What Are the Best Practices for Using Lazy Loading to Improve Largest Contentful Paint (LCP) While Maintaining Consistent Content Visibility?
Conclusion
To improve LCP while maintaining consistent content visibility, website developers should employ lazy loading practices. This can be strategically achieved by prioritizing the first fold of the page, limiting JavaScript and CSS usage, using image placeholders, and ensuring a dynamically adjusted viewport.
Lazy Loading Basics
Lazy loading refers to the practice of deferring initialization of certain elements on the page until they are necessary for user interaction. This results in faster initial page loads and better resource management in general [Lazy Loading Images and Video, Google Web Fundamentals, 2020].
Prioritizing the First Fold
First, it is crucial to prioritize the loading of elements in the first visible part of the website - "above the fold." An effective lazy loading implementation should ensure these resources are loaded immediately, while those "below the fold" are deferred until required [Load Critical Resources First, web.dev, 2021].
Limiting JavaScript and CSS Usage
Lots of JavaScript and CSS can negatively affect LCP. It might, for example, block rendering or increase the amount of data required to be downloaded before the page can be interactively used. Therefore, limit their usage or employ effective strategies such as code splitting or the async and defer attributes for JavaScript [Blocking Resources, Google Web Fundamentals, 2022].
Utilizing Image Placeholders
Using image placeholders can provide a fluid user experience while the actual images are loading. A common strategy includes using tiny low-quality image placeholders (LQIP) that take minimal resources before the actual high-quality images are loaded [Browser Event Loop Model, SessionStack Blog, 2019].
Dynamically Adjusting the Viewport
To understand when to start loading off-screen images, leverage the Intersection Observer API. This modern tool dynamically adjusts to suit the user's device and screen size, allowing more accurate determination of when off-screen images should begin loading [Intersection Observer API, Mozilla Developer Network, 2022].