React is a JavaScript library that helps developers create user interfaces for websites, mobile apps, and desktop apps. It's used because it's efficient, fast, and widely adopted.
React is a JavaScript library for building user interfaces. Created by Facebook in 2013, it revolutionized how developers build web applications by introducing a component-based approach and efficient rendering.
Think of React as a construction system with reusable building blocks. Instead of building every page from scratch, you create components (buttons, forms, cards) and assemble them into complete interfaces.
Component-Based Architecture: Break your UI into independent, reusable pieces. Build a button component once, use it everywhere. Change it once, updates everywhere.
Virtual DOM: React does not directly manipulate the browser DOM (which is slow). It maintains a virtual representation, calculates what changed, and updates only those parts. This makes React fast even with complex UIs.
Declarative Syntax: You describe what the UI should look like for a given state. React handles updating the actual DOM. No manual DOM manipulation code.
Massive Ecosystem: npm has thousands of React libraries. Need charts? Forms? Authentication? Drag-and-drop? There is a well-tested React library for it.
Industry Adoption: Facebook, Instagram, Netflix, Airbnb, Uber, WhatsApp Web - countless major applications run on React. This means jobs, resources, and community support.
Components: Everything is a component. A component is a JavaScript function that returns UI elements.
function Button() {
(
);
}
< text= onClick={handleSubmit} />
JSX: HTML-like syntax inside JavaScript. React transforms it to regular JavaScript function calls.
const element = <h1>Hello, {name}</h1>;
// Becomes: React.createElement('h1', null, 'Hello, ', name)
State Management: Components can have internal state that triggers re-renders when changed.
function Counter() {
const [count, setCount] = useState(0);
return (
<div>
<p>Count: {count}</p>
<button onClick={() => setCount(count + 1)}>Increment</button>
</div>
);
}
When count changes, React automatically re-renders the component with the new value.
Instagram Web: The entire interface - feed, stories, messages, profiles - built with React. When you like a post, React updates just that heart icon, not the entire page.
Netflix: Their complex UI with video previews, recommendations, search, profiles uses React. Hover over a show? React fetches preview data and displays it smoothly.
Airbnb: Property listings, search filters, booking flow, host dashboard - all React. The calendar selector you use when booking? A React component.
WhatsApp Web: Real-time messaging interface built with React. When messages arrive, React efficiently adds them to your chat without reloading.
React vs Vue:
React vs Angular:
React vs Vanilla JavaScript:
Props: Data passed from parent to child components. Read-only.
function UserCard({ name, age, avatar }) {
return (
<div className="card">
<img src={avatar} alt={name} />
<h3>{name}</h3>
<p>Age: {age}</p>
</div>
);
}
State: Internal component data that changes over time. When state updates, component re-renders.
Hooks: Functions that let you use React features. useState for state, useEffect for side effects, useContext for global data.
Lifecycle: Components mount (appear), update (when props/state change), unmount (disappear). Hooks like useEffect let you run code during these phases.
Next.js: React framework for production. Handles routing, server-side rendering, API routes, optimization automatically. Used by TikTok, Twitch, Hulu.
React Router: Standard library for navigation between pages in React apps.
State Management: Redux (traditional, verbose), Zustand (modern, simple), React Query (for server state).
UI Libraries: Material-UI, Chakra UI, shadcn/ui provide pre-built components so you do not start from scratch.
Testing: React Testing Library, Jest for ensuring components work correctly.
Controlled Components: Forms where React controls input values.
function LoginForm() {
const [email, setEmail] = useState('');
return (
<input
value={email}
onChange={(e) => setEmail(e.target.value)}
/>
);
}
Conditional Rendering: Show different UI based on state.
{isLoggedIn ? <Dashboard /> : <LoginPage />}
Lists and Keys: Render arrays of data efficiently.
{products.map(product => (
<ProductCard key={product.id} {...product} />
))}
Memoization: Prevent unnecessary re-renders with useMemo and React.memo.
Code Splitting: Load components only when needed with lazy() and Suspense.
Virtual Scrolling: For long lists, render only visible items.
React is fast by default, but these techniques help when building large-scale applications.
Prerequisites: Solid JavaScript knowledge. Understand functions, arrays, objects, ES6 features (arrow functions, destructuring, spread operator).
Learning Path:
Practice Projects:
Modifying State Directly: Always use setState functions, never mutate state.
Missing Keys in Lists: Causes performance issues and bugs.
Not Cleaning Up Effects: Forgetting to remove event listeners or cancel subscriptions in useEffect.
Over-Engineering: Using Redux when simple useState would work. Start simple, add complexity only when needed.
React developers are among the most in-demand. Job titles:
Salaries in India: ₹6-12 LPA for juniors, ₹15-30 LPA for mid-level, ₹40+ LPA for seniors.
In the US: $80-120k for juniors, $120-180k for mid-level, $180k+ for seniors.
Market Demand: Most frontend jobs require React. It is the default choice for startups and large companies.
Transferable Skills: Concepts you learn (components, state management, hooks) apply to React Native (mobile) and even other frameworks.
Active Development: React continues evolving. Recent additions like Server Components keep it cutting-edge.
Community: Massive community means unlimited tutorials, courses, Stack Overflow answers, npm packages.
React is not just a library - it is a skill that opens doors. Master it, and frontend development opportunities are endless.