promise-sequential/index.js

Simple like Promise.all(), but sequentially!

module.exports = function (promises) {

  if (!Array.isArray(promises)) {
    throw new Error('First argument need to be an array of Promises');
  }

  return new Promise((resolve, reject) => {

    let count = 0;
    let results = [];

    const iterateeFunc = (previousPromise, currentPromise) => {
      return previousPromise
        .then(function (result) {
          if (count++ !== 0) results = results.concat(result);
          return currentPromise(result, results, count);
        })
        .catch((err) => {
          return reject(err);
        });
    }

    promises = promises.concat(() => Promise.resolve());

    promises
    .reduce(iterateeFunc, Promise.resolve(false))
    .then(function (res) {
      resolve(results);
    })

  });
};