Typescript syntax for a function that returns an observable or multiple type

Question

I have a function that returns observables from all widgets. There are two types of widgets. Here is what I tried and the IDE does not complain, but my compiler does:

public getAllWidgets(): Observable<WidgetType1 | WidgetType2> { ... } 

Answer 1

Observed <(WidgetType1 | WidgetType2) []>

An array was returned. The error was unclear.