publishLast

Returns a connectable observable sequence that shares a single subscription to the underlying sequence containing only the last notification.

Deprecation Notes

Will be removed in v8. To create a connectable observable with an AsyncSubject under the hood, use connectable. source.pipe(publishLast()) is equivalent to connectable(source, { connector: () => new AsyncSubject(), resetOnDisconnect: false }). If you're using refCount after publishLast, use the share operator instead. source.pipe(publishLast(), refCount()) is equivalent to source.pipe(share({ connector: () => new AsyncSubject(), resetOnError: false, resetOnComplete: false, resetOnRefCountZero: false })). Details: https://rxjs.dev/deprecations/multicasting

publishLast<T>(): UnaryFunction<Observable<T>, ConnectableObservable<T>>

Parameters

There are no parameters.

Returns

UnaryFunction<Observable<T>, ConnectableObservable<T>>: A function that returns an Observable that emits elements of a sequence produced by multicasting the source sequence.

Description

Similar to publish, but it waits until the source observable completes and stores the last emitted value. Similarly to publishReplay and publishBehavior, this keeps storing the last value even if it has no more subscribers. If subsequent subscriptions happen, they will immediately get that last stored value and complete.

Example

import { ConnectableObservable, interval, publishLast, tap, take } from 'rxjs';

const connectable = <ConnectableObservable<number>>interval(1000)
  .pipe(
    tap(x => console.log('side effect', x)),
    take(3),
    publishLast()
  );

connectable.subscribe({
  next: x => console.log('Sub. A', x),
  error: err => console.log('Sub. A Error', err),
  complete: () => console.log('Sub. A Complete')
});

connectable.subscribe({
  next: x => console.log('Sub. B', x),
  error: err => console.log('Sub. B Error', err),
  complete: () => console.log('Sub. B Complete')
});

connectable.connect();

// Results:
// 'side effect 0'   - after one second
// 'side effect 1'   - after two seconds
// 'side effect 2'   - after three seconds
// 'Sub. A 2'        - immediately after 'side effect 2'
// 'Sub. B 2'
// 'Sub. A Complete'
// 'Sub. B Complete'

See Also

• ConnectableObservable
• publish
• publishReplay
• publishBehavior