React (también conocido como React.js) es una de las bibliotecas de desarrollo de front-end de JavaScript más populares. Aquí hay una colección de sintaxis y uso de React que puede usar como guía o referencia práctica.

Ejemplo de componente de reacción

Los componentes son reutilizables en React.js. Puede inyectar valor en los accesorios como se indica a continuación:

function Welcome(props) { return 
Hello, {props.name}
; } const element = ; ReactDOM.render( element, document.getElementById('root') );

name="Faisal Arkan"dará valor a {props.name}from function Welcome(props)y devolverá un componente que ha dado valor por name="Faisal Arkan". Después de eso, React renderizará el elemento en html.

Otras formas de declarar componentes

Hay muchas formas de declarar componentes al usar React.js. Hay dos tipos de componentes, componentes sin estado y componentes con estado .

Con estado

Componentes de tipo de clase

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

Componentes sin estado

Componentes funcionales (función de flecha de ES6)

const Cat = props => { return ( 
{props.name}
{props.color}
 ; ); };

Componentes de devolución implícitos

const Cat = props =>
{props.name}
{props.color}
 ;

Ejemplo de fragmento de reacción

Los fragmentos son una forma de renderizar múltiples elementos sin usar un elemento contenedor. Cuando intente representar elementos sin una etiqueta adjunta en JSX, verá el mensaje de error Adjacent JSX elements must be wrapped in an enclosing tag. Esto se debe a que cuando JSX se transpila, está creando elementos con sus correspondientes nombres de etiqueta y no sabe qué nombre de etiqueta usar si se encuentran varios elementos.

En el pasado, una solución frecuente a esto era usar un div contenedor para resolver este problema. Sin embargo, la versión 16 de React trajo la adición de Fragment, lo que hace que esto ya no sea necesario.

Fragmentactúa como envoltorio sin agregar divs innecesarios al DOM. Puede usarlo directamente desde la importación de React o deconstruirlo:

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;

React versión 16.2 simplificó aún más este proceso, permitiendo que las etiquetas JSX vacías se interpreten como Fragmentos:

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

Ejemplo de React JSX

JSX

JSX es la abreviatura de JavaScript XML.

JSX es una expresión que utiliza declaraciones HTML válidas dentro de JavaScript. Puede asignar esta expresión a una variable y usarla en otro lugar. Puede combinar otras expresiones JavaScript válidas y JSX dentro de estas declaraciones HTML colocándolas entre llaves ( {}). Babel además compila JSX en un objeto de tipo React.createElement().

Expresiones de una línea y de varias líneas

Las expresiones de una sola línea son fáciles de usar.

const one = 
Hello World!
;

Cuando necesite usar varias líneas en una sola expresión JSX, escriba el código dentro de un solo paréntesis.

const two = ( 
    

     
Once
     
Twice
    
 );

Usar solo etiquetas HTML

const greet = 
Hello World!
;

Combinando expresión JavaScript con etiquetas HTML

Podemos usar variables de JavaScript entre llaves.

const who = "Quincy Larson"; const greet = 
Hello {who}!
;

También podemos llamar a otras funciones de JavaScript entre llaves.

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

Solo se permite una etiqueta principal

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!