Async iterators!!!

async.js

async function mapAsync (iterator, fn) {
  let result = [];
  for ( let itemPromise of await iterator ) {
    let item = await itemPromise;
    result.push(await fn(item));
  }
  return result;
}

async function filterAsync (iterator, fn) {
  let result = [];
  for ( let itemPromise of await iterator ) {
    let item = await itemPromise;
    if ( await fn(item) ) {
      result.push(item);
    }
  }
  return result;
}

function * numbers () {
  for ( let i = 0; i < 10; i++ ) {
    yield Promise.resolve(i);
  }
}

const pow2 = (n) => Promise.resolve(n * n);
const isDivisibleBy2 = (n) => Promise.resolve(n !== 0 && !(n % 2));

mapAsync(filterAsync(numbers(), isDivisibleBy2), pow2).then((list) => {
  console.log(list); // [4,16,36,64]
});