Top React Interview Questions & Answers in English | Crack Your Next Interview!

Prepare for your React interview with this comprehensive list of React interview questions and answers. Covers Hooks, State Management, Lifecycle Methods, Virtual DOM & More!

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🔹 React Interview Questions & Answers

🟢 Basic React Questions

1. What is React?
   
   • React is a JavaScript library used to build user interfaces, primarily for single-page applications (SPAs). It allows developers to create reusable UI components.
2. Why use React?
   
   • React is preferred because of:
     • Fast Rendering: Uses a virtual DOM for efficient updates.
     • Reusable Components: Helps maintain clean and modular code.
     • Unidirectional Data Flow: Ensures predictable state management.
3. What is JSX?
   
   • JSX (JavaScript XML) is a syntax extension of JavaScript that allows writing UI code in a syntax similar to HTML.

Example:
jsx
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const element = <h1>Hello, World!</h1>;

4. What are Components in React?
   
   • Components are the building blocks of a React application.
   • Types of Components:
     • Functional Components: Simple and use React Hooks.
     • Class Components: Use this.state and lifecycle methods.
5. Difference between State and Props?
   
   • State: Manages data inside a component. (Mutable)
   • Props: Passes data from parent to child. (Immutable)

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🟠 Intermediate React Questions

6. What are React Hooks?
   
   • Hooks are functions that allow functional components to use state and lifecycle features.

Example:
jsx
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import { useState } from “react”;

function Counter() {

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

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

}

7. Difference between useState and useEffect?
   
   • useState: Manages component-level state.
   • useEffect: Runs side effects like API calls, event listeners, etc.
8. What is Virtual DOM? How does it work?
   
   • The Virtual DOM is a lightweight copy of the actual DOM. It updates only the changed parts instead of re-rendering the entire UI, improving performance.
9. How does React Router work?
   
   • React Router allows navigation in a React app without refreshing the page.

Example:
jsx
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import { BrowserRouter as Router, Route, Routes } from “react-router-dom”;

function App() {

  return (

    <Router>

      <Routes>

        <Route path=”/” element={<Home />} />

        <Route path=”/about” element={<About />} />

      </Routes>

    </Router>

  );

}

10. What is Redux? Why is it used?
    
    • Redux is a state management library that stores the entire application state in a single global store. It helps manage complex state changes across multiple components.

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🔴 Advanced React Questions

11. What is a Higher-Order Component (HOC)?
    
    • A HOC is a function that takes a component as input and returns a new enhanced component. It is used for code reusability.

Example:
jsx
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function withAuth(Component) {

  return function AuthenticatedComponent(props) {

    return props.isAuthenticated ? <Component {…props} /> : <p>Login required</p>;

  };

}

12. What is Lazy Loading in React?
    
    • Lazy Loading improves performance by loading components only when needed.

Example:
jsx
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import { lazy, Suspense } from “react”;

const LazyComponent = lazy(() => import(“./MyComponent”));

function App() {

  return (

    <Suspense fallback={<p>Loading…</p>}>

      <LazyComponent />

    </Suspense>

  );

}

13. What is the difference between SSR (Server-Side Rendering) and CSR (Client-Side Rendering)?
    
    • SSR: Page rendering happens on the server, improving SEO and initial load time.
    • CSR: Rendering happens in the browser, leading to faster interactions.