Promises

let newArr = [10, 100];

const first = new Promise((resolve, reject) => {
    setTimeout(resolve, 6000, 'Все ок!');
});
 
const second = new Promise((resolve, reject) => {
    setTimeout(reject, 2000, new Error('Неудачно'));
});

Promise.race([first, second]).then((result) => {
  console.log(result);
});

const third = new Promise((resolve, reject) => {
    setTimeout(resolve(1000), 2000);
});

function save(list){
    return third.then(result => {
        list.push(result);
    });
}

save(newArr)
    .then(() => console.log(newArr))
    .catch(err => console.log(err));