@phun-ky/typeof

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About

A set of JavaScript helper functions to check for types.

Table of Contents

- @phun-ky/typeof
- About
- Installation
- Usage
- API
- isBoolean()
- isBuiltInCallable()
- isBuiltInConstructor()
- isClass()
- isDefined()
- isFunction()
- isInstanceOfUnknownClass()
- isNotBoolean()
- isNotNumber()
- isNotString()
- isNotUndefined()
- isNumber()
- isObjectLoose()
- isObjectPlain()
- isObjectStrict()
- isString()
- isUndefined()
- Development
- Contributing
- License
- Changelog
- Sponsor me

Installation

``shell-session
npm i --save @phun-ky/typeof
`

Usage

Either import and run the required functions:

`javascript
import { isString } from '@phun-ky/typeof';

isString('asd'); // true;
`

API

$3

Checks if the given value is a boolean.

#### Param

The value to check.

#### Call Signature

`ts
function isBoolean(value): value is boolean;
`

Defined in: main.ts:85

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is boolean

#### Call Signature

`ts
function isBoolean(value): boolean;
`

Defined in: main.ts:90

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is a built-in JavaScript callable.

A built-in callable is either:

- a standard constructor (e.g., Object, Array, Date, Map), or
- a callable non-constructable built-in (BigInt, Symbol).

This function first verifies the value is a function, then tests identity
against a curated set of built-ins.

Overloads:

- Predicate: narrows the value to BuiltInCallable on success.
- Boolean: usable in contexts that require a plain (v) => boolean.

#### Param

The value to check.

#### Example

`ts
isBuiltInCallable(Object); // true
isBuiltInCallable(Array); // true
isBuiltInCallable(BigInt); // true (callable but not a constructor)
isBuiltInCallable(Symbol); // true (callable but not a constructor)
isBuiltInCallable(class X {}); // false
isBuiltInCallable(() => {}); // false
isBuiltInCallable(123); // false

// Type narrowing:
declare const fn: unknown;
if (isBuiltInCallable(fn)) {
// fn is now typed as BuiltInCallable
console.log(fn.name);
}
`

#### See

-
-
-

#### Call Signature

`ts
function isBuiltInCallable(value): value is BuiltInCallable;
`

Defined in: main.ts:541

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is BuiltInCallable

#### Call Signature

`ts
function isBuiltInCallable(value): boolean;
`

Defined in: main.ts:546

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is a built-in JavaScript constructor.

This function verifies whether the provided value is a function and matches
one of JavaScript's built-in constructors, such as Object, Array, Function, etc.

#### Param

The value to check.

#### Example

`ts
console.log(isBuiltInConstructor(Object)); // Output: true
console.log(isBuiltInConstructor(Array)); // Output: true
console.log(isBuiltInConstructor(class MyClass {})); // Output: false
console.log(isBuiltInConstructor(() => {})); // Output: false
console.log(isBuiltInConstructor(123)); // Output: false
`

#### Call Signature

`ts
function isBuiltInConstructor(value): value is BuiltInConstructor;
`

Defined in: main.ts:441

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is BuiltInConstructor

#### Call Signature

`ts
function isBuiltInConstructor(value): boolean;
`

Defined in: main.ts:448

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is a class constructor.

This function determines whether the provided value is a class by verifying
if it is a function and checking its prototype descriptor. Class constructors
always have a non-writable prototype, while regular functions do not.

Will always return false on built in constructors like Date or Array.

#### Param

The value to check.

#### Example

`ts
class MyClass {}
console.log(isClass(MyClass)); // Output: true

function regularFunction() {}
console.log(isClass(regularFunction)); // Output: false

console.log(isClass(() => {})); // Output: false
console.log(isClass(null)); // Output: false
`

#### Call Signature

`ts
function isClass(value): value is ClassCtor;
`

Defined in: main.ts:366

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is ClassCtor

#### Call Signature

`ts
function isClass(value): boolean;
`

Defined in: main.ts:371

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Copy of isNotUndefined

#### Param

The value to check.

#### Call Signature

`ts
function isDefined(value): value is Exclude;
`

Defined in: main.ts:166

##### Type Parameters

| Type Parameter |
| -------------- |
| T |

##### Parameters

| Parameter | Type |
| --------- | ---- |
| value | T |

##### Returns

value is Exclude

#### Call Signature

`ts
function isDefined(value): boolean;
`

Defined in: main.ts:171

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is a function.

#### Param

The value to check.

#### Call Signature

`ts
function isFunction(value): value is (args: unknown[]) => unknown;
`

Defined in: main.ts:635

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is (args: unknown[]) => unknown

#### Call Signature

`ts
function isFunction(value): boolean;
`

Defined in: main.ts:642

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is an instance of a non-standard (unknown) class.

This function determines whether the provided value is an object and has a prototype
that is neither Object.prototype (standard object) nor null (no prototype).
It helps differentiate between instances of custom classes and plain objects.

#### Param

The value to check.

#### Example

`ts
class MyClass {}
console.log(isInstanceOfUnknownClass(new MyClass())); // Output: true
console.log(isInstanceOfUnknownClass({})); // Output: false
console.log(isInstanceOfUnknownClass(Object.create(null))); // Output: false
console.log(isInstanceOfUnknownClass([])); // Output: true
`

#### Call Signature

`ts
function isInstanceOfUnknownClass(value): value is object;
`

Defined in: main.ts:597

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is object

#### Call Signature

`ts
function isInstanceOfUnknownClass(value): boolean;
`

Defined in: main.ts:602

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is not a boolean.

#### Param

The value to check.

#### Call Signature

`ts
function isNotBoolean(value): value is Exclude;
`

Defined in: main.ts:105

##### Type Parameters

| Type Parameter |
| -------------- |
| T |

##### Parameters

| Parameter | Type |
| --------- | ---- |
| value | T |

##### Returns

value is Exclude

#### Call Signature

`ts
function isNotBoolean(value): boolean;
`

Defined in: main.ts:110

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is not a number.

#### Param

The value to check.

#### Call Signature

`ts
function isNotNumber(value): value is Exclude;
`

Defined in: main.ts:65

##### Type Parameters

| Type Parameter |
| -------------- |
| T |

##### Parameters

| Parameter | Type |
| --------- | ---- |
| value | T |

##### Returns

value is Exclude

#### Call Signature

`ts
function isNotNumber(value): boolean;
`

Defined in: main.ts:70

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is not a string.

#### Param

The value to check.

#### Call Signature

`ts
function isNotString(value): value is Exclude;
`

Defined in: main.ts:25

##### Type Parameters

| Type Parameter |
| -------------- |
| T |

##### Parameters

| Parameter | Type |
| --------- | ---- |
| value | T |

##### Returns

value is Exclude

#### Call Signature

`ts
function isNotString(value): boolean;
`

Defined in: main.ts:30

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is not undefined.

#### Param

The value to check.

#### Call Signature

`ts
function isNotUndefined(value): value is Exclude;
`

Defined in: main.ts:145

##### Type Parameters

| Type Parameter |
| -------------- |
| T |

##### Parameters

| Parameter | Type |
| --------- | ---- |
| value | T |

##### Returns

value is Exclude

#### Call Signature

`ts
function isNotUndefined(value): boolean;
`

Defined in: main.ts:150

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is a number.

#### Param

The value to check.

#### Call Signature

`ts
function isNumber(value): value is number;
`

Defined in: main.ts:45

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is number

#### Call Signature

`ts
function isNumber(value): boolean;
`

Defined in: main.ts:50

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is an object or a function.

This function verifies whether the provided value is of type 'object' or 'function'
while ensuring that null is excluded.

#### Param

The value to check.

#### Example

`ts
console.log(isObjectLoose({})); // Output: true
console.log(isObjectLoose([])); // Output: true
console.log(isObjectLoose(() => {})); // Output: true
console.log(isObjectLoose(null)); // Output: false
console.log(isObjectLoose(42)); // Output: false
`

Features

- ✅ Recognizes all objects (plain objects, arrays, functions, dates, etc.).
- ✅ Recognizes functions as objects (since functions are technically objects in JavaScript).
- ❌ Does not differentiate between plain objects and special objects (like arrays, functions, DOM nodes, etc.).

Behavior

- ✅ isObjectLoose({}) → true
- ✅ isObjectLoose([]) → true
- ✅ isObjectLoose(() => {}) → true
- ❌ isObjectLoose(null) → false

When to use

- Use isObjectStrict when you need a strict check for plain objects.
- Use isObjectLoose if you need to check if a value is an object-like structure, including functions.

Comparison

| Feature | Strict Check (isObjectStrict) | Loose Check (isObjectLoose) |
| ---------------------------------------- | ------------------------------- | ----------------------------- |
| Recognizes plain objects | ✅ Yes | ✅ Yes |
| Recognizes functions | ❌ No | ✅ Yes |
| Recognizes arrays | ❌ No | ✅ Yes |
| Recognizes Object.create(null) objects | ✅ Yes | ✅ Yes |
| Recognizes class instances | ❌ No | ✅ Yes |
| Recognizes DOM elements | ❌ No | ✅ Yes |
| Complexity | 🔴 High | 🟢 Low |

#### Call Signature

`ts
function isObjectLoose(value): value is object;
`

Defined in: main.ts:303

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is object

#### Call Signature

`ts
function isObjectLoose(value): boolean;
`

Defined in: main.ts:308

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Determines whether a value is a plain object (i.e., created via an object literal,
Object.create(null), or with Object as its prototype).

This excludes arrays, functions, class instances, built-ins like Date/Map/Set,
and other exotic objects.

#### Param

The value to test.

#### Example

`ts
const a: unknown = { x: 1 };
const b: unknown = [];
const c: unknown = new Date();
const d: unknown = Object.create(null);

isObjectPlain(a); // true
isObjectPlain(b); // false (array)
isObjectPlain(c); // false (built-in)
isObjectPlain(d); // true (null prototype)

// Type narrowing example:
const value: unknown = { foo: 42 };
if (isObjectPlain(value)) {
// value is now Record
console.log(value.foo);
}
`

#### See

-
-

#### Call Signature

`ts
function isObjectPlain(value): value is Record;
`

Defined in: main.ts:187

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is Record

#### Call Signature

`ts
function isObjectPlain(value): boolean;
`

Defined in: main.ts:192

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if a given value is a plain object.

A plain object is an object created by the {} syntax, Object.create(null),
or using new Object(). This function ensures that the value is an object
and does not have an unusual prototype chain.

#### Param

The value to check.

#### Example

`ts
console.log(isObjectStrict({})); // Output: true
console.log(isObjectStrict(Object.create(null))); // Output: true
console.log(isObjectStrict([])); // Output: false
console.log(isObjectStrict(new Date())); // Output: false
console.log(isObjectStrict(null)); // Output: false
`

Features

- ✅ Recognizes only plain objects (created via {}, new Object(), Object.create(null), etc.).
- ❌ Rejects arrays, functions, DOM elements, class instances, and custom objects with modified constructors.

Behavior

- ✅ isObjectStrict({}) → true
- ❌ isObjectStrict([]) → false
- ❌ isObjectStrict(() => {}) → false
- ✅ isObjectStrict(Object.create(null)) → true

When to use

- Use isObjectStrict when you need a strict check for plain objects.
- Use isObjectLoose if you need to check if a value is an object-like structure, including functions.

#### Call Signature

`ts
function isObjectStrict(value): value is Record;
`

Defined in: main.ts:238

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is Record

#### Call Signature

`ts
function isObjectStrict(value): boolean;
`

Defined in: main.ts:245

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is a string.

#### Param

The value to check.

#### Call Signature

`ts
function isString(value): value is string;
`

Defined in: main.ts:5

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is string

#### Call Signature

`ts
function isString(value): boolean;
`

Defined in: main.ts:10

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

$3

Checks if the given value is undefined.

#### Param

The value to check.

#### Call Signature

`ts
function isUndefined(value): value is undefined;
`

Defined in: main.ts:125

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

value is undefined

#### Call Signature

`ts
function isUndefined(value): boolean;
`

Defined in: main.ts:130

##### Parameters

| Parameter | Type |
| --------- | --------- |
| value | unknown |

##### Returns

boolean

---

Development

`shell-session
// Build
$ npm run build
// Run dev
$ npm run dev
// Test
$ npm test
``

Contributing

Want to contribute? Please read the CONTRIBUTING.md and CODE_OF_CONDUCT.md

License

This project is licensed under the MIT License - see the LICENSE file for details.

Changelog

See the CHANGELOG.md for details on the latest updates.

Sponsor me

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The sponsorship is an unique opportunity to alleviate more hours for me to maintain my projects, create new ones and contribute to the large community we're all part of :)

Support me on GitHub Sponsors.

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