Lazy Loading

Lazy loading is a smart strategy that defers the loading of non-critical resources at page load time. Instead of loading every element of a webpage upfront, lazy loading waits to load certain assets until they are needed – typically when they are about to enter the user’s viewport.

How Lazy Loading Works

Imagine you’re reading a book, and instead of turning every page, the pages reveal themselves just as you’re ready to read them. Lazy loading operates on a similar principle.

It prioritizes content above the fold (the portion of the webpage visible without scrolling). Content below the fold, such as images and videos, is only loaded as the user scrolls down the page.

The Benefits of Lazy Loading

Lazy loading can significantly improve your page load times, reduce initial page weight, and save bandwidth. This leads to a smoother user experience, particularly for users on slower connections or mobile devices.

Moreover, by reducing the amount of data that needs to be loaded, lazy loading can also contribute to lower server costs and a better Download Content size.

Assets Suited for Lazy Loading

  1. Images: The most common candidates for lazy loading. Since images are often large files, loading them only when necessary can save significant bandwidth and speed up the initial page load time.
  2. Videos: Like images, videos are heavy resources. By lazy loading videos, you prevent large files from bogging down the initial page load, especially if the video is embedded further down the page.
  3. Iframes: Embedding content via iframes, such as Google Maps or YouTube videos, can slow down your page. Lazy loading iframes ensures that these resources don’t load until they’re actually needed.
  4. Scripts: Certain JavaScript widgets or plugins that are not essential for the initial user interaction can be lazy loaded. This includes social media sharing buttons, comment sections, or analytics scripts.
  5. Background Images: Applied via CSS, these images can also be lazy loaded using JavaScript libraries or by leveraging new CSS features like the loading attribute.

Implementing Lazy Loading

To implement lazy loading, you can use JavaScript libraries such as Lozad.js or Lazysizes. These libraries provide a straightforward way to add lazy loading to your site. Additionally, native lazy loading is now supported in modern browsers through the loading attribute. By simply adding loading="lazy" to your <img> and <iframe> tags, supported browsers will handle the lazy loading for you.

For WordPress, solutions like Perfmatters and WP Rocket offer great solutions to lazy load your assets.

A Word of Caution

While lazy loading offers compelling benefits, it’s important to use it judiciously. Critical content should never be lazy loaded, as it can delay the visibility of important information or functionality. Always balance the speed improvements against the user experience and business goals.

Make sure you check the impact on all Core Web Vitals when implementing any and all lazy-loading solutions.