JS轮播图的实现方法

<div id="banner">
 <div class="w">
  <!--   左右箭头-->
  <span class="iconfont icon-zuojiantou" onclick="arrow_left()"></span>
  <span class="iconfont icon-youjiantou" onclick="arrow_right()"></span>
  <!--   轮播图-->
  <ul>
   <li><img src="img/1.jpg" alt=""></li>
   <li style="left: 1000px"><img src="img/2.jpg" alt="" ></li>
   <li style="left: 1000px"><img src="img/3.jpg" alt="" ></li>
  </ul>
  <!--  /小圆点-->
  <ol id="circleContainer">
   <li onclick="move(0)"></li>
   <li onclick="move(1)"></li>
   <li onclick="move(2)"></li>
  </ol>
 </div>
</div>

<style>
  {
   margin: 0;
   padding: 0;
   list-style: none;
  }
  .w {
   width: 1000px;
   height: 600px;
   margin: 100px auto 0;
   position: relative;
   overflow: hidden;
  }
  ul {
   height: 600px;
  }
  @keyframes leftCome {
   from {
    left: -100%;
   }
   to {
    left: 0;
   }
  }
  @keyframes leftOut {
   from {
    left: 0;
   }
   to {
    left: 100%;
   }
  }
  @keyframes rightCome {
   from {
    left: 100%;
   }
   to {
    left: 0;
   }
  }
  @keyframes rightOut {
   from {
    left: 0;
   }
   to {
    left: -100%;
   }
  }
  ul li {
   position: absolute;
   width: 1000px;
  }
  ul li img {
   width: 100%;
   height: 600px;
  }
  .iconfont {
   color: white;
   position: absolute;
   font-size: 30px;
   : calc(50% - 15px);
   background-color: rgba(216, 216, 216, 0.23);
   cursor: pointer;
   opacity: 0;
   transition: opacity .3s linear;
   z-index: 999;
  }
  .iconfont:hover {
   color: palegreen;
  }
  .icon-zuojiantou {
   left: 0;
   border--right-radius: 50%;
   border-bottom-right-radius: 50%;
  }
  .icon-youjiantou {
   right: 0;
   border--left-radius: 50%;
   border-bottom-left-radius: 50%;
  }
  #circleContainer {
   position: absolute;
   bottom: 10px;
   left: calc(50% - 30px);
  }
  #circleContainer li {
   display: inline-block;
   width: 20px;
   height: 20px;
   border-radius: 50%;
   background-color: white;
   margin-right: 5px;
  }
  #circleContainer .change {
   background-color: palegreen;
   box-shadow: 0 0 10px #7dd07d;
  }
</style>

<script>
  let timer ;
  window.onload = function(){
   timer = setInterval(function () {
    arrow_left();
   },3000)
  };
  let arrow = document.querySelectorAll(".iconfont");
  let w = document.querySelector(".w");
  let circle = document.querySelectorAll("ol li");
  w.addEventListener("mouseenter",function () {
   clearInterval(timer);
   arrow[0].style.opacity = "1";
   arrow[1].style.opacity = "1";
  });
  w.addEventListener("mouseleave",function () {
   arrow[0].style.opacity = "0";
   arrow[1].style.opacity = "0";
   timer = setInterval(function () {
    arrow_left();
   },3000)
  });
  circle[0].className = "change";
  let location_i = 0;
  let li = document.querySelectorAll("ul li");
  // 移动函数
  function move(i,direcTion_) {
    if (direcTion_ === "right") {
     if (location_i !== i) {
      li[i].style.animation = "rightCome .5s ease forwards";
      li[location_i].style.animation = "rightOut .5s ease forwards";
      location_i = i;
      num = i;
     }
    } else {
     if (location_i !== i) {
      li[i].style.animation = "leftCome .5s ease forwards";
      li[location_i].style.animation = "leftOut .5s ease forwards";
      location_i = i;
      num = i;
     }
    }
    for (let i = 0 ; i<circle.length ;i++){
     circle[i].className = "";
    }
    circle[location_i].className = "change";
  }
  // 右箭头
  let flag = true;
  let num = 0;
  function arrow_right() {
   flag = false ;
   num === 2 ? num = 0 : num = location_i + 1;
   move(num);
  }
  // 左箭头
  function arrow_left() {
   num === 0 ? num = 2 : num = location_i - 1;
   move(num,"right");
  }
</script>