Lazy loading – what is it and how to use it?

Every second of website load time matters. Users expect pages to load instantly, and search engines like Google reward fast websites with higher rankings in search results. One of the effective ways to boost website performance is a technique known as lazy loading. But what is lazy loading and how can it be applied in practice?

In this article, we will discuss what lazy loading is, how it works, the benefits it brings, and how you can use it on your website. If you want your website to load faster and provide users with a better experience, this guide is for you.

Lazy loading – what is it?

Lazy loading, also known as “deferred loading,” is a web performance optimization technique that involves loading resources (such as images, scripts, or videos) only when they are actually needed. Instead of loading all elements of a page during the initial load, lazy loading delays the loading of these resources until the user scrolls to the part of the page where they become visible. This reduces the initial page load time and improves overall performance.

How does lazy loading work?

Lazy loading works by deferring the loading of website resources until they are actually needed. This process can be divided into several key steps:

1. Initial page load: When a user opens a page, only the essential resources that are visible in the user’s viewport are loaded. Resources outside this area are skipped during the initial load.
2. Scroll monitoring: Scripts on the page monitor the user’s position and track how the user scrolls up or down the page.
3. Resource visibility detection: Scripts check which resources become visible in the viewport as the user scrolls. Once a resource comes into view, it is marked as ready to be loaded.
4. Dynamic resource loading: When a resource is detected in the viewport, it is dynamically loaded from the server. Only then does the browser fetch and render the resource for the user.
5. Interface update: After the resource is loaded, the page content is updated to display the newly fetched resource, giving the user the impression of smooth, immediate loading.

Is it worth using lazy loading?

Lazy loading is a technique that offers many benefits and is, in most cases, worth implementing on a website. Here are a few key reasons to use lazy loading:

• Improved page performance: Lazy loading significantly speeds up the initial page load because only the resources visible in the user’s viewport are loaded. This allows users to see the content faster, potentially reducing bounce rates.
• Data usage reduction: Users only download the resources they actually view. This helps save data, which is particularly important for those on mobile connections or in areas with slower internet speeds.
• Server resource savings: A less burdened server can handle more users simultaneously without slowing down. Lazy loading reduces the number of requests to the server, which can improve its performance and lower hosting costs.
• SEO optimization: Faster page loading and better user experience can contribute to higher rankings in search results. Google and other search engines consider page load speed as one of the ranking factors.

How to use lazy loading?

Usage Examples

HTML loading attribute
One of the simplest ways to implement lazy loading is by using the native loading attribute in HTML. This is the easiest method, as it does not require additional libraries or scripts.

Example

Using JavaScript libraries

For more advanced use cases, you can use JavaScript libraries that offer greater control over resource loading along with additional features.

Example using Intersection Observer API

Plugins and frameworks

When using popular content management systems (CMS) or front-end frameworks, ready-made plugins or modules supporting lazy loading are often available.

Best Practices

1. Image optimization: Before implementing lazy loading, ensure that all images are optimized for size and format. Smaller and compressed images will load faster, further improving page performance.
2. Using placeholders: Employ placeholders, such as temporary images or colored backgrounds, which are displayed until the actual image loads. Placeholders can prevent page “jumps” while images are loading.
3. Prioritizing key resources: Not all resources need to be lazy loaded. Elements visible on the first screen (above the fold) should load immediately to ensure quick content display for the user.
4. Testing and monitoring: After implementing lazy loading, regularly test and monitor the website’s performance.
5. SEO and indexing: Ensure that lazy loaded resources are accessible to search engines. This can be achieved by dynamically generating content and testing how search engines index your site. Adjust the lazy loading implementation if necessary to ensure that all important resources are indexed.
6. Browser compatibility: Although lazy loading is supported by most modern browsers, it is always a good idea to check compatibility with the browsers used by your audience.

Summary

Lazy loading is a web optimization technique that significantly speeds up page load times, reduces data usage, and improves user experience. By deferring the loading of resources until they are needed, lazy loading enables more efficient resource usage and increases site responsiveness.
In this article, we discussed what lazy loading is, how it works, and the benefits it brings. We explored examples using both native browser features and more advanced JavaScript-based techniques. We also presented best practices to help you maximize the potential of lazy loading.

It is important to remember that despite its many advantages, lazy loading requires careful planning and testing to avoid potential issues with search engine indexing or browser compatibility. Regular monitoring and optimization are key to maintaining high site performance.