Express WebSocket Backend Skill

Build production-ready Express.js backends with WebSocket real-time features.

What This Skill Provides

Core Tools

• scaffold_express_api.py - Generate Express.js API structure
• setup_websocket.py - Configure WebSocket with Socket.io
• middleware_generator.py - Create auth, logging, error handling middleware

References

• express_patterns.md - Modern Express.js patterns
• websocket_realtime.md - WebSocket connection management
• best_practices.md - Production Express.js best practices
• advanced_topics.md - Scaling, clustering, monitoring
• troubleshooting.md - Common Express/WebSocket issues

Templates

• Express.js API boilerplate
• WebSocket connection manager
• Authentication middleware
• Error handling middleware

When to Use

Perfect For

• Real-time applications (chat, live updates)
• WebSocket-based features
• Express.js v4.x backends
• Middleware-heavy applications
• API versioning
• Production Express deployments

Not For

• Full-stack apps with frontend (use nodejs-fullstack-setup)
• GraphQL APIs (different patterns)
• Serverless functions (different architecture)

Quick Start

# Scaffold Express API
python scripts/scaffold_express_api.py \
  --project-name my-api \
  --output-dir ./api

# Setup WebSocket
python scripts/setup_websocket.py \
  --project-dir ./api

# Generate middleware
python scripts/middleware_generator.py \
  --type auth \
  --output ./api/middleware/auth.js

Decision Trees

Which middleware pattern?

• Authentication: JWT tokens, session-based
• Logging: Morgan, Winston
• Error handling: Centralized error middleware
• Rate limiting: Express-rate-limit

Quality Checklist

• Error handling middleware
• Request logging
• Authentication/authorization
• Rate limiting
• CORS configuration
• WebSocket connection management
• Production-ready config

Common Pitfalls

Pitfall: Memory Leaks in WebSocket Connections

Solution: Implement connection cleanup, limit concurrent connections, use heartbeat monitoring.

Pitfall: Blocking Event Loop

Solution: Use async/await, worker threads for CPU-intensive tasks, profiling.

Pro Tips

Tip 1: WebSocket Room Management

io.on('connection', (socket) => {
  socket.join(`user_${socket.userId}`);
  socket.on('disconnect', () => {
    socket.leave(`user_${socket.userId}`);
  });
});

Tip 2: Error Handling

app.use((err, req, res, next) => {
  logger.error(err.stack);
  res.status(err.status || 500).json({
    error: err.message
  });
});

Related Skills

• nodejs-fullstack-setup - Full-stack with frontend
• fastapi-backend-builder - Python alternative
• testing-infrastructure - Jest/Mocha testing