async-queue.js

function makeAsyncQueue() {
  let promise;
  let resolve;
  const queue = [];

  const setPromise = () => {
    promise = new Promise(res => {
      resolve = res;
    });
  };

  setPromise();

  let isDone;
  const send = v => {
    if (!isDone) {
      queue.push(v);
      if (queue.length === 1) resolve();
    }
  };

  const DONE = Symbol("done");
  const done = () => {
    send(DONE);
  };

  const generator = async function*() {
    let v;
    while (true) {
      if (!queue.length) await promise;
      v = queue.shift();
      if (v === DONE) {
        isDone = true;
        queue.length = 0;
        break;
      }
      if (!queue.length) setPromise();
      yield v;
    }
  };

  return {
    done,
    iterator: generator(),
    send
  };
}

(async () => {
  {
    const { done, iterator, send } = makeAsyncQueue();

    setTimeout(() => send(1), 1000);
    setTimeout(() => send(2), 2000);
    setTimeout(() => send(3), 3000);
    setTimeout(done, 4000);
    setTimeout(() => send(4), 5000); // won't print `x: 4` because it's already done

    for await (const x of iterator) {
      console.log("x:", x);
    }
  }

  console.log("-----------------");

  {
    const { iterator, send } = makeAsyncQueue();

    for (let i = 1; i <= 100; i++) {
      setTimeout(() => send(i), 0);
    }

    for await (const y of iterator) {
      console.log("y:", y);
    }
  }
})();