Ajax封装

var req; function createXMLHttpRequest(){//建立XMLHttpRequest对象  var request;   if(window.XMLHttpRequest){   request=new XMLHttpRequest();  }else if(window.ActiveXObject){    request=new ActiveXObject("Msxml2.XMLHTTP");  }   return request; } function test(method,url,param,Asyhc,handle200,handle404,handle500,locading){  var req=createXMLHttpRequest();//建立XMLHttpRequest对象  req.onreadystatechange=function(){//处理返回数据   if(4==req.readyState){//服务器已经成功接收数据    if(200==req.status){//成功返回数据     handle200(req);//一个函数也是一个对象    }else if(404==req.status){     handle404(req);    }else if(500==req.status){     handle500(req);    }   }else{    locading(req);   }  }  if("get".equals(method.toLowerCase)){//判断是get仍是post方法   req.open("get",url+(param==null?"":"?"+param),Asyhc);   req.send(null);  }else if("post".equals(method.toLowerCase)){   req.open("post",url,Asyhc);   req.setRequestHeader("Content-Type","application/x-www-form-urlencoded");   req.send(param);  } }