js 实现滚轮自动滚动``` 1 2 3 4 5 `````` 1 2 3 4 5 `````` 1 2 3 4 5 `

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <title>autoScroll</title>
</head>
<style>
  .parent {
    width: 300px;
    height: 200px;
    margin: 0 auto;
    background: #242424;
    overflow-y: scroll;
  }

  /*设置的子盒子高度大于父盒子，产生溢出效果*/
  .child {
    height: auto;
  }

  .child li {
    height: 50px;
    margin: 2px 0;
    background: #009678;
  }
</style>

<body>
  <div id="parent" class="parent">
    <div id="child1" class="child">
      <li>1</li>
      <li>2</li>
      <li>3</li>
      <li>4</li>
      <li>5</li>
    </div>
    <div id="child2" class="child"></div>
  </div>
  <script type="text/javascript">
    (function () {
      var parent = document.getElementById('parent');
      var child1 = document.getElementById('child1');
      var child2 = document.getElementById('child2');
      child2.innerHTML = child1.innerHTML;
      setInterval(function () {
        if (parent.scrollTop >= child1.scrollHeight) {
          parent.scrollTop = 0;
        } else {
          parent.scrollTop++;
        }
      }, 20);
    })()
  </script>
</body>

</html>