Admin-only React components with Flow

AdminOnly.jsx

// @flow
import React from 'react'
import type { AdminProof } from './User'

export default function AdminOnly(props: { proof: AdminProof }) {
  return <p>Secret admin stuff!</p>
}

App.jsx

// @flow

import React from 'react'
import AdminOnly from './AdminOnly'
import { checkIfAdmin } from './User'

function App() {
  const currentUser = ...
  const proof = checkIfAdmin(currentUser)
  if (proof != null) {
    return <AdminOnly proof={proof} />
  } else {
    return <p>Nothing to see here...</p>
  }
}

User.js

// @flow

class _AdminProof {}
export type AdminProof = _AdminProof

export function checkIfAdmin(user: { isAdmin: bool }): ?AdminProof {
  if (user.isAdmin) {
    return new _AdminProof
  }
}