An explanation of Promise.all that includes mention of mapping through them

promise.all.js

// This is a simple promise that will return a promise that resolves after the num
const getPromiseTimeout = num => new Promise(resolve => {
    setTimeout(() => resolve(num), num);
})

const timeouts = [getPromiseTimeout(100), getPromiseTimeout(300), getPromiseTimeout(200)];

// Promise.all will run these promises in whatever order it wants, but will resolve
// with the same order they were passed in on. They run in 'parallel'
// Will console.log(100, 300, 200) in the same order as the order above
Promise.all(timeouts).then((arrRestults) => console.log(arrRestults));

// Because Promise.all returns a promise itself, you can chain them together
Promise.all([
    Promise.all([
        getPromiseTimeout(300)
    ])
]).then(arrVal => {
    console.log(arrVal); // [[300]]
})

// As such, you can have functions that use Promise.all and return a single promise
const getTimeoutTimes = (times) => {
    const timess = times.map(time => getPromiseTimeout(time));
    return Promise.all(timess);
}

Promise.all([
    getTimeoutTimes([100, 300, 500]),
    getTimeoutTimes([200, 400, 600])
]).then(arrVal => {
    console.log(arrVal); // [[100, 300, 500], [200, 400, 600]]
})