<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type="text/javascript">
function showCity(){
//维护一个二维数组存储省份对应的城市
var citys = [[],["广州","佛山","湛江","中山"],["长沙","衡阳","岳阳","郴州"],["南宁","桂林","贵港","柳州"]];
//获取省份对应的节点
var provinceNode = document.getElementById("province");
//获取省份选中的选项
var selectIndex = provinceNode.selectedIndex;
//获取对应的城市
var cityDatas = citys[selectIndex];
//找到city节点
var cityNode = document.getElementById("city");
/*
//先清空city框所有option
var children = cityNode.childNodes;
for(var i = 0; i<children.length ; ){//每次移除，长度已经短了，不用再写i++
cityNode.removeChild(children[i]);
}
*/
//设置options的个数。
cityNode.options.length = 1 ;//保留了城市选项，清空的话就等于0
//遍历对应的所有城市然后创建对应的option添加到city上。
for(var index = 0; index<cityDatas.length ; index++){
var option = document.createElement("option");
option.innerHTML = cityDatas[index];
cityNode.appendChild(option);
}
}
</script>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
省份<select id="province" onchange="showCity()">
<option>省份</option>
<option>广东</option>
<option>湖南</option>
<option>广西</option>
</select>
城市<select id="city"><option>城市</option></select>
</body>
</html>
