es6/operator/timeoutWith.js

import { async } from '../scheduler/async';
import { timeoutWith as higherOrder } from '../operators/timeoutWith';
/* tslint:enable:max-line-length */
/**
 *
 * Errors if Observable does not emit a value in given time span, in case of which
 * subscribes to the second Observable.
 *
 * <span class="informal">It's a version of `timeout` operator that let's you specify fallback Observable.</span>
 *
 * <img src="./img/timeoutWith.png" width="100%">
 *
 * `timeoutWith` is a variation of `timeout` operator. It behaves exactly the same,
 * still accepting as a first argument either a number or a Date, which control - respectively -
 * when values of source Observable should be emitted or when it should complete.
 *
 * The only difference is that it accepts a second, required parameter. This parameter
 * should be an Observable which will be subscribed when source Observable fails any timeout check.
 * So whenever regular `timeout` would emit an error, `timeoutWith` will instead start re-emitting
 * values from second Observable. Note that this fallback Observable is not checked for timeouts
 * itself, so it can emit values and complete at arbitrary points in time. From the moment of a second
 * subscription, Observable returned from `timeoutWith` simply mirrors fallback stream. When that
 * stream completes, it completes as well.
 *
 * Scheduler, which in case of `timeout` is provided as as second argument, can be still provided
 * here - as a third, optional parameter. It still is used to schedule timeout checks and -
 * as a consequence - when second Observable will be subscribed, since subscription happens
 * immediately after failing check.
 *
 * @example <caption>Add fallback observable</caption>
 * const seconds = Rx.Observable.interval(1000);
 * const minutes = Rx.Observable.interval(60 * 1000);
 *
 * seconds.timeoutWith(900, minutes)
 *     .subscribe(
 *         value => console.log(value), // After 900ms, will start emitting `minutes`,
 *                                      // since first value of `seconds` will not arrive fast enough.
 *         err => console.log(err) // Would be called after 900ms in case of `timeout`,
 *                                 // but here will never be called.
 *     );
 *
 * @param {number|Date} due Number specifying period within which Observable must emit values
 *                          or Date specifying before when Observable should complete
 * @param {Observable<T>} withObservable Observable which will be subscribed if source fails timeout check.
 * @param {Scheduler} [scheduler] Scheduler controlling when timeout checks occur.
 * @return {Observable<T>} Observable that mirrors behaviour of source or, when timeout check fails, of an Observable
 *                          passed as a second parameter.
 * @method timeoutWith
 * @owner Observable
 */
export function timeoutWith(due, withObservable, scheduler = async) {
    return higherOrder(due, withObservable, scheduler)(this);
}
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