JavaScript polling

poll.js

// fn: () => Promise<Boolean>
const poll = (fn, interval = 100, maxWait = 60000) => {
  const start = Date.now();
  let last = 0;

  return new Promise((resolve, reject) => {
    const _poll = () => {
      const now = Date.now();
      console.log(start, last, now, interval);
      if (now > start + maxWait) {
        reject('Polling maxWait exceeded');
        return;
      }
      if (now > last + interval) {
        last = Date.now();
        fn()
          .then(predicate => predicate ? resolve(predicate) : _poll())
          .catch(_poll);
      } else {
        setTimeout(_poll, last + interval - now);
      }
    };
    _poll();
  });
};

Nice JavaScript