¿Cuál de las siguientes es una diferencia clave entre un sujeto y un ReplaySubject?

Which of the following is a key difference between a subject and a ReplaySubject?

Basically Subject only produces values to current subscribers and ReplaySubject remembers values for future subscribes (when it “replays” the values).

While plain Observables are unicast (each subscribed Observer owns an independent execution of the Observable), Subjects are multicast. A Subject is like an Observable, but can multicast to many Observers. Subjects are like EventEmitters: they maintain a registry of many listeners.

6 Answers. A BehaviorSubject holds one value. When it is subscribed it emits the value immediately. A Subject doesn’t hold a value.

ReplaySubject is a variant of a Subject which keeps a cache of previous values emitted by a source observable and sends them to all new observers immediately on subscription. This behavior of replaying a sequence of old values to new subscribes is where the name for this type of a subject comes from.

2 Answers. The Subject itself is hot/shared.

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.

A Subject is like an Observable, but can multicast to many Observers. Subjects are like EventEmitters: they maintain a registry of many listeners. Every Subject is an Observable. Given a Subject, you can subscribe to it, providing an Observer, which will start receiving values normally.

An RxJS Subject is a special type of Observable that allows values to be multicasted to many Observers. While plain Observables are unicast (each subscribed Observer owns an independent execution of the Observable), Subjects are multicast. A Subject is like an Observable, but can multicast to many Observers.

In Angular services, I would use BehaviorSubject for a data service as an angular service often initializes before component and behavior subject ensures that the component consuming the service receives the last updated data even if there are no new updates since the component’s subscription to this data.

You can either get the value by accessing the . value property on the BehaviorSubject or you can subscribe to it. If you subscribe to it, the BehaviorSubject will directly emit the current value to the subscriber. Even if the subscriber subscribes much later than the value was stored.

Observables are lazy whereas promises are not In the case of promises, they execute immediately.

Observables are lazy in the sense that they only execute values when something subscribes to it. If your Observable produces a lot of different values it can happen that two Observables that subscribe at more or less the same receive two different values.