JS文字滚动效果

<div id="test">这里是滚动的文字！</div>
<p class="btns"><button type="button" id="start">开始</button><button type="button" id="stop">结束</button></p>

function $(id) {
        return document.getElementById(id);
};

window.onload = function() {
        var t = null;
        $("start").onclick = function() {
                clearInterval(t);
                var s = $('test').innerText.split('');
                t = setInterval(function() {
                        s.push(s.shift());//滚动
                        $('test').innerText = s.join('');
                }, 300);
                $("start").disabled = true;//单击开始按钮后禁用开始按钮
                $("stop").disabled = false;//单击开始按钮后启用结束按钮
        };
        $("stop").onclick = function() {
                clearInterval(t);//清除间歇调用
                $("start").disabled = false;
                $("stop").disabled = true;
        };
}

function $(id) {
        return document.getElementById(id);
};

function ScrollText(text, fn, time) {
        this.text = text.split('');
        this.fn = fn;
        this.time = time || 300;
}
ScrollText.prototype.start = function() {
        var s = this.text;
        var fn = this.fn;
        clearInterval(this.interval);
        this.interval = setInterval(function() {
                s.push(s.shift());
                fn(s.join(""));//这个函数是处理传进来的字符串的，指定将它作为某个对象的文本
        }, this.time);
};
ScrollText.prototype.stop = function() {
        clearInterval(this.interval);
};

window.onload = function() {
        var txt = $("test").innerHTML;
        var scrollText = new ScrollText(txt, function(t) {
                $("test").innerHTML = t;
        });
        /*var txt = $("test").innerHTML;
        var scrollText = new ScrollText(txt, function(t) {
                document.title = t;
        });*/
        
        $("start").onclick = function() {
                scrollText.start();
                $("start").disabled = true;//单击开始按钮后禁用开始按钮
                $("stop").disabled = false;//单击开始按钮后启用结束按钮
        };
        $("stop").onclick = function() {
                scrollText.stop();
                $("start").disabled = false;
                $("stop").disabled = true;
        };
}