es6/observable/EmptyObservable.js

import { Observable } from '../Observable';
/**
 * We need this JSDoc comment for affecting ESDoc.
 * @extends {Ignored}
 * @hide true
 */
export class EmptyObservable extends Observable {
    constructor(scheduler) {
        super();
        this.scheduler = scheduler;
    }
    /**
     * Creates an Observable that emits no items to the Observer and immediately
     * emits a complete notification.
     *
     * <span class="informal">Just emits 'complete', and nothing else.
     * </span>
     *
     * <img src="./img/empty.png" width="100%">
     *
     * This static operator is useful for creating a simple Observable that only
     * emits the complete notification. It can be used for composing with other
     * Observables, such as in a {@link mergeMap}.
     *
     * @example <caption>Emit the number 7, then complete.</caption>
     * var result = Rx.Observable.empty().startWith(7);
     * result.subscribe(x => console.log(x));
     *
     * @example <caption>Map and flatten only odd numbers to the sequence 'a', 'b', 'c'</caption>
     * var interval = Rx.Observable.interval(1000);
     * var result = interval.mergeMap(x =>
     *   x % 2 === 1 ? Rx.Observable.of('a', 'b', 'c') : Rx.Observable.empty()
     * );
     * result.subscribe(x => console.log(x));
     *
     * // Results in the following to the console:
     * // x is equal to the count on the interval eg(0,1,2,3,...)
     * // x will occur every 1000ms
     * // if x % 2 is equal to 1 print abc
     * // if x % 2 is not equal to 1 nothing will be output
     *
     * @see {@link create}
     * @see {@link never}
     * @see {@link of}
     * @see {@link throw}
     *
     * @param {Scheduler} [scheduler] A {@link IScheduler} to use for scheduling
     * the emission of the complete notification.
     * @return {Observable} An "empty" Observable: emits only the complete
     * notification.
     * @static true
     * @name empty
     * @owner Observable
     */
    static create(scheduler) {
        return new EmptyObservable(scheduler);
    }
    static dispatch(arg) {
        const { subscriber } = arg;
        subscriber.complete();
    }
    _subscribe(subscriber) {
        const scheduler = this.scheduler;
        if (scheduler) {
            return scheduler.schedule(EmptyObservable.dispatch, 0, { subscriber });
        }
        else {
            subscriber.complete();
        }
    }
}
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