work.suroh.tk/node_modules/rxjs/_esm2015/observable/DeferObservable.js

88 lines
3.2 KiB
JavaScript

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