fastify-typescript

•

6155 months ago

Guidelines for building high-performance APIs with Fastify and TypeScript, covering validation, Prisma integration, and testing best practices

Quick Install

npxskills add mindrally/skills--skill fastify-typescript

Instructions

Fastify TypeScript Development

You are an expert in Fastify and TypeScript development with deep knowledge of building high-performance, type-safe APIs.

TypeScript General Guidelines

Basic Principles

Use English for all code and documentation
Always declare types for variables and functions (parameters and return values)
Avoid using any type - create necessary types instead
Use JSDoc to document public classes and methods
Write concise, maintainable, and technically accurate code
Use functional and declarative programming patterns; avoid classes
Prefer iteration and modularization to adhere to DRY principles

Nomenclature

Use PascalCase for types and interfaces
Use camelCase for variables, functions, and methods
Use kebab-case for file and directory names
Use UPPERCASE for environment variables
Use descriptive variable names with auxiliary verbs: isLoading, hasError, canDelete
Start each function with a verb

Functions

Write short functions with a single purpose
Use arrow functions for simple operations
Use async/await consistently throughout the codebase
Use the RO-RO pattern (Receive an Object, Return an Object) for multiple parameters

Types and Interfaces

Prefer interfaces over types for object shapes
Avoid enums; use maps or const objects instead
Use Zod for runtime validation with inferred types
Use readonly for immutable properties
Use import type for type-only imports

Fastify-Specific Guidelines

Project Structure

src/
  routes/
    {resource}/
      index.ts
      handlers.ts
      schemas.ts
  plugins/
    auth.ts
    database.ts
    cors.ts
  services/
    {domain}Service.ts
  repositories/
    {entity}Repository.ts
  types/
    index.ts
  utils/
  config/
  app.ts
  server.ts

Route Organization

Organize routes by resource/domain
Use route plugins for modular registration
Define schemas alongside route handlers
Use route prefixes for API versioning

import { FastifyPluginAsync } from 'fastify';

const usersRoutes: FastifyPluginAsync = async (fastify) => {
  fastify.get('/', { schema: listUsersSchema }, listUsersHandler);
  fastify.get('/:id', { schema: getUserSchema }, getUserHandler);
  fastify.post('/', { schema: createUserSchema }, createUserHandler);
  fastify.put('/:id', { schema: updateUserSchema }, updateUserHandler);
  fastify.delete('/:id', { schema: deleteUserSchema }, deleteUserHandler);
};

export default usersRoutes;

Schema Validation with JSON Schema / Ajv

Define JSON schemas for all request/response validation
Use @sinclair/typebox for type-safe schema definitions
Leverage Fastify's built-in Ajv integration

import { Type, Static } from '@sinclair/typebox';

const UserSchema = Type.Object({
  id: Type.String({ format: 'uuid' }),
  name: Type.String({ minLength: 1 }),
  email: Type.String({ format: 'email' }),
  createdAt: Type.String({ format: 'date-time' }),
});

type User = Static<typeof UserSchema>;

const createUserSchema = {
  body: Type.Object({
    name: Type.String({ minLength: 1 }),
    email: Type.String({ format: 'email' }),
  }),
  response: {
    201: UserSchema,
    400: ErrorSchema,
  },
};

Plugins and Decorators

Use plugins for shared functionality
Decorate Fastify instance with services and utilities
Register plugins with proper encapsulation

import fp from 'fastify-plugin';

const databasePlugin = fp(async (fastify) => {
  const prisma = new PrismaClient();

  await prisma.$connect();

  fastify.decorate('prisma', prisma);

  fastify.addHook('onClose', async () => {
    await prisma.$disconnect();
  });
});

export default databasePlugin;

Prisma Integration

Use Prisma as the ORM for database operations
Create repository classes for data access
Use transactions for complex operations

class UserRepository {
  constructor(private prisma: PrismaClient) {}

  async findById(id: string): Promise<User | null> {
    return this.prisma.user.findUnique({ where: { id } });
  }

  async create(data: CreateUserInput): Promise<User> {
    return this.prisma.user.create({ data });
  }
}

Error Handling

Use Fastify's built-in error handling
Create custom error classes for domain errors
Return consistent error responses

import { FastifyError } from 'fastify';

class NotFoundError extends Error implements FastifyError {
  code = 'NOT_FOUND';
  statusCode = 404;

  constructor(resource: string, id: string) {
    super(`${resource} with id ${id} not found`);
    this.name = 'NotFoundError';
  }
}

// Global error handler
fastify.setErrorHandler((error, request, reply) => {
  const statusCode = error.statusCode || 500;

  reply.status(statusCode).send({
    error: error.name,
    message: error.message,
    statusCode,
  });
});

Testing with Jest

Write unit tests for services and handlers
Use integration tests for routes
Mock external dependencies

import { build } from '../app';

describe('Users API', () => {
  let app: FastifyInstance;

  beforeAll(async () => {
    app = await build();
  });

  afterAll(async () => {
    await app.close();
  });

  it('should list users', async () => {
    const response = await app.inject({
      method: 'GET',
      url: '/api/users',
    });

    expect(response.statusCode).toBe(200);
    expect(JSON.parse(response.payload)).toBeInstanceOf(Array);
  });
});

Performance

Fastify is one of the fastest Node.js frameworks
Use schema validation for automatic serialization optimization
Enable logging only when needed in production
Use connection pooling for database connections

Security

Use @fastify/helmet for security headers
Implement rate limiting with @fastify/rate-limit
Use @fastify/cors for CORS configuration
Validate all inputs with JSON Schema
Use JWT for authentication with @fastify/jwt

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