Type Checking

/**
 * Checks if value is an array
 * @param {any} ar - Value to check
 * @returns {boolean} True if value is an array
 */
function isArray(ar): boolean;

/**
 * Checks if value is a boolean
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a boolean
 */
function isBoolean(arg): boolean;

/**
 * Checks if value is null
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is null
 */
function isNull(arg): boolean;

/**
 * Checks if value is null or undefined
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is null or undefined
 */
function isNullOrUndefined(arg): boolean;

/**
 * Checks if value is a number
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a number
 */
function isNumber(arg): boolean;

/**
 * Checks if value is a string
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a string
 */
function isString(arg): boolean;

/**
 * Checks if value is a symbol
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a symbol
 */
function isSymbol(arg): boolean;

/**
 * Checks if value is undefined
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is undefined
 */
function isUndefined(arg): boolean;

/**
 * Checks if value is a regular expression
 * @param {any} re - Value to check
 * @returns {boolean} True if value is a RegExp
 */
function isRegExp(re): boolean;

/**
 * Checks if value is an object (not null)
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is an object and not null
 */
function isObject(arg): boolean;

/**
 * Checks if value is a Date object
 * @param {any} d - Value to check
 * @returns {boolean} True if value is a Date
 */
function isDate(d): boolean;

/**
 * Checks if value is an Error object
 * @param {any} e - Value to check
 * @returns {boolean} True if value is an Error
 */
function isError(e): boolean;

/**
 * Checks if value is a function
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a function
 */
function isFunction(arg): boolean;

/**
 * Checks if value is a primitive type
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is null, boolean, number, string, symbol, or undefined
 */
function isPrimitive(arg): boolean;

/**
 * Checks if value is a Buffer (Node.js/browser compatible)
 * @param {any} arg - Value to check
 * @returns {boolean} True if value is a Buffer
 */
function isBuffer(arg): boolean;

const util = require('util');

// Basic type checks
util.isString('hello'); // true
util.isNumber(42); // true
util.isArray([1, 2, 3]); // true
util.isFunction(() => {}); // true
util.isObject({}); // true
util.isNull(null); // true
util.isUndefined(undefined); // true

// Date and RegExp
util.isDate(new Date()); // true
util.isRegExp(/pattern/); // true

// Error checking
util.isError(new Error('message')); // true
util.isError(new TypeError('type error')); // true

// Primitives
util.isPrimitive('string'); // true
util.isPrimitive(42); // true
util.isPrimitive({}); // false

const types: {
  // Collection Types
  isMap(value): boolean;
  isSet(value): boolean;
  isWeakMap(value): boolean;
  isWeakSet(value): boolean;

  // Array Buffer Types
  isArrayBuffer(value): boolean;
  isSharedArrayBuffer(value): boolean;
  isArrayBufferView(value): boolean;
  isDataView(value): boolean;
  isAnyArrayBuffer(value): boolean;

  // Typed Arrays
  isTypedArray(value): boolean;
  isUint8Array(value): boolean;
  isUint8ClampedArray(value): boolean;
  isUint16Array(value): boolean;
  isUint32Array(value): boolean;
  isInt8Array(value): boolean;
  isInt16Array(value): boolean;
  isInt32Array(value): boolean;
  isFloat32Array(value): boolean;
  isFloat64Array(value): boolean;
  isBigInt64Array(value): boolean;
  isBigUint64Array(value): boolean;

  // Boxed Primitives
  isNumberObject(value): boolean;
  isStringObject(value): boolean;
  isBooleanObject(value): boolean;
  isBigIntObject(value): boolean;
  isSymbolObject(value): boolean;
  isBoxedPrimitive(value): boolean;

  // Function Types
  isGeneratorFunction(value): boolean;
  isAsyncFunction(value): boolean;
  isGeneratorObject(value): boolean;

  // Iterator Types
  isMapIterator(value): boolean;
  isSetIterator(value): boolean;

  // Other Types
  isArgumentsObject(value): boolean;
  isPromise(value): boolean;
  isWebAssemblyCompiledModule(value): boolean;

  // Aliases
  isDate(value): boolean;
  isRegExp(value): boolean;
  isNativeError(value): boolean;

  // Unsupported (throw errors)
  isProxy(): never;
  isExternal(): never;
  isModuleNamespaceObject(): never;
};

const util = require('util');

// Collections
util.types.isMap(new Map()); // true
util.types.isSet(new Set()); // true
util.types.isWeakMap(new WeakMap()); // true

// Typed Arrays
util.types.isUint8Array(new Uint8Array()); // true
util.types.isFloat32Array(new Float32Array()); // true
util.types.isTypedArray(new Int16Array()); // true

// Array Buffers
util.types.isArrayBuffer(new ArrayBuffer(16)); // true
util.types.isDataView(new DataView(new ArrayBuffer(16))); // true

// Boxed Primitives
util.types.isNumberObject(new Number(42)); // true
util.types.isStringObject(new String('hello')); // true
util.types.isBoxedPrimitive(new Boolean(true)); // true

// Functions
util.types.isAsyncFunction(async () => {}); // true
util.types.isGeneratorFunction(function* () {}); // true

// Promises
util.types.isPromise(Promise.resolve()); // true
util.types.isPromise({ then: () => {}, catch: () => {} }); // true

// Arguments object
function example() {
  return util.types.isArgumentsObject(arguments); // true
}