React JS · Beginner Guide 2026

What Is React JS? A Complete Beginner Guide 2026

SECTION 01What is React JS?

React JS (commonly called React) is an open-source JavaScript library created by Facebook in 2013. It's used for building user interfaces, particularly for single-page applications where you need fast, interactive experiences.

Key characteristics:

• Component-based: Build encapsulated components that manage their own state.
• Declarative: Describe what the UI should look like, and React handles the updates.
• Efficient: Uses a virtual DOM for fast updates.
• JavaScript-based: You write components using JavaScript and a syntax extension called JSX.

SECTION 02Why is React so popular?

React has become one of the most popular frontend technologies for several reasons:

• Component reusability: Write once, use anywhere. Components can be reused across your application.
• Virtual DOM: React's virtual DOM makes updates fast and efficient.
• Huge ecosystem: Thousands of libraries, tools, and community packages.
• Great developer experience: Hot reloading, developer tools, and clear error messages.
• Backed by Facebook: Actively maintained and battle-tested at scale.
• Used by major companies: Facebook, Instagram, Netflix, Airbnb, WhatsApp, and many more.

SECTION 03Core concepts: Components

Components are the building blocks of React applications. They're reusable, self-contained pieces of UI that can be combined to create complex interfaces.

Types of components:

• Function components: JavaScript functions that return JSX. (Most common in modern React)
• Class components: ES6 classes that extend React.Component. (Less common in 2026)

Example of a function component:

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

SECTION 04Core concepts: JSX

JSX is a syntax extension that looks like HTML but is written inside JavaScript. It makes it easier to write and understand the structure of your UI.

Key points about JSX:

• JSX is not required — you can use plain JavaScript — but it's recommended.
• JSX allows you to embed JavaScript expressions inside curly braces: {expression}
• JSX is transpiled to React.createElement() calls.

SECTION 05Core concepts: State and props

State and props are how React manages data and passes it between components.

Props (Properties):

• Passed from parent to child components.
• Read-only — child components cannot modify their props.
• Used to pass data and configuration down the component tree.

State:

• Managed within the component itself.
• Mutable — can be updated using useState hook.
• Used for data that changes over time (user input, API responses, etc.).

SECTION 06Core concepts: Hooks

Hooks are functions that let you use React features in function components. They were introduced in React 16.8 and have become the standard way to write React components.

Common hooks:

• useState: Adds state to function components.
• useEffect: Handles side effects like data fetching, subscriptions, and DOM manipulation.
• useContext: Accesses context values without prop drilling.
• useReducer: For more complex state logic.
• useRef: References DOM elements or persists values across renders.

SECTION 07The virtual DOM

The virtual DOM is one of React's most important features. It makes React fast and efficient.

How it works:

• React keeps a lightweight virtual representation of the DOM in memory.
• When state changes, React creates a new virtual DOM tree.
• It compares the new tree with the previous one (diffing).
• It calculates the minimum number of changes needed and applies them to the actual DOM (reconciliation).

SECTION 08How to start learning React

Here's a step-by-step path to start your React learning journey:

Prerequisites (before React):

• HTML & CSS: Understand the basics of web structure and styling.
• JavaScript (ES6+): Know functions, arrays, objects, arrow functions, destructuring, and async/await.

React learning path:

• Step 1: Learn JSX and component basics.
• Step 2: Master state and props.
• Step 3: Learn React hooks (useState, useEffect).
• Step 4: Build projects — start with a to-do app, then a weather app, then a full-stack app.
• Step 5: Learn React Router for navigation and state management (Redux or Context API).

SECTION 09React career opportunities

React developers are in high demand with excellent career growth and earning potential:

• Frontend Developer (React): ₹4-8 LPA (entry), ₹12-20 LPA (senior)
• React Native Developer: ₹5-10 LPA (entry), ₹15-25 LPA (senior)
• Full Stack Developer (React + Node): ₹6-12 LPA (entry), ₹18-30 LPA (senior)

Career progression:

• Entry: Junior React Developer → React Developer
• Mid: Senior React Developer → Tech Lead
• Senior: Engineering Manager → Director of Engineering → CTO

SECTION 10Test yourself — React basics

SECTION 11Frequently asked questions

SECTION 12Related reads