102 lines
6.2 KiB
JavaScript
102 lines
6.2 KiB
JavaScript
"use strict";
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var multicast_1 = require('../operators/multicast');
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/* tslint:enable:max-line-length */
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/**
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* Allows source Observable to be subscribed only once with a Subject of choice,
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* while still sharing its values between multiple subscribers.
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*
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* <span class="informal">Subscribe to Observable once, but send its values to multiple subscribers.</span>
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*
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* <img src="./img/multicast.png" width="100%">
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*
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* `multicast` is an operator that works in two modes.
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*
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* In the first mode you provide a single argument to it, which can be either an initialized Subject or a Subject
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* factory. As a result you will get a special kind of an Observable - a {@link ConnectableObservable}. It can be
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* subscribed multiple times, just as regular Observable, but it won't subscribe to the source Observable at that
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* moment. It will do it only if you call its `connect` method. This means you can essentially control by hand, when
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* source Observable will be actually subscribed. What is more, ConnectableObservable will share this one subscription
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* between all of its subscribers. This means that, for example, `ajax` Observable will only send a request once,
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* even though usually it would send a request per every subscriber. Since it sends a request at the moment of
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* subscription, here request would be sent when the `connect` method of a ConnectableObservable is called.
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*
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* The most common pattern of using ConnectableObservable is calling `connect` when the first consumer subscribes,
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* keeping the subscription alive while several consumers come and go and finally unsubscribing from the source
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* Observable, when the last consumer unsubscribes. To not implement that logic over and over again,
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* ConnectableObservable has a special operator, `refCount`. When called, it returns an Observable, which will count
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* the number of consumers subscribed to it and keep ConnectableObservable connected as long as there is at least
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* one consumer. So if you don't actually need to decide yourself when to connect and disconnect a
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* ConnectableObservable, use `refCount`.
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*
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* The second mode is invoked by calling `multicast` with an additional, second argument - selector function.
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* This function accepts an Observable - which basically mirrors the source Observable - and returns Observable
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* as well, which should be the input stream modified by any operators you want. Note that in this
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* mode you cannot provide initialized Subject as a first argument - it has to be a Subject factory. If
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* you provide selector function, `multicast` returns just a regular Observable, instead of ConnectableObservable.
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* Thus, as usual, each subscription to this stream triggers subscription to the source Observable. However,
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* if inside the selector function you subscribe to the input Observable multiple times, actual source stream
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* will be subscribed only once. So if you have a chain of operators that use some Observable many times,
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* but you want to subscribe to that Observable only once, this is the mode you would use.
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*
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* Subject provided as a first parameter of `multicast` is used as a proxy for the single subscription to the
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* source Observable. It means that all values from the source stream go through that Subject. Thus, if a Subject
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* has some special properties, Observable returned by `multicast` will have them as well. If you want to use
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* `multicast` with a Subject that is one of the ones included in RxJS by default - {@link Subject},
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* {@link AsyncSubject}, {@link BehaviorSubject}, or {@link ReplaySubject} - simply use {@link publish},
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* {@link publishLast}, {@link publishBehavior} or {@link publishReplay} respectively. These are actually
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* just wrappers around `multicast`, with a specific Subject hardcoded inside.
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*
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* Also, if you use {@link publish} or {@link publishReplay} with a ConnectableObservables `refCount` operator,
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* you can simply use {@link share} and {@link shareReplay} respectively, which chain these two.
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*
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* @example <caption>Use ConnectableObservable</caption>
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* const seconds = Rx.Observable.interval(1000);
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* const connectableSeconds = seconds.multicast(new Subject());
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*
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* connectableSeconds.subscribe(value => console.log('first: ' + value));
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* connectableSeconds.subscribe(value => console.log('second: ' + value));
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*
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* // At this point still nothing happens, even though we subscribed twice.
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*
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* connectableSeconds.connect();
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*
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* // From now on `seconds` are being logged to the console,
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* // twice per every second. `seconds` Observable was however only subscribed once,
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* // so under the hood Observable.interval had only one clock started.
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*
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* @example <caption>Use selector</caption>
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* const seconds = Rx.Observable.interval(1000);
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*
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* seconds
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* .multicast(
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* () => new Subject(),
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* seconds => seconds.zip(seconds) // Usually zip would subscribe to `seconds` twice.
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* // Because we are inside selector, `seconds` is subscribed once,
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* ) // thus starting only one clock used internally by Observable.interval.
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* .subscribe();
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*
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* @see {@link publish}
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* @see {@link publishLast}
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* @see {@link publishBehavior}
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* @see {@link publishReplay}
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* @see {@link share}
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* @see {@link shareReplay}
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*
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* @param {Function|Subject} subjectOrSubjectFactory - Factory function to create an intermediate Subject through
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* which the source sequence's elements will be multicast to the selector function input Observable or
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* ConnectableObservable returned by the operator.
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* @param {Function} [selector] - Optional selector function that can use the input stream
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* as many times as needed, without causing multiple subscriptions to the source stream.
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* Subscribers to the input source will receive all notifications of the source from the
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* time of the subscription forward.
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* @return {Observable<T>|ConnectableObservable<T>} An Observable that emits the results of invoking the selector
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* on the source stream or a special {@link ConnectableObservable}, if selector was not provided.
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*
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* @method multicast
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* @owner Observable
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*/
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function multicast(subjectOrSubjectFactory, selector) {
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return multicast_1.multicast(subjectOrSubjectFactory, selector)(this);
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}
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exports.multicast = multicast;
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//# sourceMappingURL=multicast.js.map
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