promise-all.js

const timedResolve = name => {
    return new Promise(resolve =>
        setTimeout(() => {
            console.log(name)
            resolve()
        }, 500 * Math.random()),
    )
}

Promise.all([
    timedResolve('first'),
    timedResolve('second'),
    timedResolve('third'),
    timedResolve('fourth')]
).then(() => {
    console.log('done')
})