const bSubject = new Rx.BehaviorSubject<number[]>([]);

let numberList: Observable<number[]>;

​

numberList = bSubject.asObservable()

.scan((acc, val) => {

  return acc.concat(val);

});

​

numberList.subscribe((val) => {

  console.log(val);

});

​

let i = 0;

​

setInterval(() => { 

  console.log('Fetching data... Numberlist is now: ');

  bSubject.next(i);

  i++;

}, 3000);

​

setTimeout(() => { 

  console.log('Realtime push event occurred!');

  console.log('Adding number to array!');

  // This should be prepended to the beginning of the array

  // and produce the desired result [1337, 0, 1]

  const pushNumber = 1337;

  bSubject.next(pushNumber);

},6000);

​

​