The impact of overuse of lazy loading on web performance

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Lazy loading is widely used in web applications nowadays in order to improve application performance. It helps developers reduce website loading time, save traffic and improve user experience.

But overuse of lazy loading can negatively impact application performance. So in this article, I will detail the performance impact of lazy loading to help you understand when to use it.

What is lazy loading?

Lazy loading is a common technique to reduce the data usage of web pages by loading resources on demand.

Lazy loading is now a web standard, and most major browsers support lazy loading via the loading="lazy" attribute.

 // with img tag<img   src="bits.jpeg"   loading="lazy"   alt="an image of a laptop" />// with IFrame<iframe   src="about-page.html"   loading="lazy"></iframe>

Once lazy loading is enabled, the content will only be loaded when the user scrolls to where the content needs to be displayed.

Lazy loading can definitely improve application performance and user experience, which is why it has become the preferred optimization measure for developers when developing applications. But lazy loading is not always guaranteed to improve application performance. So let’s see what the performance impact of lazy loading is.

The impact of lazy loading on performance

Many studies have shown that developers can achieve two advantages through lazy loading.

  • Reduce Page Load Time (PLT): Reduce above-the-fold page load time by delaying resource loading.

  • Optimize resource consumption: Optimize system resource usage through resource lazy loading, which works better on mobile devices with low memory and processing power.

On the other hand, overuse of lazy loading can have some noticeable performance implications.

Slow down fast scrolling

If you have a web application, such as an online store, you need to allow users to quickly scroll up and down and navigate. Using lazy loading for such an app will slow down scrolling because we need to wait for the data to load to finish. This can degrade application performance and cause user experience issues.

Latency due to content changes

If you haven’t defined the width and height properties for lazy loaded images, there will be a noticeable delay in the rendering of the image. Because the resource is not loaded when the page is initialized, the browser doesn’t know the content dimensions to apply to the page layout.

Once the content is loaded and the user scrolls to a specific view, the browser needs to process the content and change the page layout again. This would displace other elements and also create a bad user experience.

content buffering

This can lead to content buffering if you use unnecessary lazy loading in your app. This happens when the user scrolls down quickly while the asset is still downloading. This can especially happen with slow bandwidth connections, which can affect the speed of web page rendering.

When should lazy loading be used

You must now be wondering how to use lazy loading properly to make the most of it and create better web performance. Here are some suggestions to help find the best place to start.

1. Lazy load the right resource in the right place

If you have a lengthy web page that requires a lot of resources, then you can consider lazy loading, but only for content that is outside the user’s view or is collapsed.

Make sure you don’t lazily load resources required for background tasks to execute, such as JavaScript components, background images, or other multimedia content. Also, you must not delay the loading of these resources. You can use Google Chrome’s Lighthouse tool to inspect and identify those resources that can be lazily loaded.

2. Lazy load content that doesn’t interfere with the use of the page

Lazy loading is best used for unimportant, non-essential web resources. Also, don’t forget about error handling and providing a good user experience if resources are not lazy loaded as expected. Note that native lazy loading is still not universally supported by all platforms and browsers.

Also, if you’re using a library or custom JavaScript, this won’t work for all users. In particular, browsers that disallow JavaScript face the technical problems of lazy loading.

3. Lazy loading of resources that are not important for SEO

As content is lazy loaded, the website will gradually render, which means that some content is not available when loaded above the fold. At first glance, it seems that lazy loading helps improve SEO page rankings because it makes pages load significantly faster.

But if you overuse lazy loading, it can have some negative effects. When SEO indexing, search engines crawl a website to crawl data in order to index pages, but due to lazy loading, web crawlers cannot fetch all page data. This way SEOs don’t ignore this information unless the user interacts with the page.

But as developers, we don’t want SEOs to leave out our important business data. So I recommend not using lazy loading for SEO-focused content, such as keywords or business information.


Lazy loading can improve web page usage and performance, and is a handy tool for web developers. Known as “overcooking and burning out the soup,” excessive use of this technique can also degrade website performance.

In this article, we focus on the performance impact of lazy loading, with a few suggestions to help you understand when you should use it. If you use this technology sparingly and understand when and where to use it, your website will see a significant performance boost. I hope you have gained useful knowledge from it, thanks for reading!

The text and pictures in this article come from the programmers


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