NodeJS
A Complete Guide to Promise.any(): When & How to Use It
Introduction
Asynchronous programming in JavaScript can be a tricky thing to get right, especially when you have multiple async operations to manage. At times, you want only the first promise to be resolved and do not care about the rest. This is where Promise.any() comes in handy.
What is Promise.any()?
Promise. any() is a method which takes an iterable (most often an array) of promises, and returns a single promise that, when one of the promises in the iterable fulfills, resolves with the value from that promise. If all of the promises reject, it returns a promise that is rejected with an AggregateError (a new kind of error that bundles together the reasons for the each promise being rejected).
When to Use Promise.any()
You can use Promise.any() in cases where you care about the first promise that resolves and other promises do not concern you. It can come in particularly handy for situations where one has to deal with multiple options and you want to move ahead once the first successful result pops in.
Real-World Example
Let’s say you are building a website that requests several image CDN servers for a specific image. You want to show the image as soon as one of them has it available, without waiting for all of them to respond.
const fetchImageFromCDN = (url) => fetch(url).then(res => res.blob());const cdnUrls = [ 'https://cdn1.example.com/image.jpg', 'https://cdn2.example.com/image.jpg', 'https://cdn3.example.com/image.jpg'];Promise.any(cdnUrls.map(fetchImageFromCDN)) .then(imageBlob => { console.log('Image fetched:', imageBlob); // Display the image }) .catch(error => { console.error('All attempts failed:', error); });
Why Use It?
Here, Promise.any() allows you to fetch the image from the first CDN that responds, thereby, showing the image faster than if you had to wait for all CDNs to respond, or even for that matter handle multiple failures. If one CDN fails others are still tried until one succeeds. All CDNs failing gives you an AggregateError, which provides a way to handle the failure gracefully.
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NodeJS
