const gservices = {
  fetchUsers: (nextPageToken, result) => {
    return Promise.try(() => {
      return admin.users.list({
        domain: '',
        maxResults: 40,
        pageToken: nextPageToken || '',
      })
    }).then(resp => {
      result = [...result || [], ...resp.data.users]
      if (resp.data.nextPageToken) gservices.fetchUsers(resp.data.nextPageToken, result)
      else return result
    })
  }
}