windowfetch.js

const delay = t => new Promise(res => setTimeout(() => res(), t))

const arr = Array(5).fill()

const delayed = async function* delayed(arr, t = 1000) {
  for(const el of arr) {
    yield delay(t)
  }
}

const it = delayed(arr)

;(async () => {
  let dArr
  let pDArr
  let tPDArr
  let notDone = true

  while (notDone) {
    dArr = Array(3).fill().map(el => it.next())
    pDArr = Promise.all(dArr)
    tPDArr = await pDArr
    notDone = !tPDArr.find(el => el.done)
  }
})()

for await (const el of delayed(arr)) {
  // one el at a time
}