<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
    <title>keep 里面的上下轮播</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        .page {
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            background-color: grey;
            width: 200px;
            height: 180px;
            overflow: hidden;
        }
        .roll-list{
            height: 800px;
        }
        .roll-list li {
            list-style: none;
            height: 60px;
            width: 100%;
        }
    </style>
</head>

<body>
    <div class="page" id="a">
        <ul class="roll-list" id="list">
            <li class="roll-item" style="background-color: hotpink">1</li>
            <li class="roll-item" style="background-color:lawngreen">2</li>
            <li class="roll-item" style="background-color:midnightblue">3</li>
            <li class="roll-item" style="background-color: rgb(255, 185, 105)">4</li>
    </div>
</body>

<script>
    let item = document.getElementsByClassName('roll-item');
    let itemWidth = item[0].offsetHeight;
    function autoScroll(obj) {
        $(obj).find("ul").animate({
            marginTop: `-${itemWidth}px`
        }, 1000, function () {
            $(this).css({ marginTop: "0px"}).find("li:first").appendTo(this);
        })
    }
    $(function () {
        var scroll = setInterval('autoScroll(".page")', 2000);
        $(".page").hover(function () {
            clearInterval(scroll);
        }, function () {
            scroll = setInterval('autoScroll(".page")', 2000);
        });
    });
</script>

</html>
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