Promise waterfall

waterfall.js

function promiseChain(list, getPromise) {
  return list.reduce((accPromise, entry) => {
    return accPromise.then(acc => {
      return getPromise(entry).then(result => {
        return acc.concat(result);
      });
    });
  }, Promise.resolve([]));
}

function getPromise(entry) {
  return new Promise((resolve, reject) => {
    setTimeout(() => resolve(entry * 2), 100);
  });
}

promiseChain([0,1,2], getPromise).then(result => console.dir(result));