🔥 Web Development Interview Questions with Sample Answers — Part 3

🧠 21) What is the difference between authentication and authorization?
👉 Answer: “Authentication verifies who the user is (login). Authorization checks what the user is allowed to do (permissions). Example: Login = authentication, Access admin panel = authorization.”

⚡ 22) What happens if you don’t use keys in React lists?
👉 Answer: “React cannot efficiently track elements, leading to incorrect UI updates and performance issues. Keys help React identify which items changed.”

🔄 23) What is the difference between useEffect with and without dependency array?
👉 Answer: “No dependency array → runs on every render, Empty array [] → runs once (on mount), With dependencies → runs when values change”

📦 24) Why should you not mutate state directly in React?
👉 Answer: “React relies on state changes to detect updates. Direct mutation does not trigger re-render. We should create a new copy using spread operator.”

🔐 25) What is the risk of storing JWT in localStorage?
👉 Answer: “It is vulnerable to XSS attacks. If attacker accesses JS, they can steal token. Safer approach is HttpOnly cookies.”

🌐 26) What is the difference between client-side and server-side rendering?
👉 Answer: “Client-side rendering → UI rendered in browser (React), Server-side rendering → UI rendered on server before sending to client, SSR improves SEO and initial load speed.”

🗄️ 27) What are indexes in MongoDB and why are they important?
👉 Answer: “Indexes improve query performance by allowing faster data retrieval instead of scanning entire collection.”

⚙️ 28) What is event loop in Node.js?
👉 Answer: “Event loop handles asynchronous operations. It allows Node.js to process multiple requests without blocking.”

🔁 29) What is difference between PUT and PATCH?
👉 Answer: “PUT replaces entire resource, PATCH updates only specific fields”

🚀 30) How would you scale your application if users increase?
👉 Answer:

I would use:
• Load balancing
• Database indexing
• Caching (Redis)
• Microservices architecture
• CDN for static assets

🎯 Bonus Tip
If stuck, always say: 👉 “Here’s how I would approach solving this…” Interviewers value thinking process more than perfect answers.

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