Branch out the source Observable values as a nested Observable using a factory function of closing Observables to determine when to start a new window.

It's like bufferWhen, but emits a nested Observable instead of an array.

Returns an Observable that emits windows of items it collects from the source Observable. The output Observable emits connected, non-overlapping windows. It emits the current window and opens a new one whenever the Observable produced by the specified closingSelector function emits an item. The first window is opened immediately when subscribing to the output Observable.

Example

Emit only the first two clicks events in every window of [1-5] random seconds

import { fromEvent, windowWhen, interval, map, take, mergeAll } from 'rxjs';

const clicks = fromEvent(document, 'click');
const result = clicks.pipe(
  windowWhen(() => interval(1000 + Math.random() * 4000)),
  map(win => win.pipe(take(2))), // take at most 2 emissions from each window
  mergeAll()                     // flatten the Observable-of-Observables
);
result.subscribe(x => console.log(x));