Too much Lazy-loading: Does it affect your website performance?

Too much Lazy-loading: Does it affect your website performance?

Lazy-loading could be a technique to defer downloading a resource till it’s required, which conserves knowledge and reduces network rivalry for vital assets. It became an online customary in 2019 and nowadays loading=”lazy” for pictures is supported by most major browsers. That sounds nice, how, is there such an issue as an excessive amount of lazy loading?

This blog summarizes how we analyzed publicly available web transparency data and impromptu A/B testing to grasp the adoption and performance characteristics of native image lazy-loading. What we tend to found is that lazy-loading may be an astonishingly effective tool for reducing needless image bytes, how, overuse will negatively affect performance. Concretely, our analysis shows that a lot of thirstily loading pictures among the initial viewport—while generously lazy-loading the rest—can provide us the most effective of each world: fewer bytes loaded and improved Core web vitals.


According to the foremost recent data in HTTP Archive, native image lazy-loading is employed by 17% of internet sites and adoption is growing apace. This abundant grip within the system is exceptional for a comparatively new API.

Querying the information within the HTTP Archive project offers us a clearer understanding of what sorts of websites are driving adoption: 84% of websites that use native image lazy-loading use WordPress, 2% use another CMS, and also the remaining14% do not use the best-known CMS. These results analyze how WordPress is leading the charge in adoption.

The rate of adoption is additionally worth noting. One year ago in July 2020, WordPress sites that use lazy-loading created up tens of thousands of websites within the corpus of concerning six million (1% of total). Lazy-loading adoption in WordPress alone has since big to over one million websites (14% of total).

Testing a fix

Before we tend to get into how the fix was enforced, let’s investigate how lazy-loading works in WordPress nowadays. the foremost necessary side of the present implementation is that it lazy-loads pictures on top of the fold (within the viewport). The CMS journal post acknowledges this as a pattern to avoid, how, experimental knowledge at the time indicated that the impact on LCP was nominal and value simplifying the implementation in WordPress core.

How might it be quicker than not lazy-loading at all? One clarification is that by not loading below-the-fold pictures, there is less network rivalry with the LCP image, which permits it to load a lot quicker.

In terms of image bytes, the fix has fully no modification as compared to the default behavior. this can be nice as a result of that was one of all the strengths of the present approach.

There are some caveats with this fix. WordPress determines that pictures lazy-load on the server-side, which implies that it does not recognize something concerning the user’s viewport size or whether or not pictures can at first load among it. that the fix uses heuristics concerning the images’ relative location within the markup to guess whether or not it’ll be within the viewport. Specifically, if the image is that the 1st featured image on the page or the primary image within the main content, it’s assumed to be on top of the fold (or about to it), and it’ll not be lazy-loaded. Page-level conditions just like the range of words within the heading or the quantity of paragraph text early within the main content could affect whether or not the image is among the viewport. There also are user-level conditions that will affect the accuracy of the heuristics, particularly the viewport size and also the usage of anchor links that modification the scroll position of the page. For those reasons, it is vital to acknowledge that the fix barely labels to supply sensible performance within the general case and fine-tuning is also required to form these results applicable to all or any real-world eventualities.

Rolling it out

Now that we’ve known a higher thanks to lazy-load pictures, all of the image savings, and quicker LCP performance, how, will we tend to get sites to start out using it? the best priority modification is to submit a patch to WordPress core to implement the experimental fix. We’ll even change the steering within the Browser-level lazy-loading for CMSs journal post to clarify the negative effects of above-the-fold lazy-loading and the way CMSs will use heuristics to avoid it.

Since these best practices apply to all or any net developers, it should even be value tired lazy-loading antipatterns in tools like pharos. discuss with the feature request on GitHub if you are interested to follow along with side progress thereon audit. Until then, one issue developers might do to search out instances of LCP parts being lazy-loaded is to feature a lot of careful work to their field knowledge.

This additionally highlights a pointy fringe of the lazy-loading technique and also the potential for API enhancements at the platform level. as an example, there is an open issue in metal to experiment with natively loading the primary few pictures thirstily, almost like the fix, despite the loading attribute.

Wrapping it up

If your website uses native image lazy-loading, check how it’s enforced and run A/B tests to understand its performance costs. It may benefit from more eagerly loading images above the fold. If you’ve got a WordPress website, there’ll hopefully be a patch landing in WordPress core shortly. And if you are using another CMS, check that they are alert to the potential performance problems described here.

Trying out comparatively new web platform APIs will escort each risk and reward—they’re known as innovative options for a reason. whereas we’re beginning to get a way of the thorniness of native image lazy-loading, we’re additionally seeing the upsides of the way to use it to realize higher performance. At Ahy Consulting, we ensure to implement the best cutting-edge technology in your website for the fastest loading.

Feel free to reach out to me if you need help with what is right for you, using this link.


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