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A Journey toward better style


  • I would like to thank Nathan Marks for the awesome work is has done addressing the styling issues.
  • I would like to thank Pete Hunt for his inspiring talk on reusable components.
  • I would like to thank the following oranizations for giving me the opportunity to share this topic:
  • Paris.js
  • ReactJS-Paris


  • 2016-10-27
  • 2017-01-26

Online version

CSS-in-JS comparaison

We started looking for the best styling solution available. Nathan Marks built a custom solution for the needs of Material-UI: stylishly. Ultimately we reverted. We think that it's much better to rely on the community. Still, that was a very valuable experimentation.

Regarding the community, looking at the MicheleBertoli's repository. You can tell that there is a lot a solution available.

What's the best one for our needs?

For the sake of this presentation, I have selected 5 libraries that I think have taken valuable tradeoffs. I'm gonna give my point of view in the rest of this section. The information given are biased by my understanding of the reality.

  • CSS modules

    • Singularity: Extended CSS DSL. Generate style at built time.
    • Motivation: Having some isolated and composable module of CSS. Stay as close as possible to the CSS ecosystem.
  • Aphrodite

    • Singularity: Per rule style usage and injection.
    • Motivation: Khan Academy was looking for a better way to style components with an existing code base. E.g. usage of !important.
  • styled-components

    • Singularity: Uses post-CSS at runtime.
    • Motivation: ? My best guess is, leveraging JS power while still using the CSS syntax.
  • JSS

    • Singularity: Has a low-level API.
    • Motivation: ? I have no clue. I should be asking @nathanmarks.
  • Fela

Interesting dimensions

We can't compare anything without some dimensions. But having too much of them add noise.

⚠️ Be aware that horse transportation is better than cars when following biased dimensions. I have sorted them by importance.

  • The API.
  • Is it taking full advantage of JavaScript? JavaScript is a much more powerful language than CSS. When using it, you no longer have to worry about CSS linter, CSS syntax, CSS pre-processor
  • Is the API low or high level? The theming requirement is quite high for Material-UI. The much freedom we have, the better.
  • Is the API declarative? The more declarative we are, the better.
  • Time to first paint. We have a legacy of poor performance with our inline-style implementation (lack of caching). Reducing the delay between an interaction and something on the screen is quite critical for us. I have run a simple benchmark on a modified version of CSS-in-JS There is quite some factor than can make a difference. I have noticed a factor x2 of difference between the fastest solution (CSS modules) and the slowest one (styled-components).
  • Is the style pre-processed at runtime of build time?
  • Is the style injected as class names used or upfront during the bootstrap?
  • How are the classNames generated? E.g. computing a hash of the rule object could be expensive.
  • Library size. Users of Material-UI could be using a single component out of the available ones. E.g. the <DatePicker />. We want to minimize the entry price of using a single component.
  • Server Rendering. Server side rendering a page drastically improve perceived performance for a user first visit (for repetitive one, Service Worker are even more efficient). Material-UI can't be taken seriously without a strong answer to this point.
  • Can requests be parallelized? I.e, not using a singleton, that's also bad for security.
  • Is the API allowing streaming the response?
  • Unbiased. The less coupled with a solution we are the better. We also want to make sure the solution we are going to use reach a broad audience. E.g. LESS is used by the Angular and React community. That's increasing odds of success.
  • Are we coupled to React?
  • Are we coupled to Webpack?
  • Debug. Users of Material-UI were complaining that the debugging experience was poor with inline-style. Browser dev tool handles much better the CSS. Still, the styling solution can impact it.
  • Are the classNames readable in dev mode?
  • Are the classNames injected into a single style element or multiple?
  • CSS output size. That last dimension is less interesting. I was just curious.


CSS modules Aphrodite styled-components JSS Fela
API -- + o + ++
Time to first paint ++ o - + o
Library size in kB ~0 18 126 22 9
Server Rendering + o - ++ o
Unbiased o o - + +
Debug - o o + -
CSS output size o ++ + + o
  • ++ awesome
  • + great
  • o enough
  • - not great
  • -- no

Going forward

Material-UI has chosen JSS. It's addressing our unique needs. Your needs are most likely different. It could be better for you to use a another solution. Be sure you make an informed choice 💡.

The compared libraries are going to improve. My comparison might not worth anything one year from now.