javascript - RxJs pipe and lettable operator `map`: 'this' context of type 'void' is not assignable to method's 'this' of type 'Observable<{}>'

Question

I have this very basic example that uses lettable operator map with pipe from rxjs@5.5:

import { map } from 'rxjs/operator/map';

let o = of(1, 2, 3, 4).pipe(
    map((v) => v * 2)
);

But it produces the error Error:(34, 5) TS2684:The 'this' context of type 'void' is not assignable to method's 'this' of type 'Observable<{}>'. What's the problem here?

Answer 1

Lettable instance operators should be imported from rxjs/operators:

import { map } from 'rxjs/operators';

As opposed to non-lettable equivalents which are imported from rxjs/operator:

import { map } from 'rxjs/operator/map';

To learn more about lettable operator read:

• RxJS: Understanding Lettable Operators