Lazy Loading Images in HTML: Improve Performance & SEO

Lazy loading is a technique that defers the loading of images until they are needed, improving page load speed, reducing bandwidth usage, and enhancing SEO. In this article, we'll explore how lazy loading works, how to implement it, and best practices for optimal performance.

1. What is Lazy Loading?

Lazy loading delays the loading of offscreen images until they are about to be displayed in the viewport. This reduces the initial page load time and saves network resources.

🚀 Benefits of Lazy Loading:

• Faster page load times by loading only visible images.
• Reduces bandwidth usage, especially for users on slow connections.
• Improves SEO & Core Web Vitals, particularly Largest Contentful Paint (LCP).

2. How to Implement Lazy Loading in HTML

2.1. Using the loading="lazy" Attribute (Native Lazy Loading)

HTML5 introduced the loading attribute, which provides native lazy loading support.

<img src="image.jpg" alt="Example Image" loading="lazy">

✅ Browser Support: Most modern browsers support loading="lazy" (Chrome, Edge, Firefox, Opera). Older browsers will simply ignore it.

2.2. Lazy Loading with JavaScript (Intersection Observer API)

For more control over lazy loading, use JavaScript and the Intersection Observer API.

<img data-src="image.jpg" alt="Lazy Image" class="lazy">

document.addEventListener("DOMContentLoaded", function () {
  const lazyImages = document.querySelectorAll(".lazy");
  const observer = new IntersectionObserver((entries, observer) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        const img = entry.target;
        img.src = img.dataset.src;
        img.classList.remove("lazy");
        observer.unobserve(img);
      }
    });
  });
  lazyImages.forEach(img => observer.observe(img));
});

✅ Advantages:

• Works in all browsers, including older versions.
• Allows more customization (e.g., animations, preload thresholds).

3. Best Practices for Lazy Loading

✅ Use loading="lazy" for simplicity

The native loading="lazy" is recommended for most use cases.

✅ Provide a placeholder or fallback

Use a low-resolution placeholder to avoid layout shifts.

<img src="placeholder.jpg" data-src="image.jpg" alt="Example" class="lazy">

✅ Optimize images for performance

• Use modern formats like WebP.
• Implement responsive images with <picture> and srcset.

<picture>
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Example" loading="lazy">
</picture>

✅ Avoid lazy loading above-the-fold images

Do not lazy load images that appear immediately on page load.

<img src="hero.jpg" alt="Hero Image" loading="eager">

4. Conclusion

Lazy loading is a simple yet powerful technique to improve website performance, reduce load times, and boost SEO. Use native lazy loading (loading="lazy") when possible, and fall back to JavaScript-based lazy loading for more advanced scenarios.

By implementing these strategies, your website will be faster, more efficient, and user-friendly!