原生jsAJax实现代码

<script type="text/javascript">

window.onload = function() {

var btn = document.getElementById("btn");

function creatXHR() {

if (typeof XMLHttpRequest != "undefined") {

creatXHR =function  () {

  return new XMLHttpRequest();

}

} else if(typeof ActiveXObject !="undefined"){

if (typeof(arguments.callee.activeString) !="undefined") {

var versions=["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"];

for (var i=0;i,versions.length;i++) {

try{

new ActiveXObject(versions[i]);

arguments.callee.activeString==versions[i];

}catch(e){

//tiaoguo

}

}

}return new ActiveXObject(arguments.callee.activeString);

}

else{

throw new Error("buzhichiajax");

}

}

var xhr=creatXHR();

xhr.readyState=function  () {

if (xhr.readyState==4) {

if (xhr.status>=200&&xhr.status<300||xhr.status==304) {

alert(xhr.responseText)

} else{

alert("falied")

}

} 

}

var url="php/index.php?rand"+Math.random();

xhr.open("GET","php/index.php",false);

xhr.send(null);

function addUrl (url ,name,value) {

url+=url.indexOf("?")==-1?"?":"&";

url+=encodeURIComponent(name)+"="+encodeURIComponent(value);

return url;

}

xhr.open("POST","php/index.php",true);

xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");

var form=document.getElementById("form")

xhr.send(serialize(form));

}

</script>