How to Measure Front-end Performance: a Checklist for 2023

Critical rendering path

The critical rendering path is the sequence of steps that the browser goes through to convert the HTML, CSS, and JavaScript into actual pages on the screen that users see. If you can optimize this path, sites will render faster and have a greater impact on front-end performance.

Checklist to boost front-end performance

1- Preload

While prefetch is useful to cache resources that will be requested some time soon, preload loads resources that need to be used right away.

This is particularly important if you want to improve front-end performance metrics such as Time To Interactive or First Input Delay. Preloading loads JavaScript bundles needed for interaction.

2- Prefetch

Prefetch is a browser optimization to prefetch resources, which are needed for subsequent pages. This optimization pattern allows import modules based on visibility or interaction.

In many cases, users will request or interact with certain resources shortly after the initial page has been rendered. Based on this information, components that are likely to be used in the near future can be prefetched.

3- List virtualization

If a website has large lists, this pattern is useful for rendering only visible rows of content instead of the entire list. Only a small subset of the full list  (what is visible as the user scrolls) is rendered. 

Displaying thousands of elements from a list at once causes slower initial rendering and can freeze user interaction. List virtualization renders only items currently visible to the user. This can have a big impact on front-end performance optimization.

4- Import on visibility

​​Users should be able to interact with your product as soon as they land on your website or application, however, they will not see and interact with the entire website or app at once. This means there will be components that are not visible on the initial page, these can be loaded later. Lazy-loading images are not visible in the viewport and only get loaded once the user scrolls down.

As a result, all images are not requested instantly, and the load time is reduced. The same can be done with components using libraries such as react-lazyload and react-loadable-visibility.

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