Typescript keyof and "valueof"

keyof-trick.ts

type Employee = {
  canWalkVeryFast: boolean;
  numberOfKeystrokes: number;
  isNiceToTheBoss: "yes" | "no" | "sometimes";
};

function foobar<T extends keyof Employee>(key: T, value: Employee[T]) {
  console.log(key, value);
}

// compiles
foobar("canWalkVeryFast", true);
foobar("numberOfKeystrokes", 100);
foobar("isNiceToTheBoss", "no");

// does not compile
foobar("catsCuddled", 7);
foobar("isNiceToTheBoss", true);
foobar("isNiceToTheBoss", "often");