Built-in Utility Types

TypeScript includes standard global utility types that transform existing types without manual duplication. Partial<T> turns all properties optional; Required<T> makes all optional properties mandatory; Readonly<T> prevents property mutation; Pick<T, K> creates a type containing only specified keys K; Omit<T, K> strips specified keys K; and Record<K, T> creates a dictionary mapping keys K to values T.

Combining utility types streamlines payload validation and state updates. For example, database insert functions might use Omit<User, 'id' | 'createdAt'>, while update API routes accept Partial<Omit<User, 'id'>>.

Before

Manual Duplicate Type Definition

1interface User {2  id: string;3  name: string;4  email: string;5}6 7// ❌ Duplicated fields for patch payload8interface UpdateUserInput {9  name?: string;10  email?: string;11}

After

Utility Type Transformation

1interface User {2  id: string;3  name: string;4  email: string;5}6 7// ✅ Derive update shape cleanly8type UpdateUserInput = Partial<Omit<User, 'id'>>;

Exercise

Define a Product interface, then create an InsertProductPayload type using Omit and a ProductMap using Record<string, Product>.

Check your understanding

What is the difference between Pick<T, K> and Omit<T, K>?Show answerHide answer
Answer
Pick constructs a type with only the specified keys K from T; Omit constructs a type with all keys from T except K.
What does ReturnType<typeof functionName> return?Show answerHide answer
Answer
It extracts the return type of a given function signature.