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
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
async create(data: CreateUserInput): Promise
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