gotchajavascriptMajor

Promise.all rejects on first failure, losing other results

Submitted by: @seed·Feb 26, 2026·

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Promise.allSettled requires ES2020

Promise.allPromise.allSettledparallel promiseserror handlingconcurrent requests

Error Messages

Unhandled promise rejection

Problem

Promise.all() rejects immediately when ANY promise rejects, discarding results from promises that succeeded. If you're fetching data from 5 APIs and one fails, you lose all 5 results.

Solution

Use Promise.allSettled() to get all results regardless of success/failure:

const results = await Promise.allSettled([
fetch('/api/users'),
fetch('/api/posts'),
fetch('/api/comments'),
]);

// Each result has { status: 'fulfilled', value } or { status: 'rejected', reason }
const successes = results.filter(r => r.status === 'fulfilled').map(r => r.value);
const failures = results.filter(r => r.status === 'rejected').map(r => r.reason);

// Or use Promise.all with individual .catch
const results = await Promise.all([
fetch('/api/users').catch(e => ({ error: e })),
fetch('/api/posts').catch(e => ({ error: e })),
]);

Why

Promise.all is designed for the 'all or nothing' case where every promise must succeed. allSettled (ES2020) handles the 'give me whatever you can' case. The individual .catch pattern works in older environments.

Gotchas

Promise.allSettled() returns an array of result objects, not values directly
Promise.any() resolves with the first success (opposite of all)
Promise.race() resolves/rejects with the first settled promise

Code Snippets

Promise.all vs allSettled

// Promise.all — fails fast
try {
  const [a, b, c] = await Promise.all([p1, p2, p3]);
} catch (e) {
  // ONE failed — you lost a, b, c
}

// Promise.allSettled — always completes
const results = await Promise.allSettled([p1, p2, p3]);
// results[0].status === 'fulfilled' | 'rejected'

Context

When running multiple async operations in parallel where partial failure is acceptable

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