TypeScript Utility Types

TypeScript ships with utility types that transform existing types into new ones. Instead of writing the same type transformations over and over, you can use these five built-ins that handle the common cases.

1. Partial

Makes all properties optional. Perfect for update functions where you only want to change some fields.

interface User {
  id: number;
  name: string;
  email: string;
}

function updateUser(id: number, updates: Partial<User>) {
  // Can update any combination of fields
}

updateUser(1, { name: "John" });
updateUser(2, { email: "john@example.com", name: "Jane" });

2. Pick<T, K>

Selects specific properties from a type.

interface Product {
  id: number;
  name: string;
  price: number;
  description: string;
  category: string;
}

type ProductCard = Pick<Product, 'id' | 'name' | 'price'>;

3. Omit<T, K>

Excludes specific properties from a type.

type CreateProduct = Omit<Product, 'id'>;

function createProduct(product: CreateProduct) {
  // id gets generated server-side
  return { id: Math.random(), ...product };
}

4. Record<K, T>

Creates an object type with specific keys and consistent value types.

type HttpMethod = 'GET' | 'POST' | 'PUT' | 'DELETE';
type RouteHandler = Record<HttpMethod, (req: Request) => Response>;

const userRoutes: RouteHandler = {
  GET: (req) => getUserById(req.params.id),
  POST: (req) => createUser(req.body),
  PUT: (req) => updateUser(req.params.id, req.body),
  DELETE: (req) => deleteUser(req.params.id)
};

5. ReturnType

Extracts the return type from a function. Keeps types in sync without duplication.

function fetchUserProfile() {
  return {
    id: 1,
    name: "John",
    email: "john@example.com",
    preferences: { theme: 'dark', notifications: true }
  };
}

type UserProfile = ReturnType<typeof fetchUserProfile>;

function cacheProfile(profile: UserProfile) {
  localStorage.setItem('profile', JSON.stringify(profile));
}

These five utility types handle most type transformation needs. They're built into TypeScript, so you can start using them right away without any setup.