Ajax实现的城市二级联动三

把之前2篇整合在一起

1、html

<select id="province">
    <option>请选择</option>
  </select>
  <select id="city">
    <option>请选择</option>
  </select>

2、javascript

//创建获取ajax核心对象的函数
      function getXhr(){
          var xhr = null;
          if(window.XMLHttpRequest){
              xhr = new XMLHttpRequest();
          }else{
              xhr = new ActiveXObject("Microsoft.XMLHttp");
          }
          return xhr;
      }
        var xhr = getXhr();
        // 第一次执行Ajax异步请求 - 省份
        window.onload = function(){
            xhr.open("get","finaly.php?state=1");
            xhr.send(null);
            xhr.onreadystatechange = function(){
            if(xhr.readyState==4&&xhr.status==200){
                    var data = xhr.responseText;
                    // 将字符串转换为数组
                    var provinces = data.split(",");
                    // 遍历数组
                    for(var i=0;i<provinces.length;i++){
                        // 创建option元素添加到id为province元素上
                        var option = document.createElement("option");
                        var text = document.createTextNode(provinces[i]);
                        option.appendChild(text);
                        var province = document.getElementById("province");
                        province.appendChild(option);
                    }
                }    
            }
        };
        // 第二次执行Ajax异步请求 - 城市
        var province=document.getElementById("province");
        province.onchange = function(){
            var city = document.getElementById("city");
            var opts = city.getElementsByTagName("option");
            for(var z=opts.length-1;z>0;z--){
                city.removeChild(opts[z]);
            }
            if(province.value != "请选择"){
                xhr.open("post","finaly.php");
                xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
                xhr.send("state=2&province="+province.value);
                xhr.onreadystatechange = function(){
                    if(xhr.readyState==4&&xhr.status==200){
                        var data = xhr.responseText;
                        var cities = data.split(",");
                        for(var i=0;i<cities.length;i++){
                            var option = document.createElement("option");
                            var text = document.createTextNode(cities[i]);
                            option.appendChild(text);
                            city.appendChild(option);
                        }
                    }
                }
            }
        };

3、finaly.php

<?php
    // 接收客户端发送的请求数据 - state
    $state = $_REQUEST['state'];
    // 判断$state的值
    if($state == 1){// 获取省份
        echo '山东省,辽宁省,吉林省';
    }else{// 获取城市
        $province = $_POST['province'];
        switch ($province){
            case '山东省':
                echo '青岛市,济南市,威海市,日照市,德州市';
                break;
            case '辽宁省':
                echo '沈阳市,大连市,铁岭市,丹东市,锦州市';
                break;
            case '吉林省':
                echo '长春市,松原市,吉林市,通化市,四平市';
                break;
        }
    }
?>