React Top Interview Questions For TCS

📘 Introduction

Are you preparing for a React.js interview at TCS (Tata Consultancy Services)? React remains one of the most in-demand skills in the front-end development space.

TCS often tests candidates on their understanding of core React concepts, including components, state, props, hooks, routing, and performance optimization.

This guide is your one-stop resource for mastering React interview questions specifically asked in TCS technical rounds.

It includes beginner-friendly concepts, intermediate logic, and advanced best practices.

✔ Covers key React fundamentals
✔ Includes code examples and scenarios
✔ Perfect for freshers, experienced devs, or TCS off-campus candidates

🔖 Bookmark this page and revise before your TCS interview for React.js roles.

🧠 Basic React.js Interview Questions

1. What is React.js?

React is a JavaScript library developed by Facebook for building interactive and dynamic user interfaces, especially single-page applications (SPAs).

2. Key Features of React

• Virtual DOM

• Component-based architecture

• Unidirectional data flow

• JSX (JavaScript XML)

• Functional components with hooks

3. What is JSX?

JSX stands for JavaScript XML. It allows you to write HTML inside JavaScript code.

const greeting = <h1>Hello, React!</h1>;

4. Real DOM vs Virtual DOM

5. What are Components in React?

Components are independent, reusable UI pieces. Two types:

• Functional Components

• Class Components

6. Difference Between Functional and Class Components

7. What are Props?

Props (short for properties) are used to pass data from parent to child components. They are read-only.

8. What is State in React?

State is used to store component data and trigger re-renders when updated.

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

9. What are React Hooks?

Hooks allow functional components to use state and lifecycle features.
Common hooks:

• useState

• useEffect

• useContext

10. What is useEffect?

useEffect performs side effects like fetching data, updating the DOM, or setting up subscriptions.

useEffect(() => {
  console.log("Component mounted");
}, []);

🧩 Intermediate React.js Questions

11. What are Keys in React?

Keys help React identify changes in a list to optimize rendering.

{items.map(item => <li key={item.id}>{item.name}</li>)}

12. Controlled vs Uncontrolled Components

• Controlled: State handled by React.

• Uncontrolled: State handled by DOM.

13. What is React Router?

A library that handles routing in SPAs.

<BrowserRouter>
  <Route path="/about" element={<About />} />
</BrowserRouter>

14. What is Redux?

A predictable state container for JavaScript apps.

• Centralized store

• Actions, Reducers

• Middleware (e.g., Redux Thunk)

15. React Context vs Redux

16. What is shouldComponentUpdate?

A lifecycle method to prevent unnecessary re-renders.

17. useMemo vs useCallback

• useMemo: Caches values

• useCallback: Caches functions

18. What are React Fragments?

They let you return multiple elements without extra nodes.

<>
  <td>Name</td>
  <td>Email</td>
</>

19. useState vs useReducer

• useState: Simple state

• useReducer: Complex state with logic

20. What is Code Splitting?

Breaking code into chunks that load on demand using:

const LazyComponent = React.lazy(() => import('./Component'));

🚀 Advanced React.js Interview Questions

21. componentDidMount vs useEffect

• componentDidMount: Class components

• useEffect(() => {}, []): Functional equivalent

22. What are Higher-Order Components (HOCs)?

Functions that enhance existing components.

const withLogger = Component => props => {
  console.log("Logging");
  return <Component {...props} />;
};

23. What are React Portals?

Allows rendering outside the root element.

ReactDOM.createPortal(<Modal />, document.getElementById('modal-root'));

24. useRef vs useState

• useRef: No re-render

• useState: Causes re-render

25. What is React.memo?

Optimizes functional components by memoizing output.

const MemoComp = React.memo(MyComponent);

26. SSR vs CSR

27. What are Error Boundaries?

Catch errors during rendering.

componentDidCatch(error, info) {
  this.setState({ hasError: true });
}

28. What is React.lazy?

Lazy loading components:

const Home = React.lazy(() => import('./Home'));

29. useLayoutEffect vs useEffect

• useLayoutEffect: Synchronous

• useEffect: Asynchronous

30. Performance Optimization in React

• Use React.memo, useMemo, useCallback

• Avoid inline functions in render

• Implement code splitting

• Optimize rendering with shouldComponentUpdate

💼 Behavioral and Scenario-Based Questions (TCS Specific)

1. Describe a Project You Built Using React

• Project: CRM dashboard

• Features: Real-time updates, charts, responsive UI

• Challenges: Handling API failure, component reusability

2. How Do You Manage State in Large Applications?

• Use Redux or Context API

• Split global and local state

• Use middleware (redux-saga/thunk)

3. How Do You Ensure Code Reusability?

• Create shared UI components

• Use HOCs and custom hooks

4. How Do You Debug React Apps?

• React Developer Tools

• Logging with console

• Debugging with breakpoints

5. How Do You Handle API Calls?

• Use fetch or axios

• Use useEffect to call API

• Handle loading and error states

💡 Tips to Crack TCS React.js Interviews

1. Master React fundamentals – Understand JSX, props, state, hooks

2. Practice coding challenges – Build small reusable components

3. Review official docs – Go through React docs

4. Build projects – Showcase projects on GitHub or portfolio

5. Mock interviews – Practice speaking clearly and explaining code

🏁 Conclusion

React is a must-have skill for front-end developers in today’s job market. Whether you’re preparing for an interview with TCS, Infosys, Wipro, or any MNC, this list will guide you through key React topics. From state management to performance tuning, you now have a roadmap to interview success.

Continue your preparation with these useful guides:

• Top 100 JavaScript Interview Questions

• Top 30 Technical Interview Questions Every Developer should know

• Top Express Js Interview Questions and Answers

📌 Don’t forget to bookmark this guide and share it with your peers preparing for React interviews!