es6/operators/defaultIfEmpty.js

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();
    }
}
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