import { Operator } from '../Operator'; import { Observable } from '../Observable'; import { Subscriber } from '../Subscriber'; import { OperatorFunction, MonoTypeOperatorFunction } from '../interfaces'; /* tslint:disable:max-line-length */ export function defaultIfEmpty(defaultValue?: T): MonoTypeOperatorFunction; export function defaultIfEmpty(defaultValue?: R): OperatorFunction; /* tslint:enable:max-line-length */ /** * Emits a given value if the source Observable completes without emitting any * `next` value, otherwise mirrors the source Observable. * * If the source Observable turns out to be empty, then * this operator will emit a default value. * * * * `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" * 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: R = null): OperatorFunction { return (source: Observable) => source.lift(new DefaultIfEmptyOperator(defaultValue)) as Observable; } class DefaultIfEmptyOperator implements Operator { constructor(private defaultValue: R) { } call(subscriber: Subscriber, source: any): any { return source.subscribe(new DefaultIfEmptySubscriber(subscriber, this.defaultValue)); } } /** * We need this JSDoc comment for affecting ESDoc. * @ignore * @extends {Ignored} */ class DefaultIfEmptySubscriber extends Subscriber { private isEmpty: boolean = true; constructor(destination: Subscriber, private defaultValue: R) { super(destination); } protected _next(value: T): void { this.isEmpty = false; this.destination.next(value); } protected _complete(): void { if (this.isEmpty) { this.destination.next(this.defaultValue); } this.destination.complete(); } }