async function* gen() {
  const x = yield 1;
  const y = yield x + 1;
  return x + y;
}

async function main() {
  const it = gen();
  const a = await it.next();
  const b = await it.next(10);
  const c = await it.next(20);
  console.log(`${a.value} ${b.value} ${c.value} ${c.done}`);
}

main();