Ajax入门学习原始代码

<script
type="text/javascript">
       
window.onload = function ()
{
           
//1、创建xmlhttprequest对象
           
var xhr =
createXHR();
           
function createXHR()
{//为了兼容新老IE的版本
               
var
request;
               
if (typeof(XMLHttpRequest)=="undefined")
{
                   
request =
ActiveXObject("Micrpsoft.XMLHTTP");
               
} else
{
                   
request = new
XMLHttpRequest();
               
}
               
return
request;
           
}
           
//Ajax围绕xhr对象操作的
           
document.getElementById("btn").onclick = function ()
{
               
//2、初始化xhr
               
xhr.open("get", "get1.ashx",
true);//参数1：请求方式（get，post）；参数2：请求的相对路径；参数3：是否为异步
               
//3、注册回调函数
               
xhr.onreadystatechange = function ()
{
                   
//readyState属性有5个状态值
                   
//0：表示 new 完
xhr
                   
//1：表示open完xhr
                   
//2：表示send完xhr
                   
//3：表示xhr正在接受服务器的数据
                   
//4：表示xhr接受完服务器数据
                   
if (xhr.readyState==4)
{
                       
var msg =
xhr.responseText;
                       
document.getElementById("dv").innerHTML =
msg;
                   
}
               
}
               
//4、send
               
xhr.send(null);//get方式为NULL
           
}
        }
   
</script>

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