What is a Promise.all Rejected?

Promise.all() rejects immediately when any one of its input promises rejects, discarding the results of all other promises even if they succeed. This fail-fast behavior is intentional but can be surprising when you need the results of the successful promises.

Why it happens

• •One of the parallel requests fails while others succeed.
• •A network error, timeout, or non-OK HTTP status causes one promise to reject.
• •An exception thrown inside one of the async operations propagates as a rejection.

Examples

const results = await Promise.all([
  fetch("/api/users"),
  fetch("/api/missing-endpoint"),  // returns 404, then .json() throws
  fetch("/api/posts"),
]);

Uncaught (in promise) SyntaxError: Unexpected token '<', "<!DOCTYPE..." is not valid JSON

const results = await Promise.allSettled([
  fetch("/api/users").then(r => r.json()),
  fetch("/api/missing-endpoint").then(r => r.json()),
  fetch("/api/posts").then(r => r.json()),
]);
const succeeded = results
  .filter(r => r.status === "fulfilled")
  .map(r => r.value);

Related errors

• UnhandledPromiseRejection
• Fetch Network Error