iterable

Aniterable (such as anArray) of promises.

APromise that is:

• Already rejected, if theiterable passed is empty.
• Asynchronously fulfilled, when any of the promises in the giveniterable fulfills. The fulfillment value is the fulfillment value of the first promise that was fulfilled.
• Asynchronously rejected, when all of the promises in the giveniterable reject. The rejection reason is anAggregateError containing an array of rejection reasons in itserrors property. The errors are in the order of the promises passed, regardless of completion order. If theiterable passed is non-empty but contains no pending promises, the returned promise is still asynchronously (instead of synchronously) rejected.

ThePromise.any() method is one of thepromise concurrency methods. This method is useful for returning the first promise that fulfills. It short-circuits after a promise fulfills, so it does not wait for the other promises to complete once it finds one.

UnlikePromise.all(), which returns anarray of fulfillment values, we only get one fulfillment value (assuming at least one promise fulfills). This can be beneficial if we need only one promise to fulfill but we do not care which one does. Note another difference: this method rejects upon receiving anempty iterable, since, truthfully, the iterable contains no items that fulfill. You may comparePromise.any() andPromise.all() withArray.prototype.some() andArray.prototype.every().

Also, unlikePromise.race(), which returns the firstsettled value (either fulfillment or rejection), this method returns the firstfulfilled value. This method ignores all rejected promises up until the first promise that fulfills.

Promise.any() fulfills with the first promise to fulfill, even if a promise rejects first. This is in contrast toPromise.race(), which fulfills or rejects with the first promise to settle.

const pErr = new Promise((resolve, reject) => {  reject(new Error("Always fails"));});const pSlow = new Promise((resolve, reject) => {  setTimeout(resolve, 500, "Done eventually");});const pFast = new Promise((resolve, reject) => {  setTimeout(resolve, 100, "Done quick");});Promise.any([pErr, pSlow, pFast]).then((value) => {  console.log(value);  // pFast fulfills first});// Logs:// Done quick

Promise.any() rejects with anAggregateError if no promise fulfills.

const failure = new Promise((resolve, reject) => {  reject(new Error("Always fails"));});Promise.any([failure]).catch((err) => {  console.log(err);});// AggregateError: No Promise in Promise.any was resolved

In this example, we have a function that fetches an image and returns a blob. We usePromise.any() to fetch a couple of images and display the first one available (i.e., whose promise has resolved).

async function fetchAndDecode(url, description) {  const res = await fetch(url);  if (!res.ok) {    throw new Error(`HTTP error! status: ${res.status}`);  }  const data = await res.blob();  return [data, description];}const coffee = fetchAndDecode("coffee.jpg", "Coffee");const tea = fetchAndDecode("tea.jpg", "Tea");Promise.any([coffee, tea])  .then(([blob, description]) => {    const objectURL = URL.createObjectURL(blob);    const image = document.createElement("img");    image.src = objectURL;    image.alt = description;    document.body.appendChild(image);  })  .catch((e) => {    console.error(e);  });

• Polyfill ofPromise.any incore-js
• es-shims polyfill ofPromise.any
• Promise
• Promise.all()
• Promise.allSettled()
• Promise.race()