三级联动省市区

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
var cityList = new Array();
var quList = new Array();
cityList['北京'] = [ '北京' ];
cityList['浙江'] = [ '杭州市', '温州市', '金华市', '临安市' ];
cityList['陕西'] = [ '西安', '宝鸡', '咸阳' ];
cityList['甘肃'] = [ '兰州市', '武威市', '酒泉市', '张掖市' ];

quList['北京'] = [ '1区', '2区', '3区', '4区' ];
quList['杭州市'] = [ '5区', '6区', '7区', '8区' ];
quList['温州市'] = [ '9区', '10区', '11区', '12区' ];
quList['西安'] = [ '13区', '14区', '15区', '16区' ];
quList['宝鸡'] = [ '17区', '18区', '19区', '20区' ];
quList['兰州市'] = [ '21区', '22区', '23区', '24区' ];

window.onload = allData;
function allData() {
var shengfen = document.getElementById('shengfen');
for ( var sf in cityList) {
shengfen.add(new Option(sf, sf));
}

}
function changeCity() {

var chengshi = document.getElementById('chengshi');
var sheng = document.getElementById('shengfen').value;

chengshi.options.length = 1;
for ( var cs in cityList[sheng]) {
chengshi.add(new Option(cityList[sheng][cs], cityList[sheng][cs]));

}
}

function changequ() {
var shiqu = document.getElementById('shiqu');
var cheng = document.getElementById('chengshi').value;
shiqu.options.length = 1;
for ( var sh in quList[cheng]) {

shiqu.add(new Option(quList[cheng][sh], quList[cheng][sh]));

}

}
</script>
</head>
<body>
<br />

</select>
<select id="chengshi" style="100px" onchange="changequ()"><option>--选择城市--</option>

</select>
<select id="shiqu" style="100px"><option>--选择区县--</option>

</select>

</body>
</html>