Solving fibonacci in reactive streams. Why? Because it's possible :)

fibonacci.ts

import {Observable} from "rxjs/Observable";
import {Subject} from "rxjs/Subject";

export function fibonacciStream() {

  let fibN2: Subject<number> = new Subject();
  // initiate the series, so that both this and fibN1 has atleast one
  setImmediate(() => { 
    fibN2.next(0);
    fibN2.next(1);
  });

  let sumOfPreviousTwo = Observable.zip(fibN2, fibN2.skip(1)) // common pattern to get successive values
    .delay(0) // avoid infinite loop, by giving the event loop a chance
    .map(([n2, n1]) => n2 + n1);

  // this is the generating part
  let initialTwoFibNumbers = Observable.from([0, 1]);
  let fibN = initialTwoFibNumbers.concat(sumOfPreviousTwo);

  return fibN.do(n => fibN2.next(n)); // feed fibN2 with fibN
}