Mapped Types

Make optional: [K in keyof T]?: T[K]
Make readonly: readonly [K in keyof T]: T[K]
Transform types: Change property types

Advanced~20 min

Mapped types transform each property in an object type, creating new types based on existing ones.

Output

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Syntax: [K in keyof T]: NewType maps over all keys

Common Patterns

Best Practice: Mapped types power utility types like Partial, Readonly, Pick, and Omit.