它可以简单地通过存储您移动的方向并在到达顶部/底部时切换来完成。检查是否需要切换的最简单方法是查看自上次迭代以来位置是否实际发生了变化。
如果您试图通过传递一个太小或太大的数字来滚动到一个位置，该位置将分别设置为顶部或底部。在这种情况下，scrollTop()将返回与之前相同的数字，我们将知道是时候切换方向了。

var up = false;
var lastPosition;

var interval = setInterval(function () {
    var $container = $("#divContainer");
    var position = $container.scrollTop();
    var height = $container[0].scrollHeight;

    // If we haven't moved, switch direction
    if(position === lastPosition) up = !up;
    lastPosition = position;

    if (up) {
        // Going up
        $container.scrollTop(position - 10);
    } else {
        // Going down
        $container.scrollTop(position + 10);
    }
}, 100);

div {
    border: 1px solid red;
    width: 200px;
    height: 200px;
    overflow: auto;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<div id="divContainer">
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</div>