Nextjs
38 bites tagged Nextjs: interview questions with model answers, and 60-second explainers.
Test yourself: Top 30 Nextjs interview questions →Multiple choice, with the correct answer and why it is correct on every question. Free, no sign-in.Next.js revises its September security release to seven vulnerabilities
Next.js revised its September security notice to seven vulnerabilities. Two more issues remain pending upstream coordination; verify the current advisory before upgrading.
Session auth in Next.js with API routes and middleware
Login route sets a signed httpOnly cookie, middleware validates the session at the edge and redirects, server components read the session.
Runtime CSS-in-JS performance pitfalls in SSR Next.js
Runtime libs serialize styles per render, need style collection on the server, risk FOUC and double work in App Router.
Kent C. Dodds Adds SQLite FTS5 to Vector Search
Kent C. Dodds added SQLite FTS5 to Vectorize embeddings after semantic search missed exact matches like "React Testing Library." The hybrid pipeline uses Reciprocal Rank Fusion. If your search fails on API names, add BM25 backup, not bigger embedding models.
Vercel Ship 2026: agent stack, eve framework, and microservices
Vercel Ship 2026 unveils open-source eve framework and Vercel Services for microservices July 1. Vercel is repositioning as agentic infrastructure with Connect credentials and expanded Python backends. Evaluate if your next agent deploys here instead of AWS.
Next.js 16.2 ships stable Adapter API for all platforms
Next.js 16.2 ships a stable Adapter API co-built with OpenNext, Netlify, and Cloudflare. The typed build contract lets any platform target full framework fidelity using the same public hooks Vercel uses. Stop reverse-engineering build output.
How do you manage database connections in serverless Next.js API routes?
This tests serverless concurrency and connection limits. A strong answer notes lambda scaling exhausts DB connections, advocates connection pooling or serverless drivers, and caches the client globally.
How can you use Edge Middleware for auth and trade-offs versus getServerSideProps?
Middleware checks cookies/JWT for fast Edge rewrites/redirects; getServerSideProps uses full Node.js for heavy sessions with colder starts.
How do you handle user-specific content on a getStaticProps page?
Tests the static generation boundary. A strong answer serves a static shell, then hydrates user state client-side via useEffect or SWR. Red flag: claiming getStaticProps can read cookies at build time.
Would you use getServerSideProps or getStaticProps for private user data?
Tests SSR vs SSG privacy. Use getServerSideProps: it runs per-request with auth cookies. getStaticProps bakes HTML/JSON at build time, leaking private data across users. Red flag: suggesting ISR or revalidation for authenticated data.
How do you manage Next.js env variables on Vercel and use NEXT_PUBLIC_?
Set DB strings in Vercel dashboard without NEXT_PUBLIC_; consume in server code only. NEXT_PUBLIC_ inlines values into the browser JS bundle, leaking them to all users.
Implement A/B testing with Middleware rewrites and cookies
Sticky cookie, internal rewrite, vary cache on cookie, server-side analytics.
How would you use generateStaticParams for known products and on-demand unknowns?
Tests App Router hybrid rendering. Export generateStaticParams for known slugs at build time; leave dynamicParams true so unknown slugs server-render on demand. Red flag: citing Pages Router fallback or ignoring route segment config.
How does Server Component fetching differ from getStaticProps and getServerSideProps?
This tests shifting from page-level fetching to component-level async fetches. Strong answers note async await inside components, zero prop drilling, streaming, and mixed static or dynamic data. Red flag: calling them a simple rename of getServerSideProps.
How do you implement SSR in Next.js App Router and configure fetch?
Tests App Router static defaults and fetch-driven dynamic rendering. Strong answer: async Server Component awaits fetch with cache no-store or next revalidate zero to force request-time rendering. Red flag: citing getServerSideProps or useEffect data fetching.
Server Component fetch vs. client-side SWR or React Query
Tests App Router cache boundaries and hydration costs. Strong answers weigh server TTFB and bundle savings against client interactivity, mutations, and background refetching. Red flag: defaulting to client fetching everywhere and ignoring waterfalls.
Recommended App Router pattern to fetch shared data once for child routes
Tests App Router layout constraints and request deduplication. Answer: wrap the user fetch in React cache, call it from layout and child Server Components, and let Next.js deduplicate. Red flag: layout prop drilling or getServerSideProps.
What is state hydration in Next.js SSR with Redux or Zustand?
Hydration attaches listeners to server HTML; serialize state to an escaped script tag; boot client store before React or markup is discarded.
How do you handle 404s in React Router and Next.js App Router?
Tests client versus server routing architecture. React Router uses a wildcard route returning HTTP 200 by default; Next.js App Router uses not-found.js for server-rendered 404s. Red flag: confusing the two routers or ignoring status code semantics.
Compare Pages Router and App Router file-based routing conventions and capabilities
Tests your grasp of the folder-as-route paradigm shift. A strong answer notes that Pages files are routes while app folders are segments requiring page.js, and cites layout.js, loading.js, and error.js as nested primitives.
Why use Link over <a> for internal navigation?
This tests client-side routing vs full page reloads. A strong answer covers click interception, History API URL updates, and route prefetching. A red flag is claiming Link is purely stylistic or identical to a plain anchor.
File-Based Routing: Your Filesystem is Your API
File-based routing makes your directory structure the single source of truth for your app's URLs. Creating a file at routes/about/+page.svelte automatically creates the /about page, no central config needed.
React Hydration: Bringing Server HTML to Life
Hydration turns static, server-rendered HTML into a fully interactive React app. It's the core of Server-Side Rendering (SSR), where the client "wakes up" the initial HTML by attaching event listeners.
Session Authentication: JWT vs. Database
Session auth gives users an ID after login. A JWT is a self-contained ID card with their data; a database session is a library card pointing to their record. The key trade-off: JWTs are fast but can't be easily revoked, while database sessions are revocable.
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