What is React? React JS Explained with Examples, Features & Advantages

What is React JS? (Complete Beginner's Guide)

Introduction

 Traditional websites reload the entire page whenever a user clicks a link or submits a form, which can make the experience feel slow. Modern web applications solve this problem by updating only the parts of the page that change.

React JS is one of the most popular JavaScript libraries used to build these modern, fast, and interactive user interfaces. It allows developers to create reusable components, efficiently update web pages, and build applications that provide a smooth user experience.

Developed by Facebook (now Meta) in 2013, React is now used by thousands of companies around the world, including Instagram, Netflix, WhatsApp Web, Airbnb, and many others. Its simplicity, speed, and flexibility have made it a favourite choice for both beginners and professional developers.

 

React applications mainly use two JavaScript libraries:

1. React JS – Used to create user interface (UI) components.
2. ReactDOM – Used to display React components inside a web page.

Think of it like this:

• React = Creates the design and logic.
• ReactDOM = Displays that design in the browser.

react installation

What is React JS?

React JS is an open-source JavaScript library used for building user interfaces (UI), especially for Single Page Applications (SPAs). It helps developers create dynamic and interactive web applications by dividing the user interface into small, reusable pieces called components.

Unlike traditional web development, where developers manually update HTML whenever data changes, React automatically updates only the parts of the page that need to change. This makes applications faster and improves the overall user experience.

 an open-source JavaScript library developed by Facebook for building fast, interactive,user interfaces.

Instead of writing the same HTML repeatedly, React allows developers to create components, which are reusable pieces of UI.

Why Was React Created?

Before React, developers often used JavaScript or jQuery to manipulate the Document Object Model (DOM) directly. As applications became larger, managing updates became more difficult, leading to slower performance and more complex code.

React was created to solve these problems by:

• Improving website performance.
• Making code easier to organise.
• Encouraging reusable components.
• Simplifying the development of complex user interfaces.
• Updating parts of the page that change. 

Where Is React Used?

1. Business websites
2. E-commerce applications
3. Social media platforms
4. Dashboard applications
5. Portfolio websites
6. Online learning platforms
7. Banking applications
8. Food delivery applications
9. Travel booking systems
10. Hospital management systems

Advantages of React

• Easy to learn for developers with JavaScript knowledge.
• Component-based architecture encourages code reuse.
• Faster performance with the Virtual DOM.
• Clean and organised code structure.
• Strong community support and extensive documentation.
• Large ecosystem of tools and libraries.
• Supports responsive and interactive user interfaces.

Limitations of React

• React focuses only on the user interface; additional libraries are needed for routing, state management, or API handling.
• Beginners may take some time to understand concepts such as JSX, components, props, and state.
• The React ecosystem evolves quickly, so developers need to keep learning new features and best practices. 

Why Should You Learn React?

Learning React opens the door to modern front-end development. It is one of the most in-demand skills for web developers because many companies use React to build professional web applications.

By learning React, you will be able to:

• Build interactive websites.
• Create reusable UI components.
• Develop fast Single Page Applications.
• Work with APIs and dynamic data.
• Improve your career opportunities in front-end and full-stack development. 

Key Points to Remember

• React JS is an open-source JavaScript library.
• It was developed by Meta (Facebook) and released in 2013.
• React is used to build fast and interactive user interfaces.
• It follows a component-based architecture.
• React uses the Virtual DOM to improve performance.
• JSX allows developers to write HTML-like code inside JavaScript.
• React updates only the changed parts of a webpage instead of reloading the entire page. 

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Key Features of React

1. Component-Based Architecture

React applications are built using components.

A component is an independent piece of the user interface that contains its own structure, logic, and styling.

For example, an e-commerce website may contain:

• Header Component
• Product Component
• Shopping Cart Component
• Footer Component

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React Working Flow

User Action

     │

    ▼

 React Component

     │

    ▼

 State / Props Change

     │       

    ▼

 Virtual DOM

     │

 Compare Changes

     │

    ▼

 Send Updated Part to ReactDOM

What is ReactDOM?

ReactDOM is a package that connects React with the browser's Document Object Model (DOM).

ReactDOM takes the components created by React and renders them inside an HTML element.

Without ReactDOM, React components cannot be displayed in a web browser.

Simple Definition

ReactDOM displays React components on the webpage.

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ReactDOM Flow

React Component

      │

  ReactDOM.render()

      │

   Browser DOM

      │

 Visible Web Page

ReactDOM Example (React 18+)

import React from "react";

import ReactDOM from "react-dom/client";

import App from "./App";

 const root = ReactDOM.createRoot(

    document.getElementById("root")

);

 root.render(<App />);

---

Step-by-Step Explanation

Step 1

Import React

import React from "react";

React allows you to create components.

---

Step 2

Import ReactDOM

import ReactDOM from "react-dom/client";

ReactDOM communicates with the browser.

---

Step 3

Import App Component

import App from "./App";

App is the main component.

---

Step 4

Find HTML Element

document.getElementById("root")

Finds

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

---

Step 5

Create Root

const root = ReactDOM.createRoot(

document.getElementById("root")

);

Creates a React Root.

---

Step 6

Render Component

root.render(<App />);

Displays

<App />

inside

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

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Final Output

-------------------------

Welcome to React

-------------------------

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React and ReactDOM Together

App.jsx

   │

 React Creates Component

   │

Virtual DOM

   │

 ReactDOM

   │

 Real DOM

   │

 Browser Screen

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React vs ReactDOM

React	ReactDOM
Creates UI components	Displays components in the browser
Manages state	Updates the browser DOM
Uses Virtual DOM	Updates the Real DOM
Contains JSX logic	Connects React with HTML
Builds the interface	Renders the interface

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Virtual DOM and ReactDOM

Old Virtual DOM

        │

  New Virtual DOM

        │

Compare Both

        │

Find Differences

        │

Update Only Changed Parts

        │

ReactDOM

        │

Real DOM Updated

This process makes React applications fast because it avoids updating the entire webpage.

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Why Do We Need ReactDOM?

• React components cannot appear in the browser.
• There is no connection between React and the HTML page.
• The browser cannot display the React application.

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Advantages of React and ReactDOM

1. Builds reusable components, reducing duplicate code.
2. Faster updates through the Virtual DOM.
3. Efficient rendering by updating only changed elements.
4. Clear separation between UI creation (React) and rendering (ReactDOM).
5. Easy to maintain and scale large applications.
6. Widely used for modern web development.

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Key Points to Remember

• React is the JavaScript library use to build user interfaces.
• ReactDOM is the package that renders React components into the browser's HTML DOM.
• React creates components and manages application state.
• ReactDOM displays those components inside an HTML element such as <div id="root"></div>.
• React uses a Virtual DOM to detect changes efficiently.
• ReactDOM updates only the necessary parts of the Real DOM, making applications faster and more responsive.

Summary

React and ReactDOM work together to build modern web applications. React focuses on creating reusable components and managing how the user interface should behave. ReactDOM takes those components and renders them in the browser, updating only the parts of the page that change. This combination of React + Virtual DOM + ReactDOM provides excellent performance, cleaner code, and a better development experience for building dynamic web applications.