Full-Stack Developer Interview Questions: React, Node.js & System Design

Expert Answer: Building a full-stack application involves planning architecture, setting up frontend (React), backend (Node.js/Express), database design, API development, authentication, testing, and deployment. Start with requirements analysis, design database schema, implement backend APIs, build responsive frontend, integrate services, and deploy to production.

Example: "I built a social media platform using MERN stack. First, I designed the database schema with users, posts, and comments tables. Created REST APIs for authentication, CRUD operations, and real-time features using Socket.io. Built React frontend with components for feeds, profiles, and messaging. Implemented JWT authentication, file uploads to AWS S3, and deployed using Docker containers on AWS ECS with load balancing."

Expert Answer: State management involves client-side state (React Context/Redux), server state (REST APIs/GraphQL), database state (SQL/NoSQL), and synchronization between layers. Use proper caching strategies, optimistic updates, real-time communication, and maintain single source of truth.

Example: "I implemented Redux Toolkit for client state management and React Query for server state caching. Used WebSocket for real-time updates, optimistic UI updates for better UX, and normalized data structures. Implemented proper error boundaries, loading states, and offline support with service workers. This reduced API calls by 60% and improved user experience significantly."

Expert Answer: Server-side rendering (SSR) generates HTML on the server for better SEO and initial page load. Client-side rendering (CSR) renders in the browser for interactive experiences. Modern approaches include static generation (SSG) and hybrid rendering for optimal performance and SEO.

Example: "I implemented Next.js for our e-commerce site to combine SSR and CSR benefits. Used SSR for product pages (better SEO), SSG for static content like homepage, and CSR for user dashboards. This improved SEO rankings by 40%, reduced initial page load to under 2 seconds, and maintained rich interactivity. Also implemented incremental static regeneration for dynamic content."

Expert Answer: Implement real-time features using WebSockets, Socket.io, Server-Sent Events, or WebRTC for different use cases. Consider connection management, message queuing, scaling across multiple servers, and fallback mechanisms for unreliable connections.

Example: "I built a real-time collaborative document editor using Socket.io. Implemented operational transformation for conflict resolution, room-based connections for document collaboration, Redis adapter for horizontal scaling across multiple servers, and reconnection logic with message queuing. Added presence indicators, cursor tracking, and real-time comments. Supported 1000+ concurrent users per document with sub-100ms latency."

Expert Answer: Implement JWT or session-based authentication, role-based access control (RBAC), secure password hashing, OAuth integration, and protect routes on both frontend and backend. Use HTTPS, implement CSRF protection, and manage token refresh securely.

Example: "I implemented a comprehensive auth system using JWT with refresh token rotation. Frontend: protected routes with React Router guards, token refresh interceptors, and secure storage. Backend: bcrypt password hashing, role-based middleware, OAuth2 integration with Google/GitHub. Added two-factor authentication using TOTP, password reset flows, and audit logging. Achieved 99.9% security compliance and seamless user experience."

Expert Answer: Optimize frontend with code splitting, lazy loading, image optimization, and CDN. Optimize backend with database indexing, caching, connection pooling, and API pagination. Implement monitoring, profiling, and performance budgets across the stack.

Example: "I optimized our e-commerce platform achieving 90+ Lighthouse scores. Frontend: implemented React.lazy, image lazy loading, service workers for caching, and webpack bundle analysis. Backend: added Redis caching, database query optimization, connection pooling, and API response compression. Used CDN for static assets, implemented infinite scrolling, and set up performance monitoring with New Relic. Reduced page load time from 8s to 2s and improved conversion rates by 25%."

Expert Answer: Implement comprehensive testing pyramid: unit tests (Jest, React Testing Library), integration tests (API testing), and E2E tests (Cypress, Playwright). Include database testing, API contract testing, visual regression testing, and performance testing.

Example: "I established testing strategies achieving 95% code coverage. Unit tests: Jest for business logic, React Testing Library for components. Integration: Supertest for API endpoints, database testing with test containers. E2E: Cypress for critical user flows, visual regression with Percy. Set up CI/CD pipeline with automated testing, database migrations testing, and deployment smoke tests. Reduced production bugs by 80% and deployment confidence increased significantly."

Expert Answer: Implement CI/CD pipelines, containerization with Docker, infrastructure as code, monitoring and logging, automated testing, database migrations, and deployment strategies like blue-green or rolling deployments for zero-downtime updates.

Example: "I set up complete DevOps pipeline using GitHub Actions, Docker, and AWS. Created multi-stage Dockerfiles for frontend and backend, implemented infrastructure as code with Terraform, set up ECS clusters with load balancing. Added comprehensive monitoring with CloudWatch, error tracking with Sentry, and log aggregation with ELK stack. Implemented automated database migrations, feature flags, and blue-green deployments. Achieved 99.9% uptime and reduced deployment time from 2 hours to 15 minutes."

Expert Answer: Design RESTful or GraphQL APIs with proper resource modeling, consistent naming conventions, versioning strategy, documentation, error handling, rate limiting, and security measures. Consider pagination, filtering, sorting, and caching strategies.

Example: "I designed a comprehensive API for our SaaS platform. Used REST with proper HTTP methods and status codes, implemented OpenAPI specification for documentation, added rate limiting with Redis, API versioning with headers. Created consistent error response format, implemented pagination with cursor-based approach, added request/response validation with Joi. Set up API monitoring with response time tracking and automated integration tests. APIs served 10M+ requests daily with 99.95% availability."

Expert Answer: Design normalized database schemas, implement proper indexing strategies, use appropriate data types, establish relationships, implement migrations, consider read/write splitting, and choose between SQL/NoSQL based on requirements. Include backup and recovery strategies.

Example: "I designed the database architecture for a multi-tenant e-commerce platform. Created normalized schema with proper foreign keys, implemented composite indexes for frequently queried columns, used UUID for primary keys for better distribution. Set up read replicas for scaling, implemented database connection pooling, and created automated backup strategies. Added database monitoring, query performance analysis, and implemented data archiving for old records. Optimized complex queries reducing response time from 2s to 200ms."