nodejs-best-practices

Node.js Best Practices

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

> Learn to THINK, not memorize code patterns.

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⚠️ How to Use This Skill

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

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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

| 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:

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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

| Runtime | Best For |

|---------|----------|

| Node.js | General purpose, largest ecosystem |

| Bun | Performance, built-in bundler |

| Deno | Security-first, built-in TypeScript |

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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:

When to Simplify:

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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

| 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 |

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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

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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

| Library | Best For |

|---------|----------|

| Zod | TypeScript first, inference |

| Valibot | Smaller bundle (tree-shakeable) |

| ArkType | Performance critical |

| Yup | Existing React Form usage |

Validation Philosophy

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7. Security Principles

Security Checklist (Not Code)

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

| Type | Purpose | Tools |

|------|---------|-------|

| Unit | Business logic | node:test, Vitest |

| Integration | API endpoints | Supertest |

| E2E | Full flows | Playwright |

What to Test (Priorities)

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:

✅ DO:

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11. Decision Checklist

Before implementing:

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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.