Node util.promisify() Method

Last Updated : 14 Jan, 2024

`util.promisify()` in Node.js converts callback-based methods to promise-based, aiding in managing asynchronous code more cleanly. This alleviates callback nesting issues, enhancing code readability, and simplifying asynchronous operations through promise chaining.

Syntax:

util.promisify(func)

Parameters: This method accepts a single parameter function that holds the callback based function.

Return Value: This method returns a promise-based function.

Example 1: Below is the code example of the util.promisify() Method:

Javascript

// Node.js program to illustrate 
// util.promisify() methods 
 
// Importing Utilities module 
const util = require('util')
 
// Importing File System module 
const fs = require('fs')
 
// Use promisify to convert callback 
// based method fs.readdir to 
// promise based method 
const readdir =
    util.promisify(fs.readdir)
 
readdir('process.cwd()')
    .then(files => {
        console.log(files)
    })
    .catch(err => {
        console.log(err)
    })

Output:

[Error: ENOENT: no such file or directory, 
scandir 'C:\Users\bhudk\Desktop\nodec\process.cwd()'] {
  errno: -4058,
  code: 'ENOENT',
  syscall: 'scandir',
  path: 'C:\\Users\\bhudk\\Desktop\\nodec\\process.cwd()'
}

Example 2: Below is the code example of the util.promisify() Method:

Javascript

// Node.js program to illustrate 
// util.promisify() methods 
 
// Since promisify function 
// returns promise version 
// of a function, it can also 
// operate using async and await 
 
// Importing Utilities module 
const util = require('util')
 
// Importing File System module 
const fs = require('fs')
 
// Use promisify to convert callback 
// based method fs.readdir to 
// promise based method 
const readdir = util.promisify(fs.readdir)
 
const readFiles = async (path) => {
    const files = await readdir(path)
    console.log(files)
}
 
readFiles(process.cwd()).catch(err => {
    console.log(err)
})

Output:

Example 3: Below is the code example of the util.promisify() Method:

Javascript

// Node.js program to illustrate 
// util.promisify() methods 
 
// Importing Utilities module 
const util = require('util')
 
// importing File System module
const fs = require('fs')
 
// Use promisify to convert 
// callback based methods to 
// promise based methods 
const readdir = util.promisify(fs.readdir)
const lstat = util.promisify(fs.lstat)
 
 
const readFiles = async (path) => {
    const files = await readdir(path)
    for (let file of files) {
        const stats = await lstat(file)
        if (stats.isFile()) {
            console.log(`${file} -----> File`)
        } else {
            console.log(`${file} -----> Folder`)
        }
    }
}
 
readFiles('process.cwd()').catch(err => {
    console.log(err)
})

Output:

We have a Cheat Sheet on Node utility methods where we covered all the utility methods to check those please go through Node.js Utility Complete Reference article.