Ways to resolve the error message "Type 'Promise<{}>' is missing certain properties from type 'Observable<any>'" in Angular

Check out this code snippet:

 const reportModules = [
      { url: '', params: { to: format(TODAY, DATE_FORMAT).toString(), from: format(TODAY, DATE_FORMAT).toString() } },
      {
        url: 'application1',
        params: { to: format(TODAY, DATE_FORMAT).toString(), from: format(TODAY, DATE_FORMAT).toString() }
      },
      {
        url: 'application2',
        params: {
          to: format(endOfWeek(TODAY), DATE_FORMAT).toString(),
          from: format(startOfWeek(TODAY), DATE_FORMAT).toString()
        }
      },
      {
        url: 'application3',
        params: {
          to: format(endOfWeek(TODAY), DATE_FORMAT).toString(),
          from: format(startOfWeek(TODAY), DATE_FORMAT).toString()
        }
      }
    ];

    const promises = reportModules.map(
  target =>
    new Promise(resolve => {
      this.notificationService
        .getSummary(target.url, target.params)
        .pipe(take(1))
        .subscribe(
          (result: Response) => {
            resolve({ target, result });
          },
          (err: Error) => {
            // return reject(err);
          }
        );
    })
);
        const observables: Observable<any>[] = promises;

        merge(...observables).subscribe((results) => { ... }

Any thoughts on how to address the error message

let observables: Observable<any>[]
'observables' is declared but its value is never read.ts(6133)
Type 'Promise<{}>[]' is not assignable to type 'Observable<any>[]'.
  Type 'Promise<{}>' is missing the following properties from type 'Observable<any>': _isScalar, source, operator, lift, and 6 more.ts(2322)
?

The main objective here is to make sequential calls to load data from different applications in order.

For instance, it starts with the call to 'application1' followed by 'application2', ensuring a step-by-step process for each application.

Answer №1

Your code has a mistake in the final two lines. You are trying to assign a list of promises to a list of observables, which are different types of objects.

An easy solution would be to stick with Promises and replace merge() with Promise.all().

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