<!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">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        #div1 {
            position: relative;
            width: 390px;
            height: 100px;
            margin: 100px auto;
            box-sizing: border-box;
            overflow: hidden;
            background-color: #111;
        }

        #div1>ul {
            position: absolute;
            background-color: #fff;
        }

        #div1>ul>li {
            list-style: none;
            border: 1px solid rebeccapurple;
            box-sizing: border-box;
            float: left;
            height: 100px;
        }
    </style>
    <script>
        window.onload = function () {
            var oDiv = document.getElementById('div1')
            var oUl = oDiv.getElementsByTagName('ul')[0]
            var list = oUl.getElementsByTagName('li')
            for (var i = 0; i < list.length; i++) {
                list[i].style.width = oDiv.offsetWidth / list.length + 'px'
            }
            oUl.innerHTML = oUl.innerHTML + oUl.innerHTML
            oUl.style.width = list[0].offsetWidth * list.length + 'px'
            setInterval(function () {
                if(oUl.offsetLeft < -oUl.offsetWidth/2) {
                    oUl.style.left = '0'
                }
                if(oUl.offsetLeft > 0) {
                    oUl.style.left =-oUl.offsetWidth/2+ 'px'
                }
                oUl.style.left = oUl.offsetLeft+2 + 'px'
            }, 100)
        }
    </script>
</head>

<body>
    <div id="div1">
        <ul>
            <li>1</li>
            <li>2</li>
            <li>3</li>
            <li>4</li>
        </ul>
    </div>
</body>

</html>