How to create a recursive observable pipe. Source: http://jsbin.com/finisab/edit?js,console

recursive-observable.ts

// A recursive function returning Observable<number>
function recurseToZero(n) {
  console.log('B. Entering recursive function for [' + n + '].');
  // Once we hit zero, bail out of the recursion. The key to recursion is that
  // it stops at some point, and the callstack can be "rolled" back up.
  if (n === 0) {
    return Rx.Observable.of(0);
  }
  // Start a NEW PROMISE CHAIN that will become the continuation of the parent
  // promise chain. This new promise chain now becomes a completely tangential
  // branch to the parent promise chain.
  return new Rx.Observable((subscriber) => {
    setTimeout(() => {
      subscriber.next(n-1);
      subscriber.complete();
    }, 500);
  })
  .flatMap(n => {
    return recurseToZero(n);
  });
}

Rx.Observable.of(null)
  .map(() => {
    console.group("A. Recursion starts.");
    return(3);
  })
  .flatMap(n => {
    // With the recursive function we are creating a totally
    // TANGENTIAL BRANCH of the Observable chain.
    // --
    // A
    // |
    // B --> B'3 --> B'2 --> B'1 --> B'0
    // |
    // C
    return recurseToZero(n);
  })
  .subscribe(() => {
    console.groupEnd("C. Recursion ended.");
  });