页面每次加载时重新获取css文件

<script>
(function(){
    var version='';
    var xmlhttp;
        // code for IE7+, Firefox, Chrome, Opera, Safari
    if (window.XMLHttpRequest){
      xmlhttp=new XMLHttpRequest();
    }
        // code for IE6, IE5
    else{
      xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
    xmlhttp.onreadystatechange=function(){
      if (xmlhttp.readyState==4 && xmlhttp.status==200){
          version=xmlhttp.responseText;
      }
    }
    xmlhttp.open("GET","test/get",false);
    xmlhttp.send();
    
    var css = document.createElement ("link");
    css.rel = "stylesheet";
    css.href = "css/reponsive.css?version="+version;
    document.getElementsByTagName("head")[0].appendChild(css);
    
    css = document.createElement("link");
    css.rel = "stylesheet";
    css.href = "./css/item-list.css?version="+version;
    document.getElementsByTagName("head")[0].appendChild(css);
})();
</script>