useSWR mutate(undefined) doesn't revalidate other windows

Question

I use uswSWR to handle user authentication:

export function useAuthenticatedUser() {
    const { data, error, isLoading, mutate } = useSWR("user",
        UserApi.getAuthenticatedUser,
        {
            shouldRetryOnError(err) {
                return !(err instanceof UnauthorizedError)
            },
        }
    );
    return {
        user: data,
        userLoading: isLoading,
        userLoadingError: error,
        mutateUser: mutate,
    }
}

Because of SWR's automatic revalidation, this user is fetched again when a browser window or tab gains focus.

Problem: Revalidation doesn't work after logging out:

const { mutateUser } = useAuthenticatedUser();
async function logout() {
    try {
        await UserApi.logout();
        mutateUser(undefined);
    } catch (error) {
        console.error(error);
        alert(error);
    }
}

This recording shows the problem in action. Note that the window gaining focus revalidates after logging in but not after logging out.

Answer 1

The problem was that I didn't return null if the user was not logged in. Logout propagates properly if I mutate with null instead of undefined.

export function useAuthenticatedUser() {
    const { data, error, isLoading, mutate } = useSWR("user",
        async () => {
            try {
                return await UsersApi.getAuthenticatedUser();
            } catch (error) {
                if (error instanceof UnauthorizedError) {
                    return null;
                } else {
                    throw error;
                }
            }
        }
    );

    return {
        user: data,
        userLoading: isLoading,
        userLoadingError: error,
        mutateUser: mutate,
    }
}

Now mutate accepts null:

const { mutateUser } = useAuthenticatedUser();
async function logout() {
    try {
        await UserApi.logout();
        mutateUser(null); // undefined won't propagate between tabs
    } catch (error) {
        console.error(error);
        alert(error);
    }
}