三级联动页面

<!DOCTYPE html>
<head>
    <title>三级联动</title>
</head>
<body>
省：
<select style="width: 100px;" id="pre" onchange="chg(this);">
    <option value="-1">请选择</option>
</select>
市：
<select style="width: 100px;" id="city" onchange="chg2(this)" ;></select>
区：
<select style="width: 100px;" id="area"></select>
</body>
<script>
//声明省
var pres = ["北京", "上海", "山东"]; //直接声明Array
 //声明市
var cities = [
    ["东城", "昌平", "海淀"],
    ["浦东", "高区"],
    ["济南", "青岛"]
];
var areas = [
        [
            ["东城1", "东城2", "东城3"],
            ["昌平1", "昌平2", "昌平3"],
            ["海淀1", "海淀2", "海淀3"]
        ],
        [
            ["浦东1", "浦东2", "浦东3"],
            ["高区1", "高区2", "高区3"]
        ],
        [
            ["济南1", "济南2"],
            ["青岛1", "青岛2"]
        ]
    ]
    //设置一个省的公共下标
var pIndex = -1;
var preEle = document.getElementById("pre");
var cityEle = document.getElementById("city");
var areaEle = document.getElementById("area");
 //先设置省的值
for (var i = 0; i < pres.length; i++) {
    //声明option.<option value="pres[i]">Pres[i]</option>
    var op = new Option(pres[i], i);
    //添加
    preEle.options.add(op);
}
function chg(obj) {
    if (obj.value == -1) {
        cityEle.options.length = 0;
        areaEle.options.length = 0;
    }
    //获取值
    var val = obj.value;
    pIndex = obj.value;
    //获取ctiry
    var cs = cities[val];
    //获取默认区
    var as = areas[val][0];
    //先清空市
    cityEle.options.length = 0;
    areaEle.options.length = 0;
    for (var i = 0; i < cs.length; i++) {
        var op = new Option(cs[i], i);
        cityEle.options.add(op);
    }
    for (var i = 0; i < as.length; i++) {
        var op = new Option(as[i], i);
        areaEle.options.add(op);
    }
}
function chg2(obj) {
    var val = obj.selectedIndex;
    var as = areas[pIndex][val];
    areaEle.options.length = 0;
    for (var i = 0; i < as.length; i++) {
        var op = new Option(as[i], i);
        areaEle.options.add(op);
    }
}
</script>
</html>
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