实现js轮播图

html样式

<div class='box'>
  <ul id="imgul">                      //把图片按顺序放入盒子
    <li><img src="./imgs/1.jpg" alt=""></li>
    <li><img src="./imgs/2.jpg" alt=""></li>
    <li><img src="./imgs/3.jpg" alt=""></li>
    <li><img src="./imgs/4.jpg" alt=""></li>
    <li><img src="./imgs/5.jpg" alt=""></li>
  </ul>
  <span id="left">
    < </span> <span id="right"> >                 //左右俩边的小按钮
  </span>    
  <ol>                                            //小按钮
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
  </ol>
</div>

css样式

* {
  margin: 0;
  padding: 0;
  list-style: none;
}   //清除默认y样式

.box {
  position: relative;
  width: 600px;
  height: 370px;
  margin: 50px auto;
  overflow: hidden;
}     //给盒子宽高，然后给图片溢出隐藏

.box #imgul {
  width: 600px;
  height: 370px;
}

.box #imgul li {
  width: 600px;
  height: 370px;
}

.box #imgul li img {
  width: 600px;
  height: 370px;
  display: block;
  float: left;
}

.box span {
  position: absolute;
  top: 50%;
  margin-top: -30px;
  width: 30px;
  height: 60px;
  background-color: rgba(0, 0, 0, 0.6);
  color: #fff;
  font-size: 40px;
}

.box #left {
  left: 0px;
}

.box #right {
  right: 0px;
}

.box ol {
  position: absolute;
  bottom: 20px;
  left: 30px;
}

.box ol li {
  width: 20px;
  height: 20px;
  background: yellow;
  font-size: 15px;
  line-height: 20px;
  float: left;
  margin: 0px 3px;
  text-align: center;
}

.box ol .active {
  background: #fff;
  color: red;
}

js样式

 function $(names) {
      return document.getElementById(names);
    }
    var left = $('left'); //左按钮
    var right = $('right'); //右按钮
    var box = document.getElementsByClassName('box')[0];
    var li_list = document.querySelectorAll('#imgul li'); //获取图片的li
    var ol_list = document.querySelectorAll('ol li');
    var timer = null; //声明定时器
    var count = 0;

    function auto() { //执行自动轮播
      count++;
      if (count > li_list.length - 1) {
        count = 0;
      }
      for (var i = 0; i < li_list.length; i++) {
        li_list[i].style = 'display:none;';
        ol_list[i].className = '';
      }
      li_list[count].style = 'display:block;'
      ol_list[count].className = 'active';

    }
    timer = setInterval(auto, 500); //调用定时器

    // 点击右侧，切换下一个
    right.onclick = function () {
      auto();
    }
    // 点击左侧，切换上一个
    left.onclick = function () {
      count--;
      if (count < 0) {
        count = li_list.length - 1;
      }
      console.log(count);
      for (var i = 0; i < li_list.length; i++) {
        li_list[i].style = 'display:none;';
        ol_list[count].className = '';
      }
      li_list[count].style = 'display:block;';
      ol_list[count].className = 'active';
    }

    box.onmouseover = function () { //鼠标划上去，停止轮播
      clearInterval(timer);
    }
    box.onmouseout = function () { //鼠标划出，继续轮播
      timer = setInterval(auto, 500); //调用定时器
    }


    //点击小按钮，切换图片
    for (var j = 0; j < ol_list.length; j++) {
      ol_list[j].ind = j; //为每个小按钮添加下标
      ol_list[j].onclick = function () { //进入点击事件
        for (var i = 0; i < li_list.length; i++) { //干掉所有人
          li_list[i].style = 'display:none;';
          ol_list[i].className = '';
        }
        li_list[this.ind].style = 'display:block;'; //留下我自己
        ol_list[this.ind].className = 'active'; //留下我自己
        count = this.ind; // 把当前的角标值赋值给count 希望他从当前再开始
      }
    }