ajax异步请求post方式

<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('MSIE')>0){xhr=new ActiveXObject('Microsoft.XMLHTTP'); }else{xhr=new XMLHttpRequest(); }return xhr; */ try{  return new ActiveXObject('Microsoft.XMLHTTP');  }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('Content-type','application/x-www-form-urlencoded')         xhr.send(data); </script>