redux-observable.js

const oauthUserEpic = (action$) => {
  let horribleSideEffect;

  return action$
    .ofType(OAUTH_USER)
    .concatMap(({ token }) => {
      horribleSideEffect = token;
      return get({
        endpoint: 'user',
        params: { access_token: token }
      });
    })
    .map((user) =>
      addUser(
        user.set('access_token', horribleSideEffect)
      )
    );
};