promise-all.js

const fetchMock = (delay) => {
    return new Promise((resolve) => setTimeout(() => resolve(delay), delay));
};

const promiseAll = async (promises) => {
    return new Promise((resolve, reject) => {
        const results = [];
        promises.forEach((promise) => {
            promise
                .then((res) => {
                    results.push(res);
                    if (results.length === promises.length) {
                        resolve(results);
                    }
                })
                .catch((e) => {
                    reject(e);
                });
        });
    });
};

promiseAll([fetchMock(800), fetchMock(500)])
    .then((data) => console.log(data))
    .catch((error) => console.log([error]));
// [800, 500]

promiseAll([fetchMock(200), fetchMock(100), Promise.reject("error")])
    .then((data) => console.log(data))
    .catch((error) => console.log([error]));
// ['error']