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How to write asynchronous function for Node.js ?
  • Last Updated : 22 Jan, 2021

The asynchronous function can be written in Node.js using ‘async’ preceding the function name. The asynchronous function returns 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.

Install async from npm in Node.js using the following command:

npm i async

Use async inside your Node.js project using require() method.

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

  • Create a project folder.
  • Use the following command to initialize the package.json file inside the project folder.
    npm init -y
  • Install async using the following command:
    npm i async
  • Create a server.js file & write the following code inside it.
  • Run the code using npm start




var 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);
var 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.




var 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:




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