ajax封装

var createXHR=function(){
      if(typeof XMLHttpRequest!="undefined"){
          return new XMLHttpRequest();
      }else if(typeof ActiveXObject!="undefined"){
          var version=["MSXML2.XMLHttp.6.0",
                       "MSXML2.XMLHttp.3.0",
                       "MSXML2.XMLHttp"];
          for(var i=0,len=version.length;i<len;i++){
              try{
                  return new ActiveXObject(version[i]);
              }catch(ex){
                  //跳过
              }
          }
      }else{
          throw new Error("您的浏览器不支持ajax");
      }
};

//名值对转化为字符串
function params(data){
    var arr=[];
    for(var i in data){
        arr.push(encodeURIComponent(i)+"="+encodeURIComponent(data[i]));
    }
    return arr.join("&");
}

//封装ajax
function ajax (obj){
    var xhr=createXHR();
    obj.url = obj.url+"?rand="+Math.random()+"&"+params(obj.data);    
    if(obj.method === "get"){  //get请求
        obj.url = obj.url+(obj.url.indexOf("?")==-1 ? "?" : "&")+params(obj.data);
    }
    
    if(obj.async==true){  //异步请求
       xhr.onreadystatechange=function(){
           if(xhr.readyState == 4){
                callback();
           }
       };
    }
    xhr.open(obj.method,obj.url,obj.async);
    
    if(obj.method === "post"){   //post请求
        xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
        xhr.send(params(obj.data));
    }else{
       xhr.send(null);
    }
    
    if(obj.async == false){
        callback();
    }
    function callback(){
        if(xhr.status == 200){
            obj.success(xhr.responseText);  //回调函数传递参数
        }else{
            alert("获取数据错误！错误代号："+xhr.status+",错误信息："+xhr.statusText);
        }
    }
}

//调用ajax
var object={
        method:"get",
        url:"demo.php",
        async:false,
        data:{
            name:"liu",
            age:25
            },
        success:function (text){
                   console.log(text);
                }
        };
document.addEventListener("click",function(){
    console.log(ajax(object));
},false);