Higher Order Components in React at italian jsDay 2016

React is “a Javascript library for building user interfaces”. The core of React follows many concepts of Functional Programming, code composition is one of its main features. In React there are 2 main types of building blocks: 'stateful' components and 'stateless' components. The former type is defined by elements owning the application logic; this kind of components often is bound to external elements and owns a state. The latter type is composed of 'pure' components where all dynamic data is received from their props and no internal state is defined. This approach often produces replication of functionalities in several components; 'Higher Order Components' (HoC) is the natural solution for this scenario and is a more functional alternative to traditional React 'mixins'. An HoC abstracts component functionalities and offers an easy way to compose them when required making the code more maintainable and avoiding duplicates. During the session we will see how to implements this pattern taking attention on its pros and cons.

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1. higher order components In react 2016
2. Senior engineer @ . Italian react & angular communities Matteo Ronchi @cef62 github/cef62
3. From Documents to components
4. <div> <h1>Title Text</h1> <p>Some text about something</p> </div> HyperText Markup Language
5. <div> <h1 id=“my-title”></h1> <p id=“my-contents”></p> </div> <script type=“text/javascript”> $(document).ready(() => { $.ajax(‘my-url.php’) .done((data) => { $(‘#my-title’).text(data.title) $(‘#my-contents’).text(data.contents) }) }) </script> jQuery
6. <div ng-app=“app”> <my-page my-url=“my-url.php”></my-page> </div> <script type=“text/javascript”> angular.module(‘app’, []).directive(‘myPage’, function($http) { return { scope: { myUrl: ‘@’} template: `<div> <h1>{{myTitle}}</h1> <p>{{myContents}}</p> </div>` link: function(scope) { $http.get(scope.myUrl).success((data) => { scope.myTitle = data.title scope.myContents = data.contents }) } } }) </script> AngularJS
7. <div id=“root” /> <script type=“text/javascript”> class App extends React.Component { componentWillMount() { axios.get(this.props.myUrl).then(({ title, contents }) => { this.setState({ title, contents }) }) } render() { return ( <div> <h1>{this.state.title}</h1> <p>{this.state.contents}</p> </div> ) } } ReactDOM.render(<App myUrl=“my-url.php” />, document.getElementById(‘root’)) </script> React
8. react angular 2 polymer all modern frameworks are component oriented
9. Everything is a Component an application is a tree of components
10. Components are • Composable • Encapsulated • Reusable • Easy to design
11. presentational components small, reusable, pure functions, easy to test
12. const Label = (props) => <h1>{props.children}</h1> const Icon = (props) => { return ( <i className="fa fa-anchor"> {props.label} </i> ) } const App = () => <div> <Label>Some label</Label> <Icon label="ready to sail" /> </div> Stateless Functional Components
13. Component lifecycle
14. class MyComponent extends React.Component { // Component Initialization constructor(props) {} // component ready to be mounted componentWillMount() {} // Props have changed componentWillReceiveProps(nextProps) {} // prevent rendering if not required shouldComponentUpdate(nextProps, nextState) {} // Prepare before rendering componentWillUpdate(nextProps, nextState) {} } Component Lifecycle
15. class MyComponent extends React.Component { // create/update the component render() {} // Component DOM it’s been created componentDidMount() {} // Component DOM it’s been updated componentDidUpdate(prevProps, prevState) {} // cleanup before component destruction componentWillUnmount() {} } Component Lifecycle
16. Container Components Context-aware, stateful, dynamic, powerful
17. class Toggle extends React.Component { constructor(props) { super(props) this.state = { enabled: false } this.toggle = this.toggle.bind(this) } toggle() { this.setState({ enabled: !this.state.enabled }) } render() { const cls = this.state.enabled ?'btn-success':'btn-danger' return ( <button className={‘btn ‘ + cls} onClick={this.toggle}> {this.props.label} </button> ) } } Stateful Components
18. REDUCE code boilerplAte
19. class Box extends React.Component { constructor(props) { this.state = { info: {} } } componentWillMount() { axios.get(this.props.url).then( ({ data }) => this.setState({ info: data }) ) } render() { return <div>{this.state.info.text}</div> } } class User extends React.Component { constructor(props) { this.state = { user: {} } } componentWillMount() { axios.get(this.props.url).then( ({ data }) => this.setState({ user: data }) ) } render() { return <div>{this.state.user.name}</div> } } Components Share Functionalities
20. REACT mixins
21. const LoadDataMixin = { loadData(url, targetField) { axios.get(url).then( ({ data }) => this.setState({ [targetField]: data }) ) } } React Mixins
22. const BoxInfo = React.createClass({ mixins: [LoadDataMixin], getInitialState() { return { info: {} } }, componentWillMount() { this.loadData(this.props.url, 'info') }, render() { return <div>{this.state.info.text}</div> } }) const UserPanel = React.createClass({ mixins: [LoadDataMixin], getInitialState() { return { user: {} } }, componentWillMount() { this.loadData(this.props.url, 'user') }, render() { return <div>{this.state.user.name}</div> } }) React Mixins
23. higher order functions
24. — Marijn Haverbeke ( eloquent javascript ) Higher-order functions allow us to abstract over actions, not just values.
25. function applyVat(vat) { return (value) => ((vat + 100) / 100) * value } const applyVat22 = applyVat(22) console.log(applyVat22(100)) // print -> 122 function maybe(condition, action) { if (condition) { action() } } const action = (msg) => () => console.log(msg) maybe(true, action(`It works!`)) maybe(false, action(`Doesn't work!`)) // print -> It works! HoF
26. From Higher order functions ( TO ) Higher order components
27. const Wrapped = () => <h1>Wrapped Comp</h1> const wrapper = (Comp) => () => { return <div><Comp /></div> } const FinalComponent = wrapper(Wrapped) const App = () => { return ( <div> <FinalComponent /> </div> ) } Simple HoC
28. const loadData = (Component) => { return class LoadDataWrapper extends React.Component { constructor(props) { this.state = { data: {} } } componentWillMount() { axios.get(this.props.url).then( ({ data }) => this.setState({ data }) ) } render() { const props = Object.assign({}, this.props, this.state) return React.createElement(Component, props) } } } const Box = loadData((props) => <div>{props.data.text}</div>) const User = loadData((props) => <div>{props.data.name}</div>) Reduce Duplication of Code
29. @loadData class Box extends React.Component { render() { return <div>{this.props.data.text}</div> } } @loadData class User extends React.Component { render() { return <div>{this.props.data.name}</div> } } // See https://github.com/wycats/javascript-decorators Decorator Proposal
30. HoC vs Mixins - Declarative - Customizable - Easy to read - Enforce composition Imperative - Favors inheritance - Hard to read - Method names collision - Access component state -
31. HoC - Best Practices • Expose wrapped component • Pass props to wrapped component • Expose statics methods and props from wrapped component
32. code See online
33. thanks ! @CEF62