原生JS实现轮播图

[Miracle]

轮播图是在前端交互中运用的非常多的一个功能，基本上所有的网站都会有类似的需求，而轮播图的实现方式也是有许许多多的，在这里我写一个我认为比较简单，而且效率比较高的轮播图功能。

实现原理

使用绝对定位，将图片分为四类，分别为前面，后面，左边，右边，四种类型的图片组成了一个环，每次图片循环时，改变对应图片的class，并在class中用css 加上过渡动画，实现一个循环播放的效果

在线demo

具体的实现代码

// html
<div class="music-carousal"></div>

// css
.music-carousal {
  height: 250px;
  position: relative;
	margin-top:30px;
}

.banner-list {
  position: absolute;
  width: 460px;
  height: 250px;
  left: 50%;
  margin-left: -230px;
  z-index: 3;
}

.banner-list .banner-item {
  position: absolute;
  width: 100%;
  height: 100%;
  transition: all 0.5s ease;
}

.banner-list .banner-item-out {
  transform: rotateY(0) translateX(0) translateZ(0) scale(.7);
  opacity: 0;
  z-index: -1;
}

.banner-list .banner-item-current {
  transform: rotateY(0) translateX(0) translateZ(0);
  z-index: 5;
}

.banner-list .banner-item-prev {
  z-index: 3;
  transform: rotateY(30deg) translate3d(-140px, -15px, -200px) scale(.7);
  opacity: 0.7;
}

.banner-list .banner-item-next {
  z-index: 3;
  transform: rotateY(-30deg) translate3d(140px, -15px, -200px) scale(.7);
  opacity: 0.7;
}

.banner-list .banner-item img {
  width: 100%;
  box-shadow: 0 8px 10px 0 rgba(88, 10, 0, 0.2);
  border-radius: 3px;
}

.pagination-box {
  position: absolute;
  bottom: 50px;
  left: 50%;
  transform: translateX(-50%);
  z-index: 5;
}

.pagination-box .pagination-item {
  width: 8px;
  height: 8px;
  background: #E2E2E3;
  border-radius: 50%;
  display: inline-block;
  margin: 0 3px;
}

.pagination-box .pagination-item.active {
  background: #D71417;
}

// javascript
let currentIndex = 1; // 当前是在第几个
  let timer;

  const carousal = {
    init: function (object) {
      const { el, banners, interval } = object;

      // banner至少为3个
      const length = banners.length;
      if (length === 1) {
        banners.push(banners[0]);
        banners.push(banners[0])
      }
      if (length === 2) {
        banners.push(banners[0]);
      }
      this._render(el, banners);
      timer = setInterval(this._next.bind(this), interval);
      this.listenPaginationTouch.apply(this);
    },

    _render: function (el, banners) {
      const imgUl = document.createElement('div');
      imgUl.className = 'banner-list';
      let imgUlInnerHTML = '';

      const paginationBox = document.createElement('div');
      paginationBox.className = 'pagination-box';
      let paginationBoxInnerHTML = '';

      banners.forEach((item, index) => {
        imgUlInnerHTML += `<div class="banner-item ${index === 0 ? 'banner-item-prev' : ''} ${index === 1 ? 'banner-item-current' : ''} ${index === 2 ? 'banner-item-next' : ''} ${index > 2 ? 'banner-item-out' : ''}"><img src="${item.imageUrl}"></div>`;

        paginationBoxInnerHTML += `<div class="pagination-item index-${index} ${index === currentIndex ? 'active' : ''}"></div>`
      });
      imgUl.innerHTML = imgUlInnerHTML;
      paginationBox.innerHTML = paginationBoxInnerHTML;
      el.appendChild(imgUl);
      el.appendChild(paginationBox);
    },

    // 右边的那个图片变成当前的大图
    _next: function () {
      let bannerList = document.querySelectorAll('.banner-item');
      let length = bannerList.length;
      currentIndex = (currentIndex + 1) % length;
      this._changeNextOrder(currentIndex);
      this._renderPagination(currentIndex);
    },

    // 向右交换顺序
    _changeNextOrder: function (_currentIndex) {
      let bannerList = document.querySelectorAll('.banner-item');
      let length = bannerList.length;

      bannerList.forEach((item, index) => {
        if (index === _currentIndex) {
          item.className = 'banner-item banner-item-current'
        } else if (index === ((_currentIndex - 1 + length) % length)) {
          item.className = 'banner-item banner-item-prev'
        } else if (index === ((_currentIndex + 1) % length)) {
          item.className = 'banner-item banner-item-next'
        } else {
          item.className = 'banner-item banner-item-out'
        }
      })
    },

    _renderPagination: function (_currentIndex) {
      let paginationList = document.querySelectorAll('.pagination-item');
      paginationList.forEach((item, index) => {
        if (index === _currentIndex) {
          item.classList.add('active');
        } else {
          item.classList.remove('active');
        }
      })
    },

    // 监听小圆点按钮点击
    listenPaginationTouch: function () {
      let paginationBox = document.querySelector('.pagination-box');
      paginationBox.addEventListener('click', (event) => {
        const target = event.target;
        if (target.classList.contains('pagination-item')) {
          try {
            let className = target.classList[1];
            let index = Number(className.split('-')[1]);
            this._changeNextOrder(index);
            this._renderPagination(index);
            currentIndex = index;
            clearInterval(timer);
            timer = setInterval(this._next.bind(this), 5000);
          } catch (error) {
            throw new Error(error);
          }
        }
      })
    }
  }
	
const carousalDom = document.querySelector('.music-carousal');
const banners = [
	{
		imageUrl: "http://p1.music.126.net/nHJXJZVMsSpi3v1ee8B8XA==/109951163797188493.jpg"
	},
	{
		imageUrl: "http://p1.music.126.net/iCrkUC8x7ViQwLULtgqkqw==/109951163797194143.jpg"
	},
	{
		imageUrl: "http://p1.music.126.net/2Jih8vXjnTeIzxtPU-gQiw==/109951163797164224.jpg"
	},
	{
		imageUrl: "http://p1.music.126.net/c1OhLIjnd9zB8NBUc3Olqg==/109951163797172654.jpg"
	},
	{
		imageUrl: "http://p1.music.126.net/SWjJnQTGa6vhBOzKrkR6wA==/109951163797179161.jpg"
	},
	{
		imageUrl: "http://p1.music.126.net/Wa9ENrBphVjH46A6Kt8yiA==/109951163797159700.jpg"
	}
]
carousal.init({
	el: carousalDom,
  banners,
  interval: 5000
});

[xiaobo]

牛逼，看这段尽然看懂了，bind和apply的作用，以及二者的微妙差别