When should I use `publishReplay` vs `shareReplay`?

Question

I already know that

• publish shares a single subscription and also returns a ConnectableObservable ( so we have to Connect() )

• Share() is publish().refcount()

The Replay postfix is pretty obvious, it returns its last emission/s.

Let's take for example an Angular HTTP request with present AND future subscription :

<p>{{ (person | async)?.id   }}</p> //present markup

<p *ngIf=”show”>{{ (person | async)?.userId }}</p> <!-- future markup -->

If I don't want multiple http requests I can use :

publishReplay().Connect()

But I can also use: shareReplay() , but I'm sure that there is one here that is more correct to use than the other.

Question :

When should I use publishReplay vs shareReplay ? What will be the difference in terms of that HTTP present & future request?

_{NB Why there's no documentation about shareReplay ?}

Answer 1

shareReplay() is basically publishReplay().refCount()

Definitely not.

Both shareReplay and publishReplay (+ calling connect on it) will make the observable behind it hot.

But the very important difference between them is :

• shareReplay : won't stop emitting until it's completed , no matter if there are no subscriptions anymore or not.
• publishReplay : will stop after the last subscriber unsubscribes if used together with refCount

Imho this is a crucial information.

Answer 2

publishReplay allows you to controls when the subscription starts. shareReplay will start automatically upon the first subscription.

Generally, if the observable is to be used in a template (html file) use shareReplay . The advantage being you won't have to worry about unsubscribing etc.

Answer 3

shareReplay() is basically publishReplay().refCount()

Here is a great article explaingin just that in detail: "Angular Async Pipes - Beware the share"

Edit:

The right thing to say is:

shareReplay() is similar to publishReplay().refCount()

see @DevRok's answer for more info why they are not exactly the same.