ObservableThe when() method on a event target returns an Observable object, which provides a declarative API for subscribing to and operating on events. It's an alternative to addEventListener() callbacks.limitedhttps://wicg.github.io/observable/https://developer.mozilla.org/docs/Web/API/EventTargetapi.EventTarget.whenapi.Observableapi.Observable.Observableapi.Observable.catchapi.Observable.dropapi.Observable.everyapi.Observable.filterapi.Observable.finallyapi.Observable.findapi.Observable.firstapi.Observable.flatMapapi.Observable.forEachapi.Observable.from_staticapi.Observable.inspectapi.Observable.lastapi.Observable.mapapi.Observable.reduceapi.Observable.someapi.Observable.subscribeapi.Observable.switchMapapi.Observable.takeapi.Observable.takeUntilapi.Observable.toArrayapi.Subscriberapi.Subscriber.activeapi.Subscriber.addTeardownapi.Subscriber.completeapi.Subscriber.errorapi.Subscriber.nextapi.Subscriber.signalhttps://nowyoucanuse.com/features--observable.html