express

name	express
description	Express.js middleware, routing, REST API, error handling. Use when building Express apps or APIs.

express

Build Express.js web servers and REST APIs.

Middleware System

• Chain request handlers via app.use() and app.VERB()
• Order matters: middleware runs top-down
• Error middleware has 4 params: (err, req, res, next)

Routing

• Express Router for modular route groups
• Route params :id with req.params
• Query strings with req.query
• Body parsing via express.json() and express.urlencoded()

Security

• helmet for HTTP headers
• cors for cross-origin requests
• Rate limiting with express-rate-limit
• Input validation with express-validator or Joi

Best Practices

• Separate routes, controllers, services layers
• Centralized error handler middleware
• Async error wrapper to catch rejected promises
• Test with supertest + jest or vitest
• Static files via express.static for assets