Get current value from Observable without subscribing (just want value one time)

Question

How can I get the current value from an Observable without subscribing to it? I just want the current value one time and not new values as they are coming in.

Answer 1

You need to use BehaviorSubject,

• BehaviorSubject is similar to ReplaySubject except it only remembers the last publication.
• BehaviorSubject also requires you to provide it a default value of T. This means that all subscribers will receive a value immediately (unless it is already completed).

It will give you the most recent value published by the Observable.

BehaviorSubject provides a getter property named value to get the most recent value passed through it.

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StackBlitz

• In this example the value 'a' is written to the console:

//Declare a Subject, you'll need to provide a default value.
const subject: BehaviorSubject<string> = new BehaviorSubject("a");

USAGE:

console.log(subject.value); // will print the current value

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Conceal the Subject and only expose it's value

In case you want to conceal your BehaviorSubject and only expose it's value, let's say from a Service, you can use a getter like this.

export class YourService {
  private subject = new BehaviorSubject('random');

  public get subjectValue() {
    return this.subject.value;
  }
}