class Ajax{

  constructor(url, method, data, callback_suc, callback_err, callback_run){
   this.RT = true;//默認(rèn)為異步請求
   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);
  }

 }
 //調(diào)用:
 new Ajax(
  "./main.php", //url：請求地址
  "POST", //method：請求方法
  "data=3&sb=2",//data：傳遞數(shù)據(jù)
  (e)=>{//callback_suc：請求完成 回調(diào)函數(shù)
   document.write(e.target.responseText);//3
  },
  (e)=>{},//callback_err：請求錯(cuò)誤 回調(diào)函數(shù)
  (e)=>{}//callback_run：請求中 回調(diào)函數(shù)
 )

<?php
 //接收客戶端請求數(shù)據(jù)data和sb
 $data = isset($_POST['data']) ? $_POST['data'] : "data為空";
 $sb = isset($_POST['sb']) ? $_POST['sb'] : "sb為空";
 //向客戶端返回?cái)?shù)據(jù)
 echo $data." ".$sb;
?>