function
stable
Emits false if the input observable emits any values, or emits true if the input observable completes without emitting any values.
isEmpty<T>(): OperatorFunction<T, boolean>
There are no parameters.
OperatorFunction<T, boolean>
: An Observable of a boolean value indicating whether observable was empty or not
Tells whether any values are emitted by an observable
isEmpty
transforms an Observable that emits values into an Observable that emits a single boolean value representing whether or not any values were emitted by the source Observable. As soon as the source Observable emits a value, isEmpty
will emit a false
and complete. If the source Observable completes having not emitted anything, isEmpty
will emit a true
and complete.
A similar effect could be achieved with count
, but isEmpty
can emit a false
value sooner.
Emit false
for a non-empty Observable
import { Subject } from 'rxjs'; import { isEmpty } from 'rxjs/operators'; const source = new Subject<string>(); const result = source.pipe(isEmpty()); source.subscribe(x => console.log(x)); result.subscribe(x => console.log(x)); source.next('a'); source.next('b'); source.next('c'); source.complete(); // Results in: // a // false // b // c
Emit true
for an empty Observable
import { EMPTY } from 'rxjs'; import { isEmpty } from 'rxjs/operators'; const result = EMPTY.pipe(isEmpty()); result.subscribe(x => console.log(x)); // Results in: // true
© 2015–2018 Google, Inc., Netflix, Inc., Microsoft Corp. and contributors.
Code licensed under an Apache-2.0 License. Documentation licensed under CC BY 4.0.
https://rxjs.dev/api/operators/isEmpty