Emits a given value if the source Observable completes without emitting any next value, otherwise mirrors the source Observable.

If the source Observable turns out to be empty, then this operator will emit a default value.

defaultIfEmpty emits the values emitted by the source Observable or a specified default value if the source Observable is empty (completes without having emitted any next value).

Example

If no clicks happen in 5 seconds, then emit 'no clicks'

import { fromEvent, takeUntil, interval, defaultIfEmpty } from 'rxjs';

const clicks = fromEvent(document, 'click');
const clicksBeforeFive = clicks.pipe(takeUntil(interval(5000)));
const result = clicksBeforeFive.pipe(defaultIfEmpty('no clicks'));
result.subscribe(x => console.log(x));