mapSeries without bluebird

native-promise-bluebird-mapSeries-alternative.js

// credit: https://hackernoon.com/functional-javascript-resolving-promises-sequentially-7aac18c4431e


const N = 5
const promiseSerial = funcs =>
  funcs.reduce(
    (promise, func) =>
      promise.then(result => func().then(Array.prototype.concat.bind(result))),
    Promise.resolve([])
  )

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms))

const jobs = Array(N)
  .fill(null)
  .map((_, i) => i + 1)
  .map(k => {
    return () => {
      return sleep(100).then(() => Promise.resolve(`result from ${k}`))
    }
  })

promiseSerial(jobs).then(data => console.log(data))