Sometimes, you might want to convert a JavaScript function that accepts a callback to one that returns a Promiseobject. This lesson shows how to manually wrap a promise-based API around the  function. It also explains how to use the  method that is built into the Node.js standard library.

 

const fs = require('fs')function readFile(path, encoding) {  return new Promise((resolve, reject) => {    fs.readFile(path, encoding, (error, contents) => {      if (error) {        reject(error)      } else {        resolve(contents)      }    })  })}readFile(__filename, "utf8").then((contents) => {  console.log(contents)}, error => {  console.error(error)})

 

In nodejs we can use util function:

const fs = require("fs");const util = require("util");const readFile = util.promisify(fs.readFile);readFile(__filename, "utf8").then(  contents => {    console.log(contents);  },  error => {    console.error(error);  });