checkAuth.js

function checkAuth(nextState, replaceState) {
  let { loggedIn } = store.getState();

  // check if the path isn't dashboard
  // that way we can apply specific logic
  // to display/render the path we want to
  if (nextState.location.pathname !== '/dashboard') {
    if (loggedIn) {
      if (nextState.location.state && nextState.location.pathname) {
        replaceState(null, nextState.location.pathname);
      } else {
        replaceState(null, '/');
      }
    }
  } else {
    // If the user is already logged in, forward them to the homepage
    if (!loggedIn) {
      if (nextState.location.state && nextState.location.pathname) {
        replaceState(null, nextState.location.pathname);
      } else {
        replaceState(null, '/');
      }
    }
  }
}