Les meilleurs exemples de réaction

React (également connu sous le nom de React.js) est l'une des bibliothèques de développement frontales JavaScript les plus populaires. Voici une collection de syntaxe et d'utilisation de React que vous pouvez utiliser comme guide pratique ou référence.

Exemple de composant React

Les composants sont réutilisables dans React.js. Vous pouvez injecter de la valeur dans les accessoires comme indiqué ci-dessous:

function Welcome(props) { return 

Hello, {props.name}

; } const element = ; ReactDOM.render( element, document.getElementById('root') );

name="Faisal Arkan"donnera une valeur à {props.name}from function Welcome(props)et retournera un composant qui a donné une valeur par name="Faisal Arkan". Après cela, React rendra l'élément en html.

Autres façons de déclarer des composants

Il existe de nombreuses façons de déclarer des composants lors de l'utilisation de React.js. Il existe deux types de composants, les composants sans état et les composants avec état .

Avec état

Composants de type classe

class Cat extends React.Component { constructor(props) { super(props); this.state = { humor: 'happy' } } render() { return( 

{this.props.name}

{this.props.color}

); } }

Composants sans état

Composants fonctionnels (fonction de flèche de ES6)

const Cat = props => { return ( 

{props.name}

{props.color}

; ); };

Composants de retour implicites

const Cat = props =>

{props.name}

{props.color}

;

Exemple de fragment de réaction

Les fragments sont un moyen de rendre plusieurs éléments sans utiliser d'élément wrapper. Lorsque vous essayez de rendre des éléments sans balise englobante dans JSX, vous verrez le message d'erreur Adjacent JSX elements must be wrapped in an enclosing tag. En effet, lorsque JSX transpile, il crée des éléments avec leurs noms de balise correspondants et ne sait pas quel nom de balise utiliser si plusieurs éléments sont trouvés.

Dans le passé, une solution fréquente à ce problème consistait à utiliser un div wrapper pour résoudre ce problème. Cependant, la version 16 de React a apporté l'ajout de Fragment, ce qui rend cela plus nécessaire.

Fragmentagit comme un wrapper sans ajouter de div inutiles au DOM. Vous pouvez l'utiliser directement depuis l'import React, ou le déconstruire:

import React from 'react'; class MyComponent extends React.Component { render(){ return ( I am an element! I am another element  ); } } export default MyComponent;
// Deconstructed import React, { Component, Fragment } from 'react'; class MyComponent extends Component { render(){ return ( I am an element! I am another element  ); } } export default MyComponent;

La version 16.2 de React a encore simplifié ce processus, permettant aux balises JSX vides d'être interprétées comme des fragments:

return ( I am an element! I am another element  );

Exemple React JSX

JSX

JSX est l'abréviation de JavaScript XML.

JSX est une expression qui utilise des instructions HTML valides dans JavaScript. Vous pouvez affecter cette expression à une variable et l'utiliser ailleurs. Vous pouvez combiner d'autres expressions JavaScript valides et JSX dans ces instructions HTML en les plaçant entre accolades ( {}). Babel compile ensuite JSX en un objet de type React.createElement().

Expressions sur une seule ligne et sur plusieurs lignes

Les expressions sur une seule ligne sont simples à utiliser.

const one = 

Hello World!

;

Lorsque vous devez utiliser plusieurs lignes dans une seule expression JSX, écrivez le code entre une seule parenthèse.

const two = ( 
  • Once
  • Twice
);

Utiliser uniquement des balises HTML

const greet = 

Hello World!

;

Combiner une expression JavaScript avec des balises HTML

Nous pouvons utiliser des variables JavaScript entre accolades.

const who = "Quincy Larson"; const greet = 

Hello {who}!

;

Nous pouvons également appeler d'autres fonctions JavaScript entre accolades.

function who() { return "World"; } const greet = 

Hello {who()}!

;

Une seule balise parent est autorisée

A JSX expression must have only one parent tag. We can add multiple tags nested within the parent element only.

// This is valid. const tags = ( 
  • Once
  • Twice
); // This is not valid. const tags = (

Hello World!

This is my special list:

  • Once
  • Twice
);

React State Example

State is the place where the data comes from.

We should always try to make our state as simple as possible and minimize the number of stateful components. If we have, for example, ten components that need data from the state, we should create one container component that will keep the state for all of them.

State is basically like a global object that is available everywhere in a component.

Example of a Stateful Class Component:

import React from 'react'; class App extends React.Component { constructor(props) { super(props); // We declare the state as shown below this.state = { x: "This is x from state", y: "This is y from state" } } render() { return ( 

{this.state.x}

{this.state.y}

); } } export default App;

Another Example:

import React from 'react'; class App extends React.Component { constructor(props) { super(props); // We declare the state as shown below this.state = { x: "This is x from state", y: "This is y from state" } } render() { let x1 = this.state.x; let y1 = this.state.y; return ( 

{x1}

{y1}

); } } export default App;

Updating State

You can change the data stored in the state of your application using the setState method on your component.

this.setState({ value: 1 });

Keep in mind that setState is asynchronous so you should be careful when using the current state to set a new state. A good example of this would be if you want to increment a value in your state.

The Wrong Way

this.setState({ value: this.state.value + 1 });

This can lead to unexpected behavior in your app if the code above is called multiple times in the same update cycle. To avoid this you can pass an updater callback function to setState instead of an object.

The Right Way

this.setState(prevState => ({ value: prevState.value + 1 }));

Updating State

You can change the data stored in the state of your application using the setState method on your component.

this.setState({value: 1});

Keep in mind that setState may be asynchronous so you should be careful when using the current state to set a new state. A good example of this would be if you want to increment a value in your state.

The Wrong Way
this.setState({value: this.state.value + 1});

This can lead to unexpected behavior in your app if the code above is called multiple times in the same update cycle. To avoid this you can pass an updater callback function to setState instead of an object.

The Right Way
this.setState(prevState => ({value: prevState.value + 1}));
The Cleaner Way
this.setState(({ value }) => ({ value: value + 1 }));

When only a limited number of fields in the state object is required, object destructing can be used for cleaner code.

React State VS Props Example

When we start working with React components, we frequently hear two terms. They are state and props. So, in this article we will explore what are those and how they differ.

State:

  • State is something that a component owns. It belongs to that particular component where it is defined. For example, a person’s age is a state of that person.
  • State is mutable. But it can be changed only by that component that owns it. As I only can change my age, not anyone else.
  • You can change a state by using this.setState()

See the below example to get an idea of state:

Person.js

 import React from 'react'; class Person extends React.Component{ constructor(props) { super(props); this.state = { age:0 this.incrementAge = this.incrementAge.bind(this) } incrementAge(){ this.setState({ age:this.state.age + 1; }); } render(){ return( My age is: {this.state.age} Grow me older !! ); } } export default Person;

In the above example, age is the state of Person component.

Props:

  • Props are similar to method arguments. They are passed to a component where that component is used.
  • Props is immutable. They are read-only.

See the below example to get an idea of Props:

Person.js

 import React from 'react'; class Person extends React.Component{ render(){ return( I am a {this.props.character} person. ); } } export default Person; const person = 

In the above example, const person = we are passing character = "good" prop to Person component.

It gives output as “I am a good person”, in fact I am.

There is lot more to learn on State and Props. Many things can be learnt by actually diving into coding. So get your hands dirty by coding.

React Higher-Order Component Example

In React, a Higher-Order Component (HOC) is a function that takes a component and returns a new component. Programmers use HOCs to achieve component logic reuse.

If you’ve used Redux’s connect, you’ve already worked with Higher-Order Components.

The core idea is:

const EnhancedComponent = enhance(WrappedComponent);

Where:

  • enhance is the Higher-Order Component;
  • WrappedComponent is the component you want to enhance; and
  • EnhancedComponent is the new component created.

This could be the body of the enhance HOC:

function enhance(WrappedComponent) { return class extends React.Component { render() { const extraProp = 'This is an injected prop!'; return ( ); } } } 

In this case, enhance returns an anonymous class that extends React.Component. This new component is doing three simple things:

  • Rendering the WrappedComponent within a div element;
  • Passing its own props to the WrappedComponent; and
  • Injecting an extra prop to the WrappedComponent.

HOCs are just a pattern that uses the power of React’s compositional nature. They add features to a component. There are a lot more things you can do with them!