Modular CSS — Agent Conf '17 Edition

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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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I design & develop User Interfaces

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Building scalable User Interfaces

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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 for web-applications

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User Interface ∋ Components

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Libraries & Frameworks based on 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 component!

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In React.js everything is a component!

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Button component Default Active Disabled

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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 += ' disabled' 4 return ( 5 10 11 { children } 12 13 14 ) 15 }

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

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Let’s add some CSS 1 .btn { 2 /* styles for button */ 3 } 4 5 .active { 6 /* styles for active button */ 7 background-color: blue; 8 } 9 10 .label { 11 /* styles for button label */ 12 }

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Button component Default Active Disabled Default Disabled Active

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Button component Active Click me! Active

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Star component

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Star.js 1 const Star = ({ active }) => { 2 let classNames = 'star' 3 if (active) classNames += ' active' 4 return ( 5 6 ) 7 }

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Let’s add some CSS 1 .star { 2 /* styles for star */ 3 } 4 5 .active { 6 /* styles for active star */ 7 background-color: orange; 8 } 9

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Star component

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f(props, state) => UI

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UI components should be pure, modular & isolated

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• Props • State • Styles Button

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• Props • State • Styles Button • Props • State • Styles • Props • State • Styles

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• Props • State • Styles Button • Props • State • Styles • Props • State • Styles

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and yet…

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• Props • State • Styles Button • Props • State • Styles • Props • State • Styles Global styles

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Global CSS 1 .btn { 2 /* styles for button */ 3 } 4 5 .active { 6 /* styles for active button */ 7 background-color: blue; 8 } 9 10 .label { 11 /* styles for button label */ 12 } 1 .star { 2 /* styles for star */ 3 } 4 5 .active { 6 /* styles for active star */ 7 background-color: orange; 8 } 9

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.btn.active

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.content .albums .album .btn

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http://www.standardista.com/css3/css-speciﬁcity/

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Debugging CSS

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.btn.active

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Where are my styles?

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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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Refactoring application.css

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Problems with CSS in Web Applications Disconnected from component’s code Implicit dependencies No styles isolation No composition & code sharing

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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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CSS pre-processors?

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Dependencies in Sass 1 /* Global styles */ 2 @import 'reset.css'; 3 @import 'typography.css'; 4 @import 'grid.css'; 5 6 /* Components */ 7 @import 'button.css';

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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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Explicit dependencies FTW! 1 import './Button.css' 2 3 const Button = ({ children, disabled, active }) => { 4 let classNames = 'btn' 5 if (disabled) classNames += ' disabled' 6 if (active) classNames += ' active' 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

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3. We want minimal number of HTTP requests

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Common build tools operate on ﬁle trees

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Dependency graph

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http://webpack.github.io/

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Allow requiring CSS with Webpack 1 module.exports = { 2 module: { 3 loaders: [ 4 { 5 test: /\.css$/, 6 use: ["style-loader", "css-loader"] 7 } 8 ] 9 } 10 };

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Now we can import CSS in JS! 1 import './Button.css' 2 3 const Button = ({ children, disabled, active }) => { 4 let classNames = 'btn' 5 if (disabled) classNames += ' disabled' 6 if (active) classNames += ' active' 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 Composition & code sharing ✅ Disconnected from component’s code ✅ Implicit dependencies

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3. Styles isolation

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BEM https://en.bem.info/

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B E M Block Element Modiﬁer Button Button__label Button --active

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Without BEM Click me!

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With BEM Click me!

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

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

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BEM ✅ Global namespace ✅ Styles isolation Not beginner friendly Very verbose Requires discipline Long class names

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

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The result 1 styles: { 2 root: "Button__root__abc5436", 3 disabled: "Button__disabled__def6 4 active: "Button__active__1638bcd" 5 label: "Button__label__5dfg462" 5 } 1 /* Button.css */ 2 3 .root { /* general rules */ } 4 .disabled { /* disabled rules */ } 5 .active { /* active rules */ } 6 .label { /* label rules */ }

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Before: BEM-style 1 import './Button.css' 2 3 const Button = ({ children, disabled, active }) => { 4 let classNames = 'Button' 5 if (disabled) classNames += ' Button --disabled' 6 if (active) classNames += ' Button --active' 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, active }) => { 4 let className = {styles.root} 5 if (disabled) className = {styles.disabled} 6 if (active) className = {styles.active} 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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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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BEM-like class names 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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import styles from './Button.css' /* styles = { button: ‘Button__root__3fslE’, label: ‘Button__label__I8bKh’ } */ name local hash BEM-like class names

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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 --active { /* active 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 --active { 7 @extends .Button --common; 8 /* white color, blue background */ 9 }

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Composition with Sass 1 .Button --common, .Button --disabled, .Button --active { 2 /* common rules */ 3 } 4 .Button --disabled { 5 /* gray color, light background */ 6 } 7 .Button --active { 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 .active { /* active 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 .active { 9 composes: root; 10 /* active 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 active: "Button__root__abc5436 Button__active__1638bcd" 5 }

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

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The result Click me! Click me!

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

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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 allow 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 https://github.com/css-modules/cssm-rails

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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 and faster than pre-processors thanks AST 2. Lots of plugins and easy to write your own 3. Tools! stylelint or automatic properties sorting 4. IDE Support (WebStorm, Atom, Sublime) 5. Shared constants between CSS and JS 6. Works not only with SPAs or React 7. It’s just CSS*

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http://postcss.org

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How to setup

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

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http://postcss.parts/ by @mxstbr

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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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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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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 Freelance UI-Developer