How to transform Observable<string[]> to Observable<string> using RxJS

Currently, I am facing the task of converting an Observable<string[]> to an Observable<string>

I'm uncertain whether the mergeAll operator is the solution for this scenario.

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

The error generated by TypeScript states:

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'.

An Observable is passed as a parameter and the construction method can be altered.

typescriptrxjsrxjs5

Answer №1

Looks like you've come across a known issue with RxJS, check out the discussion at https://github.com/ReactiveX/rxjs/issues/2759 or the more recent one at https://github.com/ReactiveX/rxjs/issues/3290.

Based on the feedback provided, it seems that this issue won't be addressed until the release of RxJS 6.

As a workaround, consider using mergeMap(o => o) or concatMap(o => o) instead of mergeAll() or concatAll().

Here's an example:

const observable1: Observable<string[]> = of(['a', 'b', 'c']);
const observable2: Observable<string> = observable1.pipe(
  mergeMap(o => o)
);

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