原生js 的ajax封装

/**
 * 封装ajax函数（包括跨域）
 * @method  ajax
 * @param   option :{type:"post" or  "get" 请求方式,url:"url" 请求地址，data:object 请求参数，async:"true" 异步or“false”同步，success:function 请求成功回调函数，error:function,请求失败函数，jsonp:"true" 表示跨域 “false”:表示不跨域;callback:function  跨域请求函数名}
 * @return {}
 *
 */
function ajax(option) {
    "use strict";
    //检测传入参数是否是一个对象
    if ({}.__proto__.toString.call(option) !== "[object Object]") {
        alert("参数格式错误！！");
        return;
    }

    var data = option.data || "";
    var async = option.async || "true";//默认是异步
    var jsonp = option.jsonp || "false"//默认是不跨域http
    var params=[];
    var postData;
    var getHttpRequest = function () {
        if (window.XMLHttpRequest) {
            //主流浏览器提供了XMLHttpRequest对象
            return new XMLHttpRequest();
        } else if (window.ActiveXObject) {
            //低版本的IE浏览器没有提供XMLHttpRequest对象
            //所以必须使用IE浏览器的特定实现ActiveXObject
            return new ActiveXObject("Microsoft.XMLHttpRequest");
        }

    };

    if(data!==""){
        for (var key in data) {
            params.push(key + '=' + data[key]);
        }
    }
    postData= params.join('&');
 if (jsonp !== "true") {//不是跨域
        var httpRequest = getHttpRequest();        
if (option.type.toUpperCase() === 'POST') {         
   httpRequest.open(option.type, option.url, async);         
   httpRequest.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');          
  　httpRequest.send(postData);        }
   else if (option.type.toUpperCase() === 'GET') {         
   httpRequest.open(option.type, option.url + '?' + postData, async);         
   httpRequest.send(null);      
  }     
   httpRequest.onreadystatechange=function(){          
  if(httpRequest.readyState==="4"&&httpRequest.state==="200"){                
    option.success(httpRequest.responseTest);            }else{               
     option.error(httpRequest.responseTest);           
 } }   
 } else {        //跨域       
 var responseContainer;       
 var overwritten;       
 var doc=document.body;      
  var  _script=document.createElement("script");    
    _script.setAttribute("type","text/javascript");     
   _script.src=option.url+"?"+postData+"&callback="+option.callback;       
 doc.appendChild(_script);    
    overwritten=window[option.callback];       
 window[option.callback]=function(){            
 responseContainer= arguments;        }       
 option.success(responseContainer[0]);      
  responseContainer = overwritten = undefined;    }}