封装ajax函数

<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<script src="new_ajax.js"></script>
<script>
window.onload=function ()
{
    var oBtn=document.getElementById('btn1');
    
    oBtn.onclick=function ()
    {
        ajax('a.txt', function (str){
            alert(str);
        });
    };
};
</script>
</head>

<body>
<input id="btn1" type="button" value="读取" />
</body>
</html>

一下是引入的封装好的new_ajax.js

function ajax(url, fnSucc, fnFaild)
{
    //1.创建Ajax对象
    if(window.XMLHttpRequest)  //低版本IE6浏览器
    {
        var oAjax=new XMLHttpRequest();
    }
    else
    {
        var oAjax=new ActiveXObject("Microsoft.XMLHTTP");
    }
    
    //2.连接服务器
    //open(方法, 文件名, 异步传输)
    oAjax.open('GET', url, true);
    
    //3.发送请求
    oAjax.send();
    
    //4.接收返回
    oAjax.onreadystatechange=function ()
    {
        //oAjax.readyState    //浏览器和服务器，进行到哪一步了
        if(oAjax.readyState==4)    //读取完成
        {
            if(oAjax.status==200)    //成功
            {
                fnSucc(oAjax.responseText);
            }
            else
            {
                if(fnFaild)
                {
                    fnFaild(oAjax.status);
                }
                //alert('失败:'+oAjax.status);
            }
        }
    };
}