const delay = (ms, val) => new Promise(res => setTimeout(res, ms, val));

async function* asyncGen() {
  yield await delay(10, "alpha");
  yield await delay(10, "beta");
  yield await delay(10, "gamma");
}

async function run() {
  const results = [];

  const gen = asyncGen();
  const [first, , third] = await Promise.all([
    gen.next(),
    gen.next(),
    gen.next()
  ]);

  results.push(first.value, third.value);

  const p1 = Promise.resolve("x").then(v => v + "1");
  const p2 = Promise.reject("err").catch(e => e + "2");

  results.push(...(await Promise.all([p1, p2])));
  console.log(results);
}

run();