网页title栏文字滚动

<script type="text/javascript">
    var text = document.title
    var timerID
    function newtext() {
        clearTimeout(timerID)
        document.title = text.substring(1, text.length) + text.substring(0, 1)
        text = document.title.substring(0, text.length)
        timerID = setTimeout("newtext()", 300)
    }
    newtext();
</script>