Callback VS Promise VS async/await

gistfile1.js

function slowDoubleCallback(x, callback) {
    setTimeout(() => {
        callback(x * 2);
    }, 200);
}

function slowDouble(x) {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve(x * 2);
        }, 200);
    });
}

// Callback Hell Version
let callBackAns = 0;
slowDoubleCallback(1, (ans) => {
    callBackAns += ans;
    slowDoubleCallback(2, (ans) => {
        callBackAns += ans;
        slowDoubleCallback(3, (ans) => {
            callBackAns += ans;
            slowDoubleCallback(4, (ans) => {
                callBackAns += ans;
                slowDoubleCallback(5, (ans) => {
                    callBackAns += ans;
                    slowDoubleCallback(6, (ans) => {
                        callBackAns += ans;
                        slowDoubleCallback(7, (ans) => {
                            callBackAns += ans;
                            slowDoubleCallback(8, (ans) => {
                                callBackAns += ans;
                                slowDoubleCallback(9, (ans) => {
                                    callBackAns += ans;
                                    slowDoubleCallback(10, (ans) => {
                                        callBackAns += ans;
                                        console.log("Callback: " + callBackAns);
                                    });
                                });
                            });
                        });
                    });
                });
            });
        });
    });
});

// Promise Version
let promiseAns = 0;
slowDouble(1).then((ans) => {
    promiseAns += ans;
    return slowDouble(2);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(3);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(4);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(5);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(6);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(7);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(8);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(9);
}).then((ans) => {
    promiseAns += ans;
    return slowDouble(10);
}).then((ans) => {
    console.log("Promise: " + (promiseAns + ans));
});


// async / await Version
(async () => {
    let ans = 0;
    ans += await slowDouble(1);
    ans += await slowDouble(2);
    ans += await slowDouble(3);
    ans += await slowDouble(4);
    ans += await slowDouble(5);
    ans += await slowDouble(6);
    ans += await slowDouble(7);
    ans += await slowDouble(8);
    ans += await slowDouble(9);
    ans += await slowDouble(10);
    console.log("async/await: " + ans);
})();

// async / await Version 2
(async () => {
    let ans = 0;
    for (let i = 1; i <= 10; i++) {
        ans += await slowDouble(i);
    }
    console.log("async/await Version 2: " + ans);
})();