Nodejs Best Practices

> Principles and decision-making for Node.js development in 2025.

> Learn to THINK, not memorize code patterns.

When to Use

Use this skill when making Node.js architecture decisions, choosing frameworks, designing async patterns, or applying security and deployment best practices.

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⚠️ 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

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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

Selection Questions to Ask:

1. What's the deployment target?

2. Is cold start time critical?

3. Does team have existing experience?

4. Is there legacy code to maintain?

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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

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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?"

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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

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5. Async Patterns Principles

When to Use Each

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

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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

Validation Philosophy

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

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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

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8. Testing Principles

Test Strategy Selection

What to Test (Priorities)

1. Critical paths: Auth, payments, core business

2. Edge cases: Empty inputs, boundaries

3. Error handling: What happens when things fail?

4. 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

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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

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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?

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