What is lazy loading and what is it for?

What is lazy loading and what is it for?

In recent years, we have witnessed a drastic change in online browsing habits, driven by the exponential growth in the number of mobile device users.

With this, a growing need to optimize the user experience has arisen, especially regarding page loading speed. Waiting for slow pages has become a relic of the past, giving way to a demand for instant interactions and agile navigation.

In this scenario, solutions such as lazy loading emerged to transform the way users interact with online content. In this article, we explain how this technique works and why you should consider adding it to your website. Follow along!

What is lazy loading?

Lazy loading  — is a loading optimization strategy in web programming.

This technique has become crucial as mobile devices evolve, producing images at increasingly higher resolutions, which can negatively impact page loading speed.

Although it is a relatively old technique, its implementation has been made easier with the advent of the Intersection Observer API. This interface allows developers to monitor changes in an element’s position relative to a container or viewport.

In this way, lazy loading has become more accessible and easier to implement, providing developers with an effective way to improve the performance of web pages, regardless of the size or resolution of the images used.

What is this technique used for?

Lazy loading is essential for improving the loading speed of web pages, especially on devices with limited bandwidth or slow internet connections. It helps reduce page load times, providing a smoother user experience.

Additionally, it is crucial to optimize performance on mobile devices where bandwidth and processing power may be limited.

By delaying the loading of non-essential elements, lazy loading significantly contributes to page loading efficiency and, consequently, user satisfaction.

How it works?

When using lazy loading, developers delay loading large files, such as high-resolution images, until they are needed.

Instead of loading all of a page’s elements simultaneously, lazy loading allows only essential elements to be loaded initially, while heavier resources are loaded only when they come into the user’s field of view.

For example, when visiting a page with a high-resolution image, lazy load prioritizes the loading of the remaining elements, ensuring a faster and more efficient user experience.

We will better understand how it can be applied to websites.

Selective loading of elements

One of the fundamental characteristics of lazy loading is its ability to selectively load elements of a web page.

Instead of loading all resources — such as images, videos, or scripts — simultaneously, lazy loading allows developers to determine which elements are essential for the initial page view.

Non-essential elements, such as images that are out of the user’s field of vision, are postponed until they become necessary, saving bandwidth and speeding up load times.

Scroll and user interactivity

Lazy load is activated based on the user’s actions, mainly the scrolling movement of the page.

When the user scrolls down, lazy load checks which elements are about to enter the field of view. If an image or other resource is about to be displayed on the screen, it springs into action, loading the resource asynchronously.

Additionally, it can also be configured to load elements based on user interactions, such as clicking a specific button, ensuring an efficient and personalized user experience.

Implementation via HTML, CSS and JavaScript

Lazy loading can be implemented in several ways depending on the developer’s needs. One of the most common approaches is by modifying the image tags in the HTML.

Using the “data-src” attribute instead of “src”, lazy load tells the browser which image should be loaded only when it is about to enter the user’s field of view.

Additionally, CSS techniques such as setting a low-resolution background that is replaced with a high-resolution image when necessary are also employed to improve performance.

In the context of JavaScript, the Intersection Observer API is often used to implement lazy loading efficiently. This API allows developers to observe changes in the intersection between the target element (e.g. an image) and its parent container (e.g. the browser window).

When the intersection reaches a certain threshold configured by the developer, the resource is loaded dynamically, ensuring a fluid and responsive user experience.

Benefits for performance and SEO

By adopting lazy loading, developers can see significant improvements in the performance of web pages.

Reducing load times not only provides a faster and more pleasant user experience but also has a positive impact on your website’s search engine rankings.

Google, for example, considers loading speed as an important factor in page ranking in search results, which makes lazy loading a crucial practice for improving a website’s SEO.

Why is lazy loading important for website optimization and monetization?

Lazy loading plays a vital role in optimizing and monetizing a website by improving user experience, increasing visitor retention, boosting conversion rates, and improving SEO as follows.

Reduced loading time

Lazy loading is crucial to reduce page loading time, loading only the essential elements initially. Heavy elements are loaded asynchronously and on-demand, significantly improving page loading speed.

Improved user experience

Pages that load quickly provide a more satisfying user experience. Visitors are more likely to stay on a website and explore its content if they don’t have to wait for long loading times.

Increased user retention

Pages optimized for lazy loading increase user retention, a vital metric for sites that rely on ad revenue. Satisfied visitors are more likely to browse more pages, increasing ad viewing opportunities.

Improved conversion rates

On eCommerce sites, where monetization occurs through sales, a frictionless and responsive user experience is essential. Lazy loading contributes to faster navigation, leading to an improvement in conversion rates, that is, more sales for the business.

Improved SEO

Google and other search engines consider loading speed as an important factor in ranking pages in search results. Lazy loading, by significantly reducing loading time, improves the website’s SEO, increasing its online visibility and attracting more organic traffic.

Reduced bounce rates

Pages that load slowly have higher bounce rates, meaning visitors leave your site without interacting with other pages. By offering a fast and responsive user experience, lazy loading helps keep bounce rates low, which is crucial for website optimization.

When considering optimizing a website’s performance, it is clear that lazy loading stands out as an effective solution for improving loading speed and, therefore, the user experience. However, it is essential to carry out tests to ensure that the strategy is applied properly and that all essential elements are loaded at the right time, providing fluid and uninterrupted navigation for visitors.

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