Primjeri najboljeg reagiranja

React (poznat i kao React.js) jedna je od najpopularnijih JavaScript knjižnica za razvojni program. Ovdje je zbirka React sintakse i upotrebe koju možete koristiti kao priručnik ili referencu.

Primjer reakcijske komponente

Komponente se mogu ponovno koristiti u React.js-u. Možete ubrizgati vrijednost u rekvizite kako je dano dolje:

function Welcome(props) { return 

Hello, {props.name}

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

name="Faisal Arkan"dat će vrijednost {props.name}iz function Welcome(props)i vraćati komponentu koja je dala vrijednost pomoću name="Faisal Arkan". Nakon toga React će element prikazati u html.

Ostali načini deklariranja komponenata

Postoji mnogo načina za deklariranje komponenata kada koristite React.js. Postoje dvije vrste komponenata, komponente bez državljanstva i komponente sa statusom države .

Državno

Komponente tipa klase

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

{this.props.name}

{this.props.color}

); } }

Komponente bez državljanstva

Funkcionalne komponente (Funkcija strelice iz ES6)

const Cat = props => { return ( 

{props.name}

{props.color}

; ); };

Implicitne komponente povratka

const Cat = props =>

{props.name}

{props.color}

;

Primjer reakcijskog fragmenta

Fragmenti su način da se više elemenata generira bez upotrebe omotnog elementa. Kad pokušavate prikazati elemente bez zatvorene oznake u JSX-u, vidjet ćete poruku pogreške Adjacent JSX elements must be wrapped in an enclosing tag. To je zato što kada se JSX transpilira, on stvara elemente s odgovarajućim imenima oznaka i ne zna koji naziv oznake treba koristiti ako se pronađe više elemenata.

U prošlosti je često rješavanje ovog problema bilo korištenje omotača div za rješavanje ovog problema. Međutim, verzija 16 React-a donijela je dodatak Fragment, što to više nije potrebno.

Fragmentdjeluje omotač bez dodavanja nepotrebnih div-ova u DOM. Možete ga koristiti izravno iz uvoza React ili ga dekonstruirati:

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 verzija 16.2 dodatno je pojednostavila ovaj postupak, omogućavajući prazne JSX oznake da se tumače kao Fragmenti:

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

Primjer reakcije JSX

JSX

JSX je kratica za JavaScript XML.

JSX je izraz koji koristi valjane HTML izjave unutar JavaScript-a. Ovaj izraz možete dodijeliti varijabli i koristiti ga negdje drugdje. U ove HTML izjave možete kombinirati druge valjane JavaScript izraze i JSX stavljanjem u zagrade ( {}). Babel dalje kompajlira JSX u objekt tipa React.createElement().

Jednoredni i višeredni izrazi

Jednoredni izrazi jednostavni su za upotrebu.

const one = 

Hello World!

;

Kada trebate koristiti više redaka u jednom JSX izrazu, napišite kôd u jednu zagradu.

const two = ( 
    
  • Once
  • Twice
);

Upotreba samo HTML oznaka

const greet = 

Hello World!

;

Kombiniranje JavaScript izraza s HTML oznakama

U zagradama možemo koristiti JavaScript varijable.

const who = "Quincy Larson"; const greet = 

Hello {who}!

;

Također možemo pozvati i druge JavaScript funkcije unutar zagrada.

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

Hello {who()}!

;

Dopuštena je samo jedna nadređena oznaka

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!