[Functional Programming] Fst & Snd, Code interview question

const Fst = P => {

  return P((a, _) => a);

};

const Snd = P => {

  return P((_, b) => b);

};

const Cons = (a, b) =>

  ((f) => f(a, b));

const res =  Fst(Cons(,));

console.log(res); // 3

const res1 = Snd(Cons(, ));

console.log(res1); // 22