Skip to content
This repository has been archived by the owner on Jan 26, 2022. It is now read-only.


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time
January 30, 2019 10:52
January 30, 2019 11:48
January 30, 2019 10:52
January 30, 2019 11:07
August 10, 2020 07:35

ECMAScript proposal: Promise.any + AggregateError

Author: Mathias Bynens, Kevin Gibbons, Sergey Rubanov

Champion: Mathias Bynens

Stage: Stage 4 of the TC39 process.


There are four main combinators in the Promise landscape.

name description
Promise.allSettled does not short-circuit added in ES2020 ✅
Promise.all short-circuits when an input value is rejected added in ES2015 ✅
Promise.race short-circuits when an input value is settled added in ES2015 ✅
Promise.any short-circuits when an input value is fulfilled this proposal 🆕 scheduled for ES2021

These are all commonly available in userland promise libraries, and they’re all independently useful, each one serving different use cases.

Proposed solution

Promise.any accepts an iterable of promises and returns a promise that is fulfilled by the first given promise to be fulfilled, or rejected with an AggregateError holding the rejection reasons if all of the given promises are rejected. (If something more fundamental goes wrong, e.g. iterating over the iterable results in an exception, Promise.any returns a rejected promise with that exception.)

High-level API

try {
  const first = await Promise.any(promises);
  // Any of the promises was fulfilled.
} catch (error) {
  // All of the promises were rejected.

Or, without async/await:

  (first) => {
    // Any of the promises was fulfilled.
  (error) => {
    // All of the promises were rejected.

In the above examples, error is an AggregateError, a new Error subclass that groups together individual errors. Every AggregateError instance contains a pointer to an array of exceptions.


Why choose the name any?

It clearly describes what it does, and there’s precedent for the name any in userland libraries offering this functionality:

Why throw an AggregateError instead of an array?

The prevailing practice within the ECMAScript language is to only throw exception types. Existing code in the ecosystem likely relies on the fact that currently, all exceptions thrown by built-in methods and syntax are instanceof Error. Adding a new language feature that can throw a plain array would break that invariant, and could be a web compatibility issue. Additionally, by using an Error instance (or a subclass), a stack trace can be provided — something that’s easy to discard if not needed, but impossible to obtain later if it is needed.

Illustrative examples

This snippet checks which endpoint responds the fastest, and then logs it.

  fetch('').then(() => 'home'),
  fetch('').then(() => 'blog'),
  fetch('').then(() => 'docs')
]).then((first) => {
  // Any of the promises was fulfilled.
  // → 'home'
}).catch((error) => {
  // All of the promises were rejected.

TC39 meeting notes