Pause and be patient while in the function that delivers an observable

Question

Pause and be patient while in the function that delivers an observable

I have a function that loads user details and returns an observable. This function is called from multiple places, but I want to prevent redundant calls by waiting until the result is loaded after the first call. Can anyone suggest how this can be accomplished using RxJs and Angular?

    getUser(): Observable<any> {
      return this.http.get('/userAuthenticated');
    }

One approach is to wait for the first call to complete and then save the result in a static variable:

    getUser(): Observable<any> {
      if(!this.userIsLoading) {
        this.userIsLoading = true;
        return this.http.get('/userAuthenticated').pipe(
          tap((res: any) => {
            this.userIsLoading = false;
            this.User = res.data;
        }));
      } else {
        // Wait for the first call to complete
        return of(this.User);
      }
    }

Another idea is to define a static variable for the observable.

Any help would be appreciated.

angular typescript rxjs

Answer 1

Answer №1

In order to accomplish this, follow these steps:

Establish a fresh Observable attribute within your service/component and utilize the shareReplay operator to prevent calling the API repeatedly and distribute the outcome among all new subscribers.
Have the getUser function return the new Observable (You cannot directly incorporate the shareReplay here as each time getUser is invoked, it generates a new Observable with shareReplay, failing to provide the same one).

Consider implementing the following code snippet:

// import { shareReplay } from 'rxjs/operators';

private userSource$ = this.http.get('/userAuthenticated').pipe(shareReplay());

getUser(): Observable<any> {
  return this.userSource$;
}

Answer 2

In order to accomplish this, follow these steps:

Establish a fresh Observable attribute within your service/component and utilize the shareReplay operator to prevent calling the API repeatedly and distribute the outcome among all new subscribers.
Have the getUser function return the new Observable (You cannot directly incorporate the shareReplay here as each time getUser is invoked, it generates a new Observable with shareReplay, failing to provide the same one).

Consider implementing the following code snippet:

// import { shareReplay } from 'rxjs/operators';

private userSource$ = this.http.get('/userAuthenticated').pipe(shareReplay());

getUser(): Observable<any> {
  return this.userSource$;
}

Answer 3

Answer №2

req$ = this.http.get('/userAuthenticated').pipe(shareReplay(1));

getUserInfo(): Observable<any> {
  return this.req$
}

Utilize the shareReplay function to store the response data from the server after the initial request. Any subsequent subscriber will receive the cached information.

For more details on how to use shareReplay, check out the official documentation: https://rxjs.dev/api/operators/shareReplay

Answer 4

req$ = this.http.get('/userAuthenticated').pipe(shareReplay(1));

getUserInfo(): Observable<any> {
  return this.req$
}

Utilize the shareReplay function to store the response data from the server after the initial request. Any subsequent subscriber will receive the cached information.

For more details on how to use shareReplay, check out the official documentation: https://rxjs.dev/api/operators/shareReplay

Answer 5

Answer №3

One of the notable features of Rxjs is the firstValueFrom() function, which allows you to get a promise that can be awaited.

  async fetchUser(): Promise<Observable<any>> {
    if (!this.loadingUser) {
      this.loadingUser = true;
      return this.http.get('/userAuthenticated').pipe(
        tap((response: any) => {
          this.loadingUser = false;
          this.UserData = response.data;
        })
      );
    } else {
      await firstValueFrom(this.http.get('/userAuthenticated'));
      return of(this.UserData);
    }
  }

Answer 6

One of the notable features of Rxjs is the firstValueFrom() function, which allows you to get a promise that can be awaited.

  async fetchUser(): Promise<Observable<any>> {
    if (!this.loadingUser) {
      this.loadingUser = true;
      return this.http.get('/userAuthenticated').pipe(
        tap((response: any) => {
          this.loadingUser = false;
          this.UserData = response.data;
        })
      );
    } else {
      await firstValueFrom(this.http.get('/userAuthenticated'));
      return of(this.UserData);
    }
  }

Pause and be patient while in the function that delivers an observable

Answer №1

Answer №2

Answer №3

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