asyncForEach.js

const startTimestamp = getMiliseconds();

function getMiliseconds() {
    return new Date(Date.now()).getMilliseconds();
}

function getMillisecondsElapsed() {
    return getMiliseconds() - startTimestamp;
}

function wait(timeout = 0) {
    return new Promise((resolve) => setTimeout(resolve, timeout));
}

const tasks = [
    () => wait(100).then(() => console.log("Task 1 finished at", getMillisecondsElapsed())),
    () => wait(100).then(() => console.log("Task 2 finished at", getMillisecondsElapsed())),
    () => wait(100).then(() => console.log("Task 3 finished at", getMillisecondsElapsed())),
];

async function run(tasks = []) {
    for (const task of tasks) {
        await task();
    }
    console.log("All tasks finished at", getMillisecondsElapsed());
}

function runForEach(tasks = []) {
    tasks.forEach(async (task) => {
        await wait(100);
        await task();
    });
    console.log("All tasks finished at", getMillisecondsElapsed());
}

function runLongerForEach(tasks = []) {
    tasks.forEach(async (task) => {
        await wait(100);
        await task();
    });
    console.log("All tasks finished at", getMillisecondsElapsed());
}

function forEach() {
    Array.prototype.forEach = function (callback) {
        for (let i = 0; i < this.length; i++) {
            callback(this[i], i, this);
        }
    };
}

function patchForEach() {
    Array.prototype.forEach = async function (callback) {
        for (let i = 0; i < this.length; i++) {
            await callback(this[i], i, this);
        }
    };
}

async function runAsyncForEach(tasks = []) {
    patchForEach();
    await tasks.forEach(async (task) => {
        await task();
    });
    console.log("All tasks finished at", getMillisecondsElapsed());
}

run(tasks);