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