tessl/npm-util

Node.js's util module for all engines providing cross-platform utility functions for formatting, type checking, inheritance, promises, and debugging.

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String Formatting

Name: tessl/npm-util
Author: tessl

Essential tools for formatted string output and detailed object inspection with customizable styling and output options.

Capabilities

Format Function

Printf-style string formatting with placeholder substitution.

/**
 * Formats a string using printf-style placeholders
 * @param {string} f - Format string with placeholders (%s, %d, %j, %%)
 * @param {...any} args - Arguments to substitute into placeholders
 * @returns {string} Formatted string
 */
function format(f, ...args): string;

Supported placeholders:

%s - String conversion
%d - Number conversion
%j - JSON.stringify conversion
%% - Literal percent sign

Usage Examples:

const util = require('util');

// Basic formatting
util.format('Hello %s', 'world'); // "Hello world"
util.format('Number: %d', 42); // "Number: 42"
util.format('JSON: %j', { a: 1 }); // "JSON: {"a":1}"
util.format('Percent: %%'); // "Percent: %"

// Multiple placeholders
util.format('%s is %d years old', 'Alice', 25); // "Alice is 25 years old"

// Extra arguments are appended
util.format('%s %s', 'a', 'b', 'c'); // "a b c"

// Non-string format argument
util.format(123, 'abc'); // "123 abc"

Inspect Function

Returns a string representation of objects with detailed formatting options.

/**
 * Returns a string representation of an object
 * @param {any} obj - Object to inspect
 * @param {InspectOptions} [opts] - Inspection options
 * @returns {string} String representation of the object
 */
function inspect(obj, opts?): string;

interface InspectOptions {
  /** Show hidden (non-enumerable) properties */
  showHidden?: boolean;
  /** Recursion depth (default: 2) */
  depth?: number;
  /** Use ANSI color codes for styling */
  colors?: boolean;
  /** Enable custom inspect functions */
  customInspect?: boolean;
}

Usage Examples:

const util = require('util');

const obj = {
  name: 'example',
  data: { numbers: [1, 2, 3], active: true },
  method: function() { return 'hello'; }
};

// Basic inspection
console.log(util.inspect(obj));

// With colors (for terminal output)
console.log(util.inspect(obj, { colors: true }));

// Show hidden properties
console.log(util.inspect(obj, { showHidden: true }));

// Control depth
console.log(util.inspect(obj, { depth: 1 }));

// Inspect primitive values
util.inspect(123); // "123"
util.inspect('hello'); // "'hello'"
util.inspect(true); // "true"
util.inspect(null); // "null"

Inspect Styling

Configuration objects for customizing inspect output appearance.

// Color codes for ANSI styling
inspect.colors: {
  bold: [number, number];
  italic: [number, number];
  underline: [number, number];
  inverse: [number, number];
  white: [number, number];
  grey: [number, number];
  black: [number, number];
  blue: [number, number];
  cyan: [number, number];
  green: [number, number];
  magenta: [number, number];
  red: [number, number];
  yellow: [number, number];
};

// Style mappings for different value types
inspect.styles: {
  special: string;
  number: string;
  boolean: string;
  undefined: string;
  null: string;
  string: string;
  date: string;
  regexp: string;
};

Usage Examples:

const util = require('util');

// Customize colors
util.inspect.colors.custom = [95, 39]; // Custom color code
util.inspect.styles.myType = 'custom';

// Default color mappings
console.log(util.inspect.styles.number); // "yellow"
console.log(util.inspect.styles.string); // "green"
console.log(util.inspect.styles.boolean); // "yellow"

Install with Tessl CLI