三级联动考察的应该是对于数据的处理，只要清楚其中的关系，再多几级都是一样的：
html部分：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>3级联动菜单</title>
<script>
var region = {
广东:
{
"广州":["广州1","广州2","广州3"],
"珠海":["珠海1","珠海2","珠海3"],
"佛山":["佛山1"]
},
湖南:
{
"常德":["石门","桃源","临澧","汉寿"],
"益阳":["益阳1","益阳2","益阳3"]
}
}
</script>
</head>
<body>
<select id="province" onchange="change(this.value);">
<option>请选择省份</option>
</select>
<select id="city" onchange="countyChange(this.value);">
<option>请选择地市</option>
</select>
<select id="county">
<option>请选择县城</option>
</select>
<script src='test.js'></script>
</body>
</html>
js部分：
var province = document.querySelector("#province");
var city = document.querySelector("#city");
var county = document.querySelector("#county");
//二级联动不用定义你选的省份,直接用省份(key)来决定下面的市(value)值
var provinceName = null;
for (ele in region){
var op = new Option(ele , ele , false , false); //new Option("文本","值",true,true).后面两个true分别表示默认被选中和有效
//console.log(op);
province.options[province.length] = op;
}
var change = function(src){
city.innerHTML = "";
if(src === '请选择省份'){
var op = new Option('请选择地市' , '请选择地市' , false , false);
city.options[0] = op;
}else{
for (index in region[src]){
//console.log(index);
var op = new Option(index , index , false , false);
city.options[city.length] = op;
}
}
//记住选择省份的值
provinceName=src;
countyChange(city.value)
}
var countyChange = function(src2){
county.innerHTML = "";
if(src2 === '请选择地市'){
var op = new Option('请选择县城','请选择县城', false , false);
county.options[0] = op;
}else{
for (index in region[provinceName][src2]){
//console.log(index);
var op = new Option(region[provinceName][src2][index] , region[provinceName][src2][index] , false , false);
county.options[county.length] = op;
}
}
}
