Share the code for implementing carousel effects using native js

This article mainly introduces the native js carousel effects in detail, simple and practical code, which has certain reference value. Interested friends can refer to it

As a front-end engineer, handwriting carousels should be the most basic skill to master. The following is a carousel written by me in native js. Comments and criticisms are welcome:

First css Code

a{text-decoration:none;color:#3DBBF5;}
   *{
    margin: 0;
    padding: 0;
   }
   .wrapper{
    width: 400px;
    height: 300px;
    margin: 100px auto;
   }
   #lunbo{
    position: relative;
    overflow: hidden;
   }
   #list{
    position: relative;
    white-space: nowrap; // 这块用行元素模拟，所以才用该属性，块元素可修改这块
   }
   #list span{
    display: inline-block;
    width: 400px;
    height: 300px;
    text-align: center;
    line-height: 300px;
    font-weight: bold;
    font-size: 100px;
    color: #fff;
   }
   #buttons{
    position: absolute;
    bottom: 0;
    text-align: center;
    width: 100%;
    height: 40px;
    line-height: 40px;
   }
   #buttons span{
    display: inline-block;
    width: 15px;
    height: 5px;
    background: #fff;
    margin: 0 10px;
    cursor: pointer;
    transition: all .5s;
   }
   #buttons span.on{
    height: 20px;
   }
   .arrow{
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    font-size: 80px;
    font-weight: bold;
    color: #fff;
    opacity: .3;
    transition: all .5s;
   }
   .wrapper:hover .arrow{
    opacity: 1;
   }
   #prev{
    left: 10px;
   }
   #next{
    right: 10px;
   }

Then HTML code

<p class="wrapper">
   <p id="lunbo">
    <p id="list" style="left: -400px;">
     <span style="background:yellow;">5</span><span style="background: red;">1</span><span style="background:black;">2</span><span style="background:green;">3</span><span style="background:blue;">4</span><span style="background:yellow;">5</span><span style="background: red;">1</span>
    </p>
    <p id="buttons">
     <span index="1" class="on"></span>
     <span index="2"></span>
     <span index="3"></span>
     <span index="4"></span>
     <span index="5"></span>
    </p>
    <a href="javascript:;" id="prev" class="arrow"><</a>
    <a href="javascript:;" id="next" class="arrow">></a>
   </p>
  </p>

Finally js code

window.onload=function () {
   var lunBo = document.getElementById("lunbo");
   var list = document.getElementById("list");
   var btn = document.getElementById("buttons").getElementsByTagName('span');
   var prev = document.getElementById("prev");
   var next = document.getElementById('next');
   var interval = 3000;
   var timer;
   var index = 1;
   var animated = false;
   for (var i=0;i<btn.length;i++) { //按钮加点击事件
    btn[i].onclick=function () {
     if(this.className==&#39;on&#39;) //如果是状态按钮直接返回节约资源
     {
      return
     };
     var myIndex =parseInt(this.getAttribute(&#39;index&#39;));//获取按钮的index属性值
     var offset = -400*(myIndex-index); //根据属性值 计算偏移量
     animate(offset)  //轮播动画
     index = myIndex; // 改变索引值
     showBtn();   //显示状态按钮
    }
   }
   function showBtn () { 
    for (var i=0;i<btn.length;i++) {
     btn[i].className=&#39;&#39;; 
    }
    btn[index-1].className=&#39;on&#39;;
   }
   prev.onclick=function () { //上一页事件
    if (animated) { //如果是动画状态 直接返回解决bug
     return;
    }
    if (index==1) { 
     index =btn.length;
    } else{
     index-=1;
    }
    animate(400); 
    showBtn();
   }
   next.onclick=function () {
    if (animated) {
     return;
    }
    if (index==btn.length) {
     index =1;
    } else{
     index+=1;
    }
    animate(-400);
    showBtn();
   }
   function animate(offset) {
    animated = true; //表示在动画状态
    var newLeft = parseInt(list.style.left) + offset; //计算新的left值
    var time = 400; //设置动画总时间
    var interval = 10; //动画帧时间
    var speed = offset/(time/interval); //每帧运动距离
    function go () { 
     if ((speed>0 && parseInt(list.style.left)<newLeft) || (speed<0 && parseInt(list.style.left)>newLeft)) { //通过条件判断到它是否还要继续进行动画
      list.style.left = parseInt(list.style.left) + speed +&#39;px&#39;;
      setTimeout(go,interval) 
     } else{
      animated = false; //动画状态结束
      list.style.left = newLeft + &#39;px&#39;; //现在的位移
      if (parseInt(list.style.left)<-2000) { // 辅助假图
       list.style.left = -400 + &#39;px&#39;;
      } else if( parseInt(list.style.left)>-400){
       list.style.left = -2000 + &#39;px&#39;;
      }
     }
    }
    go();
   }
   function play () { 
    timer = setTimeout(function () {
     next.onclick();
     play();
    },interval)
   }
   play();
   function stop () {
    clearTimeout(timer);
   }
   lunBo.onmouseover=stop;
   lunBo.onmouseout=play;
  }

The above is all the code, welcome to give advice and exchange!

【Related recommendations】

1. Free js online video tutorial

2. JavaScript Chinese Reference Manual

3. php.cn Dugu Jiujian (3) - JavaScript video tutorial

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