run async functions sequentially via reduce

sequential-async.js

/**
 * Run a series of async/promisifed functions sequentially,
 * returning an array of results and errors.
 *
 * example:
 * const values = [1, 2, 3, 4, 5];
 * const callback = async (value) => await someAsyncThing(value)
 * const result = await sequentialAsync(values, callback);
 * 
 * @param  {Iterable} values
 * @param  {Function} callback
 * @return {Object}   object with .result and .errors arrays
 */
const sequentialAsync = (values, callback) => values.reduce(async (acc, value) => {
  const resultsObject = await acc;
  try {
    const result = await callback(value);
    return {
      ...resultsObject,
      results: [...resultsObject.results, result],
    };
  } catch (error) {
    return {
      ...resultsObject,
      errors: [...resultsObject.errors, error],
    };
  }
}, Promise.resolve({
  results: [],
  errors: [],
}));