JavaScriptAsyncIntermediate

Promise.allSettled()

Waits for all promises and returns each outcome (fulfilled/rejected).

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Promise.allSettled([promise1, promise2, ...])
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What it does

Overview

Waits for all promises and returns each outcome (fulfilled/rejected).

Promise.allSettled() is a static method introduced in ES2020 that returns a promise that resolves after all given promises have either fulfilled or rejected. Unlike Promise.all(), which follows a 'fail-fast' approach and rejects immediately if any input promise fails, allSettled() ensures that every operation in the iterable completes before resolving. This makes it ideal for handling collections of independent asynchronous tasks where the success of one does not depend on the success of others. Each element in the resulting array is an object with a status property ('fulfilled' or 'rejected'). If the status is 'fulfilled', a value property is present; if 'rejected', a reason property provides the error. Performance-wise, it waits for the slowest promise to settle. If an empty iterable is passed, it returns a promise that resolves to an empty array immediately. IE not supported.

Quick reference

Syntax

Promise.allSettled([promise1, promise2, ...])

Inputs

Parameters

iterableIterable<Promise> · Promises (or values) to await.

See it in practice

Examples

1

Handling Mixed Success and Failure

var p1 = Promise.resolve(100);
var p2 = Promise.reject(new Error('Operation Failed'));
var p3 = new Promise(function(resolve) { setTimeout(resolve, 100, 'Delayed'); });

Promise.allSettled([p1, p2, p3]).then(function(results) {
  results.forEach(function(result) {
    console.log(result.status);
  });
});
Output:
"fulfilled" "rejected" "fulfilled"

Demonstrates how allSettled captures both the resolution of p1 and p3 and the rejection of p2 without stopping execution.

2

Filtering Successful Results from API Calls

var urls = ['/api/items/1', '/api/items/2'];
var requests = urls.map(function(url) { return fetch(url); });

Promise.allSettled(requests).then(function(results) {
  var successfulResponses = results
    .filter(function(res) { return res.status === 'fulfilled'; })
    .map(function(res) { return res.value; });
  console.log('Total successful:', successfulResponses.length);
});
Output:
"Total successful: 2" (if both fetches succeed)

Useful for bulk operations where you want to process whatever succeeded and ignore or log the failures separately.

3

Edge Case: Empty Iterable

Promise.allSettled([]).then(function(results) {
  console.log(Array.isArray(results));
  console.log(results.length);
});
Output:
true 0

Passing an empty array results in an immediately resolved promise with an empty array as the value.

Debug faster

Common Errors

1

LogicError

Cause: Assuming the returned promise will reject if one of the input promises rejects.

Fix: Remember that Promise.allSettled() itself only rejects if the input is not iterable. Use .then() and inspect the status of individual objects.

Promise.allSettled([Promise.reject('fail')]).catch(function(err) { 
  // This block will NOT run for the rejected input promise
  console.log(err);
});
2

TypeError

Cause: Accessing the 'value' property on a result object without checking its status first.

Fix: Always check if status === 'fulfilled' before accessing 'value', or status === 'rejected' before accessing 'reason'.

Promise.allSettled([p1, p2]).then(function(results) {
  results.forEach(function(r) {
    // Error: r.value is undefined if the promise was rejected
    console.log(r.value.toLowerCase());
  });
});

Runtime support

Compatibility

Node.js, BrowserAll modern browsersES2020

Source: MDN Web Docs

Common questions

Frequently Asked Questions

Waits for all promises and returns each outcome (fulfilled/rejected).

iterable: Promises (or values) to await.

LogicError: Remember that Promise.allSettled() itself only rejects if the input is not iterable. Use .then() and inspect the status of individual objects. TypeError: Always check if status === 'fulfilled' before accessing 'value', or status === 'rejected' before accessing 'reason'.