How to Write Asynchronous Function for Node.js ?

The asynchronous function can be written in Node.js using 'async' preceding the function name. The asynchronous function returns an implicit Promise as a result. The async function helps to write promise-based code asynchronously via the event loop. Async functions will always return a value.

Await function can be used inside the asynchronous function to wait for the promise. This forces the code to wait until the promise returns a result.

Steps to Write Asynchronous Function for Node.js

Step 1: Create a project folder

Use the following command to initialize the package.json file inside the project folder.

npm init -y

Step 2: Install async using the following command:

npm i async

Note: Installation of async library only required in older versions of node.

Step 3: Create a server.js file & write the following code inside it.

Run the code using the below command

npm start

Example 1: Create an asynchronous function to calculate the square of a number inside Node.js.

const async = require("async");

function square(x) {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve(Math.pow(x, 2));
        }, 2000);
    });
}

async function output(x) {
    const ans = square(x);
    console.log(ans);
}

output(10);
const async = require("async");

function square(x) {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve(Math.pow(x, 2));
        }, 2000);
    });
}

async function output(x) {
    const ans = await square(x);
    console.log(ans);
}

output(10);

Output:

Example 2: Create an asynchronous function to calculate the sum of two numbers inside Node.js using await. Perform the above procedure to create a Node.js project. 

const async = require("async");

function square(a, b) {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve(a + b);
        }, 2000);
    });
}

async function output(a, b) {
    const ans = await square(a, b);
    console.log(ans);
}

output(10, 20);

Output: