JavaScript数字滚动效果

   <div id="n" style="height:20px">
        <div class="num">1</div>
        <div class="num">2</div>
        <div class="num">3</div>
        <div class="num">4</div>
        <div class="num">5</div>
        <div class="num">6</div>
        <div class="num">7</div>
        <div class="num">8</div>
        <div class="num">9</div>
        <div class="num">10</div>
        <div class="num">11</div>
        <div class="num">12</div>
        <div class="num">13</div>
    </div>