Promise.allSettled() - JavaScript | MDN (original) (raw)

Baseline

Widely available

The Promise.allSettled() static method takes an iterable of promises as input and returns a single Promise. This returned promise fulfills when all of the input's promises settle (including when an empty iterable is passed), with an array of objects that describe the outcome of each promise.

Try it

const promise1 = Promise.resolve(3);
const promise2 = new Promise((resolve, reject) =>
  setTimeout(reject, 100, "foo"),
);
const promises = [promise1, promise2];

Promise.allSettled(promises).then((results) =>
  results.forEach((result) => console.log(result.status)),
);

// Expected output:
// "fulfilled"
// "rejected"

Syntax

Promise.allSettled(iterable)

Parameters

iterable

An iterable (such as an Array) of promises.

Return value

A Promise that is:

• Already fulfilled, if the iterable passed is empty.
• Asynchronously fulfilled, when all promises in the given iterable have settled (either fulfilled or rejected). The fulfillment value is an array of objects, each describing the outcome of one promise in the iterable, in the order of the promises passed, regardless of completion order. Each outcome object has the following properties:
  status
  A string, either "fulfilled" or "rejected", indicating the eventual state of the promise.
  value
  Only present if status is "fulfilled". The value that the promise was fulfilled with.
  reason
  Only present if status is "rejected". The reason that the promise was rejected with.
  If the iterable passed is non-empty but contains no pending promises, the returned promise is still asynchronously (instead of synchronously) fulfilled.

Description

The Promise.allSettled() method is one of the promise concurrency methods. Promise.allSettled() is typically used when you have multiple asynchronous tasks that are not dependent on one another to complete successfully, or you'd always like to know the result of each promise.

In comparison, the Promise returned by Promise.all() may be more appropriate if the tasks are dependent on each other, or if you'd like to immediately reject upon any of them rejecting.

Examples

Using Promise.allSettled()

Promise.allSettled([
  Promise.resolve(33),
  new Promise((resolve) => setTimeout(() => resolve(66), 0)),
  99,
  Promise.reject(new Error("an error")),
]).then((values) => console.log(values));

// [
//   { status: 'fulfilled', value: 33 },
//   { status: 'fulfilled', value: 66 },
//   { status: 'fulfilled', value: 99 },
//   { status: 'rejected', reason: Error: an error }
// ]

Specifications

Browser compatibility

See also