(()=>{//1.定义一个构造函数var ajax=function(){}//函数表达式（能够将其了解为构造函数）//2.在构造函数外部的原型对象（Prorotype）上增加ajax函数ajax.prototype={    doAjax:function(obj){//obj={type:"GET","url":url,"data":params,async:true,"ContentType":ContentType,"success":success,"error":error}    //1.创立xhr对象    const xhr=new XMLHttpRequest();    //2.设置状态监听    xhr.onreadystatechange=function(){        if(xhr.readyState==4){//服务端响应完结，客户端接管胜利        if(xhr.status==200){//200示意失常响应完结            obj.success(xhr.responseText);//回调函数        }else{//示意呈现了异样            obj.error(xhr.status);        }    }}    //3.建设连贯    let type=obj.type?obj.type:"GET";    xhr.open(obj.type,obj.type=="GET"?`${obj.url}?${obj.data}`:obj.url,obj.async?true:obj.async);    //4.发送申请    if(type!="GET"){    xhr.setRequestHeader("Content-Type",obj.ContentType?obj.ContentType:"application/x-www-form-urlencoded");    }    xhr.send(obj.type=="GET"?null:obj.data);    },    doAjaxGet:function(url,params,callback){    this.doAjax({"type":"GET","url":url,"data":params,"success":callback,"error":callback});},    doAjaxPost:function(url,params,callback){    this.doAjax({"type":"POST","url":url,"data":params,"success":callback,"error":callback,"ContentType":"application/x-www-form-urlencoded"});    }}    //3.基于ajax构造函数构建ajax对象，并将对象赋值给全局变量window.$$=new ajax();})()

html文件中：

<!DOCTYPE html><html><head><meta charset="UTF-8"><title>Insert title here</title></head><body><h1>The Ajax 05 Page</h1><fieldset><legend>Ajax 表单申请</legend><form>   <input type="text" id="nameId" name="name" onblur="doCheck()">   <input type="button" onclick="doSave()" value="Save"></form><span id="resultId"></span><!-- 此地位显示服务端响应后果 --></fieldset><script type="text/javascript" src="/js/ajaxfk2.js"></script><script type="text/javascript">   //检测名字是否已存在   function doCheck(){       //1.定义申请的url       var url="http://localhost/doCheck";       //2.定义申请参数       var name=document.forms[0].name.value;       var params=`name=${name}`;       //3.发送ajax get申请      $$.doAjaxGet(url,params,(result)=>{           document.getElementById("resultId").innerHTML=               `<font color=red>${result}</font>`;       });   }   //保留表单中名字的值   function doSave(){//debugger,log,排除法      //1.申请url      const url="http://localhost/doSave";      //2.申请参数      let name=document.forms[0].name.value;      let params=`name=${name}`;      //3.发送ajax post申请    $$.doAjaxPost(url,params,(result)=>{            alert(result);      })   }</script></body></html>