Partial, Required, Pick, and Omit

Built-in utility types transform existing types. Partial<T> makes properties optional; Required<T> makes them required; Pick<T, K> selects a subset of keys; Omit<T, K> removes selected keys. These are especially useful for create/update DTOs and separating public data from internal fields.

Utility types do not alter runtime objects. A Partial<User> is a compile-time description, not a function that removes or changes properties. Validate business rules separately: a type may permit an optional field while the domain still requires at least one field in a particular operation.

Create and update DTOs

type User = {
  id: string;
  name: string;
  email: string;
  createdAt: Date;
};

type CreateUserInput = Pick<User, "name" | "email">;
type UpdateUserInput = Partial<CreateUserInput>;
type PublicUser = Omit<User, "createdAt">;

💡 Pick selects fields for creation, Partial allows updates to include only changed fields, and Omit removes createdAt from the public type.

Key Takeaways

Utility types transform types, not runtime data.
Use Pick/Omit to define intentional API shapes.
Partial is useful for patches but may need extra business validation.

Knowledge Check

What does `Partial<T>` do?

Partial, Required, Pick, and Omit

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