Promise.allSettled with Object keys

labelledPromises.js

/**
 * Resolves all Promises from a key/val object, returning the same structure but resolved
 * @param {Object.<string, (function)>} obj - An object with any number of key-value pairs.
 * @returns {{ values: object, rejected: object }}
 */

const labelledPromises = async (obj) => {
  const keys = Object.keys(obj);
  const promises = Object.values(obj);
  const results = await Promise.allSettled(promises);

  const all = keys.reduce((acc, key, i) => {
    acc[key] = results[i];
    return acc;
  }, {});

  const rejected = Object.keys(all)
    .filter((key) => all[key].status === 'rejected')
    .reduce((acc, key) => {
      acc[key] = all[key].reason;
      return acc;
    }, {});

  const values = Object.keys(all).reduce((acc, key) => {
    acc[key] = all[key].value ?? undefined;
    return acc;
  }, {});

  return {
    values,
    rejected,
  };
};

module.exports = labelledPromises;

Given an object of labelled promises, get them back resolved with default support:

  const { values, rejected } = await labelledPromises({
    key1num: Promise.resolve(123),
    key2fail: Promise.reject(new Error("bang")),
    key3obj: Promise.resolve({}),
    key4str: Promise.resolve("hello"),
    key5nul: null,
    key6fal: false,
  });

Will result in:

  // {
  //     values: { key1num: 123, key2fail: undefined, key3obj: {}, key4str: 'hello', key5nul: undefined, key6fal: false },
  //     rejected: { key2fail: [Error: bang] }
  // }

NOTE: you can use object destructuring to assign defaults, e.g.

const { key1num = 1, key2fail = 2, key3obj = 3, key4str = 4, key5nul = 5, key6fal = 6 } = values;

console.log({ key1num, key2fail, key3obj, key4str, key5nul, key6fal });
// -> { key1num: 123, key2fail: 2, key3obj: {}, key4str: 'hello', key5nul: 5, key6fal: false }