FilipBartos

let isAlreadyFetchingAccessToken = false
let subscribers = []

function onAccessTokenFetched(access_token) {
  subscribers = subscribers.filter(callback => callback(access_token))
}

function addSubscriber(callback) {
  subscribers.push(callback)
}

indatawetrust

const waterfall = async function (input, ...funcs) {
  const list = []

  for(let f of funcs)
    if(!list.length)
      list.push(await f(input))
    else
      list.push(await f(list.shift())
  
  return list.pop()