js原生写一个小小轮播案例

先上示例：

在这里插入图片描述

附上代码

html

<!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">
  <link rel="stylesheet" href="css/index.css">
  <script src="js/index.js"></script>
  <title>轮播图</title>
</head>

<body>
  <div class="container">
    <!-- 左侧按钮 -->
    <a href="#" class="arrow-l">&lt;</a>
    <!-- 右侧按钮 -->
    <a href="#" class="arrow-r">&gt;</a>
    <ul class="foucs">
      <li><a href="#"><img src="images/2.jpg" alt=""></a></li>
      <li><a href="#"><img src="images/3.jpg" alt=""></a></li>
      <li><a href="#"><img src="images/4.jpg" alt=""></a></li>
      <li><a href="#"><img src="images/6.jpg" alt=""></a></li>
    </ul>
    <ol class="circle">
    </ol>
  </div>

</body>

</html>

document.addEventListener("DOMContentLoaded", carousel);

function carousel() {
  var container = document.querySelector(".container"),
    ul = document.getElementsByTagName('ul')[0],
    ol = document.getElementsByTagName('ol')[0],
    la = document.querySelector(".arrow-l"),
    ra = document.querySelector(".arrow-r"),
    len = ul.children.length,
    num = 0,
    flag = true,
    foucsWidth = container.offsetWidth;

  // 1.左右按钮显示隐藏
  container.addEventListener("mouseenter", lrblock);
  la.addEventListener("mouseenter", laenter);
  ra.addEventListener("mouseenter", laenter);
  container.addEventListener("mouseleave", lrnone);
  la.addEventListener("mouseleave", laleave);
  ra.addEventListener("mouseleave", laleave);
  function lrblock() {
    la.style.display = "block";
    ra.style.display = "block";
    clearInterval(autoPlay)
  }
  function lrnone() {
    la.style.display = "none";
    ra.style.display = "none";
    autoPlay = setInterval(function () {
      // 手动调用点击事件
      ra.click();
    }, 2000)
  }
  function laenter() {
    this.style.color = "red";
  }
  function laleave() {
    this.style.color = "#fff";
  }
  // 2.动态生成小圆点
  for (var i = 0; i < len; i++) {
    var li = document.createElement('li');
    li.setAttribute('index', i);
    ol.appendChild(li);
    ol.children[0].className = 'current';
    li.addEventListener('click', function () {
      for (var i = 0; i < ol.children.length; i++) {
        ol.children[i].className = ''
      }
      this.className = 'current';
      //3. 点击小圆点，移动图片 ul移动
      var index = this.getAttribute('index');
      num = index;
      animate(ul, -index * foucsWidth);
    })
  };
  // 4. 点击右侧按钮控制图片
  ra.addEventListener('click', function () {
    if (flag) {
      flag = false;
      num++;
      if (num === len) {
        ul.style.left = 0;
        num = 0;
      }
      animate(ul, - num * foucsWidth, function () {
        flag = true
      });
      // 5. 小圆点和图片对应
      for (var i = 0; i < len; i++) {
        ol.children[i].className = '';
      }
      ol.children[num].className = 'current';
    }
  })
  // 5. 点击左侧按钮控制图片
  la.addEventListener('click', function () {
    if (flag) {
      flag = false;
      num--;
      if (num < 0) {
        ul.style.left = (len - 1) * foucsWidth;
        num = len - 1;
      }
      animate(ul, - num * foucsWidth, function () {
        flag = true
      });
      // 5. 小圆点和图片对应
      for (var i = 0; i < len; i++) {
        ol.children[i].className = '';
      }
      ol.children[num].className = 'current';
    }

  })
  //  6. 自动播放
  var autoPlay = setInterval(function () {
    // 手动调用点击事件
    ra.click();
  }, 2000)
  // 动画函数
  function animate(obj, target, callback) {
    var timer = setInterval(function () {
      var step = (target - obj.offsetLeft) / 10;
      step = step > 0 ? Math.ceil(step) : Math.floor(step)
      if (obj.offsetLeft === target) {
        clearInterval(timer);
        callback && callback()
      }
      obj.style.left = obj.offsetLeft + step + 'px';
    }, 10)
  }
}

* {
  margin: 0;
  padding: 0;
  list-style: none;
}
a {
  text-decoration: none;
}
.container {
  width: 800px;
  height: 400px;
  position: relative;
  left: 50px;
  top: 50px;
  overflow: hidden;
  background-color: brown;
  color: #fff;
  font-size: 20px;
}
.arrow-l,
.arrow-r {
  width: 60px;
  height: 50px;
  display: none;
  border-radius: 25px;
  position: absolute;
  top: calc(50% - 50px);
  z-index: 2;
  background-color: rgb(125, 148, 168, 0.5);
  text-align: center;
  line-height: 50px;
  color: #fff;
  font-size: 30px;
  font-weight: bold;
}
.arrow-l {
  left: -20px;
}
.arrow-r {
  right: -20px;
}
ul.foucs {
  width: 10000px;
  height: 100%;
  position: absolute;
  left: 0;
  top: 0;
}
ul.foucs li {
  float: left;
}
ul.foucs li,
ul.foucs li img {
  width: 800px;
  height: 100%;
}
ol.circle {
  height: 30px;
  position: absolute;
  bottom: 0px;
  left: 40%;
  z-index: 2;
}
ol.circle li {
  width: 20px;
  height: 20px;
  border-radius: 10px;
  float: left;
  margin: 0 5px;
  background-color: #fff;
}
ol.circle li.current {
  background-color: blue;
}