The documentation recommends using the static assets approach and says:
"You can add the JS Interop file as a static asset from our package, instead of using a CDN. Static assets (the _content folder) are automatically included in the solution by the Nuget package, so all that's needed is then to reference the asset:"
There is no _content folder (using ZIP archive with private .nupgk files, version 2.5.0) and no assets.
Regards
Heiko