Asynchronous Sum Example with Callbacks, Promises, and Async / Await

asyncSum.js

/**
 * Asynchronous sum example with callbacks.
 */

function getX(callback) {
    setTimeout(() => {
        callback(5);
    }, 1000);
}

function getY(callback) {
    setTimeout(() => {
        callback(3);
    }, 2000);
}

function asyncSum(callback) {
    let x, y;
    getX(result => {
        x = result;
        if (y !== undefined) {
            callback(x + y);
        }
    });
    getY(result => {
        y = result;
        if (x !== undefined) {
            callback(x + y);
        }
    })
}

console.log("Loading...");
asyncSum(sum => console.log("sum", sum));

// ===================================================

/**
 * Asynchronous sum example with promises.
 */

function getX() {
    return new Promise(resolve => {
        setTimeout(() => resolve(5), 1000);
    });
}

function getY() {
    return new Promise(resolve => {
        setTimeout(() => resolve(3), 2000);
    });
}

function asyncSum() {
    return new Promise(resolve => {
        const xPromise = getX();
        const yPromise = getY();
        Promise.all([xPromise, yPromise]).then(([x, y]) => {
            resolve(x + y);
        });
    })
}

console.log("Loading...");
asyncSum().then(sum => {
    console.log("sum", sum);
});

// ===================================================

/**
 * Asynchronous sum example with async / await.
 */

function getX() {
    return new Promise(resolve => {
        setTimeout(() => resolve(5), 1000);
    });
}

function getY() {
    return new Promise(resolve => {
        setTimeout(() => resolve(3), 2000);
    });
}

async function asyncSum() {
    const xPromise = getX();
    const yPromise = getY();

    const x = await xPromise;
    const y = await yPromise;
    return x + y;
}

async function printSum() {
    const sum = await asyncSum(getX, getY);
    console.log("sum", sum);
}

console.log("Loading sum...");
printSum();