Implementing lazy loading for images with loading="lazy"for Drupal 8 , 9 , 10 , and 11

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8.x , 9.x , 10.x , 11.x

Introduction

In previous lessons of our "Performance Optimization" series, we explored strategies to optimize HTML, CSS, and JS to enhance your Drupal site’s performance. This installment focuses on optimizing image delivery—specifically through implementing lazy loading for images using the loading="lazy" attribute. Lazy loading is a powerful technique to improve initial load times and provide a smoother user experience.

What is Lazy Loading?

Lazy loading is a strategy to defer the loading of non-critical resources at page load time. Instead of loading an image when the page initially loads, images are only loaded as they are about to enter the viewport, reducing the total load time drastically. This strategy is particularly effective for content-heavy pages, where images can account for a significant portion of load time.

Benefits of Lazy Loading

  • Improved Load Times: By delaying image load, the initial page load becomes faster, improving the overall performance.
  • Reduced Bandwidth Usage: Images are only loaded if needed, reducing data usage which can be beneficial for users on limited bandwidth connections.
  • Enhanced User Experience: Users see meaningful content quicker, improving perceived performance and user engagement.

Implementing Lazy Loading in Drupal

Lazy loading can be easily implemented using the loading attribute, supported natively by modern browsers. Here’s how you can leverage this feature within Drupal:

  1. Review Your Theme Templates

    Access and modify your theme’s template files where images are rendered. This is typically done in node--type.html.twig files for specific content types, or page.html.twig files for generic page layouts.

  2. Add the Lazy Loading Attribute

    Within template files, find the image tags and add the loading="lazy" attribute. Your image tags should look like this:

    <img src="path/to/image.jpg" alt="Descriptive text" loading="lazy">

  3. Use Drupal API for Image Rendering

    If you use Drupal's image styles and render arrays, ensure the loading="lazy" attribute is added in the theme or module implementation. Modify the render array in your preprocess functions to include the attribute:

    
function THEME_preprocess_image(&$variables) {
  $variables['attributes']['loading'] = 'lazy';
}

Testing and Validation

Once changes are implemented, perform the following steps to ensure lazy loading is working correctly:

  • Clear Cache: Clear Drupal’s cache to apply changes using drush cr or through the admin interface.
  • Visual Inspection: Use your browser’s developer tools to inspect image elements and verify the presence of the loading attribute.
  • Performance Testing: Use performance tools like Google PageSpeed Insights or Lighthouse to evaluate improvement in load times and resource loading efficiency.

Considerations and Best Practices

  • User Experience: Ensure lazy loading does not disrupt visual content flow, especially for vital image elements like banners or hero images.
  • Priority Content: Exclude essential imagery from lazy loading if they are crucial for the first impression or CTAs to ensure they load as part of the critical path.
  • Monitoring: Regularly monitor performance metrics and adjust strategies as necessary based on user feedback and technical audits.

Conclusion

By implementing lazy loading for images with the loading="lazy" attribute, you can significantly improve your Drupal site’s initial load times and bandwidth efficiency. This small change can make a big difference in resource management and user satisfaction.

Next in the Series

Our next lesson will dive into Configuring Image Styles for Optimized Delivery. We’ll explore how to create image styles that balance quality and size, further enhancing your site’s performance. Don't miss it!