An improved method for merging data from numerous RxJS observables

Question

An improved method for merging data from numerous RxJS observables

Within the ngOnInit() method, I am implementing the following:

  ngOnInit() {
    const exerciseObs = this.wodService.getAllExercises().pipe(take(1), map(data => {
      return {exercises: data};
    }));
    const userObs = this.accountService.getAccountInformationObservable().pipe(take(1), map(data => {
      return {user: data};
    }));

    forkJoin([exerciseObs, userObs]).subscribe(data => {
      this.exercises = data[0].exercises as unknown as Exercise[];
      this.user = data[1].user as unknown as CWUser;
    });
  }

I am combining the results of two observables and then assigning the retrieved data to two different component properties. However, the conversion to 'unknown' followed by explicit typing seems awkward, but I have not been able to find another way to merge them without utilizing a switchMap function and performing the data merging within it. Despite feeling slightly off due to the returned array format and casting peculiarities, I believe that this approach offers a cleaner and more concise solution.

What aspect or detail am I possibly overlooking in this scenario?

typescript rxjs observable

Answer 1

Answer №1

If you want to streamline your code and ensure type safety, consider deconstructing the tuple returned by forkJoin instead of using unnecessary gymnastics with the data:

ngOnInit() {
  const exerciseObs = this.wodService.getAllExercises().pipe(take(1));
  const userObs = this.accountService.getAccountInformationObservable().pipe(take(1));

  forkJoin([exerciseObs, userObs]).subscribe({
    next: ([exercises, user]) => {
      this.exercises = exercises;
      this.user = user; 
    }
  });
}

Check out the Stackblitz example here. You can find the code in hello.component.ts.

Answer 2

If you want to streamline your code and ensure type safety, consider deconstructing the tuple returned by forkJoin instead of using unnecessary gymnastics with the data:

ngOnInit() {
  const exerciseObs = this.wodService.getAllExercises().pipe(take(1));
  const userObs = this.accountService.getAccountInformationObservable().pipe(take(1));

  forkJoin([exerciseObs, userObs]).subscribe({
    next: ([exercises, user]) => {
      this.exercises = exercises;
      this.user = user; 
    }
  });
}

Check out the Stackblitz example here. You can find the code in hello.component.ts.

Answer 3

Answer №2

By providing the types when declaring both constants above, you eliminate the need for any explicit type assertion when subscribing to the forkjoin of these observables.

const exerciseObs: Observable<Exercise[]> = this.wodService.getAllExercises()
  .pipe(
    take(1), 
    map(data => ({
      exercises: data,
    }))
);
const userObs: Observable<userObs>  = this.accountService.getAccountInformationObservable()
  .pipe(
    take(1), 
    map(data => ({
      user: data,
    }))
);

Answer 4

By providing the types when declaring both constants above, you eliminate the need for any explicit type assertion when subscribing to the forkjoin of these observables.

const exerciseObs: Observable<Exercise[]> = this.wodService.getAllExercises()
  .pipe(
    take(1), 
    map(data => ({
      exercises: data,
    }))
);
const userObs: Observable<userObs>  = this.accountService.getAccountInformationObservable()
  .pipe(
    take(1), 
    map(data => ({
      user: data,
    }))
);

An improved method for merging data from numerous RxJS observables

Answer №1

Answer №2

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