util

Cross-platform implementation of Node.js's built-in util module, providing utility functions for string formatting, type checking, inheritance, promises, and debugging. Works seamlessly across Node.js, browsers, browserify, and webpack environments.

Package Information

• Package Name: util
• Package Type: npm
• Language: JavaScript
• Installation: npm install util
• Repository: https://github.com/browserify/node-util

Core Imports

const util = require('util');

For ES modules:

import * as util from 'util';

Individual imports:

const { format, inspect, promisify, inherits } = require('util');

Basic Usage

const util = require('util');

// String formatting
const message = util.format('Hello %s, you are %d years old', 'Alice', 25);
console.log(message); // "Hello Alice, you are 25 years old"

// Object inspection
const obj = { name: 'Bob', details: { age: 30, active: true } };
console.log(util.inspect(obj, { colors: true, depth: 2 }));

// Type checking
console.log(util.isString('hello')); // true
console.log(util.isArray([1, 2, 3])); // true

// Promise conversion
const fs = require('fs');
const readFileAsync = util.promisify(fs.readFile);

Architecture

The util module is organized into several key areas:

• String Formatting: Functions for formatted string output and object inspection
• Type Checking: Comprehensive type validation utilities including basic and advanced type detection
• Promise Utilities: Tools for converting between callback and promise-based functions
• Utilities: Inheritance, deprecation warnings, debugging, and object extension helpers
• Browser Compatibility: Platform-specific implementations for cross-environment support

Capabilities

String Formatting

Essential tools for formatted output and object inspection. Provides printf-style formatting and detailed object visualization with customizable styling.

function format(f, ...args): string;
function inspect(obj, opts?): string;

String Formatting

Type Checking

Comprehensive type validation system with both basic JavaScript type checking and advanced type detection for modern JavaScript features including typed arrays, collections, and boxed primitives.

function isString(arg): boolean;
function isNumber(arg): boolean;
function isArray(ar): boolean;
function isFunction(arg): boolean;
function isObject(arg): boolean;

// Extended types via util.types
const types: {
  isMap(value): boolean;
  isSet(value): boolean;
  isPromise(value): boolean;
  isArrayBuffer(value): boolean;
  isTypedArray(value): boolean;
  // ... and many more
};

Type Checking

Promise Utilities

Conversion tools between callback-based and promise-based function patterns, enabling modern async/await usage with legacy callback APIs.

function promisify(original): Function;
function callbackify(original): Function;

Promise Utilities

Utilities

Core utilities for inheritance, deprecation warnings, debugging, object extension, and timestamp logging.

function inherits(ctor, superCtor): void;
function deprecate(fn, msg): Function;
function debuglog(set): Function;
function log(...args): void;

Utilities

Browser Support

• Uses ES5 features - requires es5-shim for IE8 support
• Promise utilities require native Promises or polyfill (e.g., es6-promise)
• Includes browser-specific Buffer detection for cross-platform compatibility
• Supports CommonJS, AMD, and global usage patterns