Utility and mapped types

Utility types transform existing types so you do not duplicate object shapes. `Pick` and `Omit` select fields, `Partial` and `Required` adjust optionality, `Readonly` changes assignment rules, `Record` creates keyed maps, and mapped types generalize these transformations with `keyof` and indexed access.

					type UserPatch = Partial<Pick<User, 'name' | 'email'>>;
type UserKeys = keyof User;
				

Derive when contracts are truly linked. Over-derived types can hide intent if the public API should evolve independently.

On interviews: explain with a concrete example and name what interviewers probe in production code.

Common pitfalls: mixing similar APIs and forgetting edge cases during live coding.

The trade-off is often clarity versus safety or expressiveness versus maintainability. Checklist:

• Derive linked contracts.
• Use keyof deliberately.
• Name important transformed shapes.