simple slim lazyload function

<script>
        document.addEventListener("DOMContentLoaded", function() {
            let lazyImages = [].slice.call(document.querySelectorAll("img.lazyload"));
            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;
                            lazyImage.classList.remove("lazyload");
                            lazyImageObserver.unobserve(lazyImage);
                        }
                    });
                });
                lazyImages.forEach(function(lazyImage) {
                    lazyImageObserver.observe(lazyImage);
                });
            } else {
                // Fallback für Browser, die IntersectionObserver nicht unterstützen
            }
        });
</script>

usage

e.g

<img data-src="logo.jpg" alt="alt text" class="lazyload">

credits

Volkan sah