Throttling notifications from multiple users with RxJS - no throttling

Notifications with noThrottling.js

let Rx = window['rxjs'];
let {from, of, asyncScheduler} = Rx;
let {mergeMap, filter, delay} = Rx.operators;
console.clear();

let notifications = [
  { userId: 1, name: 'A1', delay: 100 }, // should be shown
  { userId: 1, name: 'A2', delay: 1500 }, // shouldn't be shown
  { userId: 1, name: 'A3', delay: 2500 }, // shouldn't be shown
  { userId: 1, name: 'A4', delay: 3500 }, // should be shown
  { userId: 2, name: 'B1', delay: 200 }, // should be shown
  { userId: 2, name: 'B2', delay: 300 }, // shouldn't be shown
  { userId: 2, name: 'B3', delay: 3500 }, // should be shown
]
//mock source that emits notifications
let mockSource$ = from(notifications).pipe(
  mergeMap((notif) => {
    return of(notif).pipe(delay(notif.delay));
  }),
)

mockSource$.subscribe(showNotification);

//display notifications widget
let container =  document.querySelector('.container');
function showNotification(notif) {
 const newElem = document.createElement('div');
  newElem.classList.add('item');
  newElem.innerHTML = notif.name;
  container.appendChild(newElem);
  setTimeout(() => {newElem.remove()}, 800); // remove notification element
}