Mapped Types

Summary

Types that programmatically transform every property of an existing type (e.g. making them all optional or readonly) using a `[K in keyof T]` syntax.

• 1Write a simple mapped type that makes every property of an interface optional.
• 2Compare your hand-written version to the built-in `Partial<T>` utility.
• 3Learn key remapping (`as`) for renaming properties in a mapped type.