Node.js Middleware Patterns

Middleware is central to Node.js web frameworks. Here's how to write effective middleware.

Best Practices#

Design:
✓ Single responsibility
✓ Configurable via options
✓ Return middleware function
✓ Handle errors properly

Order:
✓ Security first (helmet, cors)
✓ Parsing (json, urlencoded)
✓ Logging
✓ Authentication
✓ Routes
✓ 404 handler
✓ Error handler

Performance:
✓ Early returns when possible
✓ Avoid blocking operations
✓ Use async properly
✓ Cache when appropriate

Testing:
✓ Test in isolation
✓ Test error cases
✓ Test middleware order
✓ Mock dependencies

Middleware is the backbone of Node.js web applications. Write focused, composable middleware functions. Handle errors properly with dedicated error middleware. Use async handlers for Promise-based code. Test middleware in isolation and consider the order carefully.

Node.js Middleware Patterns

Express Middleware Basics#

Common Middleware Types#

Async Middleware#

Error Handling Middleware#

Rate Limiting#

Caching Middleware#

Request Context#

Middleware Composition#

Koa-style Middleware#

Testing Middleware#

Best Practices#

Conclusion#

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