PromiseAll.js

const promises1 = [Promise.resolve(1), Promise.resolve(2), Promise.resolve(3)];
const promises2 = [
  Promise.resolve(1),
  Promise.reject("Error at 2"),
  Promise.resolve(3),
];

function myPromiseAll(arr) {
  let completed = 0;
  let results = new Array(arr.length);
  return new Promise((resolve, reject) => {
    arr.forEach((promise, index) => {
      Promise.resolve(promise)
        .then((val) => {
          results[index] = val;
          completed = completed + 1;
          if (completed === arr.length) {
            resolve(results);
          }
        })
        .catch((error) => {
          reject(error);
        });
    });
  });
}

myPromiseAll(promises1).then((val) => {
  console.log(val);
});

myPromiseAll(promises2)
  .then((val) => {
    console.log(val);
  })
  .catch((error) => {
    console.error(error);
  });