let refreshingPromise = null

​

const refreshToken = createEffect(() => new Promise(rs => setTimeout(rs, 1000, Math.floor(Math.random() * 10000))))

const token = restore(refreshToken, null)

​

const authenticate = attach({

  source: token,

  effect: createEffect(async (token) => {

    if (refreshingPromise) return refreshingPromise

    if (token) return token

    try {

      return await (refreshingPromise = refreshToken())

    } finally {

      refreshingPromise = null

    }

  }),

})

​

refreshToken.watch(() => console.log('refreshing'))

authenticate.doneData.watch(token => console.log('authenticated ', token))

​

authenticate()

authenticate()

authenticate()

​

setTimeout(() => token.setState(null), 2000)

setTimeout(() => authenticate(), 2500)

setTimeout(() => authenticate(), 3000)

setTimeout(() => authenticate(), 4000)

setTimeout(() => authenticate(), 4500)

​

​