class Ajax{

         constructor(url, method, data, callback_suc, callback_err, callback_run){

             this.RT = true;//默认为异步请求

             this.url = url;

             this.method = method || "POST";

             this.data = data || "";

             this.callback_suc = callback_suc || function () {};

             this.callback_err = callback_err || function () {};

             this.callback_run = callback_run || function () {};

             if(!this.url){this.callback_err(); return;}

             this.createRequest();

         }

         createRequest(){

             let xhr = new XMLHttpRequest();

             xhr.onreadystatechange = (e)=>{this.run(e);}

             xhr.open(this.method, this.url, this.RT);

             xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

             xhr.send(this.data);

         }

         run(e){

             this.callback_run(e);

             if(e.target.readyState !== 4 || e.target.status !== 200){return;}

             this.callback_suc(e);

         }

     }

     //调用:

     new Ajax(

         "./main.php", //url：请求地址

         "POST", //method：请求方法

         "data=3&sb=2",//data：传递数据

         (e)=>{//callback_suc：请求完成 回调函数

             document.write(e.target.responseText);//

         },

         (e)=>{},//callback_err：请求错误 回调函数

         (e)=>{}//callback_run：请求中 回调函数

     )

 <?php

     //接收客户端请求数据data和sb

     $data = isset($_POST['data']) ? $_POST['data'] : "data为空";

     $sb = isset($_POST['sb']) ? $_POST['sb'] : "sb为空";

     //向客户端返回数据

     echo $data." ".$sb;

 ?>