Lazy Loading

Christian Schreiber

Web Performance Consultant


What is lazy loading?

Lazy loading is a technique for optimizing the loading time of websites in which content such as images or videos are only loaded when they reach the user’s visible area. This significantly reduces the initial loading time of the page, as only the most important elements are loaded immediately, while other content is loaded as required.

How does lazy loading work?

Lazy loading works with special attributes and JavaScript code. When the website is called up, placeholders are set for the content to be loaded with a delay. As soon as the user scrolls and these placeholders enter the visible area, the actual content is loaded. This is done either through the “Intersection Observer API” or through simpler techniques such as checking the scroll position.

What are the advantages of lazy loading?

Lazy loading offers several advantages, including

Improved loading times: As only visible content is loaded initially, the website loads faster.

Reduced bandwidth usage: Not all content is loaded immediately, which reduces bandwidth usage.

Better user experience: Users experience faster and smoother navigation.

Optimization of Core Web Vitals: Better values for key figures such as “Largest Contentful Paint” (LCP) and “Cumulative Layout Shift” (CLS).

How can lazy loading be implemented?

What methods are there for implementing lazy loading?

HTML attributes: The loading="lazy" attribute can be used for images and iframes.

JavaScript libraries: There are various libraries such as “Lozad.js” or “LazyLoad” that enable simple implementation.

Intersection Observer API: This API enables more precise control and better performance when implementing lazy loading.

How can lazy loading be optimized?

What are best practices for lazy loading?

Use of placeholders: Use placeholder images or text to improve the user experience during loading.

Prioritize visible content: Load critical content first to ensure that the most important elements are available quickly.

Dynamic adjustment: Adjust the lazy loading settings depending on user interaction and behavior.

Testing and monitoring: Continuously monitor the performance of your website and adjust the lazy loading strategy to achieve optimal results.

How does lazy loading affect SEO?

What effects does lazy loading have on search engine optimization?

Lazy loading can have a positive impact on SEO by improving loading speed, which is an important ranking factor for Google. However, it is important to ensure that all content can be crawled by search engines. Use progressive enhancement techniques to ensure that the page works without JavaScript and that all content is accessible.


Lazy loading is an effective method for improving loading times and the user experience on websites. By delaying the loading of content such as images and videos, resources can be used more efficiently and core web vitals can be improved. The implementation can be done in various ways, from simple HTML attributes to advanced JavaScript techniques. To achieve the best results, best practices should be followed and website performance should be continuously monitored.

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Professional optimization of website load time, Google PageSpeed Score and Web Vitals