withAccessToken

b.js

  const getAccessToken = () => {
    const pGetToken = db ? getAccessTokenFromDB() : Promise.resolve()

    return pGetToken.then(token => {
      if (token)  return token
      
      return getAccessTokenFromRemote()
      .then(data => {
        if (!data || !data.access_token) {
          throw new Error('No access token in token api response')
        }
        
        if (!db)  return data.access_token

        return db.ref('paypal_access_token')
        .set({
          access_token: data.access_token,
          expire: new Date() * 1 + data.expires_in * 1000
        })
        .then(() => data.access_token)
      })
    })
    .then(token => {
      console.log('Got paypal access token', token)
      jwtRequest.saveToken(token)
    })
    .catch(e => {
      console.error(e.stack)
    })
  }

test.js

  const withAccessToken = (fn) => (...args) => {
    const accessToken = jwtRequest.getToken()
    const p = accessToken ? Promise.resolve()
                          : getAccessTokenFromRemote().then(data => {
                            console.log('remote access token', data.access_token)
                            jwtRequest.saveToken(data.access_token)
                          })
  
    return p.then(() => fn(...args))
  }