How to Retrieve the Current Value of an Observable or Subject?

Retrieving the Current Value of Observable or Subject

This inquiry pertains to the challenge of extracting the present value from an Observable or Subject. In the case of Observables, their purpose is to push values to subscribers upon their arrival. Once emitted, the Observable disposes of the values. Hence, accessing the current value of an Observable directly is not feasible.

Subject's Current Value

Subjects, in contrast to Observables, maintain a notion of the most recent emitted value. However, this value is not inherently accessible outside of the Subject itself.

Utilizing BehaviorSubject

A solution to this dilemma is the use of BehaviorSubject. It operates like a Subject, yet it provides a significant enhancement: it stores the last emitted value and makes it instantaneously available to new subscribers. Additionally, it offers a getValue() method for retrieving the current value explicitly.

By incorporating BehaviorSubject within the provided Angular service, you can achieve the desired functionality:

<code class="typescript">import {BehaviorSubject} from 'rxjs/BehaviorSubject';

@Injectable()
export class SessionStorage extends Storage {
  private _isLoggedInSource = new BehaviorSubject<boolean>(false); // Initialize with a default value
  isLoggedIn = this._isLoggedInSource.asObservable();

  constructor() {
    super('session');
  }

  setIsLoggedIn(value: boolean) {
    this.setItem('_isLoggedIn', value, () => {
      this._isLoggedInSource.next(value);
    });
  }

  getCurrentValue(): boolean {
    return this._isLoggedInSource.getValue(); // Access the current value using `getValue()`
  }
}</code>

This modification allows you to retrieve the latest value of isLoggedIn using getCurrentValue(). You can then leverage this value without the need for subscription.

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