TypeScript utility types cheat sheet

Need a quick reference for TypeScript's built-in utility types and when to use each.

Complete utility types reference:

interface User {
  id: number;
  name: string;
  email: string;
  role: 'admin' | 'user';
}

// Partial<T> - All properties optional
type UpdateUser = Partial<User>;
// { id?: number; name?: string; ... }

// Required<T> - All properties required
type CompleteUser = Required<Partial<User>>;

// Readonly<T> - All properties readonly
type FrozenUser = Readonly<User>;

// Pick<T, K> - Select specific properties
type UserPreview = Pick<User, 'id' | 'name'>;
// { id: number; name: string }

// Omit<T, K> - Remove specific properties
type CreateUser = Omit<User, 'id'>;
// { name: string; email: string; role: ... }

// Record<K, V> - Object type with key type K and value type V
type RolePermissions = Record<User['role'], string[]>;
// { admin: string[]; user: string[] }

// Extract<T, U> - Extract types assignable to U
type AdminRole = Extract<User['role'], 'admin'>;
// 'admin'

// Exclude<T, U> - Remove types assignable to U
type NonAdminRole = Exclude<User['role'], 'admin'>;
// 'user'

// NonNullable<T> - Remove null and undefined
type SafeString = NonNullable<string | null | undefined>;
// string

// ReturnType<T> - Get function return type
type FetchResult = ReturnType<typeof fetchUser>;

// Parameters<T> - Get function parameter types
type FetchParams = Parameters<typeof fetchUser>;

// Awaited<T> - Unwrap Promise type
type UserData = Awaited<ReturnType<typeof fetchUser>>;

Built-in utility types eliminate the need for custom type manipulations in most cases. Knowing them prevents reinventing the wheel.

TypeScript development - quick reference