js 无缝滚动实现

前端经常看到图片滚动，理清楚原理就会很简单
滚动的原理：所有的图片用li展示出来，ul设置固定宽度，超出的部分hidden，js使用定时器进行修改left，代码如下
<!doctype HTML>
<html>
<head>
    <meta charset="UTF-8">
    <title>exe1</title>
    <link href="" rel="stylesheet" type="text/css"/>
    <meta name="viewport" content="width=750">
    <style>
        * {
            padding: 0;
            margin: 0;
        }
        
        li {
            list-style: none;
        }
        
        img {
            border: 0;
        }
        
        .roll {
            width: 698px;
            height: 108px;
            margin: 50px auto 0;
            position: relative;
        }
        
        .btn_left {
            display: block;
            width: 68px;
            height: 68px;
            background: url(image/wufenggundong/btn.jpg) no-repeat -70px -69px;
            position: absolute;
            top: 20px;
            left: 1px;
            z-index: 1;
        }
        
        .btn_left:hover {
            background: url(image/wufenggundong/btn.jpg) no-repeat -70px 0;
        }
        
        .btn_right {
            display: block;
            width: 68px;
            height: 68px;
            background: url(image/wufenggundong/btn.jpg) no-repeat 1px -69px;
            position: absolute;
            top: 20px;
            right: 0;
            z-index: 1;
        }
        
        .btn_right:hover {
            background: url(image/wufenggundong/btn.jpg) no-repeat 1px 0;
        }
        
        .roll .wrap {
            width: 546px;
            height: 108px;
            margin: 0 auto;
            position: relative;
            overflow: hidden;
        }
        
        .roll ul {
            position: absolute;
            top: 0;
            left: 0;
        }
        
        .roll li {
            float: left;
            width: 182px;
            height: 108px;
            text-align: center;
        }
        
        .roll li a:hover {
            position: relative;
            top: 2px;
        }
        
        .control {
            border-bottom: 1px solid #ccc;
            background: #eee;
            text-align: center;
            padding: 20px 0;
            display: none;
        }
    </style>
    <script>
        window.onload = function(){
            var oDiv = document.getElementById("roll");
            var oUl = oDiv.getElementsByTagName("ul")[0];
            var aLi = oUl.getElementsByTagName("li");
            var aA = oDiv.getElementsByTagName('a');
            var aBtn = oDiv.getElementsByTagName("a");
            //复制li的内容，避免在滚动的时候出现后端空白
            var str=oUl.innerHTML+oUl.innerHTML;
            oUl.innerHTML=str;
            oUl.style.width = aLi[0].offsetWidth * aLi.length + "px";
            var speed = -5;
            timer =  setInterval(move,30);
            //负数，向左滚动
            aBtn[0].onmousemove = function (){
                speed = -5;
            }
            //正数，向右滚动
            aBtn[1].onmousemove = function (){
                speed = 5;
                if(oUl.offsetLeft >=0){
                    oUl.style.left = "0px";
                }
            }
            oUl.onmousemove = function (){
                clearInterval(timer);
            }
            oUl.onmouseout = function (){
                timer =  setInterval(move,30);
            }
            function move(){
                oUl.style.left = oUl.offsetLeft + speed + "px";
                // ul向作滚动，所以是负数，即比较的时候用负数进行比较
                //这里的比较是：在滚动到一半的时候其实就是重复的开始，将所有内容拉到最开始，避免出现空白
                if(oUl.offsetLeft < -oUl.offsetWidth/2){
                    oUl.style.left = "0px";
                }
                //当left=0，右边会出现百边，将内容拉到自身宽度的一半
                else if(oUl.offsetLeft >= 0){
                    oUl.style.left = "-"+ oUl.offsetWidth/2 + "px";
                }
            }
        }
    </script>
</head>
<body>
    <div class="roll" id="roll">
        <a href="javascript:void(0);" class="btn_left"></a>
        <a href="javascript:void(0);" class="btn_right"></a>
        <div class="wrap">
            <ul>
                <li><a ><img src="image/wufenggundong/1.jpg" /></a></li>
                <li><a ><img src="image/wufenggundong/2.jpg" /></a></li>
                <li><a ><img src="image/wufenggundong/3.jpg" /></a></li>
                <li><a ><img src="image/wufenggundong/4.jpg" /></a></li>
            </ul>
        </div>
    </div>
</body>
</html>
实现效果如下：
image.png
点击左右两边的按钮，可以实现左滚动有滚动，鼠标滑动到图片上可以实现暂停滚定，移除继续滚动
js 无缝滚动实现

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