@haixing_hu/typeinfo

typeinfo

typeinfo is a lightweight JavaScript library that extends the functionality of the typeof operator, allowing for getting more precise and reliable type information of JavaScript variables. It provides enhanced support for the latest ECMAScript standards and offers a comprehensive solution for type identification in your projects.

Table of Contents

• Features
• Installation
• Example
• Usage
  • Type
  • Subtype
  • Category
  • Feature Detection Constants
  • Type Prototype Constants
  • Type Detection Functions
• Why Proxy Type Information is Unavailable
• Contributing
• License

Features

• Accurate type information for JavaScript variables.
• Support for the latest ECMAScript standards.
• Easy integration into your projects.

Installation

You can install typeinfo via npm:

npm install @haixing_hu/typeinfo

or via yarn:

yarn add @haixing_hu/typeinfo

Example

The following is a usage example:

import typeInfo from '@haixing_hu/typeinfo';

function clone(value) {
  const info = typeInfo(value);
  switch (info.type) {
    case 'undefined':      // drop down
    case 'null':           // drop down
    case 'boolean':        // drop down
    case 'number':         // drop down
    case 'string':         // drop down
    case 'symbol':         // drop down
    case 'bigint':         // drop down
    case 'function':       // drop down
      return value;        // don't need to clone immutable objects
    case 'object':         // drop down
    default:
      switch (info.subtype) {
        case 'Boolean':    // drop down
        case 'Number':     // drop down
        case 'String':     // drop down
          return value;    // don't need to clone immutable objects
        case 'Date':
          return new Date(value);
        case 'RegExp':
          return new RegExp(value);
        ...
      }
  }
} 

or use info.category to simplify the code logic:

import typeInfo from '@haixing_hu/typeinfo';

function clone(value) {
  const info = typeInfo(value);
  switch (info.category) {
    case 'undefined':       // drop down
    case 'null':            // drop down
    case 'primitive':       // drop down
    case 'function':       
      return value;         // don't need to clone immutable objects
    case 'primitive-wrapper': 
      return value;         // don't need to clone immutable objects
    case 'date':
      return new Date(value);
    case 'regexp':
      return new RegExp(value);
    ...
  }
}

Usage

The library provides the following function:

function typeInfo(value)

• Parameters:
  • value: any: a specified value.
• Returns:
  • object: the information about the type of the specified value.

This function returns the information about the precise type of the specified value. The returned information is an object with the following properties:

• type: string: the name of the type of the specified value. This is the same as the value returned by the built-in typeof operator, except that the type of null is 'null' instead of 'object'. See Type for more details.
• subtype: string: the name of the subtype of the specified value. This property is only presented when the type of the specified value is 'object' or 'function'. See Subtype for more details.
• category: string: the category of ths specified value. This property is present for all type of values. See Category for more details.
• isPrimitive: boolean: whether the specified value is a primitive value.
• isBuiltIn: boolean: whether the specified value is a JavaScript built-in primitive or built-in object.
• isWebApi: boolean: whether the specified value is a Web API built-in object.
• constructor: function: the constructor function of the specified value. This property is only present when the type of the specified value is 'object'.

Type

The type information object returned by typeInfo() has a type property, which has the following possible values:

• 'undefined': if the value is undefined.
• 'null': if the value is null.
• 'boolean': if the value is a primitive boolean value.
• 'number': if the value is a primitive number value.
• 'string': if the value is a primitive string value.
• 'symbol': if the value is a symbol value.
• 'bigint': if the value is a primitive bigint value.
• 'function': if the value is a function.
• 'object': if the value is an object.

The type property value is similar to the value returned by the built-in typeof operator, except that the type of null is 'null' instead of 'object'.

Subtype

If the value is of the type is function or object, the type information object returned by typeInfo() has a subtype property, which is the name of the detailed subtype of the specified value.

The possible subtype names of the 'function' type are:

• 'Function': if the value is a sync function.
• 'GeneratorFunction': if the value is a sync generator function.
• 'AsyncFunction': if the value is an async function.
• 'AsyncGeneratorFunction': if the value is an async generator function.

Note that the 'AsyncFunction' and 'AsyncGeneratorFunction' subtypes are only available in the JavaScript engine that support the async functions.

The possible subtype names of the 'object' type are:

• 'Boolean': if the value is a JavaScript built-in Boolean object.
• 'Number': if the value is a JavaScript built-in Number object.
• 'String': if the value is a JavaScript built-in String object.
• 'RegExp': if the value is a regular expression, i.e., the JavaScript built-in RegExp object.
• 'Date': if the value is a JavaScript built-in Date object.
• 'Map': if the value is a JavaScript built-in Map object.
• 'WeakMap': if the value is a JavaScript built-in WeakMap object.
• 'Set': if the value is a JavaScript built-in Set object.
• 'WeakSet': if the value is a JavaScript built-in WeakSet object.
• 'Array': if the value is a JavaScript built-in Array object.
• 'Int8Array': if the value is a JavaScript built-in Int8Array object.
• 'Uint8Array': if the value is a JavaScript built-in Uint8Array object.
• 'Uint8ClampedArray': if the value is a JavaScript built-in Uint8ClampedArray object.
• 'Int16Array': if the value is a JavaScript built-in Int16Array object.
• 'Uint16Array': if the value is a JavaScript built-in Uint16Array object.
• 'Int32Array': if the value is a JavaScript built-in Int32Array object.
• 'Uint32Array': if the value is a JavaScript built-in Uint32Array object.
• 'BigInt64Array': if the value is a JavaScript built-in BigInt64Array object.
• 'BigUint64Array': if the value is a JavaScript built-in BigUint64Array object.
• 'Float32Array': if the value is a JavaScript built-in Float32Array object.
• 'Float64Array': if the value is a JavaScript built-in Float64Array object.
• 'ArrayBuffer': if the value is a JavaScript built-in ArrayBuffer object.
• 'SharedArrayBuffer': if the value is a JavaScript built-in SharedArrayBuffer object.
• 'DataView': if the value is a JavaScript built-in DataView object.
• 'WeakRef': if the value is a JavaScript built-in WeakRef object.
• 'Promise': if the value is a JavaScript built-in Promise object.
• 'Error': if the value is an object of the JavaScript built-in Error class.
• 'EvalError': if the value is an object of the JavaScript built-in EvalError class.
• 'RangeError': if the value is an object of the JavaScript built-in RangeError class.
• 'ReferenceError': if the value is an object of the JavaScript built-in ReferenceError class.
• 'SyntaxError': if the value is an object of the JavaScript built-in SyntaxError class.
• 'TypeError': if the value is an object of the JavaScript built-in TypeError class.
• 'URIError': if the value is an object of the JavaScript built-in URIError class.
• 'AggregateError': if the value is an object of the JavaScript built-in AggregateError class.
• 'InternalError': if the value is an object of the JavaScript built-in InternalError class.
• 'Intl.Collator': if the value is a JavaScript built-in Intl.Collator object.
• 'Intl.DateTimeFormat': if the value is a JavaScript built-in Intl.DateTimeFormat object.
• 'Intl.DisplayNames': if the value is a JavaScript built-in Intl.DisplayNames object.
• 'Intl.DurationFormat': if the value is a JavaScript built-in Intl.DurationFormat object.
• 'Intl.ListFormat': if the value is a JavaScript built-in Intl.ListFormat object.
• 'Intl.Locale': if the value is a JavaScript built-in Intl.Locale object.
• 'Intl.NumberFormat': if the value is a JavaScript built-in Intl.NumberFormat object.
• 'Intl.PluralRules': if the value is a JavaScript built-in Intl.PluralRules object.
• 'Intl.RelativeTimeFormat': if the value is a JavaScript built-in Intl.RelativeTimeFormat object.
• 'Intl.Segmenter': if the value is a JavaScript built-in Intl.Segmenter object.
• 'MapIterator': if the value is a Map Iterator returned by
  • Map.prototype.values(),
  • Map.prototype.keys(),
  • Map.prototype.entries(), and
  • Map.prototype[@@iterator]().
• 'SetIterator': if the value is a Set Iterator returned by
  • Set.prototype.values(),
  • Set.prototype.keys(),
  • Set.prototype.entries(), and
  • Set.prototype[@@iterator]().
• 'ArrayIterator': if the value is a Array iterator returned by
  • Array.prototype.values(),
  • Array.prototype.keys(),
  • Array.prototype.entries(),
  • Array.prototype[@@iterator](),
  • TypedArray.prototype.values(),
  • TypedArray.prototype.keys(), and
  • TypedArray.prototype.entries().
• 'StringIterator': if the value is a String Iterator returned by
  • String.prototype[@@iterator]().
• 'RegExpStringIterator': if the value is a RegExp String Iterator returned by
  • RegExp.prototype[@@matchAll](), and
  • String.prototype.matchAll().
• 'SegmenterStringIterator': if the value is a Segments Iterator returned by
  • the [@@iterator]() method of the Segments object returned by Intl.Segmenter.prototype.segment().
• 'FinalizationRegistry': if the value is an instance of the JavaScript built-in FinalizationRegistry class. A FinalizationRegistry object lets you request a callback when a value is garbage-collected.
• 'Arguments: if the value is the JavaScript built-in arguments object, which is a special array-like object storing the calling arguments of a function.
• 'Generator': if the value is a generator object, i.e., the object returned by a sync generator function.
• 'AsyncGenerator': if the value is an async generator object, i.e., the object returned by an async generator function.
• 'GlobalObject': if the value is the global object. A global object is an object that always exists in the global scope.
• 'Object': if the value is a plain JavaScript object, i.e., an object defined by the syntax of obj = { ... }.
• '' (empty string): if the value is an instance of a user defined anonymous class.
• value[Symbol.toStringTag]: if the value has a customized Symbol.toStringTag property.
• value.constructor.name: if the value has a constructor with a name, and the name is not 'Object'. That is, if the value is an instance of a user defined class, and the class has a name, the subtype is the name of that class. For example, if the value is an instance of the MyClass class, the subtype is 'MyClass'.
• the name extracted from value.toString(): if the value does not match any of the above cases, the subtype is the name extracted from the value.toString() result (usually a string of the form '[object XXX]'), and removes any inner spaces in the name. For example, if the value.toString() result is '[object My Class ]', the subtype is 'MyClass'.

The detailed list of supported JavaScript built-in objects can be found at Standard built-in objects.

Category

The type information object returned by typeInfo() has a category property, which is a string that describes the category of the value. The possible values of the category property are:

• 'null': if the value is null.
• 'undefined': if the value is undefined.
• 'boolean': if the value is a primitive boolean value or a built-in Boolean object.
• 'numeric': if the value is a primitive number value, or a primitive bigint value, or a built-in Number object.
• 'string': if the value is a primitive string value, or a built-in String object.
• 'symbol': if the value is a primitive symbol value.
• 'function': if the value is a function, including sync functions, async functions, sync generator functions, and async generator functions.
• 'regexp': if the value is a regular expression, i.e., the JavaScript built-in RegExp object.
• 'date': if the value is a JavaScript built-in Date object.
• 'map': if the value is a JavaScript built-in Map object.
• 'set': if the value is a JavaScript built-in Set object.
• 'array': if the value is a JavaScript built-in Array object.
• 'typed-array': if the value is a JavaScript built-in typed array object, including 'Int8Array', 'Uint8Array', 'Uint8ClampedArray', 'Int16Array', 'Uint16Array', 'Int32Array', 'Uint32Array', 'BigInt64Array', 'BigUint64Array', 'Float32Array', and 'Float64Array'.
• 'buffer': if the value is a JavaScript built-in buffer object, including 'ArrayBuffer' and 'SharedArrayBuffer'.
• 'data-view': if the value is a JavaScript built-in DataView object.
• 'weak': if the value is a JavaScript built-in WeakMap, WeakSet, or WeakRef object. Note that weak referenced objects cannot be cloned.
• 'promise': if the value is a JavaScript built-in Promise object.
• 'error': if the value is an object of the JavaScript built-in Error class, or an object of a subclass of the Error class.
• 'intl': if the value is a JavaScript built-in object under the Intl namespace, including 'Intl.Collator', 'Intl.DateTimeFormat', 'Intl.DisplayNames', 'Intl.DurationFormat', 'Intl.ListFormat', 'Intl.Locale', 'Intl.NumberFormat', 'Intl.PluralRules', and 'Intl.RelativeTimeFormat'.
• 'iterator': if the value is an iterator object, including 'MapIterator', 'SetIterator', 'ArrayIterator', 'StringIterator', 'RegExpStringIterator', and 'SegmenterStringIterator'.
• 'finalization-registry': if the value is an instance of the JavaScript built-in FinalizationRegistry class. A FinalizationRegistry object lets you request a callback when a value is garbage-collected.
• 'global': if the value is the global object.
• 'arguments': if the value is the JavaScript built-in arguments object.
• 'DOM': if the value is a DOM object, e.g., the 'Node', 'Element', 'Document', 'Window', etc.
• 'CSSOM': if the value is a CSSOM object, e.g., 'CSSStyleDeclaration', 'CSSRule', 'CSSStyleSheet', etc.
• 'event': if the value is a event object, i.e., the 'Event' and all its subclasses.
• 'console': if the value is the 'window.console' object.
• 'file': if the value is a File API object, i.e., the 'File', 'Blob', 'FileList', etc.
• 'generator': if the value is a generator object, i.e., the object returned by a sync generator function, including 'Generator' and 'AsyncGenerator'.
• 'object': if the value is a plain JavaScript object.
• 'class': if the value is an instance of a user defined class.

Feature Detection Constants

This library provides the following constants for feature detection:

• AGGREGATEERROR_EXISTS: whether the JavaScript built-in class AggregateError exists.
• ARRAYBUFFER_EXISTS: whether the JavaScript built-in class ArrayBuffer exists.
• ARRAY_ISARRAY_EXISTS: whether the JavaScript built-in function Array.isArray() exists.
• ARRAY_ITERATOR_EXISTS: whether the JavaScript built-in function Array.prototype[Symbol.iterator] exists.
• ATOMICS_EXISTS: whether the JavaScript built-in object Atomics exists.
• BIGINT64ARRAY_EXISTS: whether the JavaScript built-in class BigInt64Array exists.
• BIGINT_EXISTS: whether the JavaScript built-in primitive bigint and built-in function BigInt exists.
• BIGUINT64ARRAY_EXISTS: whether the JavaScript built-in class BigUint64Array exists.
• DATAVIEW_EXISTS: whether the JavaScript built-in class DataView exists.
• FINALIZATIONREGISTRY_EXISTS: whether the JavaScript built-in class FinalizationRegistry exists.
• FLOAT32ARRAY_EXISTS: whether the JavaScript built-in class Float32Array exists.
• FLOAT64ARRAY_EXISTS: whether the JavaScript built-in class Float64Array exists.
• INT16ARRAY_EXISTS: whether the JavaScript built-in class Int16Array exists.
• INT32ARRAY_EXISTS: whether the JavaScript built-in class Int32Array exists.
• INT8ARRAY_EXISTS: whether the JavaScript built-in class Int8Array exists.
• INTERNALERROR_EXISTS: whether the JavaScript built-in class InternalError class exists.
• INTL_COLLATOR_EXISTS: whether the JavaScript built-in class Intl.Collator class exists.
• INTL_DATETIMEFORMAT_EXISTS: whether the JavaScript built-in class Intl.DateTimeFormat class exists.
• INTL_DISPLAYNAMES_EXISTS: whether the JavaScript built-in class Intl.DisplayNames class exists.
• INTL_DURATIONFORMAT_EXISTS: whether the JavaScript built-in class Intl.DurationFormat class exists.
• INTL_EXISTS: whether the JavaScript built-in Intl namespace exists.
• INTL_LISTFORMAT_EXISTS: whether the JavaScript built-in class Intl.ListFormat exists.
• INTL_LOCALE_EXISTS: whether the JavaScript built-in class Intl.Locale exists.
• INTL_NUMBERFORMAT_EXISTS: whether the JavaScript built-in class Intl.NumberFormat exists.
• INTL_PLURALRULES_EXISTS: whether the JavaScript built-in class Intl.PluralRules exists.
• INTL_RELATIVETIMEFORMAT_EXISTS: whether the JavaScript built-in class Intl.RelativeTimeFormat exists.
• INTL_SEGMENTER_EXISTS: whether the JavaScript built-in class Intl.Segmenter exists.
• INTL_SEGMENTER_ITERATOR_EXISTS: whether the JavaScript built-in function Intl.Segmenter.prototype[Symbol.iterator] exists.
• MAP_ENTRIES_EXISTS: whether the JavaScript built-in function Map.prototype.entries() exists.
• MAP_EXISTS: whether the JavaScript built-in class Map exists.
• MAP_ITERATOR_EXISTS: whether the JavaScript built-in function Map.prototype[Symbol.iterator] exists.
• PROMISE_EXISTS: whether the JavaScript built-in class Promise exists.
• PROXY_EXISTS: whether the JavaScript built-in class Proxy exists.
• REFLECT_EXISTS: whether the JavaScript built-in namespace Reflect exists.
• REGEXP_EXISTS: whether the JavaScript built-in class RegExp exists.
• REGEXP_ITERATOR_EXISTS: whether the JavaScript built-in function RegExp.prototype[Symbol.matchAll] exists.
• SET_ENTRIES_EXISTS: whether the JavaScript built-in function Set.prototype.entries() exists.
• SET_EXISTS: whether the JavaScript built-in class Set exists.
• SET_ITERATOR_EXISTS: whether the JavaScript built-in function Set.prototype[Symbol.iterator] exists.
• SHAREDARRAYBUFFER_EXISTS: whether the JavaScript built-in class SharedArrayBuffer exists.
• STRING_ITERATOR_EXISTS: whether the JavaScript built-in function String.prototype[Symbol.iterator] exists.
• SYMBOL_EXISTS: whether the JavaScript built-in Symbol exists.
• SYMBOL_ITERATOR_EXISTS: whether the JavaScript built-in function Symbol.prototype[Symbol.iterator] exists.
• SYMBOL_MATCH_ALL_EXISTS: whether the JavaScript built-in function Symbol.prototype[Symbol.matchAll] exists.
• SYMBOL_TO_STRING_TAG_EXISTS: whether the JavaScript built-in function Symbol.prototype[Symbol.toStringTag] exists.
• UINT16ARRAY_EXISTS: whether the JavaScript built-in class Uint16Array exists.
• UINT32ARRAY_EXISTS: whether the JavaScript built-in class Uint32Array exists.
• UINT8ARRAY_EXISTS: whether the JavaScript built-in class Uint8Array exists.
• UINT8CLAMPEDARRAY_EXISTS: whether the JavaScript built-in class Uint8ClampedArray exists.
• WEAKMAP_EXISTS: whether the JavaScript built-in class WeakMap exists.
• WEAKREF_EXISTS: whether the JavaScript built-in class WeakRef exists.
• WEAKSET_EXISTS: whether the JavaScript built-in class WeakSet exists.

The following code shows how to use these constants:

import { WEAKMAP_EXISTS } from '@haixing_hu/typeinfo';

function foo(value) {
  if (WEAKMAP_EXISTS) {
    ...
  } else {
    ...
  }
}

Type Prototype Constants

This library provides the following constants for the prototypes of JavaScript built-in objects:

• AggregateErrorPrototype: the prototype of the JavaScript built-in AggregateError objects, or undefined if the AggregateError class does not exist.
• ArrayBufferPrototype: the prototype of the JavaScript built-in ArrayBuffer objects, or undefined if the ArrayBuffer class does not exist.
• ArrayIteratorPrototype: the prototype of the JavaScript built-in array iterator objects, or undefined if the array iterator does not exist.
• BigInt64ArrayPrototype: the prototype of the JavaScript built-in BigInt64Array objects, or undefined if the BigInt64Array class does not exist.
• BigIntPrototype: the prototype of the JavaScript built-in bigint primitive, or undefined if the bigint primitive does not exist.
• BigUint64ArrayPrototype: the prototype of the JavaScript built-in BigUint64Array objects, or undefined if the BigUint64Array class does not exist.
• DataViewPrototype: the prototype of the JavaScript built-in DataView objects, or undefined if the DataView class does not exist.
• FinalizationRegistryPrototype: the prototype of the JavaScript built-in FinalizationRegistry objects, or undefined if the FinalizationRegistry class does not exist.
• Float32ArrayPrototype: the prototype of the JavaScript built-in Float32Array objects, or undefined if the Float32Array class does not exist.
• Float64ArrayPrototype: the prototype of the JavaScript built-in Float64Array objects, or undefined if the Float64Array class does not exist.
• Int16ArrayPrototype: the prototype of the JavaScript built-in Int16Array objects, or undefined if the Int16Array class does not exist.
• Int32ArrayPrototype: the prototype of the JavaScript built-in Int32Array objects, or undefined if the Int32Array class does not exist.
• Int8ArrayPrototype: the prototype of the JavaScript built-in Int8Array objects, or undefined if the Int8Array class does not exist.
• IntelSegmentIteratorPrototype: the prototype of the JavaScript built-in Intl.SegmentIterator objects, or undefined if the Intl.SegmentIterator class does not exist.
• InternalErrorPrototype: the prototype of the JavaScript built-in InternalError objects, or undefined if the InternalError class does not exist.
• IntlCollatorPrototype: the prototype of the JavaScript built-in Intl.Collator objects, or undefined if the Intl.Collator class does not exist.
• IntlDateTimeFormatPrototype: the prototype of the JavaScript built-in Intl.DateTimeFormat objects, or undefined if the Intl.DateTimeFormat class does not exist.
• IntlDisplayNamesPrototype: the prototype of the JavaScript built-in Intl.DisplayNames objects, or undefined if the Intl.DisplayNames class does not exist.
• IntlDurationFormatPrototype: the prototype of the JavaScript built-in Intl.DurationFormat objects, or undefined if the Intl.DurationFormat class does not exist.
• IntlListFormatPrototype: the prototype of the JavaScript built-in Intl.ListFormat objects, or undefined if the Intl.ListFormat class does not exist.
• IntlLocalePrototype: the prototype of the JavaScript built-in Intl.Locale objects, or undefined if the Intl.Locale class does not exist.
• IntlNumberFormatPrototype: the prototype of the JavaScript built-in Intl.NumberFormat objects, or undefined if the Intl.NumberFormat class does not exist.
• IntlPluralRulesPrototype: the prototype of the JavaScript built-in Intl.PluralRules objects, or undefined if the Intl.PluralRules class does not exist.
• IntlRelativeTimeFormatPrototype: the prototype of the JavaScript built-in Intl.RelativeTimeFormat objects, or undefined if the Intl.RelativeTimeFormat class does not exist.
• IntlSegmenterPrototype: the prototype of the JavaScript built-in Intl.Segmenter objects, or undefined if the Intl.Segmenter class does not exist.
• MapIteratorPrototype: the prototype of the JavaScript built-in Map iterator objects, or undefined if the Map iterator does not exist.
• MapPrototype: the prototype of the JavaScript built-in Map objects, or undefined if the Map class does not exist.
• PromisePrototype: the prototype of the JavaScript built-in Promise objects, or undefined if the Promise class does not exist.
• RegExpIteratorPrototype: the prototype of the JavaScript built-in RegExp iterator objects, or undefined if the RegExp iterator does not exist.
• RegExpPrototype: the prototype of the JavaScript built-in RegExp objects, or undefined if the RegExp class does not exist.
• SetIteratorPrototype: the prototype of the JavaScript built-in Set iterator objects, or undefined if the Set iterator does not exist.
• SetPrototype: the prototype of the JavaScript built-in Set objects, or undefined if the Set class does not exist.
• SharedArrayBufferPrototype: the prototype of the JavaScript built-in SharedArrayBuffer objects, or undefined if the SharedArrayBuffer class does not exist.
• StringIteratorPrototype: the prototype of the JavaScript built-in String iterator objects, or undefined if the String iterator does not exist.
• SymbolPrototype: the prototype of the JavaScript built-in Symbol primitives, or undefined if the Symbol primitive does not exist.
• Uint16ArrayPrototype: the prototype of the JavaScript built-in Uint16Array objects, or undefined if the Uint16Array class does not exist.
• Uint32ArrayPrototype: the prototype of the JavaScript built-in Uint32Array objects, or undefined if the Uint32Array class does not exist.
• Uint8ArrayPrototype: the prototype of the JavaScript built-in Uint8Array objects, or undefined if the Uint8Array class does not exist.
• Uint8ClampedArrayPrototype: the prototype of the JavaScript built-in Uint8ClampedArray objects, or undefined if the Uint8ClampedArray class does not exist.
• WeakMapPrototype: the prototype of the JavaScript built-in WeakMap objects, or undefined if the WeakMap class does not exist.
• WeakRefPrototype: the prototype of the JavaScript built-in WeakRef objects, or undefined if the WeakRef class does not exist.
• WeakSetPrototype: the prototype of the JavaScript built-in WeakSet objects, or undefined if the WeakSet class does not exist.

The following code shows how to use these constants:

import { WeakMapPrototype } from '@haixing_hu/typeinfo';

function foo(value) {
  const proto = Object.getPrototypeOf(value);
  if (proto === WeakMapPrototype) {
    ...
  } else {
    ...
  }
}

Type Detection Functions

The library provides the following functions for type detection:

• isArguments(value): boolean: whether the specified value is the JavaScript built-in arguments object.
• isBoolean(value): boolean: whether the specified value is a JavaScript built-in boolean primitive or Boolean object.
• isBuffer(value): boolean: whether the specified value is a JavaScript built-in ArrayBuffer or SharedArrayBuffer object.
• isBuiltInClass(Class): boolean: whether the specified class is a JavaScript built-in class.
• isCollection(value): boolean: whether the specified value is a JavaScript built-in collection object, i.e., a Map or Set object.
• isError(value): boolean: whether the specified value is an instance of the JavaScript built-in Error class, or an instance of a subclass of the Error class.
• isIntl(value): boolean: whether the specified value is a JavaScript built-in object under the Intl namespace.
• isIterator(value): boolean: whether the specified value is an iterator object, i.e., an object with a next() method.
• isNumeric(value): boolean: whether the specified value is a JavaScript built-in number primitive, or bigint primitive, or Number object.
• isString(value): boolean: whether the specified value is a JavaScript built-in string primitive, or String object.
• isTypedArray(value): boolean: whether the specified value is a JavaScript built-in typed array object.
• isWeak(value): boolean: whether the specified value is a JavaScript built-in weak referenced object, i.e., a WeakMap, WeakSet, or WeakRef object.

The following code shows how to use these functions:

import { isTypedArray } from '@haixing_hu/typeinfo';

function foo(value) {
  if (isTypedArray(value)) {
    ...
  } else {
    ...
  }
}

Why Proxy Type Information is Unavailable

One of the primary purposes of Proxy objects in JavaScript is to allow developers to customize the behavior of object operations, acting as a delegate for another object (referred to as the target object). One of the key features of Proxy is its transparency—externally, unless the proxy object is intentionally designed to reveal itself, it is challenging to distinguish a Proxy object from the target object it represents. This is largely because Proxy can intercept and redefine almost all fundamental operations of an object, including but not limited to property access, assignment, and enumeration.

Therefore, when libraries like typeinfo attempt to retrieve type information of an object, the inherent transparency of Proxy means these libraries can only process and "see" the final outcomes of operations, without direct means to identify whether these operations were intercepted by a Proxy. If a Proxy flawlessly mimics the behavior of its target object, there exists no reliable method to determine from the operation outcomes whether an object is a Proxy. In essence, the design philosophy of Proxy aims to make it nearly invisible to external observation, making it impossible for even libraries specialized in fetching type information to definitively ascertain if an object is a Proxy, unless the proxy object deliberately exposes its identity through certain intercepting behaviors. This design significantly enhances the power and flexibility of Proxy, but it also means that directly detecting Proxy objects through external observation presents a challenge.

Contributing

If you find any issues or have suggestions for improvements, please feel free to open an issue or submit a pull request to the GitHub repository.

License

typeinfo is distributed under the Apache 2.0 license. See the LICENSE file for more details.