TypeScript Record and Mapped Type patterns

Need to create type-safe dictionaries, transform object types, or derive types from existing ones.

Common mapped type patterns:

// Type-safe config from union
type LogLevel = 'debug' | 'info' | 'warn' | 'error';
type LogConfig = Record<LogLevel, boolean>;

// Make all properties optional
type PartialUser = Partial<User>;

// Make all properties required
type RequiredConfig = Required<Config>;

// Pick specific properties
type UserPreview = Pick<User, 'id' | 'name'>;

// Omit specific properties
type CreateUser = Omit<User, 'id' | 'createdAt'>;

// Custom mapped type: make specific keys required
type RequireKeys<T, K extends keyof T> = T & Required<Pick<T, K>>;
type UserWithEmail = RequireKeys<Partial<User>, 'email'>;

// Readonly deep
type DeepReadonly<T> = {
  readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K];
};

Mapped types let you derive types from existing ones, reducing duplication and keeping types in sync.

TypeScript projects needing type transformations