js兑现滚动的网页标题

<title>欢迎你来到大学堂</title>
<script type="text/javascript">
??? function scorll(){
???var title=document.title;
???var first=title.charAt(1);
???var last=title.substring(2,title.length);
???//alert(last);
???document.title=first+last;
???if(document.title.length==0){
???document.title="欢迎你来到大学堂,欢迎你来到大学堂";?
???}
??}
??? setInterval("scorll()",500);
</script>