A complete, structured guide for mastering Node.js at an intermediate and senior level.
This documentation is divided into five main pillars, each containing detailed technical topics, best practices, and interview-grade explanations.

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1. JavaScript Foundations & Node.js Internals

This section builds the core understanding required to program effectively in Node.js.

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Core JavaScript Topics

• Scope, closures, hoisting
• Promises and async/await
• Event loop, microtasks, macrotasks
• this binding and arrow functions
• Destructuring, rest/spread
• Array and object manipulation
• Higher-order functions
• ES6+ features (modules, classes, generators)
• Error handling in async environments

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Node.js Runtime

• V8 engine internals
• Libuv event loop phases
• Call stack, callback queue, microtask queue
• Thread pool and non-blocking I/O
• Worker Threads API
• Process lifecycle
• Environment variables
• Global objects and timers
• Differences between browser and server JavaScript

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Modules & Packages

• CommonJS (require, module.exports)
• ES Modules (import, export)
• Core modules (fs, path, os, crypto, http)
• npm/yarn package management
• Semantic versioning
• Module resolution and caching
• Writing CLI tools and npm packages

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2. Async Architecture, Streams, Events & Networking

Master Node.js’ asynchronous nature and I/O systems.

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Asynchronous Programming

• Callbacks and callback hell
• Promises and chaining
• Async/await best practices
• Promise.all, Promise.race, Promise.any
• Non-blocking I/O
• Race conditions and synchronization
• Error handling in async workflows

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File System & Streams

• Reading/writing files (sync/async)
• Directories and permissions
• Readable, Writable, Duplex, Transform streams
• Piping and backpressure
• Compression (zlib)
• Large file handling
• File watchers

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Events & EventEmitter

• Creating and listening to custom events
• Removing listeners
• Error events
• Modular event-based architecture

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HTTP, HTTPS & Networking

• Creating HTTP/HTTPS servers
• Working with URL, query params
• CORS handling
• SSL/TLS configuration
• WebSockets (ws, socket.io)
• Reverse proxying with Nginx
• Clustering and load balancing

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3. Express.js, API Development & Validation

This section focuses on building production-ready APIs using Express.js.

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Express.js Fundamentals

• Creating apps and routers
• Middleware lifecycle
• Serving static files
• Error handling middleware
• Express 5 improvements
• Environment-based configuration

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Routing & Middleware

• app.use, app.get, app.post, app.put, app.delete
• Modular routing
• Route prefixes
• Chaining middlewares
• Third-party middleware (cors, helmet, morgan)
• Global vs scoped middleware

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Request Handling & Validation

• Parsing body, params, and query
• Input validation using express-validator, Joi
• Sanitizing inputs
• File uploads with multer
• Multipart form handling
• Rate limiting and throttling

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Authentication & Authorization

• Sessions and cookies
• JWT authentication
• Refresh token strategy
• OAuth2 and OpenID Connect
• Passport.js strategies
• Role-based and policy-based access
• CSRF and CORS security
• Password hashing (bcrypt, argon2)

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4. Databases, Caching, Queues & Performance

Modern backend systems depend on databases, caching layers, and performance techniques.

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Database Integration

• MongoDB with Mongoose
• PostgreSQL, MySQL using query clients
• SQLite for testing
• Connection pooling
• Transactions and ACID
• Database indexing and query optimization

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ORMs & Query Builders

• Prisma ORM
• Sequelize
• TypeORM
• Knex.js
• Handling relationships
• Lazy vs eager loading
• Migrations and seeding

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Caching & Queues

• In-memory cache
• Redis distributed caching
• TTL strategies
• Rate limiting with Redis
• Queues with BullMQ, RabbitMQ, Kafka
• Background processing
• Pub/Sub architecture

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Performance Optimization

• Cluster mode
• Worker threads
• Streams vs buffering
• Load balancing
• Database connection pooling
• CPU/memory profiling
• PM2 for multi-process management
• Lazy loading modules
• Monitoring GC and event loop delays

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5. Microservices, DevOps, Deployment & System Design

Advanced topics required to build scalable Node.js systems in real-world production environments.

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Microservices & Distributed Systems

• Designing microservices with Express/Fastify
• Communication via HTTP, gRPC, or message queues
• API Gateway pattern
• Event-driven architecture
• Circuit breaker and retry patterns
• Service discovery
• Saga pattern for distributed transactions

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Background Jobs & Scheduling

• Cron jobs (node-cron)
• BullMQ delayed, retry, backoff jobs
• Scheduled notifications
• Queue-based processing workflows
• Cleaning stale data

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DevOps & Deployment

• Environment configuration (dotenv, config)
• Docker and multi-stage builds
• CI/CD pipelines (GitHub Actions, CircleCI)
• Deployments on AWS, GCP, Azure
• PM2/systemd for production
• Reverse proxy with Nginx
• Zero-downtime deployments

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Monitoring & Observability

• Application metrics
• Uptime and health checks
• Logging aggregation (ELK stack, Graylog)
• Distributed tracing (Jaeger, OpenTelemetry)
• Alerts and dashboards (Prometheus, Grafana)
• API analytics and audit logs

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System Design Concepts

• Designing scalable REST APIs
• Stateless and idempotent services
• Real-time architecture via WebSockets
• Caching layers and CDNs
• Database sharding and partitioning
• Multi-tenant architecture
• Fault tolerance and graceful degradation

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Start Learning

Choose a topic below to begin your Node.js learning journey.