文字多处出现

下面为效果显示区!点击按钮文字停止!!

脚本说明:
把如下代码加入<body>区域中
<SCRIPT language="javascript">

</SCRIPT>
<form name="form1">
<input name="stopIt" type="button" value="Stop Scrolling"
onClick="       if (scroll == false)
                        scroll = true;
                else
                        scroll = false;
                scrollStatus();
                scrollButton();
        ">
</form>

var num = 0;
scrollButton();

function scrollButton() {
        var buttonChars = new Array('S', 't', 'o', 'p', ' ', 'S', 'c', 'r', 'o', 'l', 'l', 'i', 'n', 'g', ' ', ' ');
        var buttonText = "";
        for (var a = num; a < buttonChars.length; a++)
                buttonText += buttonChars[a];
        for (var b = 0; b < num; b++)
                buttonText += buttonChars[b];
        num++;
        if (num >= buttonChars.length)
                num = 0;
        document.form1.stopIt.value = buttonText;
        if (scroll) {
                setTimeout("scrollButton();", 100);
                }
        }

</SCRIPT>