@lopatnov/get-internal-type

Determine the internal JavaScript [[Class]] of an object. A lightweight, cross-platform TypeScript library for reliable runtime type detection.

Supported Types
Installation
Usage
API
Demo
Contributing
Built With
License

Supported Types

Primitives

Object Value	Result	Since
`undefined`	`"undefined"`	1.0.0
`null`	`"null"`	1.0.0
`false`	`"boolean"`	1.0.0
`123`	`"number"`	1.0.0
`BigInt(9007199254740991)`	`"bigint"`	1.0.0
`"hello"`	`"string"`	1.0.0
`Symbol("123")`	`"symbol"`	1.0.0

Functions

Object Value	Result	Since
`function(){}`	`"function"`	1.0.0
`() => {}`	`"function"`	1.0.0
`class Simple {}`	`"function"`	1.0.0
`async function(){}`	`"function"`	2.0.0
`function* () {}`	`"generatorfunction"`	1.4.1
`async function* () {}`	`"generatorfunction"`	2.0.0

Objects

Object Value	Result	Since
`{}`	`"object"`	1.0.0
`new (class SomeCustomClass {})`	`"object"`	1.0.0
`[1,2,3]`	`"array"`	1.0.0
`/s+/gi`	`"regexp"`	1.0.0
`new Date()`	`"date"`	1.0.0
`new Error("A mistake")`	`"error"`	1.0.0
`Promise.resolve('any')`	`"promise"`	1.4.0

Collections

Object Value	Result	Since
`new Map()`	`"map"`	1.2.0
`new WeakMap()`	`"map"`	1.3.1
`new Set()`	`"set"`	1.2.0
`new WeakSet()`	`"set"`	1.3.1

Generators

Object Value	Result	Since
`(function* () {})()`	`"generator"`	1.4.1
`(async function* () {})()`	`"generator"`	2.0.0

Typed Arrays

All typed arrays return "typedarray" (since 1.3.0):

Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, Float32Array, Float64Array, BigInt64Array, BigUint64Array

Structured Data

Object Value	Result	Since
`new ArrayBuffer(8)`	`"arraybuffer"`	1.5.0
`new SharedArrayBuffer(8)`	`"arraybuffer"`	2.0.0
`new DataView(buffer)`	`"dataview"`	1.5.0

Weak References

Object Value	Result	Since
`new WeakRef(obj)`	`"weakref"`	2.0.0
`new FinalizationRegistry(cb)`	`"finalizationregistry"`	2.0.0

Installation

npm install @lopatnov/get-internal-type

Browser:

<script src="https://lopatnov.github.io/get-internal-type/dist/get-internal-type.umd.min.js"></script>

Usage

ES Modules

import getInternalType from "@lopatnov/get-internal-type";
// or named import:
// import { getInternalType } from "@lopatnov/get-internal-type";

getInternalType(42); // "number"
getInternalType("hello"); // "string"
getInternalType([1, 2, 3]); // "array"
getInternalType(new Map()); // "map"
getInternalType(new Set()); // "set"
getInternalType(Promise.resolve()); // "promise"
getInternalType(null); // "null"
getInternalType(undefined); // "undefined"

CommonJS

const getInternalType = require("@lopatnov/get-internal-type");

getInternalType({}); // "object"
getInternalType(new Date()); // "date"
getInternalType(/regex/); // "regexp"
getInternalType(new Error()); // "error"

Browser (UMD)

<script src="https://lopatnov.github.io/get-internal-type/dist/get-internal-type.umd.min.js"></script>
<script>
  console.log(getInternalType([1, 2, 3])); // "array"
</script>

API

`getInternalType(obj: any): string`

Returns a lowercase string representing the internal [[Class]] of the given object.

Parameter	Type	Description
`obj`	`any`	The value to determine the type of

Returns: string — a lowercase type identifier.

// Primitives
getInternalType(undefined); // "undefined"
getInternalType(null); // "null"
getInternalType(false); // "boolean"
getInternalType(Symbol("123")); // "symbol"
getInternalType(123); // "number"
getInternalType(BigInt(9007199254740991)); // "bigint"
getInternalType("hello"); // "string"

// Objects
getInternalType({}); // "object"
getInternalType([1, 2, 3]); // "array"
getInternalType(/s+/gi); // "regexp"
getInternalType(new Date()); // "date"
getInternalType(new Error("oops")); // "error"

// Collections
getInternalType(new Map()); // "map"
getInternalType(new WeakMap()); // "map"
getInternalType(new Set()); // "set"
getInternalType(new WeakSet()); // "set"

// Functions & Generators
getInternalType(() => {}); // "function"
getInternalType(async () => {}); // "function"
getInternalType(function* () {}); // "generatorfunction"
getInternalType(async function* () {}); // "generatorfunction"
getInternalType((function* () {})()); // "generator"

// Structured Data
getInternalType(Promise.resolve("any")); // "promise"
getInternalType(new ArrayBuffer(16)); // "arraybuffer"
getInternalType(new DataView(new ArrayBuffer(16))); // "dataview"
getInternalType(new Int8Array(8)); // "typedarray"

// Weak References
getInternalType(new WeakRef({})); // "weakref"
getInternalType(new FinalizationRegistry(() => {})); // "finalizationregistry"

Demo

Contributing

Contributions are welcome! Please read CONTRIBUTING.md before opening a pull request.

Bug reports → open an issue
Questions → Discussions
Found it useful? A star on GitHub helps others discover the project

Built With

TypeScript — strict typing throughout
Rollup — bundled to ESM, CJS, and UMD formats
Jest — unit testing with coverage
ESLint + Prettier — linting and formatting

get-internal-type

A TypeScript library. Some cross-browser techniques to determine the JavaScript [[Class]] of an object.