SOURCE

const source$ = Rx.Observable.interval(1000).take(3);

const observerA = {
    next: value => console.log('A next: ' + value),
    error: error => console.log('A error: ' + error),
    complete: () => console.log('A complete!')
}

const observerB = {
    next: value => console.log('B next: ' + value),
    error: error => console.log('B error: ' + error),
    complete: () => console.log('B complete!')
}

source$.subscribe(observerA);
setTimeout(() => {
  source$.subscribe(observerB);
}, 2000)
// source$.subscribe(observerB);