'Observable' is not a class derived from 'Observable'

Question

When trying to extend a class from a class in a node_modules the typescript compiler throws a error saying:

Property \'source\' is protected but

Answer 1

For me it was my editor issue. VSCode was including an import from the declaration files (*.d.ts) while the actual class was in another place.

I replaced the declaration file import with the actual class file import.