Constança Melo Antunes

Constança Melo Antunes

1660223460

Uma Explicação Simples De React.useEffect()

Estou impressionado com a expressividade dos ganchos do React. Você pode fazer muito escrevendo tão pouco.

Mas a brevidade dos ganchos tem um preço – eles são relativamente difíceis de começar. Especialmente useEffect()— o gancho que gerencia os efeitos colaterais em componentes funcionais do React.

Neste post, você aprenderá como e quando usar useEffect()hook.

1. useEffect() é para efeitos colaterais

Um componente funcional do React usa props e/ou state para calcular a saída. Se o componente funcional fizer cálculos que não visam o valor de saída, esses cálculos serão chamados de efeitos colaterais .

Exemplos de efeitos colaterais são solicitações de busca, manipulação direta do DOM, uso de funções de timer como setTimeout(), e muito mais.

A renderização do componente e a lógica do efeito colateral são independentes . Seria um erro realizar efeitos colaterais diretamente no corpo do componente, que é usado principalmente para calcular a saída.

A frequência com que o componente renderiza não é algo que você pode controlar — se o React quiser renderizar o componente, você não pode pará-lo.

function Greet({ name }) {
  const message = `Hello, ${name}!`; // Calculates output
  // Bad!
  document.title = `Greetings to ${name}`; // Side-effect!
  return <div>{message}</div>;       // Calculates output
}

Como dissociar a renderização do efeito colateral? Welcome useEffect()— o gancho que executa efeitos colaterais independentemente da renderização.

import { useEffect } from 'react';
function Greet({ name }) {
  const message = `Hello, ${name}!`;   // Calculates output
  useEffect(() => {
    // Good!
    document.title = `Greetings to ${name}`; // Side-effect!
  }, [name]);
  return <div>{message}</div>;         // Calculates output
}

useEffect()hook aceita 2 argumentos:

useEffect(callback[, dependencies]);

  • callbacké a função que contém a lógica do efeito colateral. callbacké executado logo após as alterações serem enviadas para o DOM.
  • dependenciesé um array opcional de dependências. useEffect()é executado callbackapenas se as dependências foram alteradas entre as renderizações.

Coloque sua lógica de efeito colateral na callbackfunção e use o dependenciesargumento para controlar quando você deseja que o efeito colateral seja executado. Esse é o único propósito de useEffect().

React useEffect() Hook: quando o callback é invocado

Por exemplo, no snippet de código anterior, você viu o useEffect()em ação:

useEffect(() => {
  document.title = `Greetings to ${name}`;
}, [name]);

A atualização do título do documento é o efeito colateral porque não calcula diretamente a saída do componente. É por isso que a atualização do título do documento é colocada em um retorno de chamada e fornecida ao useEffect().

Além disso, você não deseja que a atualização do título do documento seja executada toda vez Greetque o componente for renderizado. Você só quer que ele seja executado quando nameo prop mudar - essa é a razão pela qual você forneceu namecomo uma dependência para useEffect(callback, [name]).

2. Argumento de dependências

dependenciesO argumento de useEffect(callback, dependencies)permite controlar quando o efeito colateral é executado. Quando as dependências são:

A) Não fornecido: o efeito colateral ocorre após cada renderização.

import { useEffect } from 'react';
function MyComponent() {
  useEffect(() => {
    // Runs after EVERY rendering
  });  
}

B) Um array vazio []: o efeito colateral é executado uma vez após a renderização inicial.

import { useEffect } from 'react';
function MyComponent() {
  useEffect(() => {
    // Runs ONCE after initial rendering
  }, []);
}

C) Tem props ou valores de estado [prop1, prop2, ..., state1, state2]: o efeito colateral é executado apenas quando qualquer valor de dependência muda .

import { useEffect, useState } from 'react';
function MyComponent({ prop }) {
  const [state, setState] = useState('');
  useEffect(() => {
    // Runs ONCE after initial rendering
    // and after every rendering ONLY IF `prop` or `state` changes
  }, [prop, state]);
}

Vamos detalhar os casos B) e C), pois são usados ​​com frequência.

3. Ciclo de vida do componente

3.1 O componente foi montado

Use um array de dependências vazio para invocar um efeito colateral uma vez após a montagem do componente:

import { useEffect } from 'react';
function Greet({ name }) {
  const message = `Hello, ${name}!`;
  useEffect(() => {
    // Runs once, after mounting
    document.title = 'Greetings page';
  }, []);
  return <div>{message}</div>;
}

useEffect(..., [])foi fornecido com um array vazio como argumento de dependências. Quando configurado desta forma, useEffect()executa o callback apenas uma vez , após a montagem inicial.

Mesmo que o componente seja renderizado novamente com namepropriedades diferentes, o efeito colateral é executado apenas uma vez após a primeira renderização:

// First render
<Greet name="Eric" />   // Side-effect RUNS
// Second render, name prop changes
<Greet name="Stan" />   // Side-effect DOES NOT RUN
// Third render, name prop changes
<Greet name="Butters"/> // Side-effect DOES NOT RUN

Experimente a demonstração.

3.2 O componente foi atualizado

Cada vez que o efeito colateral usa props ou valores de estado, você deve indicar esses valores como dependências:

import { useEffect } from 'react';
function MyComponent({ prop }) {
  const [state, setState] = useState();
  useEffect(() => {
    // Side-effect uses `prop` and `state`
  }, [prop, state]);
  return <div>....</div>;
}

O useEffect(callback, [prop, state])chama o callbackdepois que as alterações estão sendo confirmadas no DOM e se e somente se algum valor na matriz de dependências [prop, state]foi alterado.

Usando o argumento de dependências, useEffect()você controla quando invocar o efeito colateral, independentemente dos ciclos de renderização do componente. Novamente, essa é a essência do useEffect()gancho.

Vamos melhorar o Greetcomponente usando nameprop no título do documento:

import { useEffect } from 'react';
function Greet({ name }) {
  const message = `Hello, ${name}!`;
  useEffect(() => {
    document.title = `Greetings to ${name}`; 
  }, [name]);
  return <div>{message}</div>;
}

nameprop é mencionado no argumento de dependências do useEffect(..., [name]). useEffect()hook executa o efeito colateral após a renderização inicial e em renderizações posteriores somente se o namevalor for alterado.

// First render
<Greet name="Eric" />   // Side-effect RUNS
// Second render, name prop changes
<Greet name="Stan" />   // Side-effect RUNS
// Third render, name prop doesn't change
<Greet name="Stan" />   // Side-effect DOES NOT RUN
// Fourth render, name prop changes
<Greet name="Butters"/> // Side-effect RUNS

Experimente a demonstração.

5. Limpeza de efeitos colaterais

Alguns efeitos colaterais precisam de limpeza: feche um soquete, limpe os temporizadores.

Se o callbackof useEffect(callback, deps)retorna uma função, useEffect()considera isso como uma limpeza de efeito :

useEffect(() => {
  // Side-effect...
  return function cleanup() {
    // Side-effect cleanup...
  };
}, dependencies);

A limpeza funciona da seguinte maneira:

A) Após a renderização inicial, useEffect()invoca o retorno de chamada com efeito colateral. cleanupfunção não é invocada .

B) Em renderizações posteriores, antes de invocar o próximo retorno de chamada de efeito colateral, useEffect() invoca a cleanupfunção da execução de efeito colateral anterior (para limpar tudo após o efeito colateral anterior) e, em seguida, executa o efeito colateral atual.

C) Finalmente, após desmontar o componente, useEffect() invoca a função de limpeza do último efeito colateral.

React useEffect() Hook: quando callback e cleanup são invocados

Vamos ver um exemplo quando a limpeza de efeito colateral é útil.

O componente a seguir <RepeatMessage message="My Message" />aceita um prop message. Então, a cada 2 segundos, o messageprop é registrado no console:

import { useEffect } from 'react';
function RepeatMessage({ message }) {
  useEffect(() => {
    setInterval(() => {
      console.log(message);
    }, 2000);
  }, [message]);
  return <div>I'm logging to console "{message}"</div>;
}

Experimente a demonstração.

Abra a demonstração e digite algumas mensagens. O console registra a cada 2 segundos qualquer mensagem que já tenha sido digitada na entrada. No entanto, você precisa registrar apenas a mensagem mais recente.

Esse é o caso para limpar o efeito colateral: cancele o cronômetro anterior ao iniciar um novo. Vamos retornar uma função de limpeza que interrompe o cronômetro anterior antes de iniciar um novo:

import { useEffect } from 'react';
function RepeatMessage({ message }) {
  useEffect(() => {
    const id = setInterval(() => {
      console.log(message);
    }, 2000);
    return () => {
      clearInterval(id);
    };
  }, [message]);
  return <div>I'm logging to console "{message}"</div>;
}

Experimente a demonstração.

Abra a demonstração e digite algumas mensagens. Você verá que a cada 2 segundos apenas as mensagens mais recentes são registradas no console. O que significa que todos os temporizadores anteriores foram de limpeza.

6. useEffect() na prática

6.1 Buscando dados

useEffect()pode executar o efeito colateral de busca de dados.

O componente a seguir FetchEmployeesbusca a lista de funcionários pela rede:

import { useEffect, useState } from 'react';
function FetchEmployees() {
  const [employees, setEmployees] = useState([]);
  useEffect(() => {
    async function fetchEmployees() {
      const response = await fetch('/employees');
      const fetchedEmployees = await response.json(response);
      setEmployees(fetchedEmployees);
    }
    fetchEmployees();
  }, []);
  return (
    <div>
      {employees.map(name => <div>{name}</div>)}
    </div>
  );
}

useEffect()inicia uma solicitação de busca chamando fetchEmployees()a função assíncrona após a montagem inicial.

Quando a solicitação for concluída, setEmployees(fetchedEmployees)atualiza o employeesestado com a lista de funcionários recém-obtidas.

Observe que o callbackargumento de useEffect(callback)não pode ser uma asyncfunção. Mas você sempre pode definir e invocar uma asyncfunção dentro do próprio retorno de chamada:

function FetchEmployees() {
  const [employees, setEmployees] = useState([]);
  useEffect(() => {  // <--- CANNOT be an async function
    async function fetchEmployees() {
      // ...
    }
    fetchEmployees(); // <--- But CAN invoke async functions
  }, []);
  // ...
}

Para executar a solicitação de busca dependendo de um valor de prop ou de estado, basta indicar a dependência necessária no argumento de dependências: useEffect(fetchSideEffect, [prop, stateValue]).

7. Conclusão

useEffect(callback, dependencies)é o gancho que gerencia os efeitos colaterais em componentes funcionais. callbackargumento é uma função para colocar a lógica do efeito colateral. dependenciesé uma lista de dependências do seu efeito colateral: sendo props ou valores de estado.

useEffect(callback, dependencies)invoca o callbackapós a montagem inicial e em renderizações posteriores, se algum valor interno dependenciesfoi alterado.

O próximo passo para dominar useEffect()é entender e evitar a armadilha do loop infinito .

Fonte: https://dmitrupavlutin.com/react-useeffect-explanation/

#react 

What is GEEK

Buddha Community

Uma Explicação Simples De React.useEffect()
Autumn Blick

Autumn Blick

1598839687

How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

  • Performance: It delivers optimal performance.
  • Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
  • UI design: React Native enables you to design simple and responsive UI for your mobile app.
  • 3rd party plugins: This framework supports 3rd party plugins.
  • Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

  • Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
  • Near-native user experience: React Native provides several native components, and these are platform agnostic.
  • The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

#android app #frontend #ios app #mobile app development #benefits of react native #is react native good for mobile app development #native vs #pros and cons of react native #react mobile development #react native development #react native experience #react native framework #react native ios vs android #react native pros and cons #react native vs android #react native vs native #react native vs native performance #react vs native #why react native #why use react native

Mark Mara

Mark Mara

1607399166

Class-less Components in React

While coding this week, I had to convert one of my class components in React to a functional component.

Why would I need to do that? After all, the parent component sees the two types of components as identical. Sure, functional components can be shorter, require less boilerplate, and maybe even perform better. But that’s not why I needed to do it. I was using an npm package that had React hooks and hooks are for functional components only. React Hooks, added in React 16.8, allow functional components to manage state and replace lifecycle methods. To use the hook I needed I had to convert my class components to a functional.

Here are the steps I followed to change my class component to a functional component:

#react-hook-useeffect #useeffect #react-hook #react-hook-usestate #react

Aubrey Price

Aubrey Price

1589722410

Build a simple React Native Pokemon app with React-Navigation

As we start learning new technologies we want to start building something or work on a simple project to get a better understanding of the technology. So, let’s build this simple app.
For this app, we will be using PokeApi to get our pokemon data, and also we will be using Hooks. I am using pokemondb for pokemon sprites. It’s just a personal preference you can use whatever you want.

#react-native #react-native-app #react-navigation #react-native-development #react

Mathew Rini

1615544450

How to Select and Hire the Best React JS and React Native Developers?

Since March 2020 reached 556 million monthly downloads have increased, It shows that React JS has been steadily growing. React.js also provides a desirable amount of pliancy and efficiency for developing innovative solutions with interactive user interfaces. It’s no surprise that an increasing number of businesses are adopting this technology. How do you select and recruit React.js developers who will propel your project forward? How much does a React developer make? We’ll bring you here all the details you need.

What is React.js?

Facebook built and maintains React.js, an open-source JavaScript library for designing development tools. React.js is used to create single-page applications (SPAs) that can be used in conjunction with React Native to develop native cross-platform apps.

React vs React Native

  • React Native is a platform that uses a collection of mobile-specific components provided by the React kit, while React.js is a JavaScript-based library.
  • React.js and React Native have similar syntax and workflows, but their implementation is quite different.
  • React Native is designed to create native mobile apps that are distinct from those created in Objective-C or Java. React, on the other hand, can be used to develop web apps, hybrid and mobile & desktop applications.
  • React Native, in essence, takes the same conceptual UI cornerstones as standard iOS and Android apps and assembles them using React.js syntax to create a rich mobile experience.

What is the Average React Developer Salary?

In the United States, the average React developer salary is $94,205 a year, or $30-$48 per hour, This is one of the highest among JavaScript developers. The starting salary for junior React.js developers is $60,510 per year, rising to $112,480 for senior roles.

* React.js Developer Salary by Country

  • United States- $120,000
  • Canada - $110,000
  • United Kingdom - $71,820
  • The Netherlands $49,095
  • Spain - $35,423.00
  • France - $44,284
  • Ukraine - $28,990
  • India - $9,843
  • Sweden - $55,173
  • Singapore - $43,801

In context of software developer wage rates, the United States continues to lead. In high-tech cities like San Francisco and New York, average React developer salaries will hit $98K and $114per year, overall.

However, the need for React.js and React Native developer is outpacing local labour markets. As a result, many businesses have difficulty locating and recruiting them locally.

It’s no surprise that for US and European companies looking for professional and budget engineers, offshore regions like India are becoming especially interesting. This area has a large number of app development companies, a good rate with quality, and a good pool of React.js front-end developers.

As per Linkedin, the country’s IT industry employs over a million React specialists. Furthermore, for the same or less money than hiring a React.js programmer locally, you may recruit someone with much expertise and a broader technical stack.

How to Hire React.js Developers?

  • Conduct thorough candidate research, including portfolios and areas of expertise.
  • Before you sit down with your interviewing panel, do some homework.
  • Examine the final outcome and hire the ideal candidate.

Why is React.js Popular?

React is a very strong framework. React.js makes use of a powerful synchronization method known as Virtual DOM, which compares the current page architecture to the expected page architecture and updates the appropriate components as long as the user input.

React is scalable. it utilises a single language, For server-client side, and mobile platform.

React is steady.React.js is completely adaptable, which means it seldom, if ever, updates the user interface. This enables legacy projects to be updated to the most new edition of React.js without having to change the codebase or make a few small changes.

React is adaptable. It can be conveniently paired with various state administrators (e.g., Redux, Flux, Alt or Reflux) and can be used to implement a number of architectural patterns.

Is there a market for React.js programmers?
The need for React.js developers is rising at an unparalleled rate. React.js is currently used by over one million websites around the world. React is used by Fortune 400+ businesses and popular companies such as Facebook, Twitter, Glassdoor and Cloudflare.

Final thoughts:

As you’ve seen, locating and Hire React js Developer and Hire React Native developer is a difficult challenge. You will have less challenges selecting the correct fit for your projects if you identify growing offshore locations (e.g. India) and take into consideration the details above.

If you want to make this process easier, You can visit our website for more, or else to write a email, we’ll help you to finding top rated React.js and React Native developers easier and with strives to create this operation

#hire-react-js-developer #hire-react-native-developer #react #react-native #react-js #hire-react-js-programmer

Franz Becker

Franz Becker

1651604400

React Starter Kit: Build Web Apps with React, Relay and GraphQL.

React Starter Kit — "isomorphic" web app boilerplate   

React Starter Kit is an opinionated boilerplate for web development built on top of Node.js, Express, GraphQL and React, containing modern web development tools such as Webpack, Babel and Browsersync. Helping you to stay productive following the best practices. A solid starting point for both professionals and newcomers to the industry.

See getting started guide, demo, docs, roadmap  |  Join #react-starter-kit chat room on Gitter  |  Visit our sponsors:

 

Hiring

Getting Started

Customization

The master branch of React Starter Kit doesn't include a Flux implementation or any other advanced integrations. Nevertheless, we have some integrations available to you in feature branches that you can use either as a reference or merge into your project:

You can see status of most reasonable merge combination as PRs labeled as TRACKING

If you think that any of these features should be on master, or vice versa, some features should removed from the master branch, please let us know. We love your feedback!

Comparison

 

React Starter Kit

React Static Boilerplate

ASP.NET Core Starter Kit

App typeIsomorphic (universal)Single-page applicationSingle-page application
Frontend
LanguageJavaScript (ES2015+, JSX)JavaScript (ES2015+, JSX)JavaScript (ES2015+, JSX)
LibrariesReact, History, Universal RouterReact, History, ReduxReact, History, Redux
RoutesImperative (functional)DeclarativeDeclarative, cross-stack
Backend
LanguageJavaScript (ES2015+, JSX)n/aC#, F#
LibrariesNode.js, Express, Sequelize,
GraphQL		n/aASP.NET Core, EF Core,
ASP.NET Identity
SSRYesn/an/a
Data APIGraphQLn/aWeb API

Backers

♥ React Starter Kit? Help us keep it alive by donating funds to cover project expenses via OpenCollective or Bountysource!

lehneres Tarkan Anlar Morten Olsen Adam David Ernst Zane Hitchcox  

How to Contribute

Anyone and everyone is welcome to contribute to this project. The best way to start is by checking our open issues, submit a new issue or feature request, participate in discussions, upvote or downvote the issues you like or dislike, send pull requests.

Learn More

Related Projects

  • GraphQL Starter Kit — Boilerplate for building data APIs with Node.js, JavaScript (via Babel) and GraphQL
  • Membership Database — SQL schema boilerplate for user accounts, profiles, roles, and auth claims
  • Babel Starter Kit — Boilerplate for authoring JavaScript/React.js libraries

Support

License

Copyright © 2014-present Kriasoft, LLC. This source code is licensed under the MIT license found in the LICENSE.txt file. The documentation to the project is licensed under the CC BY-SA 4.0 license.

Author: kriasoft
Source Code: https://github.com/kriasoft/react-starter-kit
License: MIT License

#graphql #react