How to Optimize Lazy-loaded Images for Better Cls Scores

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Improving your website’s Cumulative Layout Shift (CLS) scores is essential for a better user experience and higher search engine rankings. Lazy loading images is a popular technique to enhance page load times, but if not implemented correctly, it can negatively impact CLS. This article provides practical tips to optimize lazy-loaded images for better CLS scores.

Understanding CLS and Lazy Loading

CLS measures how much the layout shifts during page load. Unexpected shifts can frustrate users and harm your SEO. Lazy loading defers loading images until they are needed, reducing initial load time. However, if image sizes are not specified, placeholders may shift when images load, increasing CLS.

Best Practices for Lazy-Loaded Images

  • Specify Width and Height Attributes: Always include width and height attributes or CSS aspect ratios to reserve space.
  • Use Placeholder Images: Use low-resolution or blurred placeholders to prevent layout shifts.
  • Implement Proper CSS: Use CSS to define aspect ratios and container sizes.
  • Choose the Right Lazy-Loading Technique: Use native loading="lazy" attribute or reputable JavaScript libraries.

Implementing Proper Image Dimensions

Specifying image dimensions is crucial. For example, in HTML:

<img src="image.jpg" width="800" height="600" alt="Sample Image">

If you prefer CSS, use aspect-ratio properties:

.image-container { aspect-ratio: 4 / 3; }

Using Placeholders Effectively

Loading low-resolution or blurred images as placeholders helps maintain layout stability. Many lazy-loading libraries support placeholder images or CSS effects to create a smooth loading experience.

Choosing the Right Lazy-Loading Method

Modern browsers support native lazy loading with the loading="lazy" attribute:

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

For older browsers or advanced control, consider JavaScript libraries like Lozad.js or LazyLoad. Ensure these libraries also support placeholders and aspect ratio preservation.

Conclusion

Optimizing lazy-loaded images for CLS involves specifying dimensions, using placeholders, and selecting appropriate lazy-loading techniques. By following these best practices, you can significantly improve your website’s CLS scores, leading to a better user experience and improved SEO rankings.