Tips for retrieving the present value of a piped/converted BehaviorSubject

Question

Tips for retrieving the present value of a piped/converted BehaviorSubject

How do I retrieve the current value of the observable generated by readValue() below without subscribing to it?

var subject = new BehaviorSubject<Object>({});

observe(): Observable<Object> {
  return subject.pipe(map(mappingfunction));
}

Do I need to create another BehaviourSubject as shown here?

var other_subject = new BehaviorSubject<Object>();
observer().subscribe(other_subject);

var value = other_subject.currentValue();

In theory, it should be possible to access the currentValue directly since it will always be available due to the original behavioursubject passing the last result through the pipe. However, unless complicating factors are introduced, like bouncing, I don't foresee any issues.

typescript rxjs observable

Answer 1

Answer №1

If you want to retrieve the current value synchronously, you can use the take(1) or first() operator like this:

getCurrentValue(): Blah {
    let x: Blah = null;
    this.observe().pipe(take(1)).subscribe((a) => x = a);
    return x;
}

This method specifically works with BehaviorSubjects because they always provide the current value synchronously upon initial subscription. When creating a BehaviorSubject, an initial value is provided, ensuring that there is always a value available in this case.

It's important to note that this approach is limited to BehaviorSubjects and observables linked to them. Other types of subjects may not offer the current value synchronously like BehaviorSubjects do.

As long as the pipe functions used do not delay emissions from the BehaviorSubject (such as debounceTime or delay), this method should work regardless of the pipe configuration.

Answer 2

If you want to retrieve the current value synchronously, you can use the take(1) or first() operator like this:

getCurrentValue(): Blah {
    let x: Blah = null;
    this.observe().pipe(take(1)).subscribe((a) => x = a);
    return x;
}

This method specifically works with BehaviorSubjects because they always provide the current value synchronously upon initial subscription. When creating a BehaviorSubject, an initial value is provided, ensuring that there is always a value available in this case.

It's important to note that this approach is limited to BehaviorSubjects and observables linked to them. Other types of subjects may not offer the current value synchronously like BehaviorSubjects do.

As long as the pipe functions used do not delay emissions from the BehaviorSubject (such as debounceTime or delay), this method should work regardless of the pipe configuration.

Answer 3

Answer №2

If you're looking for an alternative way to monitor the current value, consider utilizing the tap operator:

let subject = new BehaviorSubject<Object>({});
let currentValue: Object = null;

observe(): Observable<Object> {
    return subject.pipe(
        map(mappingfunction),
        tap((value) => currentValue = value)
    );
}

By using this method, the variable currentValue will always hold the most recently emitted value from the observable (although it will remain empty until a subscriber is connected to the observe() function).

Answer 4

If you're looking for an alternative way to monitor the current value, consider utilizing the tap operator:

let subject = new BehaviorSubject<Object>({});
let currentValue: Object = null;

observe(): Observable<Object> {
    return subject.pipe(
        map(mappingfunction),
        tap((value) => currentValue = value)
    );
}

By using this method, the variable currentValue will always hold the most recently emitted value from the observable (although it will remain empty until a subscriber is connected to the observe() function).

Answer 5

Answer №3

With BehaviorSubject, you can use the method getValue() to retrieve the current value.

https://example.com/behaviorsubject-method-getvalue

Answer 6

With BehaviorSubject, you can use the method getValue() to retrieve the current value.

https://example.com/behaviorsubject-method-getvalue

Tips for retrieving the present value of a piped/converted BehaviorSubject

Answer №1

Answer №2

Answer №3

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