JavaScript 弹出画廊优化：实现页面加载时默认显示首张大图

// ... 其他变量定义 ...
let index = 0;

images.forEach((item, i) => {
  item.addEventListener('click', () => {
    updateImage(i); // 更新大图内容
    popup.classList.toggle('active'); // 显示弹出层
  })
})

const updateImage = (i) => {
  let path = `img/img${i+1}.png`;
  largeImage.src = path;
  imageName.innerHTML = path;
  imageIndex.innerHTML = `0${i+1}`;
  index = i;
}
// ... 其他事件监听器 ...

const setPopupImage = index => {
  updateImage(index); // 更新大图内容
  popup.classList.toggle('active'); // 激活弹出层
}

images.forEach((item, i) => {
  item.addEventListener('click', () => setPopupImage(i));
})

// ... 其他代码 ...
setPopupImage(0); // 页面加载时默认显示第一张图片

const images = [...document.querySelectorAll('.image')];
const popup = document.querySelector('.popup');
const closeBtn = document.querySelector('.close-btn');
const imageName = document.querySelector('.image-name');
const largeImage = document.querySelector('.large-image');
const imageIndex = document.querySelector('.index');
const leftArrow = document.querySelector('.left-arrow');
const rightArrow = document.querySelector('.right-arrow');

let index = 0; // 当前显示图片的索引

// 为每个缩略图添加点击事件监听器
images.forEach((item, i) => {
  item.addEventListener('click', () => setPopupImage(i));
})

// 更新弹出层中大图内容的函数
const updateImage = (i) => {
  let path = `img/img${i+1}.png`; // 假设图片路径为 img/img1.png, img/img2.png...
  largeImage.src = path;
  imageName.innerHTML = path;
  imageIndex.innerHTML = `0${i+1}`;
  index = i; // 更新当前索引
}

// 封装设置弹出图片和激活弹出层的逻辑
const setPopupImage = index => {
  updateImage(index); // 更新图片内容
  popup.classList.add('active'); // 激活弹出层，确保其显示
}

// 关闭按钮事件监听器
closeBtn.addEventListener('click', () => {
  popup.classList.remove('active'); // 隐藏弹出层
})

// 左箭头（上一张）事件监听器
leftArrow.addEventListener('click', () => {
  if (index > 0) {
    updateImage(index - 1);
  }
})

// 右箭头（下一张）事件监听器
rightArrow.addEventListener('click', () => {
  if (index < images.length - 1) {
    updateImage(index + 1);
  }
})

// 页面加载时，默认显示第一张图片
// 注意：这里使用 add 而不是 toggle，因为我们希望确保它在加载时是激活状态
setPopupImage(0); 

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

*:focus {
  outline: none;
}

body {
  width: 100%;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #ff7a2d;
  font-family: 'roboto', sans-serif;
}

.gallery {
  width: 80%;
  height: 90vh;
  max-width: 1600px;
  max-height: 800px;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
}

.gallery-image {
  width: 30%;
  height: calc(50% - 20px);
  min-width: 300px;
  min-height: 200px;
  margin: 10px;
  overflow: hidden;
}

.image {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: 1s;
}

.popup {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) scale(0); /* 初始隐藏并缩小 */
  width: 80%;
  max-width: 1600px;
  height: 90vh;
  max-height: 800px;
  border-radius: 20px;
  background: rgba(0, 0, 0, 0.75);
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: 5;
  overflow: hidden;
  transition: 1s;
  opacity: 0;
}

.popup.active {
  transform: translate(-50%, -50%) scale(1); /* 激活时放大显示 */
  opacity: 1;
}

.popup.active .close-btn,
.popup.active .image-name,
.popup.active .index,
.popup.active .large-image,
.popup.active .arrow-btn {
  opacity: 1;
  transition: opacity .5s;
  transition-delay: 1s; /* 延迟显示内部元素 */
}

.top-bar {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 50px;
  background: #000;
  color: #fff;
  text-align: center;
  line-height: 50px;
  font-weight: 300;
}

.image-name {
  opacity: 0;
}

.close-btn {
  opacity: 0;
  position: absolute;
  top: 15px;
  right: 20px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #f00;
  cursor: pointer;
}

.arrow-btn {
  opacity: 0;
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  padding: 10px;
  border-radius: 50%;
  border: none;
  background: none;
  cursor: pointer;
}

.left-arrow {
  left: 10px;
}

.right-arrow {
  right: 10px;
  transform: translateY(-50%) rotate(180deg);
}

.arrow-btn:hover {
  background: rgba(0, 0, 0, 0.5);
}

.index {
  position: absolute;
  bottom: 10px;
  right: 10px;
  font-size: 80px;
  font-weight: 100;
  color: rgba(255, 255, 255, 0.4);
  opacity: 0;
}

.large-image {
  margin-top: 5%;
  width: 80%;
  height: 80%;
  object-fit: contain;
  opacity: 0;
}

<div class="popup">
  <div class="top-bar">
    <p class="image-name">img1.png</p>
    <span class="close-btn"></span>
  </div>
  <button class="arrow-btn left-arrow"><img src="img/arrow.png" alt=""></button>
  <button class="arrow-btn right-arrow"><img src="img/arrow.png" alt=""></button>
  <img src="img/img1.png" class="large-image" alt="">
  <h1 class="index">01</h1>
</div>
<div class="gallery">
  <div class="gallery-image">
    <img src="img/img1.png" alt="" class="image">
  </div>
  <div class="gallery-image">
    <img src="img/img2.png" alt="" class="image">
  </div>
  <div class="gallery-image">
    <img src="img/img3.png" alt="" class="image">
  </div>
  <div class="gallery-image">
    <img src="img/img4.png" alt="" class="image">
  </div>
  <div class="gallery-image">
    <img src="img/img5.png" alt="" class="image">
  </div>
  <div class="gallery-image">
    <img src="img/img6.png" alt="" class="image">
  </div>
</div>