=labels;
document.frm.mainclass.options[i].value=values;
}
}
</script>
<script language="JavaScript" >
var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
var i=0;
var j=0;
function setsubclass(main){
var is_selected="N";
if (document.frm.subclass.options.length!=0) {
for (i=0;i<=document.frm.subclass.options.length;i++)
document.frm.subclass.options[i]=null ;
}
//重复才有效
if (document.frm.subclass.options.length!=0) {
for (i=0;i<=document.frm.subclass.options.length;i++){
document.frm.subclass.options[i]=null ;
document.frm.subclass.options.remove(i);
}
}
for (i=0;i<xmlObj.childNodes.length;i++){
var values="";
var lables="";
if (is_selected=="Y") return;
labels=xmlObj.childNodes(i).getAttribute("display_name");
values=xmlObj.childNodes(i).text;
//alert(labels+ " | "+main);
if (labels==main){
is_selected="Y";
for (j=0;j<xmlObj.childNodes(i).childNodes.length;j++){
//subclass_name="document.frm.subclass";
labels=xmlObj.childNodes(i).childNodes(j).getAttribute("display_name");
values=xmlObj.childNodes(i).childNodes(j).text;
//alert(values);
document.frm.subclass.add(document.createElement("OPTION"));
document.frm.subclass.options[j].text=labels;
document.frm.subclass.options[j].value=values;
}
}
}
}
</script>
<title>在HTML中调用XML数据</title>
</head>
<body bgcolor="#FFFFFF">
<FORM NAME="frm">
类型<SELECT NAME="mainclass" OnChange='setsubclass(this[selectedIndex].text)'></SELECT>
<option selected value="" ></option>
子类<SELECT NAME="subclass"></SELECT>
</form>
</body>
</html>
account.xml 如下：
<?xml version="1.0" encoding="gb2312"?>
<item>
<class display_name="未选定">
<subclass display_name="">Not Available</subclass>
</class>
<class display_name="推荐网站">
<subclass display_name="看上去很美">www.7say.com</subclass>
<subclass display_name="移动互联">www.xj139.com</subclass>
<subclass display_name="众信实业">www.xjzxsy.com</subclass>
</class>
<class display_name="门户网站">
<subclass display_name="新浪">www.sina.com</subclass>
<subclass display_name="搜狐">www.sohu.com</subclass>
</class>
<class display_name="其它网站">
<subclass display_name="蓝色理想">www.blueidea.com</subclass>
</class>
</item>