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JavaScript

What is a Promise.all Rejected?

← Errors

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

JavaScript

Code that triggers the error

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

Error output

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

How to fix it

Use Promise.allSettled() to get the results of all promises regardless of individual failures. Filter the results by status === 'fulfilled' to extract successful values. Use Promise.all() only when you want all-or-nothing semantics.

Fixed code

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

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