How to pass concatMap projection to subscribe next?-CodePudding

How can I use the concatMap projection in the subscribe.next()?

    private onSomethingChange(): Subscription {
        // somethingChanged is a Subject
        return this.somethingChanged.pipe(
            concatMap(somethingProjection =>
                combineLatest([
                    this.firstObservable(somethingProjection),
                    this.secondObservable()
                ])
            )).subscribe(([firstResponse, secondResponse]) => {
                // I need to use somethingProjection here too
        });
    }

I found suggestions to use RxJS map, but I haven't found a way to use it correctly:

    private onSomethingChange(): Subscription {
        // somethingChanged is a Subject
        return this.somethingChanged.pipe(
           concatMap(somethingProjection =>
               combineLatest([
                   this.firstObservable(somethingProjection),
                   this.secondObservable()
               ]).pipe(map(([firstResponse, secondResponse]) => [somethingProjection, firstResponse, secondResponse])
           )).subscribe(([somethingProjection, firstResponse, secondResponse]) => {
               // ...
        });
   }

In the first code snippet, each item in the subscribe projection is of the correct type. If I replace the projection with just response, its type would be [firstResponseType, secondResponseType].
In the second code snippet, each item in the subscribe projection is of type somethingProjectionType | firstResponseType | secondResponseType. If I replace the projection with just response, its type would be (somethingProjectionType | firstResponseType | secondResponseType)[].
How to pass somethingProjection to the subcribe next so that each item in the array descrtion is of the correct type?

CodePudding user response：

Instead of returning an array from the map operator, you have to return an object with the required properties.

You can try something like the following:

private onSomethingChange(): Subscription {
  // somethingChanged is a Subject
  return this.somethingChanged
    .pipe(
      concatMap((somethingProjection) =>
        combineLatest([
          this.firstObservable(somethingProjection),
          this.secondObservable(),
        ]).pipe(
          map(([firstResponse, secondResponse]) => ({
            somethingProjection,
            firstResponse,
            secondResponse,
          }))
        )
      )
    )
    .subscribe(({ somethingProjection, firstResponse, secondResponse }) => {
      // ...
    });
}