RxJS convert Observable<string[]> into Observable<string>

Question

RxJS 5.5.6. I'm trying to convert an Observable<string[]> into Observable<string>

I'm not sure if mergeAll operator is what I'm looking for

const o1: Observable<string[]> = of(['a', 'b', 'c']);
const o2: Observable<string> = o1.pipe(
  mergeAll()
);

Typescript will return this error:

Type 'Observable<string | string[]>' is not assignable to type 'Observable<string>'.
  Type 'string | string[]' is not assignable to type 'string'.
    Type 'string[]' is not assignable to type 'string'.

I receive Observable as parameter and I can change the way is constructed.

Answer 1

It looks like you've encountered an already reported RxJS issue, see https://github.com/ReactiveX/rxjs/issues/2759 and even more recent https://github.com/ReactiveX/rxjs/issues/3290.

From the comments it looks like it won't be fixed until RxJS 6.

However you can always use mergeMap(o => o)/concatMap(o => o) instead of mergeAll()/concatAll().

For example:

const o1: Observable<string[]> = of(['a', 'b', 'c']);
const o2: Observable<string> = o1.pipe(
  mergeMap(o => o)
);