React (also known as React.js or ReactJS) is a free and open-source front-end JavaScript library for building user interfaces based on UI components. It is maintained by Meta (formerly Facebook) and a community of individual developers and companies. React can be used as a base in the development of single-page, mobile, or server-rendered applications with frameworks like Next.js. However, React is only concerned with state management and rendering that state to the DOM, so creating React applications usually requires the use of additional libraries for routing, as well as certain client-side functionality. It is a view layer MVC app that is used to create custom and reusable components. It's quick and efficient for building UIs.

Why React?

• Reactjs is extremely efficient

React.js from Facebook generates its own virtual DOM in which your components reside. Because React.js calculates what changes need to be made in the DOM in advance and updates the DOM trees accordingly, this approach provides your developer with high flexibility and amazing performance gains. React.js avoids costly DOM operations and efficiently updates.

• The JavaScript Library

The JSX syntax is a healthy mix of JavaScript and HTML. It is specifically used in ReactJS. JSX simplifies the process of creating website components, while HTML allows your developers to render functions without concatenating strings.

• It’s awesome for SEO

One of the most significant issues with JavaScript frameworks is that they are not search engine friendly. Though there have been some recent improvements in this area, they are not very helpful. Surprisingly, React.js stands out because you can run it on the server and have the virtual DOM returned and rendered to the browser as a regular web page. There's no need for any other tricks

• Focused on the User interface

In comparison to MeteorJS, Firebase, and AngularJS, React is much more focused on the user interface. It provides your users with a highly responsive interface by utilizing JavaScript interactions between the device's environment and React. As a result, the application's load time increases, and it runs more smoothly and without interruptions.

• It’s easy and out of the box

When you begin working with React.js, don't forget to install the official React.js Chrome extension. It greatly simplifies debugging your app. After installing the extension, you can view the virtual DOM in the element's panel as if you were browsing a regular DOM tree. It's incredible, isn't it?

• Reusable React Components

Another advantage of React.js is the ability to reuse code components of various levels at any time. This is a significant time saver. Because ReactJS components are isolated, changes to one do not affect the others. This enables you to reuse components that do not generate changes on their own to make programming more precise, ergonomic, and comfortable for developers. It's no surprise that Facebook, Instagram, and Netflix prefer React and React Native.

Your First React Application

Create-react-app has everything you need to get started building a react app. Webpack compiles react, ES6auto prefix CSS files, and ESLint for highlighting code errors and ensuring that your code adheres to some Javascript module standards. It configures your development environment to use the most recent JavaScript features, provides a pleasant developer experience, and optimizes your app for production.

To generate react boilerplate for launching your project, run the below commands where the new app is the name of your folder.

$ npx create-react-app new_app
$ cd new_app
$ npm start

The above commands generate the folder structure to get you started.

| public- index.html/among other static files
| src - react code(components/containers/index.js/state management/css/tests)
|.gitignore
|node_modules
|package.json

Rendering Elements React DOM updates the DOM to match the React elements.

<div id="root"></div>

Because React DOM will manage everything inside it, we call this a "root" DOM node. Applications built entirely with React typically have a single root DOM node. You can have as many isolated root DOM nodes as you want when integrating React into an existing app. First, pass the DOM element to ReactDOM to render a React element. Then call createRoot() and pass the React element to the root. render():

const element = <h1>Hello, world</h1>;
const root = ReactDOM.createRoot(
  document.getElementById('root')
);
root.render(element);

In your application the index.js file renders the elements into the reactDOM by passing App with your app’s root DOM reactDOM will manage the app.

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
ReactDOM.render(<App />, document.getElementById('root'));

ReactDOM is a representation of our app's user interface. Any changes to the application's state result in an update to the app's UI. Frequent DOM manipulation slows the App's performance. Because react-dom is represented by a tree data structure, changes and updates are quick. The virtualDOM receives updates rather than the realDOM, making it faster and more efficient.

Components

React is made up of components, which are smaller components that feed into larger components that you can customize. The index.js file contains the main component. The component files include React, other components, installed npm packages, and a stylesheet. It also employs JSX to generate React code, which is then compiled into es6. The JSX tags are self-closing and must be closed at the end of the code.

const App = (
  <div>
    <h1>React is cool!</h1>
    <h2>Start writing code today!</h2>
    <img src={image} alt={name} />
  </div>
);

There are class components and React hooks:

Props for properties and those for handling state are hard-coded in the class components. React hooks simplify coding and increase productivity. Hooks in React are not the same as inside loops, conditions, or nested functions.

Some of the hook examples include:

useState hook: which adds some local state. It returns the current state and the updated state.

useEffect hook: it performs some side effects, i.e., is used for API calls/fetches, search buttons, and cleaning up after running effects. Replace componentDidMount/componentDidUnmount/componentDidUpdate

useContext hook: renders and re-renders on the current context

useReducer hook: manages the local state of complex components with a reducer that passes actions and state(at times there’s the debate between React hooks vs redux for state management)

useCallbacks hook: remembers actual function (as the name suggests its call back function)

useCustom hook: remembers returned value from the function

Custom Hooks: React offers a convenient feature to use and call other hooks in order to extract component logic into reusable functions.

Styling

Different frameworks, libraries, and methods are available for styling examples. Bootstrap, styled-components, sass, TailWind CSS, CSS, etc

Testing

Similar to testing JavaScript code, you can test React in the same way. There are a few ways to test React components. Broadly, they divide into two categories:

1. Rendering component trees in a simplified test environment and asserting their output.

2. Running a complete app in a realistic browser environment (also known as “end-to-end” tests).

When choosing testing tools, it is worth considering a few tradeoffs:

• I**teration speed vs Realistic environment:** Some tools offer a very quick feedback loop between making a change and seeing the result but don’t model the browser behavior precisely. Other tools might use a real browser environment, but reduce the iteration speed and are flakier on a continuous integration server.

• How much to mock*:* With components, the distinction between a “unit” and an “integration” test can be blurry. If you’re testing a form, should its test also test the buttons inside of it? Or should a button component have its own test suite? Should refactoring a button ever break the form test?

  The most recommended tools are :

• Jest: It is good for testing React components. It provides a great iteration speed combined with powerful features like mocking modules and timers so you can have more control over how the code executes.

• React-Testing Library: It offers a set of helpers like the ByTestId function that let you test React components without relying on their implementation details. This approach makes refactoring a breeze and also nudges you towards best practices for accessibility.

The reason for using ReactJS or this convertible framework is because of its performance and all of the features or components that it contributes to making development easier. Virtual DOM, component reusability, backward compatibility, and flexibility for other platforms allow developers to create applications with excellent UI and intricate workings. When it comes to the impact of ReactJS on business app productivity, apps built with ReactJS provide transcendent UI with consumer-grade simplicity. That is why ReactJS is the best choice for developing business apps. Many businesses are perplexed about technology adoption because there are numerous technologies on the market, and new technologies are released on a daily basis. So, which technology is the most effective? Is that ReactJS?

Wanna learn React? Check out the official React documentation here. Thank you for reading !!!!!