TypeScript Development
Project Setup
# Initialize with pnpm
pnpm init
pnpm add -D typescript @types/node
# TypeScript config
npx tsc --init
tsconfig.json
{
"compilerOptions": {
"target": "ES2022",
"module": "NodeNext",
"moduleResolution": "NodeNext",
"strict": true,
"noUncheckedIndexedAccess": true,
"noImplicitReturns": true,
"esModuleInterop": true,
"skipLibCheck": true,
"outDir": "./dist"
},
"include": ["src/**/*"]
}
Type Patterns
Discriminated Unions
type Result<T> =
| { success: true; data: T }
| { success: false; error: Error };
function handleResult(result: Result<User>) {
if (result.success) {
console.log(result.data); // User
} else {
console.error(result.error); // Error
}
}
Branded Types
type UserId = string & { readonly brand: unique symbol };
type OrderId = string & { readonly brand: unique symbol };
function createUserId(id: string): UserId {
return id as UserId;
}
Utility Types
// Make all properties optional
Partial<User>
// Make all properties required
Required<User>
// Pick specific properties
Pick<User, 'id' | 'email'>
// Omit specific properties
Omit<User, 'password'>
// Make properties readonly
Readonly<User>
Error Handling
// Result type pattern
type Result<T, E = Error> =
| { ok: true; value: T }
| { ok: false; error: E };
async function fetchUser(id: string): Promise<Result<User>> {
try {
const user = await db.users.findById(id);
if (!user) {
return { ok: false, error: new Error('User not found') };
}
return { ok: true, value: user };
} catch (error) {
return { ok: false, error: error as Error };
}
}
Testing with Vitest
import { describe, test, expect, vi } from 'vitest';
describe('UserService', () => {
test('creates user with valid email', async () => {
const service = new UserService(mockRepo);
const user = await service.create('test@example.com');
expect(user.email).toBe('test@example.com');
});
test('throws on invalid email', async () => {
const service = new UserService(mockRepo);
await expect(service.create('invalid')).rejects.toThrow();
});
});
Tooling
# Biome (linting + formatting)
pnpm add -D @biomejs/biome
pnpm biome check --apply .
# Vitest (testing)
pnpm add -D vitest
pnpm vitest
