When creating an RxJS BehaviorSubject, it stays a BehaviorSubject until it's pipe'd. As soon a pipe'd version is returned, it bees an AnonymousSubject.

Examples:

// Instance of `BehaviorSubject`
const behaviorSubject$ = new BehaviorSubject({ someValue: null })

// Suddenly bees an Anonymous Subject
const anonymousSubject$ = (
    behaviorSubject$
    .pipe(
        pluck('someValue')
    )
)

// Also suddenly bees an Anonymous Subject
const anonymousSubject$ = (
    new BehaviorSubject({ someValue: null })
    .pipe(
        pluck('someValue')
    )
)

When creating an RxJS BehaviorSubject, it stays a BehaviorSubject until it's pipe'd. As soon a pipe'd version is returned, it bees an AnonymousSubject.

Examples:

// Instance of `BehaviorSubject`
const behaviorSubject$ = new BehaviorSubject({ someValue: null })

// Suddenly bees an Anonymous Subject
const anonymousSubject$ = (
    behaviorSubject$
    .pipe(
        pluck('someValue')
    )
)

// Also suddenly bees an Anonymous Subject
const anonymousSubject$ = (
    new BehaviorSubject({ someValue: null })
    .pipe(
        pluck('someValue')
    )
)

I experience this same issue with ReplaySubject as well. I can't seem to pipe through the subject and return that subject back. It always converts to an AnonymousSubject. I think what I'm looking for here is Promise-like behavior where I can subscribe to this observable from anywhere and grab the one value passed into it.

• javascript
• rxjs
• rxjs5
• behaviorsubject
• subject-observer

Share Improve this question Follow edited Apr 24, 2018 at 16:35 Kevin Ghadyani asked Apr 24, 2018 at 3:53 Kevin GhadyaniKevin Ghadyani 7,30788 gold badges4747 silver badges6666 bronze badges 8

• 1 Do you have code that cares? If you do you shouldn't. – Aluan Haddad Commented Apr 24, 2018 at 3:58
• I need to do behaviorSubject$.value. Should I be using a ReplaySubject instead? – Kevin Ghadyani Commented Apr 24, 2018 at 3:59
• You need to pass an argument to BehaviorSubject() – siva636 Commented Apr 24, 2018 at 4:01
• 1 IMO using value is a code smell and even if lift returned a BehaviorSubject, what would you expect the value if the lifted subject to be? The original value or the plucked value? I think you should seriously reconsider using value. – cartant Commented Apr 24, 2018 at 4:43
• 1 BehaviorSubject allows you to do subject.value. I can't do that with AnonymousSubject. – Kevin Ghadyani Commented Dec 18, 2019 at 19:46

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1 Answer 1

Sorted by: Reset to default 10

This is happening due to lift called on Subject.

Let's take a deeper look at your example:

1. You are instantiating a BehaviorSubject which extends Subject
2. You are calling pluck operator which internally calls map operator
3. map operator internally calls lift on BehaviorSubject which is delegated to Subject which then returns an AnonymousSubject