2019-07-11-Ajax

Ajax：在不刷新页面的情况下，异步的服务器进行交互；

示例：

function getAjax(httpUrl,fn){

        //1实例化xhr对象

        var xhr = new XMLHttpRequest()

        //2设置请求的路径和方法

        xhr.open("GET",httpUrl);

        //3发送请求

        xhr.send()

        //4监听事件，接收请求

        xhr.onreadystatechange = function(){

                if(xhr.readyState==4&&xhr.status==200){

                /*console.log(xhr.readyState);

                console.log(xhr.status)

                console.log(xhr)*/

                fn(xhr)

                }

        }

}

getAjax("http://127.0.0.1:8020/5-1ajax/hello.txt",function(xhr){

        var h1 = document.createElement("h1");

        h1.innerHTML = xhr.responseText;

        h1.style.color = "pink"

        document.body.appendChild(h1)

})