Actually, it was as easy as pairing pairwise() with startWith() operators: subject .startWith(null) // emitting first empty value to fill-in the buffer .pairwise() .subscribe([previousValue, currentValue] => { if (null === previousValue) { console.log(‘Probably first emission…’); } }) ;
I’m going to describe the difference between them in terms of their Time versions as that’s how I understand them best. Both auditTime and debounceTime will initially start a timer when an event comes in. Both will wait the given amount of time before they emit an event. The difference is that debounceTime resets the … Read more
In the ES7 spec, which RxJS 5.0 follows (but RxJS 4.0 does not), the two are NOT the same. subscribe public subscribe(observerOrNext: Observer | Function, error: Function, complete: Function): Subscription Observable.subscribe is where you will do most of your true Observable handling. It returns a subscription token, which you can use to cancel your subscription. … Read more
Before RxJs 6: Observable.timer(0, 1000) will start immediately. RxJs 6+ import {timer} from ‘rxjs/observable/timer’; timer(0, 1000).subscribe(() => { … });
You are correct; switchMap will unsubscribe from the Observable returned by its project argument as soon as it has invoked the project function again to produce a new Observable. RxJs is incredibly powerful and dense, but its high level of abstraction can sometimes make code hard to understand. Let me debunk the marble diagrams and … Read more
It turns out the answer is quite simple: the operator is called mergeMap in this version of rxjs EDIT: Furthermore, you might have to use import ‘rxjs/add/operator/mergeMap’.
Rx schedulers provide an abstraction that allows work to be scheduled to run, possibly in the future, without the calling code needing to be aware of the mechanism used to schedule the work. Whenever an Rx method needs to generate a notification, it schedules the work on a scheduler. By supplying a scheduler to the … Read more
Each serves a different purpose so it’s hard to compare them. In general if you take this source: const source = range(1,3); … and consume it with subscribe() followed immediately by unsubscribe(): source.subscribe( console.log, undefined, () => console.log(‘complete’) ).unsubscribe(); … then all values from source are going to be emitted even though we called unsubscribe() … Read more
Not only does forkJoin require all input observables to be completed, but it also returns an observable that produces a single value that is an array of the last values produced by the input observables. In other words, it waits until the last input observable completes, and then produces a single value and completes. In … Read more
When to use Subject.prototype.asObservable() The purpose of this is to prevent leaking the “observer side” of the Subject out of an API. Basically to prevent a leaky abstraction when you don’t want people to be able to “next” into the resulting observable. Example (NOTE: This really isn’t how you should make a data source like … Read more