Node.js Best Practices

Principles and decision-making for Node.js development in 2025. Learn to THINK, not memorize code patterns.

⚠️ How to Use This Skill

This skill teaches decision-making principles, not fixed code to copy.

ASK user for preferences when unclear
Choose framework/pattern based on CONTEXT
Don't default to same solution every time

1. Framework Selection (2025)

Decision Tree

What are you building?
│
├── Edge/Serverless (Cloudflare, Vercel)
│   └── Hono (zero-dependency, ultra-fast cold starts)
│
├── High Performance API
│   └── Fastify (2-3x faster than Express)
│
├── Enterprise/Team familiarity
│   └── NestJS (structured, DI, decorators)
│
├── Legacy/Stable/Maximum ecosystem
│   └── Express (mature, most middleware)
│
└── Full-stack with frontend
    └── Next.js API Routes or tRPC

Comparison Principles

Factor	Hono	Fastify	Express
Best for	Edge, serverless	Performance	Legacy, learning
Cold start	Fastest	Fast	Moderate
Ecosystem	Growing	Good	Largest
TypeScript	Native	Excellent	Good
Learning curve	Low	Medium	Low

Selection Questions to Ask:

What's the deployment target?
Is cold start time critical?
Does team have existing experience?
Is there legacy code to maintain?

2. Runtime Considerations (2025)

Native TypeScript

Node.js 22+: --experimental-strip-types
├── Run .ts files directly
├── No build step needed for simple projects
└── Consider for: scripts, simple APIs

Module System Decision

ESM (import/export)
├── Modern standard
├── Better tree-shaking
├── Async module loading
└── Use for: new projects

CommonJS (require)
├── Legacy compatibility
├── More npm packages support
└── Use for: existing codebases, some edge cases

Runtime Selection

Runtime	Best For
Node.js	General purpose, largest ecosystem
Bun	Performance, built-in bundler
Deno	Security-first, built-in TypeScript

3. Architecture Principles

Layered Structure Concept

Request Flow:
│
├── Controller/Route Layer
│   ├── Handles HTTP specifics
│   ├── Input validation at boundary
│   └── Calls service layer
│
├── Service Layer
│   ├── Business logic
│   ├── Framework-agnostic
│   └── Calls repository layer
│
└── Repository Layer
    ├── Data access only
    ├── Database queries
    └── ORM interactions

Why This Matters:

Testability: Mock layers independently
Flexibility: Swap database without touching business logic
Clarity: Each layer has single responsibility

When to Simplify:

Small scripts → Single file OK
Prototypes → Less structure acceptable
Always ask: "Will this grow?"

4. Error Handling Principles

Centralized Error Handling

Pattern:
├── Create custom error classes
├── Throw from any layer
├── Catch at top level (middleware)
└── Format consistent response

Error Response Philosophy

Client gets:
├── Appropriate HTTP status
├── Error code for programmatic handling
├── User-friendly message
└── NO internal details (security!)

Logs get:
├── Full stack trace
├── Request context
├── User ID (if applicable)
└── Timestamp

Status Code Selection

Situation	Status	When
Bad input	400	Client sent invalid data
No auth	401	Missing or invalid credentials
No permission	403	Valid auth, but not allowed
Not found	404	Resource doesn't exist
Conflict	409	Duplicate or state conflict
Validation	422	Schema valid but business rules fail
Server error	500	Our fault, log everything

5. Async Patterns Principles

When to Use Each

Pattern	Use When
`async/await`	Sequential async operations
`Promise.all`	Parallel independent operations
`Promise.allSettled`	Parallel where some can fail
`Promise.race`	Timeout or first response wins

Event Loop Awareness

I/O-bound (async helps):
├── Database queries
├── HTTP requests
├── File system
└── Network operations

CPU-bound (async doesn't help):
├── Crypto operations
├── Image processing
├── Complex calculations
└── → Use worker threads or offload

Avoiding Event Loop Blocking

Never use sync methods in production (fs.readFileSync, etc.)
Offload CPU-intensive work
Use streaming for large data

6. Validation Principles

Validate at Boundaries

Where to validate:
├── API entry point (request body/params)
├── Before database operations
├── External data (API responses, file uploads)
└── Environment variables (startup)

Validation Library Selection

Library	Best For
Zod	TypeScript first, inference
Valibot	Smaller bundle (tree-shakeable)
ArkType	Performance critical
Yup	Existing React Form usage

Validation Philosophy

Fail fast: Validate early
Be specific: Clear error messages
Don't trust: Even "internal" data

7. Security Principles

Security Checklist (Not Code)

Input validation: All inputs validated
Parameterized queries: No string concatenation for SQL
Password hashing: bcrypt or argon2
JWT verification: Always verify signature and expiry
Rate limiting: Protect from abuse
Security headers: Helmet.js or equivalent
HTTPS: Everywhere in production
CORS: Properly configured
Secrets: Environment variables only
Dependencies: Regularly audited

Security Mindset

Trust nothing:
├── Query params → validate
├── Request body → validate
├── Headers → verify
├── Cookies → validate
├── File uploads → scan
└── External APIs → validate response

8. Testing Principles

Test Strategy Selection

Type	Purpose	Tools
Unit	Business logic	node:test, Vitest
Integration	API endpoints	Supertest
E2E	Full flows	Playwright

What to Test (Priorities)

Critical paths: Auth, payments, core business
Edge cases: Empty inputs, boundaries
Error handling: What happens when things fail?
Not worth testing: Framework code, trivial getters

Built-in Test Runner (Node.js 22+)

node --test src/**/*.test.ts
├── No external dependency
├── Good coverage reporting
└── Watch mode available

10. Anti-Patterns to Avoid

❌ DON'T:

Use Express for new edge projects (use Hono)
Use sync methods in production code
Put business logic in controllers
Skip input validation
Hardcode secrets
Trust external data without validation
Block event loop with CPU work

✅ DO:

Choose framework based on context
Ask user for preferences when unclear
Use layered architecture for growing projects
Validate all inputs
Use environment variables for secrets
Profile before optimizing

11. Decision Checklist

Before implementing:

Asked user about stack preference?
Chosen framework for THIS context? (not just default)
Considered deployment target?
Planned error handling strategy?
Identified validation points?
Considered security requirements?

Remember: Node.js best practices are about decision-making, not memorizing patterns. Every project deserves fresh consideration based on its requirements.

name	nodejs-best-practices
description	Node.js development principles and decision-making. Framework selection, async patterns, security, and architecture. Teaches thinking, not copying.
allowed-tools	Read, Write, Edit, Glob, Grep