图片懒加载

图片懒加载

// <img src="default.png" data-src="https://xxxx/real.png">
function isVisible(el) {
  const position = el.getBoundingClientRect()
  const windowHeight = document.documentElement.clientHeight
  // 顶部边缘可见
  const topVisible = position.top > 0 && position.top < windowHeight;
  // 底部边缘可见
  const bottomVisible = position.bottom < windowHeight && position.bottom > 0;
  return topVisible || bottomVisible;
}

function imageLazyLoad() {
  const images = document.querySelectorAll('img')
  for (let img of images) {
    const realSrc = img.dataset.src
    if (!realSrc) continue
    if (isVisible(img)) {
      img.src = realSrc
      img.dataset.src = ''
    }
  }
}

// 测试
window.addEventListener('load', imageLazyLoad)
window.addEventListener('scroll', imageLazyLoad)
// or
window.addEventListener('scroll', throttle(imageLazyLoad, 1000))