round 1 1. Explain the difference between var, let, and const and how scoping affects closures. 2. What are pure functions and how do they improve maintainability in React applications? 3. How does React Fiber enhance rendering performance? 4. What’s the difference between virtual DOM and real DOM? 5. How do you optimize React re-rendering — besides using React.memo()? 6. What are Higher-Order Components (HOCs) and how do they differ from hooks? 7. How would you manage global state across multiple components without Redux? 8. What are child processes in Node.js and how do you use them for heavy computations? 9. How do you manage rate limiting in Express to prevent abuse? 10. Explain the concept of circular dependencies in Node.js and how to resolve them. 11. Explain MongoDB indexing strategies and their trade-offs. 12. How do you handle large file uploads or streaming data in Node.js? 💡 Scenario-Based Questions 13. A React form is re-rendering on every keystroke — how do you optimize it? 14. A MongoDB query is taking too long — how do you debug and optimize it? 15. You discover memory leaks in your Node.js app. How do you identify and fix them? 💻 Technical Round 2 1. How would you structure a microservices architecture for a multi-tenant SaaS platform? 2. Explain how to implement API Gateway + Authentication + Rate Limiting in Express. 3. Discuss different caching layers (Redis, CDN, browser caching) and where to apply each. 4. How would you ensure observability in a distributed MERN app (logging, tracing, metrics)? 5. How can you use Docker and Kubernetes to scale your Node.js services? 6. What strategies do you use to secure APIs from XSS, CSRF, and injection attacks? 7. How do you implement role-based access control (RBAC) in your MERN stack app? 💡Scenario-Based Questions (System Design Level) 8. Your React app bundle has grown too large, causing slow load times. Describe how you’d analyze and reduce it. 9. You need to integrate a third-party API with strict rate limits — how would you design your system? 10. How would you implement real-time notifications efficiently for thousands of connected clients? 11. How do you ensure database consistency and rollback when multiple services are involved in a transaction?