🤯 Frontend Interviews Are Not Easy Anymore — Be Ready for These 10 Tough Questions

Landing a frontend developer role in 2025 is no longer just about knowing JavaScript or popular frameworks like React, Angular, or Vue.
Today’s interviews go much deeper — hiring managers expect you to understand how the web actually works under the hood.

If you’re preparing for a frontend interview, here are 10 real-world questions that can make or break your chances 👇

1️⃣ What Exactly Happens When You Type google.com in the Browser?

This is a classic systems design question for frontend developers. You’re expected to explain DNS lookup, TCP handshake, TLS setup, HTTP request, server response, rendering pipeline, and even how JavaScript execution fits in.

2️⃣ TCP vs UDP — Can You Explain With Real-World Examples?

• TCP: Reliable, ordered, error-checked delivery (think web browsing, emails, file transfers).
• UDP: Faster, connectionless, but no delivery guarantees (think video streaming, gaming, VoIP).

3️⃣ How Does HTTP vs HTTPS Work Under the Hood?

Here, interviewers expect you to explain TLS/SSL encryption, how it prevents MITM (Man-in-the-Middle) attacks, and why HTTPS is mandatory for modern apps (especially with browsers marking HTTP as insecure).

4️⃣ HTTP/1.1 vs HTTP/2.0 — Why Does It Matter for Performance?

• HTTP/1.1: Limited parallelism, head-of-line blocking.
• HTTP/2: Multiplexing, header compression, server push. Understanding this shows you care about performance optimization. 👉 Explained on FrontendGeek

5️⃣ Walk Me Through the HTTP Request/Response Lifecycle

From typing a URL to final render, explain:

1. Request sent → Headers, body.
2. Server processing → Response with headers + data.
3. Browser parsing & rendering → HTML, CSSOM, JS execution, layout, paint, composite.

6️⃣ JWT vs OAuth 2.0 vs OpenID — When Would You Use Each?

Authentication & authorization often come up:

• JWT (JSON Web Tokens) → Stateless authentication, simple use cases.
• OAuth 2.0 → Authorization for third-party access (e.g., “Login with Google”).
• OpenID Connect → Identity layer built on OAuth 2.0 for user authentication.

7️⃣ How Would You Protect a Web App Against XSS, CSRF, and CORS Issues?

• XSS → Escape input, CSP headers, sanitizer libraries.
• CSRF → CSRF tokens, SameSite cookies.
• CORS → Correct server headers, understanding preflight requests.

8️⃣ DOM vs Canvas Rendering — When to Use Each?

• DOM Rendering → Great for UI-driven, accessible, text-heavy apps.
• Canvas Rendering → Best for games, heavy graphics, animations, real-time rendering.

9️⃣ Long Polling vs WebSockets vs Server-Sent Events (SSE)

Frontend interviews often test your real-time data knowledge:

• Long Polling → Repeated requests for updates.
• WebSockets → Full-duplex, persistent connection.
• SSE → Server pushes events to client (unidirectional).

🔟 Local Storage vs Session Storage vs Cookies — Which One Should You Choose?

• Local Storage → Persistent key-value store (5–10 MB).
• Session Storage → Cleared when tab is closed.
• Cookies → Smaller, sent with requests (good for auth tokens).

🧠 Final Thoughts

Frontend interviews are getting tougher because companies want developers who can debug, optimize, and scale real-world applications — not just build a to-do app in React.

If you can confidently answer these 10 questions, you’ll stand out in your next interview.

👉 Which one of these have you been asked in an interview?

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