Promise.any

mediumcodingJavaScriptPromises~25 min

Asked at Google, Meta, Amazon

Overview

Implement promiseAny(promises) that returns the first fulfilled promise. If all reject, throws an AggregateError.

Examples

await promiseAny([Promise.reject('a'), Promise.resolve('b')]); // 'b'

Solution

Reveal solution

function promiseAny(promises) {
  return new Promise((resolve, reject) => {
    const errors = [];
    let count = 0;
    const arr = Array.from(promises);
    if (arr.length === 0) reject(new AggregateError([], 'All promises were rejected'));
    arr.forEach((p, i) => {
      Promise.resolve(p).then(resolve, (err) => {
        errors[i] = err;
        count++;
        if (count === arr.length) reject(new AggregateError(errors, 'All promises were rejected'));
      });
    });
  });
}

promise-any.js

Promise.any

mediumcodingJavaScriptPromises

Overview

Implement promiseAny(promises) that returns the first fulfilled promise. If all reject, throws an AggregateError.

Examples

await promiseAny([Promise.reject('a'), Promise.resolve('b')]); // 'b'

Solution

Reveal solution

function promiseAny(promises) {
  return new Promise((resolve, reject) => {
    const errors = [];
    let count = 0;
    const arr = Array.from(promises);
    if (arr.length === 0) reject(new AggregateError([], 'All promises were rejected'));
    arr.forEach((p, i) => {
      Promise.resolve(p).then(resolve, (err) => {
        errors[i] = err;
        count++;
        if (count === arr.length) reject(new AggregateError(errors, 'All promises were rejected'));
      });
    });
  });
}

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