图片懒加载

//日后施工
    // 图片懒加载
    const imgs = document.querySelectorAll('img')
    
    const callback = entries => {
      entries.forEach(entry => {
        if(entry.isIntersecting) {
          const image = entry.target
          const data_src = image.getAttribute('data-src')
          image.setAttribute('src', data_src)
          observer.unobserve( image )
          console.log('触发');
        }
      })
    }

    const observer = new IntersectionObserver(callback)
    
    imgs.forEach((img)=>{
      observer.observe(img)
    })