CSS in JS: The Good & Bad Parts

Slides for my talk at ReactiveConf 2017 in Bratislava, Slovakia.

1. CSS in JS The Good & Bad Parts ReactiveConf 2017
2. Robin Frischmann @rofrischmann @rofrischmann
4. rofrischmann/fela
5. Who is already familiar with CSS in JS ?
6. CSS in JS
 101
7. CSS in JS !!!== inline style
8. const style = { fontSize: 12, color: 'red', ':hover': { color: 'blue' }, '@media (min-width:320px)' { fontSize: 12 } } const style = ` font-size: 12px; color: red; &:hover {
 color: blue; } @media (min-width:320px) { font-size: 14px; } } ` Objects Template strings
9. The Problems
10. Choosing the “right” library 1
11. • aphrodite • babel-plugin-css- in-js • babel-plugin-pre- style • bloody-react-styled • classy • csjs • css-constructor • css-light • css-loader • css-ns • cssobj • cssx-loader • emotion • es-css-modules • glamor • glamorous • hyperstyles • i-css • j2c • jsxstyle • linaria • pre-style • radium • react-css-builder • react-css- components • react-css-modules • react-cssom • react-cxs • react-fela • react-free-style • react-inline-css • react-inline-style • react-inline • react-jss • react-look • react-native-web • react-statics-styles • react-styl • react-style • react-styleable • react-stylematic • react-theme • react-vstyle • reactcss • restyles • scope-styles • smart-css • stile-react-media- queries • stilr • style-it • styled-components • styled-jsx • styletron-react • styling • superstyle • typestyle • uranium
12. Use what works for you!
13. 1. Objects or Template Strings? 2. Working with Designers? 3. Simplicity or Flexibility? 4. React-centric or Framework-agnostic? 5. Server-side Rendering?
15. Not everyone is used to JavaScript 2
16. 1. Choosing a library is hard 2. Using CSS in JS does not always turn out to be a good choice at all
17. The Benefits
18. It’s JavaScript! 1
19. Who has used or is using a preprocessor like Sass, Less or Stylus? ?
20. JavaScript everywhere!
21. $primary-color = red .button { color: $primary-color; padding: 15px 20px; font-size: 20px; } const primaryColor = 'red' const buttonStyle = { color: primaryColor, padding: '15px 20px', fontSize: 20 } (S)CSS JS
22. $vendors: "-webkit-", "-ms-", ""; @mixin prefix($property, $value) { @each $vendor in $vendors { !#{$vendor}!#{$property}: !#{$value}; } } .button { @include prefix( 'border-radius', '5px' ) } const vendors = ['-webkit-', '-ms-', ''] function prefix(property, value) { return vendors.reduce( (style, vendor) !=> { style[vendor + property] = value return style }, {} ) } const buttonStyle = { !!...prefix( 'border-radius', '5px' ) } SCSS JS
23. Ecosystem
24. styled-components/polished
25. Computers do the hard work 2
26. – Phil Karlton “There are only two hard things in Computer Science: cache invalidation and naming things.”
27. Naming CSS classes is hard
28. BEM smacss.com oocss.org getbem.com OOCSS SMACSS
29. Conventions !!!== enforced
30. Computers for the rescue!
31. Class Names?
 Non of my business!
32. – Alan B Smith “[…] the appeal of CSS-in-JS is not simplicity, rather predictability and consistency.” Source: https://hackernoon.com/why-we-use-styled-components-at-decisiv-a8ac6e1507ac
33. Predictable Styling 3
34. Who has ever accidentally destroyed the layout or styles of some part of the application, while actually working on something completely different? ?
35. const view = () !=> ( <div className={ 'text_green' }> Some Text !</div> ) .text_green { color: green } JS(X) CSS
36. const view = state !=> ( <div className={ state.error ? 'text_red' : 'text_green' }> Some Text !</div> ) .text_red { color: red } .text_green { color: green } JS(X) CSS
37. const view = state !=> ( <div className={ state.error ? 'text_red' : 'text_green' }> Some Text !</div> ) .text_red { font-size: 20px; color: yellow; } .text_green { color: green } JS(X) CSS
38. UI = f(state)
39. #1 What is displayed #2 How is it displayed
40. How What Markup Styling HTML CSS
41. UI = f(state)
42. Style = f(state)
43. import { css } from 'any-css-in-js-library' const style = state !=> ({ color: state.error ? 'red' : 'green' }) const view = state !=> ( <div className={css(style(state))}> Simple Text !</div> ) JS(X)
44. - Choosing a library is hard - Using CSS in JS is not necessarily the best choice ✓ Power of JavaScript ✓ Unique generated classes ✓ Predictable UI Benefits Problems
45. @rofrischmann @rofrischmann
46. Thank you! @rofrischmann @rofrischmann