Throttling notifications from multiple users with RxJS - with throttling by custom throttleSelectiveFilter operator

throttleSelectiveFilter.js

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


let throttleSelectiveFilter = (throttleTime = 0, selector = (x) => x) => {
 let setOfEntities =  new Set();
  return (source) => {
      return source.pipe(
          filter((notif) => {
            if (throttleTime === 0) return true;
            const id = selector(notif);
            console.log('Checking id ', id, new Set(setOfEntities))
            if (setOfEntities.has(id)) return false;

            const clearId = setTimeout(() => {
              clearTimeout(clearId);
              setOfEntities.delete(id);
            }, throttleTime);
            setOfEntities.add(id);
            return true;
          })
       )
     }  
}

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
]
let source$ = from(notifications).pipe(
  mergeMap((notif) => {
    return of(notif).pipe(delay(notif.delay));
  }),
)

source$
  .pipe(throttleSelectiveFilter(3000, (x) => x.userId))
  .subscribe(showNotification);


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);
 
}