Execute Promises in Sequence

executePromisesInSequence.js

/**
 * executePromisesInSequence
 *
 * Given an array of functions, each of which return a Promise,
 * fire off each promise in sequence, one after the other.
 *
 * @param {func[]} promises
 * @returns {Promise}
 */
module.exports = function executePromisesInSequence(promises, {
  willCatchErrors = true,
} = {}) {
  const successes = [];
  const errors = [];
  const onReduce = (promiseChain, currentTask) => {
    if (!promiseChain.then) {
      return Promise.resolve();
    }
    return promiseChain.then(() => {
      if (typeof currentTask !== 'function') {
        return Promise.resolve();
      }
      const invoked = currentTask();
      if (!invoked.then) {
        return Promise.resolve();
      }
      const executedPromise = invoked.then((currentResult) => {
        successes.push(currentResult);
      });
      if (willCatchErrors) {
        return executedPromise.catch((err) => {
          errors.push(err);
        });
      }
      return executedPromise;
    });
  };
  return promises
    .reduce(onReduce, Promise.resolve())
    .then(() => ({
      successes,
      errors,
    }));
};