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5 reasons to go with CSS in JS for your next application

Ruben on March 19, 2019

original post @ Linguine Blog CSS is awesome, and it’s easy to get started with. But front-end applications have been scaling at a massive, and c...

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Anton Korzunov • Mar 20 '19

1. CSS problem #1: Global namespace

And there is nothing to stop me from using class names that was designed for the home page.

CSSModules or BEM, as just a "more safe way to name things" could save the day. But CSSModules would be enough.

Is there anything, that CSS-in-js could improve? No.

2. CSS problem #2: Implicit dependencies

BEM, SMACSS, SUITCSS, Atomic, Nonetheless, each of these solutions are just a quick patch solution.

In short - you are wrong. This is not quick patch solutions, and BEM/Atomic approach(even if there is no similarity between then) could be used with "CSS-in-JS". You just don't get the point - they are about "structuring" the rules, not writing/naming them

Is there anything, that CSS-in-js could improve? No. The problem is perpendicular.

3. CSS problem #3: Dead code elimination

CSS in JS can dynamically clean up CSS code that is not being used.

How? Probably you might just delete it?
What if you have a one style file per component? - You probably might just delete it. Or not import it if you didn't use component.

Is there anything, that CSS-in-js could improve? No. It's the same.

4. CSS problem #4: Minification

For big applications unminified CSS code can get fairly big, especially with crazy amount of white space (indentation) we add to the stylesheet. Which just creates another dependency your CSS.

Miniwhatthing? How you think CSS-in-JS "minifies" their code? It does NOT do it. Instead of it you have to download some(a huge amount) of JS to parse, prefix and apply your styles in runtime.

CSS-in-JS usually consumes more space.

Is there anything, that CSS-in-js could improve? No. They even much worse.

5. CSS problem #5: Sharing constants

CSS supports a sharing constants with their built-in function called var().

constants are supported by SASS or LESS. Supported perfectly, and you can build bridges between JS and CSS using webpack loaders.
The problem is with variables, which you might not need.

Is there anything, that CSS-in-js could improve? Yes. The only thing CSS-in-JS can rule.

Total

Generates minimum CSS requires? NO.
Good runtime performance? RUNTIME? CSS does not require any runtime, and vanilla CSS parsers are much faster than js parsers. Keep CSS as CSS if you need "speed".
Supports dynamic styling? Yes, but do you need it really?
Easy to pre-render important CSS? And inline it into HTML? What are you doing?

Zero-runtime

If you like "CSS-in-JS" - use "zero-runtime" CSS-in-JS libraries. They produce CSS, while being "JS" for you

Styled-Components? All the reasons you listed - are falsy. Believe the old pirate.

Ruben • Mar 20 '19

Those are nice libraries that I've never seen until now. I'll have to do a deep dive on them.

Overall, I don't believe traditional CSS architecture belongs in a 2019 (mid to big size) application.

We're moving towards a componentize architecture and traditional CSS structure doesn't work because of the problems I've mentioned above.

With that said, CSS modules I have heard of and I think it's great but it adds more dependencies to an application and more knowledge about Webpack configuration that an engineer needs to know.

I don't think there is a good enough reason to why need to add all that complexity or even know it.

Writing CSS in a JS file does solve the problems above, and you honestly don't need a library to do so. You can inject it inline.

Now you might say, INLINE CODE IS THE WORST!

It was horrible before because you had to write it manually, but now you can just have a style object and inject into the style attribute. You may also move the style object to it's own file for "separation of concerns".

You're still writing CSS, but just doing it through JavaScript.

Anton Korzunov • Mar 20 '19

We're moving towards a componentize architecture and traditional CSS structure doesn't work because of the problems I've mentioned above.

Probably the problem is with traditional CSS structure.

With that said, CSS modules I have heard of and I think it's great but it adds more dependencies to an application and more knowledge about Webpack configuration that an engineer needs to know.

It's one line. And even CRA supports it. So - there is no complexity.

Writing CSS in a JS file does solve the problems above

The problems are solved by a specialized library, not CSS-in-JS as technology itself

you honestly don't need a library to do so. You can inject it inline. Now you might say, INLINE CODE IS THE WORST!

I would say - INLINE CODE IS THE WORST!!! You got me :P

There is one, a single one reason not to use inline css - meta selectors.

Meta selectors give you the ability to:

target :hover, :focused, :active states, which you still could emulate with a pure js, but better dont
target different medias, which enables responsive and fluid designs. You still can use window.matchMedia, and produce the right styles for a current media, but it's not quite maintainable (and SSR/cache friendly)
use pseudo selectors, like :before or :after, which could simplify your html and make code cleaner. It's still possible to just add mode nodes to the markup, and joggling everything with javascript. But there are situations, when you have to use all features listed above simultaneously, like add :after element for :hover state on some @media, and CSS code shall be preferred.

And every time, when you are writing MORE CSS code than JS code, and that could be a thing, if you really use all possibilities of CSS - you might prefer CSS-in-CSS, not in JS.

It seems to me - you are underusing CSS features. And, actually, shall not have any issues in this case - CSS problems are problems of a scale.

Bohdan Kostrytskyi • Mar 21 '19

Agree. CSS module system is the best

import styles from './App.module.scss';

which can be use after as

<div className={styles.App}> ... </div>

mkenzo_8 • Mar 20 '19

var() is actually very useful when you only have to focus on one browser, in this case Chrome. When will that happen? ElectronJS.

ElectronJS uses chromium so it supports the lastest CSS features as var() and you can actually build apps on it.

Ruben • Mar 20 '19

That’s true. Most modern browsers support var().

I currently have the misfortune of working on applications that need to support IE 9

Bohdan Kostrytskyi • Mar 21 '19

The main issue with CSS in JS libs like Styled Component in that it reloads the whole app on every change. While CSS module system works perfect atm for me.

Vladislav Guleaev • Feb 1 '20

I would never put my css into components so they grow as hell. Why should i do it?
Also zero linting and intelesence. Who invented this and why?

Ruben • Feb 1 '20

You don't get linting or intellisense in traditional CSS anyways, so... By the way, why not? If it works it works...

Matthias • Feb 10 '20 • Edited

Well IntelliJ Idea checks your csss.

.myClass {
  display: blocks; <-- error is shown
}

whereas

<style jsx>{`
  .myClass {
    display: blocks; <-- no error shown (cause it is just a 'string')
  }
`}</style

Petr Kučera • Mar 20 '19

And what about CSP?
Does it inclide nonce?
Or must be unsafe-inline enabled?

Ruben • Mar 20 '19

This might help

Resource link