util

What is util?

The 'util' package is a core Node.js module that provides utilities for programmatic use in JavaScript. It includes a collection of helper functions for various tasks such as formatting strings, inspecting objects, and using inheritance.

What are util's main functionalities?

format

Formats a string using placeholders and returns it. Similar to printf in C.

const util = require('util');
console.log(util.format('%s:%s', 'foo', 'bar', 'baz')); // 'foo:bar baz'

inspect

Returns a string representation of an object for debugging purposes, with options to show hidden properties and control the depth of inspection.

const util = require('util');
console.log(util.inspect({ foo: 'bar' }, { showHidden: false, depth: null }));

inherits

Allows one constructor to inherit the prototype methods from another, a utility for implementing object-oriented inheritance.

const util = require('util');
function Base() {}
function Derived() {}
util.inherits(Derived, Base);

promisify

Converts a callback-based function to a function that returns a promise, facilitating the use of async/await.

const util = require('util');
const fs = require('fs');
const readFileAsync = util.promisify(fs.readFile);
readFileAsync('example.txt', 'utf8').then(console.log).catch(console.error);

Other packages similar to util

lodash

Lodash is a utility library offering a wide range of methods for manipulating objects, arrays, strings, etc. It's more comprehensive than 'util' but doesn't include some of the Node.js-specific utilities like promisify.

underscore

Underscore.js is a utility library similar to Lodash, providing functional programming helpers without extending any built-in objects. It's less feature-rich compared to Lodash and doesn't include Node.js-specific utilities.

chalk

Chalk is a library for styling terminal strings. It doesn't offer the broad utility functions of 'util' but focuses on a specific area of string styling which 'util' doesn't cover.

bluebird

Bluebird is a library focused on providing advanced features for promises, such as cancellation, progress, and long stack traces. It complements 'util' by enhancing promise functionality beyond what 'util.promisify' offers.

README

util

Node.js's util module for all engines.

This implements the Node.js util module for environments that do not have it, like browsers.

Install

You usually do not have to install util yourself. If your code runs in Node.js, util is built in. If your code runs in the browser, bundlers like browserify or webpack (up to version 4 -- see this documentation for how to include polyfills like util in webpack 5+) also include the util module.

But if none of those apply, with npm do:

npm install util

Usage

var util = require('util')
var EventEmitter = require('events')

function MyClass() { EventEmitter.call(this) }
util.inherits(MyClass, EventEmitter)

Browser Support

The util module uses ES5 features. If you need to support very old browsers like IE8, use a shim like es5-shim. You need both the shim and the sham versions of es5-shim.

To use util.promisify and util.callbackify, Promises must already be available. If you need to support browsers like IE11 that do not support Promises, use a shim. es6-promise is a popular one but there are many others available on npm.

API

See the Node.js util docs. util currently supports the Node 8 LTS API. However, some of the methods are outdated. The inspect and format methods included in this module are a lot more simple and barebones than the ones in Node.js.

Contributing

PRs are very welcome! The main way to contribute to util is by porting features, bugfixes and tests from Node.js. Ideally, code contributions to this module are copy-pasted from Node.js and transpiled to ES5, rather than reimplemented from scratch. Matching the Node.js code as closely as possible makes maintenance simpler when new changes land in Node.js. This module intends to provide exactly the same API as Node.js, so features that are not available in the core util module will not be accepted. Feature requests should instead be directed at nodejs/node and will be added to this module once they are implemented in Node.js.

If there is a difference in behaviour between Node.js's util module and this module, please open an issue!

License

MIT

Changelog

0.12.5

• Move safe-buffer dependency to a dev-only dependency. (@goto-bus-stop in e84cfd5)
• Document usage with webpack 5+. (@MatrixFrog in #69)