原生的js 发出Ajax请求

var AjaxHelp={
    var GetXhr:function(){
        var xhr;
        if(windows.XMLHttpRequest){
                xhr=new XMLHttpRequest();
        }esle 
        {
             xhr=new ActiveXObject("Microsoft.XMLHTTP");
        }
    },
    var AjaxProcess:function(url,method,params,callback){
       var xhr=this.GetXhr();//1 .0 创建异步对象
        xhr.open();//2 发送请求
           if (method.toLowerCase=="get"){
                xhr.setRquestHeader("If-Modified-Since","0");
        }  else {
                xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
        }
        
     xhr.onreadystatechange=function(){//4 设置请求状态变换事件
        if(xhr.readstate==4&&xhr.Status==200){
            var resText=JSON.parse(xhr.ReponseText);//返回结果
      }  
  }
    xhr.Send(params);//发送请求
   }
 
};