Can't subscribe to results of combineLatest - firebase

Question

My app broke when I updated to RxJS 6. I got most of it working but this one method has me stumped.
Previously we had an array of observables being flatMapped and then used combineLatest like this:
const newObservable = myArrayOfObservables
.flatMap(observables => {
return Observable.combineLatest(observables);
});
And I could subscribe to the newObservable and get an array of the latest outputs from all the others.
Now I'm trying to do something like this:
const mergedList$ = chatList$.pipe(
mergeMap(res => {
return combineLatest(res);
}));
This gives me one of those really long and convoluted
Argument of type '(res: Observable<{ $key: string; }>[]) => OperatorFunction<{}, [{}, Observable<{ $key: string; }>]>' is not assignable to parameter of type '(value: Observable<{ $key: string; }>[], index: number) => ObservableInput<{}>'.
Type 'OperatorFunction<{}, [{}, Observable<{ $key: string; }>]>' is not assignable to type 'ObservableInput<{}>'.
Type 'OperatorFunction<{}, [{}, Observable<{ $key: string; }>]>' is not assignable to type 'Iterable<{}>'.
Property '[Symbol.iterator]' is missing in type 'OperatorFunction<{}, [{}, Observable<{ $key: string; }>]>'.
which quite frankly my dyslexia prevents me from parsing.
If I just return res in the above, and then try
const mergeCombo = combineLatest(mergedList$);
now mergeCombo is not an observable. Instead it's a
OperatorFunction<{}, [{}, Observable<{
$key: string;
}>]>
It could be worth noting that my original observables are being emitted by AngularFireObject.snapshotChanges()

Answer 1

You don't show how you imported combineLatest. It sort of looks like you are importing it as an operator, which has been deprecated.
Make sure you import it like so:
import {combineLatest} from "rxjs";
Then your original code should work just fine:
const mergedList$ = chatList$.pipe(
mergeMap(res => combineLatest(res))
);