1 import { Observable } from '../Observable';
2 import { Unsubscribable, ObservableInput } from '../types';
3 import { from } from './from'; // from from from! LAWL
4 import { EMPTY } from './empty';
7 * Creates an Observable that uses a resource which will be disposed at the same time as the Observable.
9 * <span class="informal">Use it when you catch yourself cleaning up after an Observable.</span>
11 * `using` is a factory operator, which accepts two functions. First function returns a disposable resource.
12 * It can be an arbitrary object that implements `unsubscribe` method. Second function will be injected with
13 * that object and should return an Observable. That Observable can use resource object during its execution.
14 * Both functions passed to `using` will be called every time someone subscribes - neither an Observable nor
15 * resource object will be shared in any way between subscriptions.
17 * When Observable returned by `using` is subscribed, Observable returned from the second function will be subscribed
18 * as well. All its notifications (nexted values, completion and error events) will be emitted unchanged by the output
19 * Observable. If however someone unsubscribes from the Observable or source Observable completes or errors by itself,
20 * the `unsubscribe` method on resource object will be called. This can be used to do any necessary clean up, which
21 * otherwise would have to be handled by hand. Note that complete or error notifications are not emitted when someone
22 * cancels subscription to an Observable via `unsubscribe`, so `using` can be used as a hook, allowing you to make
23 * sure that all resources which need to exist during an Observable execution will be disposed at appropriate time.
27 * @param {function(): ISubscription} resourceFactory A function which creates any resource object
28 * that implements `unsubscribe` method.
29 * @param {function(resource: ISubscription): Observable<T>} observableFactory A function which
30 * creates an Observable, that can use injected resource object.
31 * @return {Observable<T>} An Observable that behaves the same as Observable returned by `observableFactory`, but
32 * which - when completed, errored or unsubscribed - will also call `unsubscribe` on created resource object.
34 export function using<T>(resourceFactory: () => Unsubscribable | void,
35 observableFactory: (resource: Unsubscribable | void) => ObservableInput<T> | void): Observable<T> {
36 return new Observable<T>(subscriber => {
37 let resource: Unsubscribable | void;
40 resource = resourceFactory();
42 subscriber.error(err);
46 let result: ObservableInput<T> | void;
48 result = observableFactory(resource);
50 subscriber.error(err);
54 const source = result ? from(result) : EMPTY;
55 const subscription = source.subscribe(subscriber);
57 subscription.unsubscribe();
59 resource.unsubscribe();