Simple promise waterfall.

waterfall.ts

function waterFallExec<T, S>(listOfItems: T[], func: (item: T) => Promise<S>): Promise<S[]> {
  const results: S[] = []
  return listOfItems.reduce(function (lastPromise, item) {
    return lastPromise.then(function (res) {
      return func(item).then(function (result) {
        res.push(result);
        return res;
      });
    });
  }, Promise.resolve(results));
}



const promiseOfResults = waterFallExec(['1', '2', '3'], (item) => {
  return Promise.resolve(
    parseInt(item, 10)
  );
});

promiseOfResults.then((results) => {
  console.log(results);
})