PromiseQueueAsyncGen

index.js

function aitGen() {
  let i = 1;
  return {
    async next() {
      if(i > 5) return  Promise.resolve({ value: void 0, done: true });
      const res = await fetch(`https://jsonplaceholder.typicode.com/posts/${i++}`).then(x => x.json());
      return Promise.resolve({ value: res, done: false });
    }
  }
}

const ait = aitGen();


// general time consistency is lost, because e.g. the fifth call could end before the others
// but the 'i' state is correctly shared so the fifth call is correctly requesting the element number five to the source
// and the last call will correctly receive { done: true }
;(async () => {
  ait.next();
  ait.next();
  ait.next();
  ait.next();
  console.log(await ait.next()); // { done: false, value: { userId: 1, id: 5, title: ... } }
  
  console.log(await ait.next()); // { done: true, value: undefined }
})();