The example below doesn't work as a straight conversion from the chained operator in version 5. It gives a Typescript compiler error.

```js
from([1, 2]).pipe(
    reduce((acc, curr) => {
        return acc + ' ';
    }, '')
);
```

> 
> Argument of type 'MonoTypeOperatorFunction' is not assignable
>  to parameter of type 'OperatorFunction'. Types of
>  parameters 'source' and 'source' are incompatible.
>  Type 'Observable' is not assignable to type 'Observable'.
>  Type 'number' is not assignable to type 'string'. [2345]
> 
> 
>