原生Js 实现简单无缝滚动轮播图

效果展示如下：
当前面滚动出去的left比-1470还小时，就要让图片位置重新归0
<html>
<head>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .scroll{
            position: relative;
             830px;/*展示宽度 展示4个图+3个边框=830*/
            height: 130px;
            border: 10px solid rgb(15, 15, 15);
            margin: 100px auto;
            overflow: hidden;
        }
        .scroll ul{
            position: absolute;
             5000px;/*ul能存下所有li的宽*/
            height: 130px;
            top: 0;
            left: 0;
        }
        .scroll ul li{
            float: left;
             200px;
            height: 130px;
            margin-right: 10px;
            overflow: hidden;
        }

    </style>
</head>
<body>
    <div id="scroll" class="scroll">
        <ul id="munit">
            <li><img src="../BOM/shuzi/3.png" alt=""></li>
            <li><img src="../BOM/shuzi/4.png" alt=""></li>
            <li><img src="../BOM/shuzi/5.png" alt=""></li>
            <li><img src="../BOM/shuzi/6.png" alt=""></li>
            <li><img src="../BOM/shuzi/7.png" alt=""></li>
            <li><img src="../BOM/shuzi/8.png" alt=""></li>
            <li><img src="../BOM/shuzi/9.png" alt=""></li>

            <li><img src="../BOM/shuzi/3.png" alt=""></li>
            <li><img src="../BOM/shuzi/4.png" alt=""></li>
            <li><img src="../BOM/shuzi/5.png" alt=""></li>
            <li><img src="../BOM/shuzi/6.png" alt=""></li>
            <li><img src="../BOM/shuzi/7.png" alt=""></li>
            <li><img src="../BOM/shuzi/8.png" alt=""></li>
            <li><img src="../BOM/shuzi/9.png" alt=""></li>
        </ul>
    </div>

    <script>
        //获取元素
        var scroll = document.getElementById("scroll");
        var munit = document.getElementById("munit");
        var li = munit.children;
        // 进行滚动
        var nowLeft = 0;
        //要找到ul元素运动的折返点
        var back = -1470;//图和边框的宽度，有7张图，所以折返点就是1470
        //定时器
        var timer = setInterval(run,20);

        // 鼠标移上scroll停止
        scroll.onmouseover = function(){
            clearInterval(timer);
        }
        // 移开轮播
        scroll.onmouseout = function(){
            timer = setInterval(run,20);
        }

        //运动函数
        function run(){
            nowLeft -= 2;
            //判断是否走到了折返点，走到了，则瞬间切换到0位置
            if(nowLeft <= back){
                nowLeft = 0;
            }
            munit.style.left = nowLeft + "px";
        }

    </script>
</body>
</html>