const Maybe = {
  of: (value) => ({ value, map: f => value == null ? Maybe.nothing() : Maybe.of(f(value)) }),
  nothing: () => ({ value: null, map: () => Maybe.nothing() })
};

const result = Maybe.of(5)
  .map(x => x * 2)
  .map(x => x > 15 ? null : x)
  .map(x => x + 1)
  .map(x => x.toString());

console.log(result.value);