serialFetchGen.js

const mockFetch = url => new Promise(
  res => setTimeout(
    x => res(`url:${url} mockFetched`)
    , 300
  )
)

var arr = ["a", "e", "i", "o", "u"]

const serial_____Gen = fn => async function* serial (arr) {
  for (const url of arr) {
    yield fn(url)
  }
}
const serialFetchGen = serial_____Gen(mockFetch)

;(async function(){
  for await(const data of serialFetchGen(arr)) {
    console.log(data)
  }
return 'async ends'
})().then(console.log)