work.suroh.tk/node_modules/rxjs/_esm2015/operators/defaultIfEmpty.js

66 lines
2.2 KiB
JavaScript

import { Subscriber } from '../Subscriber';
/* tslint:enable:max-line-length */
/**
* 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>
*
* <img src="./img/defaultIfEmpty.png" width="100%">
*
* `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 <caption>If no clicks happen in 5 seconds, then emit "no clicks"</caption>
* var clicks = Rx.Observable.fromEvent(document, 'click');
* var clicksBeforeFive = clicks.takeUntil(Rx.Observable.interval(5000));
* var result = clicksBeforeFive.defaultIfEmpty('no clicks');
* result.subscribe(x => console.log(x));
*
* @see {@link empty}
* @see {@link last}
*
* @param {any} [defaultValue=null] The default value used if the source
* Observable is empty.
* @return {Observable} An Observable that emits either the specified
* `defaultValue` if the source Observable emits no items, or the values emitted
* by the source Observable.
* @method defaultIfEmpty
* @owner Observable
*/
export function defaultIfEmpty(defaultValue = null) {
return (source) => source.lift(new DefaultIfEmptyOperator(defaultValue));
}
class DefaultIfEmptyOperator {
constructor(defaultValue) {
this.defaultValue = defaultValue;
}
call(subscriber, source) {
return source.subscribe(new DefaultIfEmptySubscriber(subscriber, this.defaultValue));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class DefaultIfEmptySubscriber extends Subscriber {
constructor(destination, defaultValue) {
super(destination);
this.defaultValue = defaultValue;
this.isEmpty = true;
}
_next(value) {
this.isEmpty = false;
this.destination.next(value);
}
_complete() {
if (this.isEmpty) {
this.destination.next(this.defaultValue);
}
this.destination.complete();
}
}
//# sourceMappingURL=defaultIfEmpty.js.map