88 lines
3.2 KiB
JavaScript
88 lines
3.2 KiB
JavaScript
import { Observable } from '../Observable';
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import { subscribeToResult } from '../util/subscribeToResult';
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import { OuterSubscriber } from '../OuterSubscriber';
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/**
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* We need this JSDoc comment for affecting ESDoc.
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* @extends {Ignored}
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* @hide true
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*/
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export class DeferObservable extends Observable {
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constructor(observableFactory) {
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super();
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this.observableFactory = observableFactory;
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}
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/**
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* Creates an Observable that, on subscribe, calls an Observable factory to
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* make an Observable for each new Observer.
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*
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* <span class="informal">Creates the Observable lazily, that is, only when it
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* is subscribed.
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* </span>
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*
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* <img src="./img/defer.png" width="100%">
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*
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* `defer` allows you to create the Observable only when the Observer
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* subscribes, and create a fresh Observable for each Observer. It waits until
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* an Observer subscribes to it, and then it generates an Observable,
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* typically with an Observable factory function. It does this afresh for each
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* subscriber, so although each subscriber may think it is subscribing to the
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* same Observable, in fact each subscriber gets its own individual
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* Observable.
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*
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* @example <caption>Subscribe to either an Observable of clicks or an Observable of interval, at random</caption>
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* var clicksOrInterval = Rx.Observable.defer(function () {
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* if (Math.random() > 0.5) {
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* return Rx.Observable.fromEvent(document, 'click');
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* } else {
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* return Rx.Observable.interval(1000);
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* }
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* });
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* clicksOrInterval.subscribe(x => console.log(x));
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*
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* // Results in the following behavior:
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* // If the result of Math.random() is greater than 0.5 it will listen
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* // for clicks anywhere on the "document"; when document is clicked it
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* // will log a MouseEvent object to the console. If the result is less
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* // than 0.5 it will emit ascending numbers, one every second(1000ms).
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*
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* @see {@link create}
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*
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* @param {function(): SubscribableOrPromise} observableFactory The Observable
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* factory function to invoke for each Observer that subscribes to the output
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* Observable. May also return a Promise, which will be converted on the fly
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* to an Observable.
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* @return {Observable} An Observable whose Observers' subscriptions trigger
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* an invocation of the given Observable factory function.
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* @static true
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* @name defer
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* @owner Observable
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*/
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static create(observableFactory) {
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return new DeferObservable(observableFactory);
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}
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/** @deprecated internal use only */ _subscribe(subscriber) {
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return new DeferSubscriber(subscriber, this.observableFactory);
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}
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}
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class DeferSubscriber extends OuterSubscriber {
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constructor(destination, factory) {
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super(destination);
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this.factory = factory;
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this.tryDefer();
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}
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tryDefer() {
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try {
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this._callFactory();
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}
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catch (err) {
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this._error(err);
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}
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}
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_callFactory() {
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const result = this.factory();
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if (result) {
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this.add(subscribeToResult(this, result));
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}
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}
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}
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//# sourceMappingURL=DeferObservable.js.map
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