.

Considering this, what is subject and BehaviorSubject?

BehaviorSubject is a special type of Subject whose only different is that it will emit the last value upon a new observer's subscription.

Beside above, what is the difference between observable and subject? Probably a more important distinction between Subject and Observable is that a Subject has state, it keeps a list of observers. On the other hand, an Observable is really just a function that sets up observation. While Subjects are Observables, Subjects also implement an Observer interface.

Subsequently, one may also ask, what is Behavioural subject?

“Behavior Subject is a type of subject, a subject is a special type of observable so you can subscribe to messages like any other observable. The unique features of a behavior subject are: at any point you can retrieve the last value of the subject in a non-observable code using the getValue() method.

What is a replay subject?

A variant of Subject that "replays" or emits old values to new subscribers. It buffers a set number of values and will emit those values immediately to any new subscribers in addition to emitting new values to existing subscribers.