利用JS制作无缝轮播图的过程和思路是什么-群英

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上效果

一、实现过程

1）首先实现基本布局

 <div class="carousel-container">
    //图片列表
    <div class="carousel-list"></div>
    //上一张
    <div class="carousel-arrow carousel-arrow-left">&lt</div>
    //下一张
    <div class="carousel-arrow carousel-arrow-right">&gt</div>
    //导航点
    <div class="indicator">
      <span class="active"></span>
      <span></span>
      <span></span>
    </div>
  </div>

2）主要样式

简单布局样式就不说了，主要讲如何将图片横向排列起来

先给容器设置相对定位，通过overflow将超出部分隐藏

.carousel-container {
      position: relative;
      width: 500px;
      height: 300px;
      /* overflow: hidden; */
      background-color: #ccc;
 }

然后图片列表设置相对定位和flex盒子，这样每一个滑块就横向排列成一排了

.carousel-container .carousel-list {
      position: relative;
      display: flex;
      height: 100%;
      width: 100%;
 }

左右滑动按钮通过绝对定位+transform的方式移动到两边，导航点也是一样，就不一一详说了

二、如何实现无缝呢（重点来了）

思路：

1、先实现向后滚动无缝连接，将最后一张复制一份放到最前面，当滚动到最后一张时，再次滚动，将要滚动到第一张时，先取消过渡transition，瞬间跳到最前面复制的那张上，然后继续运行动画到第一张，这样看起来就无缝了

2、向前滚动无缝连接，思路同上，复制第一张图片放到最后，当滚动到第一张，再次滚动时，瞬间跳到最后复制的那张图片上，继续滚动到轮播图的最后一张上。

主要代码

先获取到dom元素，currentIndex是当前轮播到的图片下标

let currentIndex = 0;
const doms = {
      carouselList: document.querySelector('.carousel-list'),
      arrowLeft: document.querySelector('.carousel-arrow-left'),
      arrowRight: document.querySelector('.carousel-arrow-right'),
      indicator: document.querySelectorAll('.indicator span')
    }

先初始化dom，复制图片

// 复制第一张放最后，最后一张图片放第一张之前
    function init() {
      let lastImg = doms.carouselList.lastElementChild.cloneNode(true)
      let firstImg = doms.carouselList.firstElementChild.cloneNode(true)

      doms.carouselList.appendChild(firstImg)
      doms.carouselList.insertBefore(lastImg, doms.carouselList.firstElementChild)
      lastImg.style.position = 'absolute'
      lastImg.style.transform = 'translateX(-100%)'
    }
    //执行一下
    init()

实现到任意一张图片的方法

function moveTo(index) {
      doms.carouselList.style.transform = `translateX(-${index * 100}%)`
      doms.carouselList.style.transition = '.5s'

      // 去掉导航点选中效果
      let active = document.querySelector('.indicator span.active')
      active.classList.remove('active')
      // 添加选中效果
      doms.indicator[index].classList.add('active')
      currentIndex = index
    }

给导航点绑定点击跳转事件

// 给导航点添加事件
    doms.indicator.forEach((item, i) => {
      item.onclick = function () {
        moveTo(i);
      }
    })

给前后按钮绑上执行事件,判断边界图片，及时取消过渡效果，瞬间跳到复制的图片位置，调用moveTo到第一张或最后一张图片上。

let indicatorLength = doms.indicator.length;
    function preSlide() {
      if (currentIndex === 0) {
        doms.carouselList.style.transition = 'none'
        doms.carouselList.style.transform = `translateX(-${indicatorLength * 100}%)`
        doms.carouselList.clientHeight
        moveTo(indicatorLength - 1)
      } else {
        moveTo(currentIndex - 1)
      }
    }
    function nextSlide() {
      if (currentIndex === doms.indicator.length - 1) {
        doms.carouselList.style.transition = 'none'
        doms.carouselList.style.transform = 'translateX(100%)'
        doms.carouselList.clientHeight
        moveTo(0)
      } else {
        moveTo(currentIndex + 1)
      }
    }

    doms.arrowLeft.onclick = function () {
      preSlide();
    }

    doms.arrowRight.onclick = function () {
      nextSlide()
    }

最后使用定时器调用nertSlide方法就实现自动播放了

function start(time = 2000) {
      setInterval(() => {
        nextSlide()
      }, time)
    }
    start()

完整代码

<!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>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    .carousel-container {
      margin: 0 auto;
      position: relative;
      width: 500px;
      height: 300px;
      /* overflow: hidden; */
      background-color: #ccc;
    }

    .carousel-container .carousel-list {
      position: relative;
      display: flex;
      height: 100%;
      width: 100%;
    }

    .carousel-container .carousel-list .slide {
      flex: 0 0 100%;
      height: 100%;
      width: 100%;
    }

    .slide a {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100%;
      width: 100%;
    }

    .slide a img {
      width: 100%;
    }

    .carousel-container .carousel-arrow {
      display: none;
      position: absolute;
      width: 36px;
      height: 36px;
      border-radius: 50%;
      color: white;
      text-align: center;
      line-height: 36px;
      cursor: pointer;

      background-color: rgba(31, 45, 61, .2);
    }

    .carousel-container:hover .carousel-arrow {
      display: block;
    }

    .carousel-container:hover .carousel-arrow:hover {
      background-color: rgba(31, 45, 61, .4);
    }

    .carousel-container .carousel-arrow-left {
      top: 50%;
      left: 2%;
      transform: translateY(-50%);
    }

    .carousel-container .carousel-arrow-right {
      top: 50%;
      right: 2%;
      transform: translateY(-50%);
    }

    .carousel-container .indicator {
      display: flex;
      position: absolute;
      left: 50%;
      top: 90%;
      transform: translateX(-50%)
    }

    .carousel-container .indicator span {
      margin: 2px 5px;
      padding: 3px;
      width: 5px;
      height: 5px;
      border: 1px solid white;
      border-radius: 5px;
    }

    .active {
      background-color: #fff;
    }
  </style>
</head>


<body>
  <div class="carousel-container">
    <div class="carousel-list">
      <div class="slide">
        <a href="">
          <img
            src="https://ts4.cn.mm.bing.net/th?id=OIP-C.kB-Ovasi0GW67-rmwnAcwAHaEo&w=316&h=197&c=8&rs=1&qlt=90&o=6&dpr=1.25&pid=3.1&rm=2">
        </a>
      </div>
      <div class="slide">
        <a href="">
          <img
            src="https://ts1.cn.mm.bing.net/th?id=OIP-C.QPH1IBosDYBqaU3O6wV3YAHaEo&w=316&h=197&c=8&rs=1&qlt=90&o=6&dpr=1.25&pid=3.1&rm=2"></a>
      </div>
      <div class="slide">
        <a href="">
          <img
            src="https://ts2.cn.mm.bing.net/th?id=OIP-C.P3NSGTdAYdyqy5zJpb5QXQHaEo&w=316&h=197&c=8&rs=1&qlt=90&o=6&dpr=1.25&pid=3.1&rm=2"
            alt=""></a>
      </div>
    </div>
    <div class="carousel-arrow carousel-arrow-left">&lt</div>
    <div class="carousel-arrow carousel-arrow-right">&gt</div>
    <div class="indicator">
      <span class="active"></span>
      <span></span>
      <span></span>
    </div>
  </div>
</body>

<script>
  window.onload = function () {
    const doms = {
      carouselList: document.querySelector('.carousel-list'),
      arrowLeft: document.querySelector('.carousel-arrow-left'),
      arrowRight: document.querySelector('.carousel-arrow-right'),
      indicator: document.querySelectorAll('.indicator span')
    }
    let currentIndex = 0;

    function moveTo(index) {
      doms.carouselList.style.transform = `translateX(-${index * 100}%)`
      doms.carouselList.style.transition = '.5s'

      // 去掉导航点选中效果
      let active = document.querySelector('.indicator span.active')
      active.classList.remove('active')
      // 添加选中效果
      doms.indicator[index].classList.add('active')
      currentIndex = index
    }

    // 给导航点添加事件
    doms.indicator.forEach((item, i) => {
      item.onclick = function () {
        moveTo(i);
      }
    })
    // 复制第一张放最后，最后一张图片放第一张之前
    function init() {
      let lastImg = doms.carouselList.lastElementChild.cloneNode(true)
      let firstImg = doms.carouselList.firstElementChild.cloneNode(true)

      doms.carouselList.appendChild(firstImg)
      doms.carouselList.insertBefore(lastImg, doms.carouselList.firstElementChild)
      lastImg.style.position = 'absolute'
      lastImg.style.transform = 'translateX(-100%)'
    }

    let indicatorLength = doms.indicator.length;
    function preSlide() {
      if (currentIndex === 0) {
        doms.carouselList.style.transition = 'none'
        doms.carouselList.style.transform = `translateX(-${indicatorLength * 100}%)`
        doms.carouselList.clientHeight
        moveTo(indicatorLength - 1)
      } else {
        moveTo(currentIndex - 1)
      }
    }
    function nextSlide() {
      if (currentIndex === doms.indicator.length - 1) {
        doms.carouselList.style.transition = 'none'
        doms.carouselList.style.transform = 'translateX(100%)'
        doms.carouselList.clientHeight
        moveTo(0)
      } else {
        moveTo(currentIndex + 1)
      }
    }

    doms.arrowLeft.onclick = function () {
      preSlide();
    }

    doms.arrowRight.onclick = function () {
      nextSlide()
    }

    function start(time = 2000) {
      setInterval(() => {
        nextSlide()
      }, time)
    }
    start()
    init()

  }
</script>

</html>

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