What do keyof and typeof do in TypeScript?

Question presented to candidate: "What do keyof and typeof do in TypeScript? How is TypeScript's typeof different from JavaScript's, and how would you combine them with generics?"

What a strong answer should cover:

• keyof T is a type operator: the union of T's property names (keyof User is "id" | "name" | "admin"); it arrived in TypeScript 2.1 with indexed access types
• typeof x in a type position captures the static type of an existing value; in a value position it is JavaScript's run-time operator returning a string like "object"
• keyof typeof obj gives the keys of a value without writing a separate type; ReturnType<typeof fn> reuses a function's result type
• The generic pattern <T, K extends keyof T>(obj: T, key: K): T[K] for type-safe property access
• Edge cases: index signatures (keyof { [k: string]: X } is string | number), keyof (A | B) is only the shared keys, keyof of a class omits private members, and Object.keys returns string[] on purpose
• A type name cannot be used with value typeof (TS2693): types and values live in separate namespaces

Code / implementation expected: Yes — keyof typeof on a config object and a getProperty or pluck helper.