MERN Stack Senior Interview Project

A comprehensive MERN (MongoDB, Express.js, React.js, Node.js) stack project designed for senior-level technical interviews. This project demonstrates advanced concepts, best practices, and real-world scenarios.

🚀 Features

Backend (Node.js/Express)

• Authentication & Authorization: JWT-based auth with role-based access control
• Database: MongoDB with Mongoose ODM
• Caching: Redis integration for performance optimization
• Real-time Communication: Socket.io for live features
• File Upload: Multer with image processing (Sharp)
• Email Service: Nodemailer integration
• Security: Helmet, rate limiting, input validation
• Logging: Winston logger with different levels
• Testing: Jest with supertest for API testing
• API Documentation: Swagger/OpenAPI
• Error Handling: Centralized error handling middleware
• Validation: Joi schema validation

Frontend (React)

• Modern React: Hooks, Context API, Custom hooks
• State Management: Redux Toolkit with RTK Query
• UI Framework: Material-UI with custom theming
• Real-time Updates: Socket.io client integration
• Form Handling: React Hook Form with validation
• Routing: React Router with protected routes
• Testing: Jest with React Testing Library
• Performance: Code splitting, lazy loading
• PWA: Service workers, offline support

📋 Interview Tasks

Task 1: Authentication System Enhancement

Difficulty: Senior Time: 2-3 hours

Implement a multi-factor authentication system:

• Add TOTP (Time-based One-Time Password) using Google Authenticator
• Implement backup codes generation and validation
• Add device fingerprinting for suspicious login detection
• Create admin dashboard for user management

Requirements:

• Use speakeasy library for TOTP
• Implement rate limiting for MFA attempts
• Add audit logging for security events
• Create comprehensive test coverage

Task 2: Real-time Chat Application

Difficulty: Senior Time: 3-4 hours

Build a real-time chat system with advanced features:

• Private and group chat rooms
• Message encryption (end-to-end)
• File sharing with progress indicators
• Typing indicators and read receipts
• Message search and filtering
• Chat history pagination

Requirements:

• Use Socket.io for real-time communication
• Implement message encryption using crypto-js
• Add file upload with size limits and type validation
• Create responsive UI with Material-UI
• Add comprehensive error handling

Task 3: E-commerce API with Advanced Features

Difficulty: Senior Time: 4-5 hours

Develop a complete e-commerce API:

• Product catalog with advanced filtering
• Shopping cart with Redis
• Order management with status tracking
• Payment integration (Stripe/PayPal)
• Inventory management
• Discount and coupon system
• Analytics and reporting

Requirements:

• Implement proper data validation and sanitization
• Add comprehensive error handling
• Create API documentation with Swagger
• Implement caching strategies
• Add unit and integration tests

Task 4: Performance Optimization

Difficulty: Senior Time: 2-3 hours

Optimize the application for high performance:

• Implement Redis caching for frequently accessed data
• Add database query optimization
• Implement CDN integration for static assets
• Add compression and minification
• Implement lazy loading and code splitting
• Add performance monitoring

Requirements:

• Use Redis for session storage and caching
• Optimize MongoDB queries with proper indexing
• Implement CDN for image and static file delivery
• Add performance metrics collection
• Create load testing scenarios

Task 5: Microservices Architecture

Difficulty: Senior+ Time: 5-6 hours

Refactor the application into microservices:

• User service (authentication, profiles)
• Product service (catalog, inventory)
• Order service (orders, payments)
• Notification service (emails, push notifications)
• API Gateway with rate limiting and routing
• Service discovery and health checks

Requirements:

• Use Docker for containerization
• Implement service-to-service communication
• Add circuit breaker pattern
• Create comprehensive monitoring
• Implement proper logging and tracing

🛠️ Setup Instructions

Prerequisites

• Node.js >= 16.0.0
• MongoDB >= 5.0
• Redis >= 6.0
• Git

Installation

1. Clone the repository

git clone <repository-url>
cd mern-interview-project

2. Install dependencies

npm run install-all

3. Environment Setup

cp .env.example .env
# Edit .env with your configuration

4. Database Setup

# Start MongoDB and Redis
# Update connection strings in .env

5. Run the application

# Development mode
npm run dev

# Production build
npm run build
npm start

🧪 Testing

# Run all tests
npm test

# Run tests with coverage
npm run test:coverage

# Run tests in watch mode
npm run test:watch

📊 Project Structure

├── server/                 # Backend API
│   ├── config/            # Configuration files
│   ├── controllers/       # Route controllers
│   ├── middleware/        # Custom middleware
│   ├── models/           # Mongoose models
│   ├── routes/           # API routes
│   ├── services/         # Business logic
│   ├── utils/            # Utility functions
│   └── tests/            # Backend tests
├── client/               # Frontend React app
│   ├── public/           # Static files
│   ├── src/              # Source code
│   │   ├── components/   # React components
│   │   ├── hooks/        # Custom hooks
│   │   ├── pages/        # Page components
│   │   ├── services/     # API services
│   │   ├── store/        # Redux store
│   │   └── utils/        # Utility functions
│   └── tests/            # Frontend tests
├── docs/                 # Documentation
├── docker/               # Docker configuration
└── scripts/              # Build and deployment scripts

🔧 Configuration

Environment Variables

Create a .env file in the root directory:

# Server Configuration
NODE_ENV=development
PORT=5000
MONGODB_URI=mongodb://localhost:27017/mern-interview
REDIS_URL=redis://localhost:6379

# JWT Configuration
JWT_SECRET=your-super-secret-jwt-key
JWT_EXPIRES_IN=7d

# Email Configuration
SMTP_HOST=smtp.gmail.com
SMTP_PORT=587
SMTP_USER=your-email@gmail.com
SMTP_PASS=your-app-password

# File Upload
MAX_FILE_SIZE=5242880
UPLOAD_PATH=uploads/

# External APIs
STRIPE_SECRET_KEY=sk_test_...
PAYPAL_CLIENT_ID=your-paypal-client-id
PAYPAL_CLIENT_SECRET=your-paypal-secret

🚀 Deployment

Docker Deployment

# Build and run with Docker
npm run docker:build
npm run docker:up

Manual Deployment

# Build for production
npm run build

# Start production server
npm start

📈 Performance Monitoring

The project includes:

• Winston logging with different levels
• Performance metrics collection
• Error tracking and monitoring
• Health check endpoints
• Load testing scenarios

🔒 Security Features

• JWT-based authentication
• Role-based access control
• Input validation and sanitization
• Rate limiting
• CORS configuration
• Helmet security headers
• SQL injection prevention
• XSS protection

📝 API Documentation

Access the API documentation at:

• Swagger UI: http://localhost:5000/api-docs
• API Endpoints: http://localhost:5000/api/v1

🤝 Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for new features
5. Submit a pull request

📄 License

This project is licensed under the MIT License.

🎯 Interview Tips

Before the Interview

• Review the project structure and understand the architecture
• Practice explaining your design decisions
• Be prepared to discuss trade-offs and alternatives
• Review common MERN stack interview questions

During the Interview

• Start with understanding the requirements clearly
• Ask clarifying questions about edge cases
• Explain your approach before coding
• Write clean, readable code with proper comments
• Consider performance and security implications
• Be ready to discuss scalability and optimization

After Completing Tasks

• Be prepared to explain your implementation
• Discuss potential improvements and optimizations
• Show understanding of best practices and patterns
• Demonstrate knowledge of testing and deployment strategies

Good luck with your interview! 🚀