AJAX

oBtn.onclick = function(){
            //1.创建AJAX对象
            if(window.XMLHttpRequest){
                //非IE6
                var oAjax = new XMLHttpRequest();
            }
            else{
                //兼容IE6
                var oAjax = new ActiveXObject("Microsoft.XMLHttp");
            }

            //2.连接服务器
            //open(方法,文件名,异步传输true/同步传输false)
            oAjax.open('GET','data.json',true);

            //3.发送请求
            oAjax.send();

            //4.接收返回
            oAjax.onreadystatechange = function(){
                //已经接收到全部响应数据
                if(oAjax.readyState == 4){ 
                    if(oAjax.status == 200){
                        console.log("成功"+oAjax.responseText);
                    }
                    else{
                        console.log("失败");
                    }
                }
            }
        }
    }