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

Source: Dev.to

Overview

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?

Explain the full flow:

1. DNS lookup
2. TCP handshake
3. TLS setup
4. HTTP request
5. Server response
6. Rendering pipeline
7. JavaScript execution

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

• TCP – Reliable, ordered, error‑checked delivery (e.g., web browsing, emails, file transfers).
• UDP – Faster, connectionless, no delivery guarantees (e.g., video streaming, gaming, VoIP).

3️⃣ How Does HTTP vs HTTPS Work Under the Hood?

Describe TLS/SSL encryption, how it prevents MITM (Man‑in‑the‑Middle) attacks, and why HTTPS is mandatory for modern apps (browsers now mark 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, cover:

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 Connect — When Would You Use Each?

• 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 – Ideal 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)

• 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 the tab is closed.
• Cookies – Smaller, sent with every request (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?