Node.js

16.6    Promises in Node.js

A promise represents the result of an asynchronous operation and a kind of return value for such an operation that allows you to better handle asynchronicity in your application. What was only possible with libraries for a long time has now found its way into the JavaScript engine. Listing 16.20 shows how you can use promises based on a small example.

import { readFile } from 'fs'; function promisedReadFile(filename) {  return new Promise((resolve, reject) => {    readFile(filename, 'utf-8', (err, data) => {      if (err) {        reject(err);      } else {        resolve(data);      }    });  });} promisedReadFile('input.txt')  .then((data) => {    console.log('Content of the file: ', data);  })  .catch((error) => {    console.error('An error occured: ', error ...