Modular CSS - Speaker Deck

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Modular CSS with @okonetchnikov

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Andrey Okonetchnikov @okonetchnikov

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ColorSnapper http://colorsnapper.com

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kaﬀemik Zollergasse 5, 1070 Wien

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I ❤ Open Source github.com/okonet/react-dropzone github.com/okonet/lint-staged and many more…

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Modular CSS

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I design & develop User Interfaces

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Building scalable User Interfaces

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User Interface ∋ Components

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Libraries & Frameworks using UI components

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What are UI Components?

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List component Button Button

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List Item Component Button

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Atomic components Button

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Let’s build a Button!

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Button component Default Primary Disabled

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In React.js everything is a component!

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Button.js 1 const Button = ({ children }) => { 2 return ( 3 6 { children } 7 8 ) 9 }

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Button.js 1 const Button = ({ children }) => { 2 return ( 3 7 8 { children } 9 10 11 ) 12 }

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Button.js 1 const Button = ({ children, disabled }) => { 2 return ( 3 8 9 { children } 10 11 12 ) 13 }

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Button.js 1 const Button = ({ children, disabled }) => { 2 let classNames = 'btn' 3 if (disabled) classNames += ' btn --disabled' 4 return ( 5 10 11 { children } 12 13 14 ) 15 }

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Button.js 1 const Button = ({ children, disabled, primary }) => { 2 let classNames = 'btn' 3 if (disabled) classNames += ' btn --disabled' 4 if (primary) classNames += ' btn --primary’ 5 return ( 6 11 12 { children } 13 14 15 ) 16 }

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Button component Default Primary Disabled Default Disabled Primary

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Anatomy of the component

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• Input • State • Behavior • Styles Button

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f(props) => UI

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UI components should be pure, self-contained & isolated

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• Input • State • Behavior • Styles Button • Input • State • Behavior • Styles • Input • State • Behavior • Styles

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• Input • State • Behavior • Styles Button • Input • State • Behavior • Styles • Input • State • Behavior • Styles

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and yet…

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• Input • State • Behavior • Styles Button • Input • State • Behavior • Styles • Input • State • Behavior • Styles Global styles

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CSS is to blame?

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Problems with CSS on scale Disconnected from component’s code Implicit dependencies No styles isolation Constants sharing Miniﬁcation

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What can we do about it?

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Where is my CSS? 1 const Button = ({ children }) => { 2 return ( 3 7 8 { children } 9 10 11 ) 12 }

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Where is my CSS? Where is this class coming from? 1 const Button = ({ children }) => { 2 return ( 3 7 8 { children } 9 10 11 ) 12 }

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Let’s search quickly…

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CSS Monolith!

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application.css

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1. Split your code

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Components > Files public ├── images │ └── icon.svg ├── javascripts │ ├── Button.js │ └── Dropdown.js └── stylesheets ├── Buttons.css └── Dropdown.css public ├── images │ └── icon.svg ├── javascripts │ └── application.js └── stylesheets └── application.css

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1. Split & co-locate

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Separation of concerns? public ├── images │ └── icon.svg ├── javascripts │ ├── Button.js │ └── Dropdown.js └── stylesheets ├── Buttons.css └── Dropdown.css

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Separation of concerns technologies public ├── images │ └── icon.svg ├── javascripts │ ├── Button.js │ └── Dropdown.js └── stylesheets ├── Buttons.css └── Dropdown.css

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Separation of concerns components ├── Button │ ├── Button.css │ ├── Button.js │ ├── Button.spec.js │ ├── icon.svg │ └── index.js └── Dropdown public ├── images │ └── icon.svg ├── javascripts │ ├── Button.js │ └── Dropdown.js └── stylesheets ├── Buttons.css └── Dropdown.css

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2. Dependencies

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Explicit dependencies 1 import './Button.css' 2 3 const Button = ({ children, disabled, primary }) => { 4 let classNames = 'btn' 5 if (disabled) classNames += ' btn-disabled' 6 if (primary) classNames += ' btn-primary' 7 return ( 8 13 14 { children } 15 16 17 ) 18 } 19 export default Button

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1. We can’t require CSS in JS

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2. Browsers expect and tags

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3. We want minimize the number of requests

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Common build tools operate on ﬁle trees

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Dependency graph FTW!

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http://webpack.github.io/

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Allow requiring CSS with Webpack module.exports = { module: { loaders: [ { test: /\.css$/, loader: "style-loader!css-loader" }, { test: /\.png$/, loader: "url-loader?limit=10000" }, { test: /\.js$/, loader: "babel-loader" } ] } }; • Load CSS ﬁles, • Embed PNG images under 10Kb as Data URIs • Transpile JS ﬁles with Babel

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Now we can just import CSS! 1 import './Button.css' 2 3 const Button = ({ children, disabled, primary }) => { 4 let classNames = 'btn' 5 if (disabled) classNames += ' btn-disabled' 6 if (primary) classNames += ' btn-primary' 7 return ( 8 13 14 { children } 15 16 17 ) 18 } 19 export default Button

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Tips & Tricks ✅ Split your code by components ✅ One directory per UI component ✅ One CSS ﬁle per UI component ✅ Explicit dependencies ✅ Co-locate JS, CSS and assets

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How are we doing so far? No styles isolation Constants sharing Miniﬁcation ✅ Disconnected from component’s code ✅ Implicit dependencies

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3. Styles isolation

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– http://www.csszengarden.com/ “CSS allows complete and total control over the style of a hypertext document…”

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CSS was designed for documents, not web-applications

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CSS = Cascading Style Sheets

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– MDN “Three main sources of style information form a cascade. […] The user's style modiﬁes the browser's default style. The document author's style then modiﬁes the style some more.”

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Designing with cascade is like extending the DOM with JavaScript!

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– by @kangax http://perfectionkills.com/whats-wrong-with-extending-the-dom/ “DOM extension seemed so temptingly useful that few years ago, Prototype Javascript library made it an essential part of its architecture. But what hides behind seemingly innocuous practice is a huge load of trouble. […] DOM extension is one of the biggest mistakes Prototype.js has ever done.”

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Debugging CSS

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BEM https://en.bem.info/

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Using BEM 1 import './Button.css' 2 3 const Button = ({ children, disabled, primary }) => { 4 let classNames = 'Button' 5 if (disabled) classNames += ' Button --disabled' 6 if (primary) classNames += ' Button --primary' 7 return ( 8 13 14 { children } 15 16 17 ) 18 } 19 export default Button

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Using BEM 1 /* Button.css */ 2 3 .Button { /* general rules */ } 4 .Button --disabled { /* disabled rules */ } 5 .Button --primary { /* primary rules */ } 6 .Button__label { /* label rules */ }

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BEM ✅ Global namespace ✅ Cascade* ✅ No styles isolation Not beginner friendly Very verbose Requires discipline Miniﬁcation

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@markdalgleish

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CSS-modules https://github.com/css-modules/css-modules

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How CSS-modules work

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Enabling CSS-modules 1 // webpack.config.js 2 3 module.exports = { 4 module: { 5 loaders: [ 6 { 7 test: /\.css$/, 8 loader: "css" 9 } 10 ] 11 } 12 };

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Enabling CSS-modules 1 // webpack.config.js 2 3 module.exports = { 4 module: { 5 loaders: [ 6 { 7 test: /\.css$/, 8 loader: "css?modules" 9 } 10 ] 11 } 12 };

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Before: BEM-style 1 /* Button.css */ 2 3 .Button { /* general rules */ } 4 .Button --disabled { /* disabled rules */ } 5 .Button --primary { /* primary rules */ } 6 .Button__label { /* label rules */ }

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After: CSS-modules 1 /* Button.css */ 2 3 .root { /* general rules */ } 4 .disabled { /* disabled rules */ } 5 .primary { /* primary rules */ } 6 .label { /* label rules */ }

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Before: BEM-style 1 import './Button.css' 2 3 const Button = ({ children, disabled, primary }) => { 4 let classNames = 'Button' 5 if (disabled) classNames += ' Button --disabled' 6 if (primary) classNames += ' Button --primary' 7 return ( 8 13 14 { children } 15 16 17 ) 18 } 19 export default Button

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1 import styles from './Button.css' 2 3 const Button = ({ children, disabled, primary }) => { 4 let className = {styles.root} 5 if (disabled) className = {styles.disabled} 6 if (primary) className = {styles.primary} 7 return ( 8 13 14 { children } 15 16 17 ) 18 } 19 export default Button After: CSS-modules

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The result Click me! Click me!

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The result 1 styles: { 2 root: "Button__root__abc5436", 3 disabled: "Button__disabled__def6 4 primary: "Button__primary__1638bc 5 label: "Button__label__5dfg462" 5 } 1 /* Button.css */ 2 3 .root { /* general rules */ } 4 .disabled { /* disabled rules */ } 5 .primary { /* primary rules */ } 6 .label { /* label rules */ }

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Prettier class names in dev 1 // webpack.config.js 2 3 module.exports = { 4 module: { 5 loaders: [ 6 { 7 test: /\.css$/, 8 loader: "css?modules 9 &localIdentName=[name]__[local]__[hash:base64:5]" 10 11 } 12 ] 13 } 14 };

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Prettier class names in dev import styles from './Button.css' /* styles = { button: ‘Button__root__3fslE’, label: ‘Button__label__I8bKh’ } */ name local hash

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BEM for free! ❤

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4. Composition & code sharing

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Composition with Sass 1 /* Button.css */ 2 3 .Button { /* common rules */ } 4 .Button --disabled { /* disabled rules */ } 5 .Button --primary { /* primary rules */ }

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Composition with Sass 1 .Button --common { /* common rules */ } 2 .Button --disabled { 3 @extends .Button --common; 4 /* gray color, light background */ 5 } 6 .Button --primary { 7 @extends .Button --common; 8 /* white color, blue background */ 9 }

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Composition with Sass 1 .Button --common, .Button --disabled, .Button --primary { 2 /* common rules */ 3 } 4 .Button --disabled { 5 /* gray color, light background */ 6 } 7 .Button --primary { 8 /* white color, blue background */ 9 }

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Composition with CSS-modules 1 /* Button.css */ 2 3 .root { /* general rules */ } 4 .disabled { /* disabled rules */ } 5 .primary { /* primary rules */ }

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Composition with CSS-modules 1 /* Button.css */ 2 3 .root { /* general rules */ } 4 .disabled { 5 composes: root; 6 /* disabled rules */ 7 } 8 .primary { 9 composes: root; 10 /* primary rules */ 11 }

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Composition with CSS-modules 1 styles: { 2 root: "Button__root__abc5436", 3 disabled: "Button__root__abc5436 Button__disabled__def6547", 4 primary: "Button__root__abc5436 Button__primary__1638bcd" 5 }

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Use only one class name! 1 /* Don't do this */ 2 `class=${[styles.normal, styles['primary']].join(" ")}` 3 4 /* Using a single name makes a big difference */ 5 `class=${styles['primary']}` 6 7 /* camelCase makes it even better */ 8 `class=${styles.isPrimary}`

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The result Click me! Click me!

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Compose from other ﬁles! 1 /* colors.css */ 2 .primary { 3 background-color: #4399fa; 4 } 5 .secondary { 6 background-color: #999; 7 } 1 /* Button.css */ 2 .root { /* general rules */ } 3 .primary { 4 composes: root; 5 composes: primary from ' ../colors.css'; 6 /* primary rules */ 7 }

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Or use variables! /* variables.css */ @value small: (max-width: 599px); /* component.css */ @value small from "./variables.css"; .pageContent { background: green; @media small { background: red; } }

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5. Miniﬁcation

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Miniﬁcation 1 // webpack.config.js 2 3 module.exports = { 4 module: { 5 loaders: [ 6 { 7 test: /\.css$/, 8 loader: "css?modules" 9 } 10 ] 11 } 12 };

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Miniﬁcation Click me! Click me!

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Solved with CSS-modules ✅ No styles isolation ✅ Constants sharing ✅ Miniﬁcation ✅ Disconnected from component’s code ✅ Implicit dependencies

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CSS-modules overview

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Local by default but allows exceptions .local-class { color: red; } :global(.prefix-modal-open) .local-class { color: green; }

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Composition .common { /* all the common styles you want */ } .normal { composes: common; /* anything that only applies to Normal */ } .disabled { composes: common; /* anything that only applies to Disabled */ }

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Explicit dependencies .otherClassName { composes: className from "./style.css"; }

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Import variables /* variables.css */ @value small: (max-width: 599px); /* component.css */ @value small from "./breakpoints.scss"; .pageContent { background: green; @media small { background: red; } }

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Use with pre-processors like Sass or Less :global { .this-is-global { color: yellow; } .potential-collision-city { color: crap; } }

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Works on server, too! https://github.com/css-modules/postcss-modules

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FTW!

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PostCSS http://postcss.org

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Like Babel, but for CSS

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How PostCSS works

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What’s possible?

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Autopreﬁxer :full-screen { } :-webkit-:full-screen { } :-moz-:full-screen { } :full-screen { }

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Sass/less syntax

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Browser hacks

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Local CSS .name { color: gray; } .Logo__name__SVK0g { color: gray; }

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CSS next :root { --red: #d33; } a { &:hover { color: color(var( --red) a(54%)); } } a:hover { color: #dd3333; color: rgba(221, 51, 51, 0.54); }

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Stylelint a { color: #4f; }

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PostCSS overview 1. More powerful than pre-processors thanks AST 2. ⚡Fast (a few times faster than Sass) 3. Lots of plugins and easy to write your own 4. Tools like linting or automatic properties sorting 5. IDE Support (WebStorm, Atom, Sublime) 6. Shared constants between CSS and JS 7. Works not only with SPAs or React 8. It’s just CSS*

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How to setup

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http://postcss.org

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Example setup with Webpack module.exports = { module: { loaders: [ { test: /\.css$/, loader: ‘style!css&importLoaders=1!postcss-loader' } ] }, postcss: function() { return [ require('precss'), require('postcss-calc'), require('autoprefixer')({ browsers: ['last 2 version'] }) ]; } };

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Lint CSS as pre-commit hook 1 { 2 "lint-staged": { 3 "*.css": "stylelint" 4 }, 5 "pre-commit": "lint-staged", 6 "stylelint": { 7 "extends": "stylelint-config-standard" 8 } 9 } https://github.com/okonet/lint-staged

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http://postcss.parts/ by @mxstbr

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Do I need it?

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Do I need it? ✅ You work in a team ✅ You plan to update your CSS in the future ✅ You use third-party CSS and don’t want to break things ✅ You care about code readability and reusability ✅ You hate manual work

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What about CSS-in-JS?

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Inline styles in JSX ✅ JS is more powerful ✅ Runtime re-calculation ✅ Dead code elimination No pseudo-selectors No media queries React.js-only Harder to debug in DevTools No IDE support No tooling

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CSS-in-JS ✅ JS is more powerful ✅ Shared variables ✅ Dead code elimination No sourcemaps* No IDE support* No related tools*

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Worth checking out by @mxstbr and @glennmaddern by @oleg008

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– Glen Maddern https://github.com/css-modules/css-modules/issues/187#issuecomment-257752790 “[…] I wouldn’t suggest using any CSS-in-JS tool over CSS Modules for decent-sized projects in the near term.”

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Final thoughts

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It’s not about writing code, it’s about reading it.

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Build isolated components.

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Separate concerns, not technologies.

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Treat CSS seriously. It’s here to stay.

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Choose the right tool for the job.

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Stay open-minded & keep experimenting!

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Thank you!

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Andrey Okonetchnikov @okonetchnikov http://okonet.ru https://github.com/okonet UI Engineer