Promise.any(): Get the Fastest Successful Result

Why it exists

Promise.any() was created to handle redundancy gracefully. When you have multiple ways to get the same result, you often don't care about the ones that fail or are slow; you just want the first successful outcome as quickly as possible. This method simplifies that logic.

The mental model

Think of Promise.any() as sending out three couriers to retrieve a package from three different warehouses. You don't care if one courier gets a flat tire (a rejected promise) or another is stuck in traffic (a slow promise). The moment the first courier arrives with the package (the first fulfilled promise), your job is done, and you can send the others home.

How it works

You provide an iterable (like an array) of promises. Promise.any() returns a single new promise. This new promise fulfills as soon as any of the input promises fulfills, adopting its fulfillment value. It short-circuits, meaning it stops waiting once it has a winner. If and only if ALL input promises reject, the promise returned by Promise.any() will reject with a special AggregateError, which contains an array of all the individual rejection reasons.

When to use it

Use Promise.any() for failover and redundancy. A classic case is fetching a critical asset from multiple CDNs or API mirrors. You request the asset from all sources simultaneously and use whichever responds successfully first, improving resilience and speed.

When not to use it

Do not use Promise.any() when you need the results from every promise; use Promise.all() for that. Also, do not use it if you need to react to the very first promise that settles, whether fulfilled or rejected. For that, use Promise.race(). If a fast failure is a meaningful signal in your application, Promise.race() is the correct tool.

One canonical example

Let's try to fetch an image from two servers, where one is offline. const promise1 = fetch('//server-A.com/image.png'); // Rejects const promise2 = fetch('//server-B.com/image.png'); // Fulfills

const promises = [promise1, promise2];
Promise.any(promises).then((response) => console.log('Got a response from a working server!'));

This code will successfully log the message, using the response from server-B and ignoring the failure from server-A.