1 JavaScript Style JavaScript Style Sheets Sheets by Oleg Slobodskoi jss React Amsterdam 2016

2 Plan Plan 1. React and CSS. 2. What are inline styles. 3. Problems solved by inline styles. 4. Interesting CSS in JS libs. 5. What is JSS. 6. Problems solved by JSS. 7. Unsolved problems.

3 React and CSS React and CSS React is about React is about components components. . CSS is for CSS is for documents. documents.

4 First JSS release First JSS release

5

6 Inline styles Inline styles const style = {color: red} HTML React const element = document.createElement('div') element.style.color = 'red' DOM

7 Global Namespace Global Namespace Selectors are the evil. Try to write an application inside of one function.

8 Implicit Implicit Dependencies Dependencies My Button /* buttons.css */ .default-button { cursor: pointer; } /* my-component.css */ .my-button { color: red; }

9 Dead code Dead code A task for a compiler. function module() { var styles = { button: { color: 'green' }, myButton: { color: 'red' } } // Renders a button. button({style: styles.myButton}) } function module(){button({style:{color:"red"}})};

10 Minification Minification function test(a) { var obj = {a: a, b: 2}; return obj.a + obj.b; } window.a = test(1) window.a=3; No selectors to minify. JavaScript compressor for the rest.

11 Sharing Constants Sharing Constants Data driven styling Shared Breakpoints Javascript Layouts

12 Non-deterministic Non-deterministic Resolution Resolution CSS Specificity Concept. /* my-button-1.css */ .my-button.my-blue-button { color: blue; } /* my-button-2.css */ button.my-button { color: red; } My Button

13 Isolation Isolation No access to external components. Very high specificity.

14 Complex Selectors Complex Selectors .article #comments ul > li > a.button

15 Redundancy Redundancy Smaller payload.

16 Can we do even Can we do even better? better? YES. YES.

17 Other alternatives? Other alternatives?

18 And more ... And more ...

19 And more ... And more ... Text https://github.com/MicheleBertoli/css-in-js

20 3 Categories 3 Categories 1. Pure Inline 2. Mixed Mode 3. Pure Style Sheets

21 Pure Pure Inline Inline Already built in React No support for @media, @keyframes etc. Performance Downsides

22 Mixed Mode Mixed Mode Radium is using: React Events for Pseudo Selectors. Style Sheets for @media and co. Inline for everything else.

23 Pure Pure Style Sheets Style Sheets Aphrodite JSS

24 What is JSS. What is JSS. Good parts of CSS only. Designed with components in mind. Declarative JavaScript. JavaScript to CSS compiler. Easy to reason about.

25 How does it work. How does it work. Virtual CSS Tree Process Render Run plugins on every VRule Output with CSS. Abstraction for CSS Rules Manipulation

26 React-JSS React-JSS Lazy compilation Ref counting

27 Example with React Example with React import React from 'react' import {useSheet} from 'react-jss' @useSheet({ button: { color: 'green' } }) export default function Button(props) { const {classes} = props.sheet return {props.text} } No magic in code.

28

29 Boring CSS output. Boring CSS output.

30 Problems it solves. Problems it solves. 1. All issues solved by Inline Styles. 2. Issues introduced by Inline Styles. 3. More CSS Issues.

31 Plan Plan 1. Media Queries 2. Keyframes Animation 3. Font Face 4. Pseudo Selectors 5. Fallbacks 6. Rules Caching 7. Rules Sharing 8. Extensible Architecture 9. Tools Agnostic 10. Vendor Prefixer 11. Inheritance DSL Library

32 Media Queries Media Queries export default { '@media (min-width: 1024px)': { button: { minWidth: 200 } } } const breakpoint = 1024 export default { [`@media (min-width: ${breakpoint}px)`]: { button: { minWidth: 200 } } } @media (min-width: 1024px) { .button-jss-0 { min-width: 200px; } } JSS in ES5 JSS in ES6 CSS Not possible Inline.

33 Keyframes Animation Keyframes Animation export default { '@keyframes my-animation': { from: {opacity: 0}, to: {opacity: 1} } } const identifier = random() export default { [`@keyframes ${identifier}`]: { from: {opacity: 0}, to {opacity: 1} } } @keyframes my-animation { from { opacity: 0; } to { opacity: 1; } } JSS in ES5 JSS in ES6 CSS Not possible Inline.

34 Font Face Font Face export default { '@font-face': { fontFamily: 'MyWebFont', src: [ 'url(webfont.eot)', 'url(webfont.eot?#iefix) format(embedded-opentype)', 'url(webfont.woff2) format(woff2)' ] } } @font-face { font-family: 'MyWebFont'; src: url('webfont.eot'); src: url('webfont.eot?#iefix') format('embedded-opentype'), url('webfont.woff2') format('woff2'); } JSS CSS Not possible Inline.

35 Pseudo Selectors Pseudo Selectors export default { button: { color: 'green' '&:hover': { color: 'red' }, '&:active': { color: blue }, '&:before': { content: '"icon"' }, '& span': { verticalAlign: 'middle' } } } .jss-0-1 { color: green; } .jss-0-1:hover { color: red; } .jss-0-1:active { color: blue; } .jss-0-1:before { content: "icon"; } .jss-0-1 span { vertical-align: middle; } JSS CSS Not possible Inline. Inspired by Sass.

36 Fallbacks Fallbacks export default { container: { display: ['box', 'flexbox','flex'] } } .jss-0-1 { display: box; display: flexbox; display: flex; } JSS CSS Not possible Inline.

37 Rules Caching Rules Caching Not possible Inline. CSS Rules are created just once.

38 Rules Sharing Rules Sharing Not possible Inline. One rule applies to all list items

39 Class Names are fast. Class Names are fast. 1. Find modified props. 2. Find props to unset. 3. Ensure valid property name, value, default unit. 4. Apply each property to an element

40 Smaller Payload Smaller Payload Up to 50% smaller payload when rendered at runtime.

41 Tools Agnostic Tools Agnostic Library agnostic. Infrastructure agnostic.

42 Extensible Extensible Small Core Plugins API.

43 Vendor Prefixer Vendor Prefixer Plugin export default { container: { display: 'flex' } } .jss-0-1 { display: -webkit-flex; } JSS CSS

44 Inheritance Inheritance Styles inherit from parent. Still no TRUE Isolation.

45 JSS-ISOLATE JSS-ISOLATE Created a JSS plugin. and SOLVED INHERITANCE PROBLEM Maxim Koretskiy “ This plugin protects styles from inheritance. It automatically creates a reset rule and applies it to every user's rule.

46 Unsolved Problems Unsolved Problems :( :(

47 Overengineered Overengineered Solution Solution If you feel it - don't use it.

48 Wrong Language? Wrong Language? import color from 'color' import fonts from 'theme/fonts' import mixins from 'jss-mixins' import {gainsboroLight, grapeTypo, grey, blue, white} from 'theme/colors' const grapeTypoSemi = color(grapeTypo).alpha(0.5).rgbaString() export default { datalist: { background: white, border: `1px solid ${gainsboroLight}`, boxShadow: `0px 3px 4px 0 ${grapeTypoSemi}`, overflow: 'auto' }, item: { extend: [fonts.normal, mixins.ellipsis], padding: `5px 7px`, color: grey, cursor: `pointer` }, `@media (min-width: 1024px)`: { item: { color: blue } } }

49 Let's experiment! Let's experiment! export default css` datalist { background: ${white}; border: 1px solid ${gainsboroLight}; box-shadow: 0px 3px 4px 0 ${grapeTypoSemi}; overflow: auto } item { extend: ${[fonts.normal, mixins.ellipsis]}; padding: 5px 7px; color: ${grey}; cursor: ${pointer}; } @media (min-width: 1024px) { item { color: ${blue} } } ` Tagged template literals

50 No standard DSL No standard DSL Styles reuse only together with the lib.

51 Missing dev tools Missing dev tools There is no autocomplete tools like Emmet or IntelliSense. There is no CSS specific highlighting. No linters.

52 Blocks initial Blocks initial rendering. rendering. Use it where it doesn't matter. Use server-side rendering. Use a hybrid approach.

53 Takeaways Takeaways CSS in JS is not only for big projects, it's for any maintainable project. Use Inline Styles for: 1. State styles. For e.g. when a "width" of a component depends on its state. 2. Animations. Don't be religious. Keep an open mind. Use tools that solve your problems!

54 Thank You Thank You #reactamsterdam @oleg008 https://github.com/jsstyles/jss