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# Type Checking
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Comprehensive type validation system with both basic JavaScript type checking and advanced type detection for modern JavaScript features.
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## Capabilities
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### Basic Type Checking
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Fundamental type checking functions for JavaScript primitives and common objects.
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```javascript { .api }
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/**
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 * Checks if value is an array
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 * @param {any} ar - Value to check
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 * @returns {boolean} True if value is an array
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 */
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function isArray(ar): boolean;
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/**
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 * Checks if value is a boolean
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a boolean
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 */
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function isBoolean(arg): boolean;
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/**
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 * Checks if value is null
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is null
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 */
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function isNull(arg): boolean;
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/**
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 * Checks if value is null or undefined
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is null or undefined
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 */
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function isNullOrUndefined(arg): boolean;
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/**
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 * Checks if value is a number
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a number
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 */
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function isNumber(arg): boolean;
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/**
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 * Checks if value is a string
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a string
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 */
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function isString(arg): boolean;
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/**
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 * Checks if value is a symbol
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a symbol
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 */
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function isSymbol(arg): boolean;
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/**
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 * Checks if value is undefined
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is undefined
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 */
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function isUndefined(arg): boolean;
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/**
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 * Checks if value is a regular expression
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 * @param {any} re - Value to check
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 * @returns {boolean} True if value is a RegExp
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 */
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function isRegExp(re): boolean;
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/**
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 * Checks if value is an object (not null)
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is an object and not null
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 */
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function isObject(arg): boolean;
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/**
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 * Checks if value is a Date object
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 * @param {any} d - Value to check
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 * @returns {boolean} True if value is a Date
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 */
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function isDate(d): boolean;
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/**
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 * Checks if value is an Error object
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 * @param {any} e - Value to check
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 * @returns {boolean} True if value is an Error
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 */
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function isError(e): boolean;
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/**
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 * Checks if value is a function
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a function
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 */
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function isFunction(arg): boolean;
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/**
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 * Checks if value is a primitive type
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is null, boolean, number, string, symbol, or undefined
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 */
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function isPrimitive(arg): boolean;
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/**
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 * Checks if value is a Buffer (Node.js/browser compatible)
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 * @param {any} arg - Value to check
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 * @returns {boolean} True if value is a Buffer
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 */
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function isBuffer(arg): boolean;
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```
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**Usage Examples:**
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```javascript
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const util = require('util');
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// Basic type checks
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util.isString('hello'); // true
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util.isNumber(42); // true
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util.isArray([1, 2, 3]); // true
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util.isFunction(() => {}); // true
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util.isObject({}); // true
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util.isNull(null); // true
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util.isUndefined(undefined); // true
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// Date and RegExp
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util.isDate(new Date()); // true
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util.isRegExp(/pattern/); // true
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// Error checking
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util.isError(new Error('message')); // true
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util.isError(new TypeError('type error')); // true
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// Primitives
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util.isPrimitive('string'); // true
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util.isPrimitive(42); // true
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util.isPrimitive({}); // false
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```
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### Extended Type Checking (util.types)
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Advanced type detection for modern JavaScript features including collections, typed arrays, and boxed primitives.
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```javascript { .api }
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const types: {
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  // Collection Types
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  isMap(value): boolean;
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  isSet(value): boolean;
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  isWeakMap(value): boolean;
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  isWeakSet(value): boolean;
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  // Array Buffer Types
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  isArrayBuffer(value): boolean;
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  isSharedArrayBuffer(value): boolean;
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  isArrayBufferView(value): boolean;
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  isDataView(value): boolean;
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  isAnyArrayBuffer(value): boolean;
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  // Typed Arrays
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  isTypedArray(value): boolean;
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  isUint8Array(value): boolean;
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  isUint8ClampedArray(value): boolean;
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  isUint16Array(value): boolean;
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  isUint32Array(value): boolean;
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  isInt8Array(value): boolean;
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  isInt16Array(value): boolean;
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  isInt32Array(value): boolean;
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  isFloat32Array(value): boolean;
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  isFloat64Array(value): boolean;
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  isBigInt64Array(value): boolean;
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  isBigUint64Array(value): boolean;
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  // Boxed Primitives
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  isNumberObject(value): boolean;
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  isStringObject(value): boolean;
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  isBooleanObject(value): boolean;
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  isBigIntObject(value): boolean;
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  isSymbolObject(value): boolean;
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  isBoxedPrimitive(value): boolean;
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  // Function Types
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  isGeneratorFunction(value): boolean;
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  isAsyncFunction(value): boolean;
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  isGeneratorObject(value): boolean;
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  // Iterator Types
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  isMapIterator(value): boolean;
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  isSetIterator(value): boolean;
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  // Other Types
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  isArgumentsObject(value): boolean;
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  isPromise(value): boolean;
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  isWebAssemblyCompiledModule(value): boolean;
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  // Aliases
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  isDate(value): boolean;
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  isRegExp(value): boolean;
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  isNativeError(value): boolean;
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  // Unsupported (throw errors)
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  isProxy(): never;
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  isExternal(): never;
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  isModuleNamespaceObject(): never;
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};
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```
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**Usage Examples:**
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```javascript
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const util = require('util');
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// Collections
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util.types.isMap(new Map()); // true
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util.types.isSet(new Set()); // true
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util.types.isWeakMap(new WeakMap()); // true
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// Typed Arrays
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util.types.isUint8Array(new Uint8Array()); // true
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util.types.isFloat32Array(new Float32Array()); // true
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util.types.isTypedArray(new Int16Array()); // true
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// Array Buffers
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util.types.isArrayBuffer(new ArrayBuffer(16)); // true
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util.types.isDataView(new DataView(new ArrayBuffer(16))); // true
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// Boxed Primitives
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util.types.isNumberObject(new Number(42)); // true
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util.types.isStringObject(new String('hello')); // true
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util.types.isBoxedPrimitive(new Boolean(true)); // true
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// Functions
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util.types.isAsyncFunction(async () => {}); // true
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util.types.isGeneratorFunction(function* () {}); // true
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// Promises
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util.types.isPromise(Promise.resolve()); // true
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util.types.isPromise({ then: () => {}, catch: () => {} }); // true
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// Arguments object
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function example() {
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  return util.types.isArgumentsObject(arguments); // true
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}
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```