js制作轮播图效果

轮播图在前端开发中我认为是一个比较重要的点，因为包含了很多原生js知识点，以下是我学习制作轮播图的过程

难点：

1、如何让底下圆圈和图片所对应自动动态生成
2、如何让底下圆圈和图片所对应的起来
3、上一页和下一页所在盒子所移动的距离
4、图片切换时的渐出动画效果
5、节流阀的概念

效果：

代码：

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        a {
            text-decoration: none;
            color: white;
            line-height: 50px;
            text-align: center;
        }

        li {
            list-style: none;
        }

        .tb-promo {
            position: relative;
            width: 700px;
            height: 300px;
            margin: auto;
            overflow: hidden;
        }

        .tb-promo .imgg {
            position: absolute;
            top: 0;
            left: 0;
            width: 3000px;
        }

        .tb-promo .imgg li {
            float: left;

        }

        .tb-promo .imgg li img {
            width: 700px;
            height: 300px;
        }

        .tb-promo .prev {
            display: none;
            position: absolute;
            top: 125px;
            left: 0;
            width: 25px;
            height: 50px;
            background-color: rgba(0, 0, 0, 0.2);
            border-top-right-radius: 25px;
            border-bottom-right-radius: 25px;
            z-index: 999;
        }

        .tb-promo .prev:hover {
            background-color: rgba(0, 0, 0, 0.5);
        }

        .tb-promo .next {
            display: none;
            position: absolute;
            top: 125px;
            right: 0;
            width: 25px;
            height: 50px;
            background-color: rgba(0, 0, 0, 0.2);
            border-top-left-radius: 25px;
            border-bottom-left-radius: 25px;
            z-index: 999;
        }

        .tb-promo .next:hover {
            background-color: rgba(0, 0, 0, 0.5);
        }

        .tb-promo .promo-nav {
            position: absolute;
            top: 270px;
            left: 50%;
            margin-left: -40px;

            height: 25px;

        }

        .tb-promo .promo-nav li {
            float: left;
            width: 16px;
            height: 16px;
            background-color: white;
            border-radius: 8px;
            margin: 4px;

        }

        .tb-promo .promo-nav .one {

            background-color: tomato;
        }
    </style>
</head>

<body>
    <div class="tb-promo">

        <a href="javascript:;" class="prev"><</a>
                <a href="javascript:;" class="next">></a>
                <ul class="imgg">
                    <li><img src="./61.jpeg" alt=""></li>
                    <li><img src="./62.jpeg" alt=""></li>
                    <li><img src="./63.jpeg" alt=""></li>

                </ul>
                <ol class="promo-nav">

                </ol>
    </div>
    <script>
        var prev = document.querySelector('.prev');
        var next = document.querySelector('.next');
        var tbpromo = document.querySelector('.tb-promo');
        var ul = document.querySelector('ul');
        var ol = document.querySelector('ol');
        //动画函数
        function animate(obj, target) {
            clearInterval(obj.timer);//调用防止点击多次调用
            obj.timer = setInterval(function () {
                var step = (target - obj.offsetLeft) / 10;
                step = step > 0 ? Math.ceil(step) : Math.floor(step); //正直和负值取整
                if (obj.offsetLeft == target) {
                    clearInterval(obj.timer);
                } else {
                    obj.style.left = obj.offsetLeft + step + 'px';
                }
            }, 10)
        }

        //生成动态导航圈圈
        var tbpromWidth = tbpromo.offsetWidth;
        for (var i = 0; i < ul.children.length; i++) {
            var li = document.createElement('li');
            ol.appendChild(li);
            //记录索引号 通过自定义属性
            li.setAttribute('index', i);
            //排他思想 写圆圈变色
            li.addEventListener('click', function () {
                //清除所有圈圈颜色
                for (var i = 0; i < ol.children.length; i++) {
                    ol.children[i].className = '';
                }
                this.className = 'one';

                var index = this.getAttribute('index');
                //点击li 把li 的索引号分别给控制变量
                num = index;
                circle=index;
                animate(ul, -index * tbpromWidth);

            })
            ol.children[0].className = 'one';
        }
        //克隆第一张图片li放在最后面 无缝切换
        var frist = ul.children[0].cloneNode(true);
        ul.appendChild(frist);

        //隐藏显示 下一页上一页
        tbpromo.addEventListener('mouseenter', function () {
            prev.style.display = 'block';
            next.style.display = 'block';
            clearInterval(timer);
            timer=0;//清除定时器变量
        })
        tbpromo.addEventListener('mouseleave', function () {
            prev.style.display = 'none';
            next.style.display = 'none';
            timer=setInterval(function () {
            next.click();//手动调动点击事件
        },1500)

        })

        //next prev动画
        var num = 0;
        //控制圆圈
        var circle = 0;
        //节流阀变量
        var flag=true;

        //下一页
        next.addEventListener('click', function () {

                //最后一张进行判断 ul复原 left为0
            if (num == (ul.children.length - 1)) {
                ul.style.left = 0;
                num = 0;
            }

                num++;
                animate(ul, -num * tbpromWidth);
                circle++;
                if (circle == 3) {
                    circle = 0;
                }
                for (var i = 0; i < ol.children.length; i++) {
                    ol.children[i].className = '';
                }
                ol.children[circle].className = 'one';

        })
        //上一页
        prev.addEventListener('click', function () {

            if (num == 0) {
                num = ul.children.length-1;
                ul.style.left = -num*tbpromWidth+'px';

            }
            else {
                num--;
                animate(ul, -num * tbpromWidth);
                circle--;
                if (circle <0) {
                    circle = 2;
                }
                for (var i = 0; i < ol.children.length; i++) {
                    ol.children[i].className = '';
                }
                ol.children[circle].className = 'one';
            }
        })
        //自动播放
        var timer=setInterval(function () {
            next.click();//手动调动点击事件
        },2000)
    </script>
</body>

</html>

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