React Interview Questions

React remains one of the most in-demand frontend skills in 2026. Whether you're interviewing at a startup or a FAANG company, these questions cover the core concepts interviewers actually ask — from hooks and lifecycle patterns to advanced performance optimization and architectural decisions. Each question includes a detailed explanation and what interviewers are really looking for in your answer.

10 questions • 6 categories • Updated March 2026

Hooks

Mid-Level 5 min

Explain useEffect Cleanup Functions in React

What is a useEffect cleanup function, when does it run, and why is it important?

Mid-Level 5 min

useState vs useRef — When to Use Each in React

What are the differences between useState and useRef? When would you choose one over the other?

Mid-Level 6 min

Building Custom Hooks in React — Best Practices

How do you design a custom hook? What are the best practices and common patterns?

Performance

Mid-Level 6 min

useMemo vs useCallback — React Performance Hooks Explained

What is the difference between useMemo and useCallback? When should you actually use them?

Mid-Level 5 min

React.memo — When Should You Actually Use It?

What is React.memo and when should you use it? When should you avoid it?

Core Concepts

How Does React's Rendering Cycle Work?

Walk me through React's rendering cycle. What happens when state changes?

Entry-Level 4 min

What is the Virtual DOM and Why Does React Use It?

What is the virtual DOM? How does it work and why does React use it?

State Management

React Context vs Redux vs Zustand — Which Should You Use?

When would you use React Context vs. a state management library like Redux or Zustand?

Error Handling

Mid-Level 5 min

Error Boundaries in React — How to Catch and Handle Errors

What are error boundaries in React? What errors do they catch and what don't they catch?

Advanced Patterns

React Suspense — What It Is and How to Use It

What is React Suspense? What can you use it for today and what's still experimental?