Maybe Functor

maybeFunctor.ts

class Just<Data> {
  value: Data;
  constructor(value: Data) {
    this.value = value;
  }
  fmap<NextData>(f: (x: Data) => NextData) {
    return new Just<NextData>(f(this.value))
  }
}
class Nothing {
  fmap(f: (x: any) => any) {
    return new Nothing();
  }
}

type Maybe<Data> = Just<Data> | Nothing;

const something = new Just(1); something.fmap(x => x + 1).fmap(x => x + 2); // is doing comutation
const nothing = new Nothing(); nothing.fmap(x => x + 1).fmap(x => x + 2); // id doing nothing