Async polling generator function with stop condition

poll-value-until-done.js

const wait = (time) => {
  return new Promise((resolve) => {
    setTimeout(resolve, time);
  });
};

// Fake polling data
const fakeData = [null, null, null, { data: { foo: 'bar' } }];

let i = 0;

// Fake fetch of real time data
async function fakeFetch(url) {
  if (i === fakeData.length) i = 0;
  const currentData = fakeData[i++];
  return currentData;
}

// Function that calls an endpoint repeatedly and yields the result
// for a duration of "max" ms in intervals of "interval" ms
async function* createPoller({ url, max = 10000, interval = 500 }) {
  for (let time = 0; time <= max; time += interval) {
    const data = await fakeFetch(url);
    yield data;
    await wait(interval);
  }
}

// Consumes the poller generator and stops
// when the "isDone" callback returns true, with data
async function runPollerUntilDone({ poller, isDone }) {
  for await (const data of poller) {
    if (isDone(data)) {
      return data;
    }
  }
  return null;
}

// Create poller
const dataPoller = createPoller({
  max: 5000,
  interval: 500,
});

// Execute the poller and stop when data is found
const data = await runPollerUntilDone({
  poller: dataPoller,
  isDone: (_data) => Boolean(_data),
});

console.log(data);