Maybe Monad

maybeMonad.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))
  }
  private flat() {
    return this.value
  }
  flatMap<NextData>(f: (x: Data) => Maybe<NextData>): Maybe<NextData> {
    return this.fmap(f).flat()
  }
}
class Nothing {
  fmap(f: (x: any) => any) {
    return new Nothing()
  }
  flatMap(f: (x: any) => Maybe<any>): Maybe<any> {
    return new Nothing()
  }
}

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

const something = new Just(1); 
const val = something
  .fmap(x => x + 1)
  .fmap(x => x + 2)
  .flatMap(x => new Nothing())
  .flatMap((x:number) => new Just(x + 2))