What are async functions in Node? Provide some examples.

With the release of Node.js 8, the long awaited async functions have landed in Node.js as well. ES 2017 introduced Asynchronous functions. Async functions are essentially a cleaner way to work with asynchronous code in JavaScript.

Async/Await is:

• The newest way to write asynchronous code in JavaScript.
• It is non blocking (just like promises and callbacks).
• Async/Await was created to simplify the process of working with and writing chained promises.
• Async functions return a Promise. If the function throws an error, the Promise will be rejected. If the function returns a value, the Promise will be resolved.

Async functions can make use of the await expression. This will pause the async function and wait for the Promise to resolve prior to moving on.

Consider the code:

function doubleAfter2Seconds(x) {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve(x * 2);
        }, 2000);
    });
}

What if we want to run a few different values through our function and add the result?

Promise-based solution will be:

function addPromise(x) {
    return new Promise(resolve => {
        doubleAfter2Seconds(10).then((a) => {
            doubleAfter2Seconds(20).then((b) => {
                doubleAfter2Seconds(30).then((c) => {
                    resolve(x + a + b + c);
                })
            })
        })
    });
}

addPromise(10).then((sum) => {
  console.log(sum);
});

Async/Await solution will look like:

async function addAsync(x) {
    const a = await doubleAfter2Seconds(10);
    const b = await doubleAfter2Seconds(20);
    const c = await doubleAfter2Seconds(30);
    return x + a + b + c;
}

addAsync(10).then((sum) => {
  console.log(sum);
});