What is React: a complete walkthrough for beginners


What is React: a complete walkthrough for beginners

Welcome to this comprehensive guide on React.js, one of the most popular and powerful JavaScript libraries for building user interfaces. In today’s fast-paced world of web development, React.js has emerged…

What is React: a complete walkthrough for beginners

Welcome to this comprehensive guide on React.js, one of the most popular and powerful JavaScript libraries for building user interfaces. In today’s fast-paced world of web development, React.js has emerged as a go-to solution for creating modern, high-performance web applications.

The purpose of this article is to provide you with a detailed understanding of React.js, its advantages over other front-end frameworks, and practical guidance on how to use it effectively in your projects. By the end of this article, you’ll have a solid foundation in React.js and be well on your way to becoming a skilled React developer.

I. What is React.js?

  • Definition of React.js
  • History of React.js
  • React.js features
    • Virtual DOM
    • Component-based architecture
    • One-way data binding
    • JSX Syntax
    • React Native

React.js, often simply called React, is an open-source JavaScript library for building user interfaces, particularly web applications. Developed and maintained by Facebook, React.js was first introduced in 2013 and has since gained widespread popularity in the web development community.

React.js is known for its unique features that enable developers to create complex applications with greater efficiency and ease. Some of these key features include the Virtual DOM, a component-based architecture, one-way data binding, JSX syntax, and the ability to create cross-platform mobile applications with React Native.

The Virtual DOM is a lightweight, in-memory representation of the actual DOM (Document Object Model) that enables React to efficiently update the user interface without making expensive updates to the actual DOM. This results in faster rendering times and improved performance in comparison to traditional methods.

Component-based architecture is another major feature of React.js. It encourages the development of modular and reusable code, making it easier to manage and maintain even large-scale applications. Each component is responsible for rendering a specific part of the user interface and can be reused throughout the application as needed.

One-way data binding in React.js ensures a unidirectional flow of data, minimizing the potential for bugs and making it easier to reason about the application state. This is achieved through the use of props and state, which we will explore later in this article.

React.js uses JSX syntax, which is an XML-like syntax extension for JavaScript. JSX enables developers to write HTML-like code within JavaScript, making it easier to create and manage complex UI structures. Although not required, JSX is highly recommended for writing React components.

Lastly, React Native is a framework built on top of React.js, allowing developers to create cross-platform mobile applications for iOS, Android, and other platforms using React and native components.

II. Why use React.js?

  • Advantages of using React.js
    • Reusable components
    • Easy to learn
    • Improved performance
    • Large community support

React.js offers several advantages that make it an attractive choice for developers building user interfaces:

  1. Reusable components: React’s component-based architecture promotes code modularity and reusability. This leads to faster development times and easier maintenance of large applications, as developers can reuse components instead of rewriting the same code multiple times.
  2. Easy to learn: React.js is known for its relatively shallow learning curve compared to some other front-end frameworks. Its focus on components, coupled with its straightforward API and a clear separation of concerns, makes it easy for beginners to pick up and start building applications quickly.
  3. Improved performance: React.js employs a Virtual DOM, which significantly improves rendering performance compared to traditional DOM manipulation techniques. This results in more responsive applications and a better user experience overall.
  4. Large community support: React.js enjoys a vibrant and active community of developers, contributing to a vast ecosystem of libraries, tools, and resources. This support not only makes it easier to find help when needed but also allows developers to benefit from the collective knowledge and experience of the community.

III. Getting started with React.js

  • Installation and setup
    • Prerequisites
    • Installing React.js
    • Setting up the development environment
  • Creating a React.js application
    • Creating a new project
    • Understanding the file structure
    • Writing the first React component
    • Running the application

Before diving into React.js, it’s essential to have some prerequisites in place. You should have a basic understanding of HTML, CSS, and JavaScript, including concepts like variables, functions, loops, and objects.

To get started with React.js, you’ll need to install it on your local machine. The easiest way to do this is by using the Create React App (CRA) tool, which sets up a new React.js project with a pre-configured development environment, including all the necessary dependencies, build tools, and configurations.

To install Create React App, you’ll need to have Node.js and npm (Node Package Manager) installed on your computer. If you don’t have them already, you can download them from the official Node.js website (https://nodejs.org).

Once Node.js and npm are installed, open a command prompt or terminal and run the following command:

npx create-react-app my-app

Replace “my-app” with the name you want for your project. This command will create a new directory with the specified name and set up the basic React.js application structure inside.

After running the “npx create-react-app” command, navigate to the newly created project directory using the command line:

cd my-app

Inside the project directory, you’ll find several files and folders that make up the basic structure of a React.js application. The “src” folder contains the source code for your app, including the main entry point, “index.js”, and the default “App” component in “App.js”.

To write your first React component, open the “App.js” file and replace its contents with the following code:

import React from 'react';

function MyComponent() {
  return (
      <h1>Hello, React.js!</h1>

export default MyComponent;

This simple functional component renders a “Hello, React.js!” heading when included in the application. Save the file and return to the command line to run your React.js app:

npm start

This command will start a development server and open your application in a web browser. You should see the “Hello, React.js!” heading displayed on the page.

IV. React.js Components

  • Introduction to components
    • Functional components
    • Class components

React.js components are the building blocks of your application’s user interface. They can be thought of as reusable, self-contained pieces of code that define how a specific part of the UI should look and behave.

There are two types of components in React.js: functional components and class components.

Functional components are simple JavaScript functions that return JSX. They are stateless, meaning they do not manage their state, and they typically have no side effects. Functional components are recommended for most use cases, as they are more concise and easier to understand.

Here’s an example of a functional component:

import React from 'react';

function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;

export default Greeting;

Class components, on the other hand, are JavaScript classes that extend the React.Component class. They have a more complex syntax and can manage their state and use lifecycle methods. Class components were the standard way to write components before React introduced functional components and hooks.

Here’s an example of a class component:

import React, { Component } from 'react';

class Greeting extends Component {
  render() {
    return <h1>Hello, {this.props.name}!</h1>;

export default Greeting;
  • Props and state
    • Passing props to components
    • Changing component state

Props, short for “properties,” are the way React components receive data from their parent components. Props are read-only and should not be modified within the component. They enable you to pass data down the component tree and create more dynamic and reusable components.

To pass props to a component, simply include them as attributes when rendering the component in the parent component, like this:

<Greeting name="John" />

Within the child component, you can access the passed props using the props object:

function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;

State, on the other hand, is the internal data that a component can manage and update. Unlike props, state is mutable and can be changed within the component. To manage state in a functional component, you can use the useState hook provided by React.

Here’s an example of using state in a functional component:

import React, { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(0);

  return (
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>

export default Counter;
  • Lifecycle methods
    • ComponentDidMount
    • ComponentDidUpdate
    • ComponentWillUnmount

Lifecycle methods are special methods in class components that allow you to run side effects, such as fetching data, updating the DOM, or subscribing to events, at specific points during the component’s lifecycle. The three most commonly used lifecycle methods are componentDidMount, componentDidUpdate, and componentWillUnmount.

componentDidMount is called after the component is rendered and mounted in the DOM. This is where you would typically fetch data, subscribe to events, or perform other side effects that need to occur after the component is displayed.

componentDidUpdate is called whenever the component updates due to changes in its props or state. This method allows you to perform side effects in response to these changes, such as updating the DOM or fetching new data.

componentWillUnmount is called just before the component is removed from the DOM. This is where you would typically clean up any side effects or subscriptions that were created during the component’s lifecycle.

In functional components, you can achieve similar behavior using the useEffect hook.

V. React.js and API integration

  • Introduction to APIs
  • Making API calls in React.js
    • Fetch API
    • Axios

APIs, or Application Programming Interfaces, are a way for different software applications to communicate with each other. In web development, APIs often refer to web services that provide data to front-end applications. Integrating APIs in a React.js application enables you to fetch and display data from external sources, such as databases or third-party services.

There are several ways to make API calls in a React.js application. Two popular options are the Fetch API and Axios.

  1. Fetch API: The Fetch API is a built-in JavaScript API for making HTTP requests. It returns a Promise that resolves with the Response object representing the response to the request.

Here’s an example of using the Fetch API to fetch data from a REST API and display it in a React component:

import React, { useState, useEffect } from 'react';

function DataFetcher() {
  const [data, setData] = useState([]);

  useEffect(() => {
      .then(response => response.json())
      .then(data => setData(data));
  }, []);

  return (
      {data.map(item => (
        <p key={item.id}>{item.name}</p>

export default DataFetcher;
  1. Axios: Axios is a popular third-party library for making HTTP requests. It offers a more feature-rich and convenient API than the Fetch API, with built-in support for request and response interception, error handling, and more.

To use Axios, first install it using npm:

npm install axios

Then, you can use Axios in your React component like this:

import React, { useState, useEffect } from 'react';
import axios from 'axios';

function DataFetcher() {
  const [data, setData] = useState([]);

  useEffect(() => {
      .then(response => setData(response.data))
      .catch(error => console.error(error));
  }, []);

  return (
      {data.map(item => (
        <p key={item.id}>{item.name}</p>

export default DataFetcher;

Once you have fetched data from an API, you can display it in your React components by mapping over the data and rendering elements for each item. The example above demonstrates how to do this using the .map() method to iterate over an array of data and render a <p> element for each item.

VI. React.js and Routing

  • Introduction to routing
  • React Router library
    • Installation and setup
    • Creating routes
    • Nested routes
    • Route parameters

In single-page applications (SPAs), routing is the process of displaying different views based on the current URL without reloading the page. React.js doesn’t include built-in routing functionality, but you can easily add routing to your application using the popular React Router library.

To get started with React Router, first install it using npm:

npm install react-router-dom

Once installed, you can import the necessary components from the library and set up your routes. Here’s a basic example of how to create routes with React Router:

import { BrowserRouter as Router, Route, Switch, Link } from 'react-router-dom';
import Home from './components/Home';
import About from './components/About';

function App() {
  return (
            <Link to="/">Home</Link>
            <Link to="/about">About</Link>

        <Route exact path="/" component={Home} />
        <Route path="/about" component={About} />

export default App;

This example sets up a simple navigation bar with two links and uses the Route component to render either the Home or About component based on the current URL.

Nested routes allow you to create more complex routing structures with parent and child routes. To create nested routes, simply include a Route component within another component that is already being rendered by a route.

Route parameters enable you to capture values from the URL and pass them as props to your components. To create a route with parameters, include a colon followed by a variable name in the path prop of the Route component:

<Route path="/user/:id" component={User} />

In the User component, you can access the route parameter using the useParams hook from React Router:

import { useParams } from 'react-router-dom';

function User() {
  const { id } = useParams();

  // Use the id parameter to fetch data or perform other actions

  return <div>User ID: {id}</div>;

export default User;

VII. Best practices in React.js

  • Writing reusable and maintainable code
  • Using state and props effectively
  • Following the Single Responsibility Principle
  • Testing React.js applications
  • Writing reusable and maintainable code

To write reusable and maintainable code in React.js, consider the following guidelines:

  1. Break down large components into smaller, more manageable ones.
  2. Use functional components and hooks where possible, as they tend to be more concise and easier to understand.
  3. Create custom hooks for reusing stateful logic across components.
  4. Keep your components focused on a single responsibility.

Using state and props effectively

  1. Pass data between components using props.
  2. Lift state up to the nearest common ancestor if multiple components need to share the same state.
  3. Use the useState and useEffect hooks in functional components to manage state and side effects.
  4. Avoid unnecessary re-renders by only updating state when necessary.

Following the Single Responsibility Principle

The Single Responsibility Principle (SRP) states that a class or module should have only one reason to change. In the context of React.js, this means that each component should be responsible for only one aspect of the user interface.

To follow the SRP in your React.js applications:

  1. Keep your components small and focused.
  2. Break down complex components into smaller, more manageable subcomponents.
  3. Separate presentation from logic by using container and presentational components, or custom hooks.

Testing React.js applications

Testing is essential for ensuring the quality and reliability of your React.js applications. To test your React.js components:

  1. Write unit tests for your components using testing libraries like Jest and React Testing Library.
  2. Test the behavior of your components, rather than their implementation details.
  3. Write integration tests to ensure that different parts of your application work together as expected.
  4. Set up continuous integration to automatically run tests when changes are made to the codebase.


In this article, we covered the fundamentals of React.js, including its definition, features, advantages, and how to get started with it. We also discussed best practices for writing reusable, maintainable, and testable code in React.js.

React.js is an essential tool in modern web development, offering a powerful, component-based approach to building user interfaces. With its large community, strong ecosystem, and continued development, React.js will likely remain a popular choice for front-end developers in the future. As you continue to learn and work with React.js, remember to stay up-to-date with the latest best practices, libraries, and community resources to make the most of this powerful framework.