Senior React/Next.js Hiring Guide: Questions and Tasks
Great senior hires pair sharp technical judgment with delivery discipline. Use the following interview prompts and take-home tasks to reveal how candidates think, ship, and prevent costly regressions across web and mobile surfaces.
Architecture and scaling questions
Probe decisions that trade simplicity for speed safely. Ask:
- Walk me through how you would structure a Next.js 14 app using App Router, Server Components, and route groups. Where do you draw the line between server and client components, and why?
- How would you design data fetching with React Server Actions, ISR, and caching to serve personalized dashboards at scale?
- What's your approach to auth in Next.js (OAuth/OpenID, session vs JWT, rotating refresh tokens), and how do you handle RBAC on the server?
- How would you use middleware, Edge runtime, and CDN caching to localize content while keeping TTFB low?
Performance audits for web apps
Senior engineers should run repeatable audits, not one-off tweaks. Explore:
- Explain your Core Web Vitals playbook. Which issues do you chase first and why (render-blocking, hydration waterfalls, or script bloat)?
- Show how you'd profile a slow route: React Profiler flame charts, Next.js route-level timings, Lighthouse CI budgets, and Chrome performance traces.
- How do you prevent regressions? Discuss bundle analysis (Source Map Explorer), dynamic imports, selective re-exports, image/CDN strategy, and font loading.
- What's your RUM setup? Outline web-vitals collection, sampling, Sentry/Datadog integration, and guardrails in CI.
Live exercise: Given a Next.js repo with a 5.5s LCP, reduce LCP under 2.2s by deferring non-critical JS, streaming server-rendered content, and converting images to responsive formats. Ask for a written audit with before/after metrics and a prevention plan.
Delivery mindset: MVP development sprints
Assess whether they can cut scope without cutting value. Discuss:
- Story slicing by outcomes, not UI screens; using vertical slices aligned to a measurable KPI.
- Trunk-based development, feature flags, and progressive delivery to keep the main branch releasable daily.
- Forecasting via throughput and WIP limits.
- Definition of Done that includes a performance check, accessibility scan, and observability hooks.
Case prompt: You have two weeks to ship paid subscriptions. Design MVP development sprints with a compliance-safe Stripe flow, minimal billing UI, and explicit cut lines. Require an event schema, rollback plan, and success metrics.
Release rigor: app store deployment and release management
Even web-first teams touch mobile. Ask how they handle React Native or Expo alongside Next.js:
- Outline app store deployment and release management: semantic versioning, build signing, TestFlight/internal tracks, phased rollouts, and rollback triggers.
- Explain OTA updates (Expo EAS/CodePush), when they are appropriate, and how to keep JS/Native parity.
- For web, describe blue/green or canary releases on Vercel, feature-flag kill switches, sourcemaps, and crash triage with Sentry.
- What's your plan for Apple review edge cases (privacy manifests, entitlement audits) and Google Play policy changes?
Take-home task (6-hour cap)
Deliver a production-grade slice, not a toy:
- Build a Next.js 14 app with an authenticated dashboard. Use Server Components, React Server Actions, route groups, and ISR caches with explicit revalidation.
- Create a searchable table (debounced), optimistic mutations, and streaming SSR for detail views.
- Add an audit: run Lighthouse CI, record Web Vitals, capture bundle sizes, and define budgets that fail CI on regression.
- Implement A11y basics (focus order, ARIA where needed, color contrast) and unit/e2e tests with Vitest and Playwright.
- Ship with a small release plan: canary strategy, observability wiring, and a rollback checklist. Extra credit: PWA manifest and store-readiness notes.
Deliverables: repo URL, short ADRs explaining key trade-offs, a 1-page performance audit, and a 5-minute loom showing the release flow.
Evaluation rubric
- Architecture: clear boundaries, minimal client JS, cache correctness.
- Performance: audited improvements, budgets in code, no layout shifts.
- Reliability: tests tied to risk, resilient network logic, idempotent actions.
- Security: secrets handling, authz checks server-side, dependency hygiene.
- DX: scripts, linting, and readable ADRs; thoughtful README with runbooks.
- Release: canary plan, alerts, and a path to phased rollout on web and stores.
Red and green flags
- Green: speaks in measurable outcomes, uses tracing and budgets, designs for rollback.
- Green: proactively proposes de-scope paths and observes DORA metrics.
- Red: blames framework for slowness, disables SSR broadly, or rejects tests as "later."
- Red: confuses caching with persistence; no plan for secrets or PII.
Where to find this caliber
If you need pre-vetted experts who can run performance audits for web apps, lead MVP development sprints, and handle app store deployment and release management, consider slashdev.io. They provide excellent remote engineers and software agency expertise for founders and enterprises who need to move fast without breaking trust.
