keyof, typeof, Indexed & Mapped Types

keyof produces a union of an object type's keys: interface Car { make: string; year: number } type CarKey = keyof Car; // "make" | "year"

typeof (in a type position) gets the type of a value: const defaults = { theme: "light", pageSize: 20 }; type Defaults = typeof defaults; // { theme: string; pageSize: number }

Combined: keyof typeof defaults is "theme" | "pageSize".