Async iterators

for.async.js

const delay = ms => new Promise(resolve => setTimeout(resolve, ms))
const inc = async i => (await delay(500), ++i)

const foo = async () => {
  for(let i = 1; i <= 5; i = await inc(i)) 
    console.log(i) // prints 1, 2, 3, 4, 5 with a delay 
}

foo()

while.async.js

const delay = ms => new Promise(resolve => setTimeout(resolve, ms))
const dec = async i => (await delay(500), --i)

const foo = async () => {
  let i = 5;
  
  while(i = await dec(i)) 
    console.log(i) // prints 4, 3, 2, 1 with a delay 
}

foo()