REACT IN 50 MINUTES #reactin50mins Maarten Mulders (@mthmulders) 

ABOUT ME @mthmulders @Java_Champions @OracleACE @InfoSupportBV #reactin50mins Maarten Mulders (@mthmulders) 

REACT... “ React is a library for declaratively building user interfaces using JavaScript and (optionally) XML. #reactin50mins Maarten Mulders (@mthmulders) 

REACT VS. OTHERS No two-way data binding No templating language Just user interface (no routing, no HTTP client) Plain JavaScript (or add JSX, TypeScript, ...) Virtual DOM vs. actual DOM #reactin50mins Maarten Mulders (@mthmulders) 

MODERN JAVASCRIPT #reactin50mins Maarten Mulders (@mthmulders) 

CLASSES class Amount { constructor(currency, value) { this.currency = currency; this.value = value; } getCurrency() { return this.currency; } } const text = new Amount('EUR', 15).getCurrency(); document.getElementById('app').innerText = text; 1 2 3 4 5 6 7 8 9 10 11 12 13 EUR #reactin50mins Maarten Mulders (@mthmulders) 

FUNCTIONS function isEven(number) { return number % 2 == 0; } const text = isEven(42) document.getElementById('app').innerText = text; 1 2 3 4 5 6 true #reactin50mins Maarten Mulders (@mthmulders) 

ARROW FUNCTIONS const isEven = (number) => { return number % 2 == 0; } const text = isEven(42) document.getElementById('app').innerText = text; 1 2 3 4 5 6 true #reactin50mins Maarten Mulders (@mthmulders) 

OBJECT DECOMPOSITION const person = { name : 'Jane Doe', age: 42, occupancy: 'JavaScript dev' }; const { name, age } = person; const text = age document.getElementById('app').innerText = text; 1 2 3 4 5 42 #reactin50mins Maarten Mulders (@mthmulders) 

ARRAY DECOMPOSITION const numbers = [ 'one', 'two', 'three' ]; const [ first, second ] = numbers; const text = second document.getElementById('app').innerText = text; 1 2 3 4 5 two #reactin50mins Maarten Mulders (@mthmulders) 

OBJECT SHORTHAND NOTATION const name = 'Jane Doe'; const age = 42; const person = { name, age }; const text = JSON.stringify(person) document.getElementById('app').innerText = text; 1 2 3 4 5 6 {"name":"Jane Doe","age":42} #reactin50mins Maarten Mulders (@mthmulders) 

STRING INTERPOLATION class Amount { constructor(currency, value) { this.currency = currency; this.value = value; } toString() { return `${this.currency} - ${this.value}`; } } const text = new Amount('EUR', 150).toString(); document.getElementById('app').innerText = text; 1 2 3 4 5 6 7 8 9 10 11 12 13 EUR - 150 #reactin50mins Maarten Mulders (@mthmulders) 

BASIC JSX #reactin50mins Maarten Mulders (@mthmulders) 

WHAT IS JSX? A syntax extension to JavaScript real XML, not a string of characters allows embedded expressions supports attributes Can be nested Automatic XSS prevention But it has its limitations Needs to be transpiled to JavaScript e.g. React.createElement(...) #reactin50mins Maarten Mulders (@mthmulders) 

ELEMENTS Elements can be regular DOM elements... (for now, but not for long) const element = ReactDOM.render(element, document.getElementById('app')); 1 2 Hello, world #reactin50mins Maarten Mulders (@mthmulders) 

ATTRIBUTES Elements can have attributes, but they can have different names than HTML attributes: const element = ReactDOM.render(element, document.getElementById('app')); 1 2 I'm blue #reactin50mins Maarten Mulders (@mthmulders) 

... and they can behave differently: const style = { color: 'red', fontWeight: 'bold' }; const element = ReactDOM.render(element, document.getElementById('app')); 1 2 3 I'm blue #reactin50mins Maarten Mulders (@mthmulders) 

SINGLE ROOT NODE Values must have a single root node (or an array) const element = [,] ReactDOM.render(element, document.getElementById('app')); 1 2 3 x y #reactin50mins Maarten Mulders (@mthmulders) 

COMPONENTS Function that returns a React element. const Greeter = (props) => ReactDOM.render(, document.getElementById('app')); 1 2 Hello, world! #reactin50mins Maarten Mulders (@mthmulders) 

ADVANCED JSX #reactin50mins Maarten Mulders (@mthmulders) 

EXPRESSIONS IN JSX const answerToQuestionOfLife = 40 + 2; const askQuestionOfLife = () => answerToQuestionOfLife; const Example = () => ; ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 The answer to the ultimate question of life, universe and everything: 42 #reactin50mins Maarten Mulders (@mthmulders) 

OR USE YOUR PROPS / ARGUMENTS! const Greeter = (props) => ReactDOM.render(, document.getElementById('app')); 1 2 Hello Dublin! #reactin50mins Maarten Mulders (@mthmulders) 

OR USE YOUR PROPS / ARGUMENTS! Alternatively, using object decomposition: const Greeter = ({ name }) => ReactDOM.render(, document.getElementById('app')); 1 2 Hello Dublin! #reactin50mins Maarten Mulders (@mthmulders) 

CONTROL STATEMENTS INSIDE JSX const ClapHands = () => Clapping hands...; const DryTears = () => Drying tears...; const ShowEmotion = ({ happy }) => happy ? : ; ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 Clapping hands... #reactin50mins Maarten Mulders (@mthmulders) 

CONTROL STATEMENTS INSIDE JSX (2) const Ticker = ({ symbol }) => ; const TickerList = ({ symbols }) => symbols.map( (symbol) => ); const symbols = ['HEIA', 'PHIA']; ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 HEIA PHIA #reactin50mins Maarten Mulders (@mthmulders) 

REACT "MAGIC" #reactin50mins Maarten Mulders (@mthmulders) 

AT BUILD TIME So far, we've written components and wired them together. Babel or tsc transpiles them to React.createElement(...) invocations: /** transpiles into */ React.createElement(Greeter, { name: 'World' }, null) #reactin50mins Maarten Mulders (@mthmulders) 

AT RUN TIME The React.createElement invocations form a tree of components. React maintains a virtual DOM based on your component tree. The virtual DOM is compared to the actual DOM. Only necessary changes are executed. #reactin50mins Maarten Mulders (@mthmulders) 

RECONCILIATION React syncs the virtual and the actual DOM based on two assumptions: 1. If two elements are of different type, the (sub) tree will be different. 2. The key prop identifies child elements over re-renders. This tells React what makes two elements "the same". #reactin50mins Maarten Mulders (@mthmulders) 

1. ELEMENTS OF DIFFERENT TYPE const DutchGreeter = ({ name }) => ; const EnglishGreeter = ({ name }) => ; const IrishGreeter = ({ name }) => ; const App = ({ lang, name }) => { switch(lang) { case 'ie': return case 'nl': return case 'en': default : return } }; ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 10 11 12 13 🇳🇱 Hallo, Dublin! #reactin50mins Maarten Mulders (@mthmulders) 

2. THE key PROP const randomPrice = () => 100 + Math.floor(Math.random() * 900) const Ticker = ({ symbol }) => { symbol }: { randomPrice() } — ; const symbols = ['HEIA', 'PHIA', 'ASML', 'KLMR'].map( (symbol) => ); ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 #reactin50mins Maarten Mulders (@mthmulders) 

YOUR ENVIRONMENT 1. Keeping state 2. Reacting to events 3. Fetching data over HTTP 4. Storing data #reactin50mins Maarten Mulders (@mthmulders) 

LOCAL STATE INSIDE A COMPONENT const Counter = () => { const [ counter, setCounter ] = React.useState(0); return } ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 Counter: 0 #reactin50mins Maarten Mulders (@mthmulders) 

REACTING TO EVENTS Similar to DOM event handling, but 1. event names are different: onClick vs onclick. 2. event handlers are always functions, never strings. 3. event handlers are bound to a component, should not live globally. 4. event handlers receive an synthetic event - browser-agnostic! #reactin50mins Maarten Mulders (@mthmulders) 

CLICK CALLBACKS const Counter = () => { const [ counter, setCounter ] = React.useState(0); const increase = () => setCounter(counter + 1); const decrease = () => setCounter(counter - 1); return } ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 10 11 12 Counter: 0 + - #reactin50mins Maarten Mulders (@mthmulders) 

CHANGE CALLBACKS const Greeter = () => { const [ name, setName ] = React.useState(''); const updateName = (e) => setName(e.target.value); const callback = () => alert(`Hi ${name}`); return } ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 10 Greet ! #reactin50mins Maarten Mulders (@mthmulders) 

FETCHING DATA OVER HTTP What we need: 1. A bit of Plain Old JavaScript to fetch some data 2. A component to show the fetched data #reactin50mins Maarten Mulders (@mthmulders) 

1. A DATA RETRIEVAL API const url = 'https://opendata.rdw.nl/resource/m9d7-ebf2.json'; const getCar = (licenseNumber) => { return fetch(url + '?kenteken=' + licenseNumber) }; #reactin50mins Maarten Mulders (@mthmulders) 

1. A DATA RETRIEVAL API const checkStatus = (response) => { if (response.status >= 200 && response.status < 300) { return Promise.resolve(response); } else { return Promise.reject(`HTTP error ${response.status}: ${response.statusText}`); } }; const url = 'https://opendata.rdw.nl/resource/m9d7-ebf2.json'; const getCar = (licenseNumber) => { return fetch(url + '?kenteken=' + licenseNumber) .then(checkStatus) }; #reactin50mins Maarten Mulders (@mthmulders) 

1. A DATA RETRIEVAL API const checkStatus = (response) => { if (response.status >= 200 && response.status < 300) { return Promise.resolve(response); } else { return Promise.reject(`HTTP error ${response.status}: ${response.statusText}`); } }; const parseJson = (response) => response.json(); const url = 'https://opendata.rdw.nl/resource/m9d7-ebf2.json'; const getCar = (licenseNumber) => { return fetch(url + '?kenteken=' + licenseNumber) .then(checkStatus) .then(parseJson) }; #reactin50mins Maarten Mulders (@mthmulders) 

1. A DATA RETRIEVAL API const checkStatus = (response) => { if (response.status >= 200 && response.status < 300) { return Promise.resolve(response); } else { return Promise.reject(`HTTP error ${response.status}: ${response.statusText}`); } }; const parseJson = (response) => response.json(); const url = 'https://opendata.rdw.nl/resource/m9d7-ebf2.json'; const getCar = (licenseNumber) => { return fetch(url + '?kenteken=' + licenseNumber) .then(checkStatus) .then(parseJson) .then(response => `${response[0].merk} ${response[0].handelsbenaming}`); }; #reactin50mins Maarten Mulders (@mthmulders) 

2. A COMPONENT TO SHOW THE FETCHED DATA const ShowCar = () => { const [ { car, loading }, setState ] = React.useState({ loading: true }); const fetchCarDetails = async (licenseNumber) => { const car = await getCar(licenseNumber); setState({loading: false, car}); } React.useEffect(() => { fetchCarDetails('33JFX4'); }, [ ]); return loading ? : ; }; ReactDOM.render(, document.getElementById('app')); 1 2 3 4 5 6 7 8 9 10 11 12 13 OPEL ZAFIRA #reactin50mins Maarten Mulders (@mthmulders) 

STORING DATA IN YOUR BROWSER Local Storage & Session Storage Part of the Stores and retrieves string values Serialise objects with JSON.stringify() Deserialise with JSON.parse() Persistent during browser session with sessionStorage over browser shutdowns with localStorage Web Storage API #reactin50mins Maarten Mulders (@mthmulders) 

DELIVERING APPS 1. Debugging 2. Testing 3. Building #reactin50mins Maarten Mulders (@mthmulders) 

DEBUGGING Install the React Developer Tools for your browser of choice. #reactin50mins Maarten Mulders (@mthmulders) 

INSPECTING COMPONENT TREE #reactin50mins Maarten Mulders (@mthmulders) 

DEBUGGING #reactin50mins Maarten Mulders (@mthmulders) 

TESTING YOUR COMPONENTS Use Jest (test platform & library) and (React) Testing Library (testing utilities) Render a React component in a unit test Make assertions about its output and behaviour #reactin50mins Maarten Mulders (@mthmulders) 

TESTING A SIMPLE COMPONENT import { render, screen } from '@testing-library/react' describe('', () => { it('should render text', () => { render(); expect(screen.getByText(/hello, Dublin/i)).toBeVisible(); }); }); #reactin50mins Maarten Mulders (@mthmulders) 

TESTING BEHAVIOUR OF A COMPONENT import { fireEvent, render, screen } from '@testing-library/react' describe('', () => { it('should invoke action on click', () => { const callback = jest.mock(); render(); fireEvent.click(screen.getByRole('link')); expect(callback).toHaveBeenCalled(); }); }); #reactin50mins Maarten Mulders (@mthmulders) 

DEVELOPING & SHIPPING AN APP tl;dr: use (CRA) Uses Webpack, Babel, ESLint and a dozen of other tools Tested to work together Live-reloading of changed code Source maps for easy debugging Have an ready-to-go app in one command Create React App npx create-react-app my-next-killer-app // or npm i -g create-react-app create-react-app my-next-killer-app #reactin50mins Maarten Mulders (@mthmulders) 

USING CRA npm run start to start developing npm run build to create a production build npm run test to run unit tests #reactin50mins Maarten Mulders (@mthmulders) 

TAKE AWAYS Use Create React App Think in (small) components Think declaratively #reactin50mins Maarten Mulders (@mthmulders) 

THANK YOU! REFERENCES & MORE INFORMATION Create React App Philippe De Ryck on "Building Secure React Applications" @mthmulders #reactin50mins Maarten Mulders (@mthmulders)