function foo() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve("foo")
        }, 100)
    })
}

function bar() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve("bar")
        }, 200)
    })
}

// Instead of doing:
// foo().then(a => {
//     bar().then(b => {
//         console.log(a)
//         console.log(b)
//     })
// })

// do this instead:

Promise.all([foo(), bar()]).then(([a, b]) => {
    console.log(a)
    console.log(b)
})