js原生实现三级联动下拉菜单

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js代码：

<!doctype html>

<html>

<head>

<meta charset="utf-8">

<title>三级联动</title>

<style>

select{ width:150px; height:35px;}

</style>

</head>

<body>

    <select class="sheng">

        <option>请选择</option>

    </select>

    <span>省</span>

    <select class="shi">

    </select>

    <span>市</span>

    <select class="qu">

    </select>

    <span>区</span>

    <script>

        //获取到三个选择列表

        var shengSelect =document.querySelector(".sheng");

        var shiSelect =document.querySelector(".shi");

        var quSelect =document.querySelector(".qu");

        var shenglist=['广西壮族自治区','广东','湖北'];

        var shilist=[['南宁','桂林','柳州'],['广州','深圳','东莞'],['武汉','荆门','襄阳']];

        var qulist=[

            [['南1区','南2区','南3区'],['桂1区','桂2区','桂3区'],['柳1区','柳2区','柳3区']],

            [['广1区','广2区','广3区'],['深1区','深2区','深3区'],['东1区','东2区']],

            [['武1区','武2区','武3区'],['荆1区','荆2区','荆3区'],['襄1区','襄2区','襄3区']]

        ];

        //选择省的下标

        var shengIndex =0;

        //加载省

        for(var i=0;i<shenglist.length;i++){

            var shengOption = new Option(shenglist[i]);

            shengSelect.options.add(shengOption);

        }

        //选择省后加载市

        shengSelect.onchange =function(eve){

            shengIndex =eve.target.selectedIndex-1;

            if(shengIndex == -1){

                shiSelect.options.length= 0;

                quSelect.options.length=0;

            }else{

                shiSelect.options.length= 0;

                quSelect.options.length=0;

                for(var j=0;j<shilist.length;j++){

                    var shiOption =new Option(shilist[shengIndex][j]);

                    shiSelect.options.add(shiOption);

                }

                //加载市的同时，加载第一个市的全部区

                for(var k=0;k<qulist[shengIndex][0].length;k++){

                    var quOption =new Option(qulist[shengIndex][0][k]);

                    quSelect.options.add(quOption);

                }

            }

        }
　　　　　//选择市后加载区

        shiSelect.onchange=function(eve){

            var shiIndex =eve.target.selectedIndex;

            quSelect.options.length =0;

            for(var n =0;n<qulist[shengIndex][shiIndex].length;n++){

                var quOption =new Option(qulist[shengIndex][shiIndex][n]);

                quSelect.options.add(quOption);

            }

        }

    </script>

</body>

</html>

js写出来基本样子就这样了，下面我们从后台进行获取数据将他显示在页面里面

<!doctype html>

<html>

<head>

<meta charset="utf-8">

<title>三级联动</title>

<style>

select{ width:150px; height:35px;}

</style>

</head>

<body>

    <select class="sheng">

        <option>请选择</option>

    </select>

    <span>省</span>

    <select class="shi">

    </select>

    <span>市</span>

    <select class="qu">

    </select>

    <span>区</span>

    <script>

        //获取到三个选择列表

        var shengSelect =document.querySelector(".sheng");

        var shiSelect =document.querySelector(".shi");

        var quSelect =document.querySelector(".qu");

        //var shenglist=['广西壮族自治区','广东','湖北'];

        //页面加载完成发送ajax请求，获取省数据

        var shengIndex =0;

        (function(){

            var xhr = new XMLHttpRequest();

            xhr.onreadystatechange =function(){

                if(xhr.readyState==4){

                    if(xhr.status==200){

                        shenglist = JSON.parse(xhr.responseText);

                        //加载省

                        for(var i=0;i<shenglist.length;i++){

                            var shengOption = new Option(shenglist[i]);

                            shengSelect.options.add(shengOption);

                        }

                    }

                }

            }

            xhr.open('get','selectDemo.php?type=0',true);

            xhr.send();

        }());

        //点击省加载市

        shengSelect.onchange =function(eve){

            shengIndex =eve.target.selectedIndex-1;

            if(shengIndex== -1){

                shiSelect.options.length = 0;

                quSelect.options.length = 0;

            }else{

                var xhr = new XMLHttpRequest();

                xhr.onreadystatechange =function(){

                    if(xhr.readyState==4){

                        if(xhr.status==200){

                            //console.log(JSON.parse(xhr.responseText));

                            var success = JSON.parse(xhr.responseText);

                            var shilist =success[0];

                            shiSelect.options.length = 0;

                            for(var j=0;j<shilist.length;j++){

                                var shiOption = new Option(shilist[j]);

                                shiSelect.options.add(shiOption);

                            }

                            //加载市的同时加载第一个区

                            var qulist = success[1];

                            quSelect.options.length =0;

                            for(var n=0;n<qulist.length;n++){

                                var quOption = new Option(qulist[n]);

                                quSelect.options.add(quOption);

                            }

                        }

                    }

                }

                xhr.open('get','selectDemo.php?type=1&sheng='+shengIndex,true);

                xhr.send();

            }

        }

        //点击市加载区

        shiSelect.onchange =function(eve){

            shiIndex =eve.target.selectedIndex;

            var xhr = new XMLHttpRequest();

            xhr.onreadystatechange =function(){

                if(xhr.readyState==4){

                    if(xhr.status==200){

                        //console.log(JSON.parse(xhr.responseText));

                        var qulist = JSON.parse(xhr.responseText);

                        //shiSelect.options.length = 0;

                        quSelect.options.length =0;

                        for(var n=0;n<qulist.length;n++){

                            var quOption = new Option(qulist[n]);

                            quSelect.options.add(quOption);

                        }

                    }

                }

            }

            xhr.open('get','selectDemo.php?type=2&sheng='+shengIndex+'&shi='+shiIndex,true);

            xhr.send();

        }

    </script>

</body>

</html>

下面是一个简单的后台，方便测试

<?php

    $shengList = ['广西壮族自治区','广东','湖北'];

    $shilist=[['南宁','桂林','柳州'],['广州','深圳','东莞'],['武汉','荆门','襄阳']];

    $qulist=[[['南1区','南2区','南3区'],['桂1区','桂2区','桂3区'],['柳1区','柳2区','柳3区']],

            [['广1区','广2区','广3区'],['深1区','深2区','深3区'],['东1区','东2区']],

            [['武1区','武2区','武3区'],['荆1区','荆2区','荆3区'],['襄1区','襄2区','襄3区']]];

    $type=$_GET['type'];

    if($type==0){

        echo json_encode($shengList);

    }elseif($type==1){

        $shengInedx=$_GET['sheng'];

        $success = [$shilist[$shengInedx],$qulist[$shengInedx][0]];

        echo json_encode($success);

    }else if($type==2){

        $shengInedx=$_GET['sheng'];

        $shinInedx=$_GET['shi'];

        echo json_encode($qulist[$shengInedx][$shinInedx]);

    }

?>