banner左右切换js代码

<div id="banner">
  <div class="banner-item">图片 1</div>
  <div class="banner-item">图片 2</div>
  <div class="banner-item">图片 3</div>
</div>
<button id="prevBtn">上一张</button>
<button id="nextBtn">下一张</button>

#banner {
  width: 500px;
  height: 300px;
  overflow: hidden;
  position: relative;
}

.banner-item {
  width: 100%;
  height: 100%;
  position: absolute;
  opacity: 0;
  transition: opacity 0.5s;
}

.banner-item:first-child {
  opacity: 1;
}

const bannerItems = document.querySelectorAll('.banner-item');
let currentIndex = 0;

function showItem(index) {
  bannerItems.forEach((item, i) => {
    item.style.opacity = i === index ? 1 : 0;
  });
}

document.getElementById('prevBtn').addEventListener('click', () => {
  currentIndex = (currentIndex - 1 + bannerItems.length) % bannerItems.length;
  showItem(currentIndex);
});

document.getElementById('nextBtn').addEventListener('click', () => {
  currentIndex = (currentIndex + 1) % bannerItems.length;
  showItem(currentIndex);
});