Full Stack Developer Interview Questions India 2026

Tip: SSR: HTML generated on server per request — better SEO, slower TTFB on cold starts. CSR: shell HTML sent, JS renders content in browser — fast after initial load, poor SEO without hydration. Next.js blends both.

Tip: CORS is a browser security mechanism blocking cross-origin requests. Fix: add `Access-Control-Allow-Origin` header on the server. In dev, use a proxy. In production, whitelist specific origins — never use `*` with credentials.

Tip: Cookies: sent with every HTTP request, can be httpOnly/secure, 4KB limit. localStorage: persistent across tabs/sessions, 5-10MB. sessionStorage: per-tab, cleared on close. Use httpOnly cookies for auth tokens, localStorage for UI preferences.

Tip: ORM maps objects to DB tables, removing boilerplate. Pros: type safety, migrations, prevents SQL injection by default. Cons: N+1 trap, complex queries are awkward, performance overhead. Use ORM by default; drop to raw SQL for reporting queries.

Tip: Node.js is single-threaded. The event loop processes callbacks from I/O operations without blocking. Never run CPU-heavy synchronous code on the main thread — it blocks all incoming requests. Offload heavy work to worker threads.

Tip: Use optimistic UI updates for fast UX, revert on error. Use React Query or SWR for server state — they handle caching, background refetch, and stale-while-revalidate. Avoid storing server data in Redux unless you need complex client-side transformations.

Tip: Cover the full stack: frontend framework, API design (REST vs tRPC), database choice, auth approach, deployment. Focus on ONE key architectural decision and explain the trade-off — shows depth over breadth.

Tip: Deploy in expand-contract pattern: (1) add new DB column as nullable, (2) deploy API that writes both old and new column, (3) migrate data, (4) deploy frontend, (5) clean up old column. Never schema-change and code-change in one atomic deploy.

Tip: Check bundle size (webpack-bundle-analyzer), LCP image optimisation, unused CSS, third-party script blocking render. On the API side: check Time to First Byte, slow DB queries. Run Lighthouse and fix the top 3 issues first.

Tip: Microservices suit teams with clear bounded contexts. Avoid for: early-stage products (premature complexity), small teams (DevOps overhead), monolithic databases. Start monolith, extract services when a clear seam exists.

Tip: Use idempotent API calls with client-generated request IDs. Implement retry with exponential backoff. For mutations: optimistic UI with rollback on error. Offline-first apps use a local queue and sync on reconnect.

Tip: Show pragmatism: quick wins are OK when time-boxed and tracked. Mention concrete practices like tagging TODOs with a ticket or scheduling a refactor sprint quarterly. Avoid both extremes: perfectionism and ignoring debt entirely.