Must read Topics for Mid Level Node.js Developer Interview Preparation

1. Core Node.js Fundamentals

1. Node.js Architecture (Single-threaded, Event Loop, Non-blocking I/O)✅
2. Understanding require and ES Modules (import/export)✅
3. Core Modules:
   • fs
   • path
   • os
   • events
   • http / https
   • stream (Readable, Writable, Transform, Duplex)
4. Process Management:
   • process (environment variables, process.nextTick, process.exit)
   • Handling Uncaught Exceptions
5. Timers (setTimeout, setInterval, setImmediate)
6. Working with Buffers
7. Working with the File System (fs.promises, async/await with fs)
8. Child Processes (child_process, exec, spawn, fork)

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2. Package Management with npm and Yarn

1. Managing dependencies (package.json, package-lock.json)✅
2. Semantic Versioning (^, ~, exact versions)✅
3. Local vs. global packages✅
4. Scripts in package.json (e.g., npm run dev)✅
5. Using npx✅

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3. Asynchronous Programming

1. Callbacks✅
2. Promises✅
3. async/await✅
4. Event Emitters
5. Streams and Pipelining
6. Error handling in async code (try/catch, .catch)✅

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4. Express.js Framework

1. Setting up an Express.js server✅
2. Middleware:
   • Custom Middleware✅
   • Built-in Middleware (express.json, express.urlencoded)✅
   • Third-party Middleware (e.g., cors, body-parser, morgan)✅
3. Routing (dynamic and static routes)✅
4. Handling Query Parameters, Route Parameters, and Request Body✅
5. Error Handling Middleware✅
6. Working with Static Files✅
7. Express Router✅
8. Security Middleware (helmet, cors, rate-limiting)

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5. RESTful API Development

1. HTTP Methods (GET, POST, PUT, DELETE, PATCH)✅
2. Status Codes and Responses (200, 201, 400, 401, 403, 404, 500)✅
3. Query Parameters vs. Route Parameters✅
4. Pagination, Sorting, and Filtering✅
5. Validations (e.g., joi, express-validator)
6. Authentication and Authorization:
   • Token-based Authentication (e.g., JWT)
   • Role-based Authorization
   • OAuth basics

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6. Database Integration

1. SQL vs NoSQL (basics of when to use which)
2. Working with MongoDB:
   • Mongoose ORM (Schemas, Models, Queries)
   • Aggregation Pipelines
   • Indexing for Optimization
3. Working with PostgreSQL or MySQL:
   • Sequelize ORM (or raw queries)
   • Relationships (One-to-Many, Many-to-Many)
4. Basic CRUD Operations in databases
5. Transactions
6. Connection Pooling

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7. Authentication and Security

1. Hashing Passwords (e.g., bcrypt)
2. JSON Web Tokens (JWT):
   • Signing, verifying, and expiration
3. OAuth 2.0 basics
4. Security Best Practices:
   • Protecting Sensitive Data (e.g., environment variables)
   • Avoiding SQL Injection (Parameterized Queries)
   • Preventing XSS, CSRF, and other vulnerabilities
   • Using Helmet.js for securing HTTP headers
5. CORS (Cross-Origin Resource Sharing)✅
   • Configuring and debugging

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8. Advanced Node.js Concepts

1. Clustering and Load Balancing
2. Worker Threads
3. Scaling Applications
4. Streams (Advanced Usage)
5. Profiling and Debugging:
   • Using node --inspect
   • Chrome DevTools for Node.js
   • Memory Leak Detection

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9. Testing

1. Unit Testing:
   • jest
   • mocha and chai
2. Integration Testing:
   • Testing APIs with supertest
3. Mocking Dependencies
4. Code Coverage Tools (nyc)

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10. Deployment and CI/CD

1. Process Managers (e.g., PM2)
2. Building Docker Containers for Node.js apps
3. Environment Variables:
   • Using .env and dotenv✅
4. Hosting:
   • AWS (EC2, Elastic Beanstalk)
   • Heroku
   • Vercel/Netlify (for serverless deployments)
5. Continuous Integration:
   • GitHub Actions
   • Jenkins basics
6. Monitoring:
   • Tools like New Relic, Sentry

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11. Real-Time Communication

1. WebSockets with socket.io✅
2. Long Polling
3. Event-Driven Architecture
4. Handling Real-Time Data Updates

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12. Build Tools

1. Using Babel for Transpiling
2. Webpack Basics
3. Nodemon for Development✅
4. ESLint and Prettier for Code Quality✅

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13. Logging and Debugging

1. Using console.log effectively
2. Debugging with Chrome DevTools
3. Using Logging Libraries (winston, morgan)✅
4. Writing logs to files or external services (e.g., ELK stack)

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14. Message Queues and Task Scheduling

1. Working with Message Queues:
   • RabbitMQ
   • Kafka (basic concepts)
2. Task Scheduling:
   • Using node-schedule
   • Cron Jobs

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15. Microservices (if applicable for your target role)

1. Basics of Microservices Architecture
2. Communication between services:
   • REST APIs
   • Message Brokers (e.g., Kafka, RabbitMQ)
3. API Gateways
4. Handling Distributed Systems Challenges (e.g., consistency, retries)

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16. Documentation and Best Practices

1. Writing API Documentation:
   • Using Swagger/OpenAPI
2. Structuring Code for Scalability:
   • MVC (Model-View-Controller)
   • Feature-Based Architecture
3. Following Code Best Practices:
   • DRY (Don’t Repeat Yourself)
   • KISS (Keep It Simple, Stupid)
   • SOLID Principles
4. Error Handling Best Practices