The Unseen Performance Costs of Modern CSS-in-JS Libraries

This article is full of a bunch of data from Aggelos Arvanitakis. But lemme just focus on his final bit of advice:

Investigate whether a zero-runtime CSS-in-JS library can work for your project. Sometimes we tend to prefer writing CSS in JS for the DX (developer experience) it offers, without a need to have access to an extended JS API. If you app doesn’t need support for theming and doesn’t make heavy and complex use of the css prop, then a zero-runtime CSS-in-JS library might be a good candidate.

“Zero-runtime” meaning you author your styles in a CSS-in-JS syntax, but what is produced is .css files like any other CSS preprocessor would produce. This shifts the tool into a totally different category. It’s a developer tool only, rather than a tool where the user of the website pays the price of using it.

The flagship zero-runtime CSS-in-JS library is Linaria. I think the syntax looks really nice.

import { css } from 'linaria';
import fonts from './fonts';

const header = css`
  text-transform: uppercase;
  font-family: ${fonts.heading};
`;

<h1 className={header}>Hello world</h1>;

I’m also a fan of the just do scoping for me ability that CSS modules brings, which can be done zero-runtime style.

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