rxjs
Version:
Reactive Extensions for modern JavaScript
37 lines • 1.44 kB
TypeScript
import { OperatorFunction } from '../types';
/**
* Emits a given value if the source Observable completes without emitting any
* `next` value, otherwise mirrors the source Observable.
*
* <span class="informal">If the source Observable turns out to be empty, then
* this operator will emit a default value.</span>
*
* 
*
* `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"
* ```ts
* import { fromEvent, interval } from 'rxjs';
* import { defaultIfEmpty, takeUntil } from 'rxjs/operators';
*
* 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));
* ```
*
* @see {@link empty}
* @see {@link last}
*
* @param defaultValue The default value used if the source
* Observable is empty.
* @return A function that returns an Observable that emits either the
* specified `defaultValue` if the source Observable emits no items, or the
* values emitted by the source Observable.
*/
export declare function defaultIfEmpty<T, R>(defaultValue: R): OperatorFunction<T, T | R>;
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