Promise polling

README.md

Usage

promisePoll(
  // a function that takes no param and return a promise
  // `.bind(...)` as much a you want!
  () => { return aPromise; },
  // a function that will be called with the resolved value
  // of return value of the first function
  // and that should return true if the condition is satisfied
  (res) => { return res.prop = 'expectedValue'; },
  // wait: number of milliseconds between 2 function1 calls
  500,
  // failAfter: number of milliseconds between 2 function1 calls
  3000);

Gotcha

• We do not garantee that this function will take a most failAfterms: if the condition is never satisfied and failAfter is not a multiple of wait, then the returned promise might fail after Math.ceil(failAfter / wait) * wait ( which is > failAfter)

This will resolve after ~600ms:

let a = 1;
setTimeout(() => { a = 2; }, 500);
return promisePoll(
  function () { return Promise.resolve(a); },
  (res) => res === 2,
  200,
  1000
);

This is rejected after ~1000ms, even if failedAfter is 900:

let a = 1;
setTimeout(() => { a = 2; }, 5000);
return promisePoll(
  function () { return Promise.resolve(a); },
  (res) => res === 2,
  200,
  900
);

until.js

import Bluebird from 'bluebird';

const hasExpired = (startedAt, failAfter) => {
  return startedAt + failAfter < Date.now();
};

const PromisePoll = (promiseFunc, conditionFunction, wait = 500, failAfter = 4000) => {
  const startedAt = Date.now();

  return new Bluebird((resolve, reject) => {
    // to fail "exactly" after `failAfter`,
    // we have to reject in a `setInterval()`
    const interval = setInterval(() => {
      console.log('in setInterval...');
      if (hasExpired(startedAt, failAfter)) {
        clearInterval(interval);
        reject(new Error(`Promise Poll: cannot meet the condition after ${failAfter}ms`));
      }
    }, wait);
    // define a recursive function that gets executed
    // until timeout or the condition is satisfied
    const executeAndCheckCondition = () => {
      return promiseFunc()
        .then((res) => {
          if (hasExpired(startedAt, failAfter)) {
            // we already `reject()` in `setInterval()`
            return;
          }
          if (conditionFunction(res)) {
            // success
            clearInterval(interval);
            return resolve(res);
          }
          // no timeout and not satisfied? retry after `wait`ms
          Bluebird.delay(wait).then(executeAndCheckCondition);
        });
    };
    // execute the recursive function
    executeAndCheckCondition();
  });
};

export default PromisePoll;