ajax asynchronous request post method

<script>
//创建浏览器对象
function createXhr(){
 //判定浏览器类型处理第一种方法 
/*  var xhr;
 var str=window.navigator.userAgent;
 if(str.indexOf(&#39;MSIE&#39;)>0){
	xhr=new ActiveXObject(&#39;Microsoft.XMLHTTP&#39;);
 }else{
	xhr=new XMLHttpRequest();
 }
return xhr;
 */
 try{
	  return new ActiveXObject(&#39;Microsoft.XMLHTTP&#39;);
  }catch(e){
   }
  try{
	  return new XMLHttpRequest();
  }catch(e){
  }
   
};
//ajax Post请求
 	     var data="username=zs&&password=123456";
           var xhr=createXhr();
           xhr.onreadystatechange=function(){
        	    if(xhr.readyState==4&&xhr.status==200){
              };
           }
   		  xhr.open("post","/ajaxPost1");
   		  xhr.setRequestHeader(&#39;Content-type&#39;,&#39;application/x-www-form-urlencoded&#39;)
   	      xhr.send(data);
	 
</script>