parallel.js

const fn1 = async () => {
    console.log('fn1: started');

    const promise = new Promise((resolve, reject) => {
        setTimeout(() => resolve({ fn1: 'data' }), 1000)
    });

    console.log(await promise);
    return promise;
};

const fn2 = async () => {
    console.log('fn2: started');

    const promise = new Promise((resolve, reject) => {
        setTimeout(() => resolve({ fn2: 'data' }), 100)
    });

    console.log(await promise);
    return promise;
};

const fn3 = async () => {
    console.log('fn3: started');

    const promise = new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve({ fn3: 'data' })
        }, 500)
    });

    return promise;
};

const parallel = (...fns) => async (payload) => {
    const data = await Promise.allSettled(
        fns.map((fn) => fn(payload))
    );

    return data.reduce(
        (acc, resultItem) => ({ ...acc, ...resultItem.value }),
        {}
    );
}

console.log(await parallel(fn3, fn2, fn1)('payload'));