README

Combine-Promises

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Like Promise.all(array) but with an object.

import combinePromises from 'combine-promises';

const { user, company } = await combinePromises({
  user: fetchUser(),
  company: fetchCompany(),
});

Why:

Insensitive to destructuring order typos
Simpler async functional code

Features:

TypeScript support
Lightweight
Feature complete
Well-tested
ESM / CJS

TypeScript support

Good, native and strict TypeScript support:

Return type correctly inferred from the input object
All object values should be async
Only accept objects (reject arrays, null, undefined...)

const result: { user: User; company: Company } = await combinePromises({
  user: fetchUser(),
  company: fetchCompany(),
});

Insensitive to destructuring order

A common error with Promise.all is to have a typo in the destructuring order.

// Bad: destructuring order reversed
const [company, user] = await Promise.all([fetchUser(), fetchCompany()]);

This code becomes particularly dangerous as size of the array promise grows over time.

With combinePromises, you are using explicit names instead of array indices, which makes the code more robust and not sensitive to destructuring order:

// Good: we don't care about the order anymore
const { company, user } = await combinePromises({
  user: fetchUser(),
  company: fetchCompany(),
});

Simpler async functional code

Suppose you have an object representing a friendship like {user1: "userId-1", user2: "userId-2"}, and you want to transform it to {user1: User, user2: User}.

You can easily do that:

import combinePromises from 'combine-promises';
import { mapValues } from 'lodash';

const friendsIds = { user1: 'userId-1', user2: 'userId-2' };

const friends = await combinePromises(mapValues(friendsIds, fetchUserById));

Without this library: good luck to keep your code simple.

Inspirations

Name inspired by combineReducers from Redux.