props are returned as string instead of object

Question

I'm currently implementing user authentication on my website, and I'm trying to restrict access to the login and signup pages if the user is logged in. To do so, I am implementing this getServerSideProps to redirect the user if they're logged in:

export async function getServerSideProps(context) {
  if (context.req.cookies.user) {
    return {
      redirect: {
        destination: '/',
        permanent: true,
      },
    }
  }
  return {}
}

If I return an empty object ({}), next gives me this error:

Reason: Props must be returned as a plain object from getServerSideProps: `{ props: { ... } }` (received: `[object Array]`).

If instead of returning {}, I return

{
  props: {}
}

the code works all right. Does anyone know why this is happening?

I'm using a custom _app.jsx file.

In the documentation, it's clearly mentioned that the props argument is optional:

Answer 1

This is actually intended. If you were using TypeScript, return {} would have thrown you error as GetServerSidePropsResult is defined like this here:

export type GetServerSidePropsResult<P> =
  | { props: P | Promise<P> }
  | { redirect: Redirect }
  | { notFound: true }

It means that any one of props, redirect, notFound needs to be present in the returned object. Perhaps you can create an issue at their GitHub (and maybe a PR) to fix the documentation.