Promise.all

The Promise.all() method executes many promises in parallel. It accepts an array of promises and returns a single promise.

• It will only resolve if all the promises passed have been resolved.
• If any promise in an array of promises fails then it will reject

function customPromiseAll(promises) {
  return new Promise((resolve, reject) => {
    if (!Array.isArray(promises)) {
      return reject(new TypeError("Argument must be an array"));
    }

    let resolvedCount = 0;
    const results = [];
    const promisesCount = promises.length;

    if (promisesCount === 0) {
      return resolve([]);
    }

    promises.forEach((promise, index) => {
      Promise.resolve(promise)
        .then((value) => {
          resolvedCount++;
          results[index] = value;
          if (resolvedCount === promisesCount) {
            resolve(results);
          }
        })
        .catch((error) => {
          reject(error);
        });
    });
  });
}

// Example usage
const promise1 = Promise.resolve(3);
const promise2 = 42;
const promise3 = new Promise((resolve, reject) => {
  setTimeout(resolve, 100, "foo");
});

customPromiseAll([promise1, promise2, promise3])
  .then((values) => {
    console.log(values); // [3, 42, "foo"]
  })
  .catch((error) => {
    console.error(error);
  });