Today I Learned

The challenge I encountered was accessing the Meteor.user() in React Router's route loader property.

Alternatively, instead of querying the server, I'm picking up the user id from localStorage. The absence of it indicates the user is logged off or never logged in. Until Meteor kicks off, no sensitive data is displayed anyway.

...
{
  path: '/',
  element: <App />,
  errorElement: <ErrorPage />,
  loader: async () => window.localStorage.getItem('Meteor.userId'),
}
...

and in app.tsx:

const userId: UserId | null = useLoaderData()
const navigate = useNavigate()

useEffect(() => {
  if (userId === null) navigate('/login')
}, [userId])