bedrock/web/app/themes/badegg/resources/js/lib/Lazy.js

export default function LazyLoadInit()
{
  document.addEventListener('DOMContentLoaded', LazyLoad());
}

function LazyLoad() {

  var lazyImages = [].slice.call(document.querySelectorAll('img.lazy'));

  if ('IntersectionObserver' in window) {
    let lazyImageObserver = new IntersectionObserver(function(entries, observer) {
      entries.forEach(function(entry) {
        if (entry.isIntersecting) {
          let lazyImage = entry.target;
          lazyImage.src = lazyImage.dataset.src;

          if(lazyImage.dataset.srcset) {
            lazyImage.srcset = lazyImage.dataset.srcset;
          }

          lazyImage.classList.remove('lazy');
          lazyImageObserver.unobserve(lazyImage);
        }
      });
    });

    lazyImages.forEach(function(lazyImage) {
      lazyImageObserver.observe(lazyImage);
    });
  } else {
    // Possibly fall back to a more compatible method here
  }
}