phun-ky@phun-ky/typeof
About
A set of JavaScript helper functions to check for types.
Table of Contents
Installation
npm i --save @phun-ky/typeofUsage
Either import and run the required functions:
import { isString } from '@phun-ky/typeof';
isString('asd'); // true;API
isBoolean()
Checks if the given value is a boolean.
Param
The value to check.
Call Signature
function isBoolean(value): value is boolean;Defined in: main.ts:85
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is boolean
Call Signature
function isBoolean(value): boolean;Defined in: main.ts:90
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isBuiltInCallable()
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
BuiltInCallableon success. - Boolean: usable in contexts that require a plain
(v) => boolean.
Param
The value to check.
Example
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
- https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global\_Objects
- https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global\_Objects/BigInt
- https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global\_Objects/Symbol
Call Signature
function isBuiltInCallable(value): value is BuiltInCallable;Defined in: main.ts:539
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is BuiltInCallable
Call Signature
function isBuiltInCallable(value): boolean;Defined in: main.ts:544
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isBuiltInConstructor()
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
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: falseCall Signature
function isBuiltInConstructor(value): value is BuiltInConstructor;Defined in: main.ts:439
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is BuiltInConstructor
Call Signature
function isBuiltInConstructor(value): boolean;Defined in: main.ts:446
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isClass()
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-writeable prototype, while regular functions do not.
Will always return false on built in constructors like Date or Array.
Param
The value to check.
Example
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: falseCall Signature
function isClass(value): value is ClassCtor<any>;Defined in: main.ts:364
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is ClassCtor<any>
Call Signature
function isClass(value): boolean;Defined in: main.ts:369
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isDefined()
Copy of isNotUndefined
Param
The value to check.
Call Signature
function isDefined<T>(value): value is Exclude<T, undefined>;Defined in: main.ts:165
Type Parameters
| Type Parameter |
|---|
T |
Parameters
| Parameter | Type |
|---|---|
value |
T |
Returns
value is Exclude<T, undefined>
Call Signature
function isDefined(value): boolean;Defined in: main.ts:170
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isInstanceOfUnknownClass()
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
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: trueCall Signature
function isInstanceOfUnknownClass(value): value is object;Defined in: main.ts:595
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is object
Call Signature
function isInstanceOfUnknownClass(value): boolean;Defined in: main.ts:600
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isNotBoolean()
Checks if the given value is not a boolean.
Param
The value to check.
Call Signature
function isNotBoolean<T>(value): value is Exclude<T, boolean>;Defined in: main.ts:105
Type Parameters
| Type Parameter |
|---|
T |
Parameters
| Parameter | Type |
|---|---|
value |
T |
Returns
value is Exclude<T, boolean>
Call Signature
function isNotBoolean(value): boolean;Defined in: main.ts:110
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isNotNumber()
Checks if the given value is not a number.
Param
The value to check.
Call Signature
function isNotNumber<T>(value): value is Exclude<T, number>;Defined in: main.ts:65
Type Parameters
| Type Parameter |
|---|
T |
Parameters
| Parameter | Type |
|---|---|
value |
T |
Returns
value is Exclude<T, number>
Call Signature
function isNotNumber(value): boolean;Defined in: main.ts:70
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isNotString()
Checks if the given value is not a string.
Param
The value to check.
Call Signature
function isNotString<T>(value): value is Exclude<T, string>;Defined in: main.ts:25
Type Parameters
| Type Parameter |
|---|
T |
Parameters
| Parameter | Type |
|---|---|
value |
T |
Returns
value is Exclude<T, string>
Call Signature
function isNotString(value): boolean;Defined in: main.ts:30
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isNotUndefined()
Checks if the given value is not undefined.
Param
The value to check.
Call Signature
function isNotUndefined<T>(value): value is Exclude<T, undefined>;Defined in: main.ts:145
Type Parameters
| Type Parameter |
|---|
T |
Parameters
| Parameter | Type |
|---|---|
value |
T |
Returns
value is Exclude<T, undefined>
Call Signature
function isNotUndefined(value): boolean;Defined in: main.ts:150
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isNumber()
Checks if the given value is a number.
Param
The value to check.
Call Signature
function isNumber(value): value is number;Defined in: main.ts:45
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is number
Call Signature
function isNumber(value): boolean;Defined in: main.ts:50
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isObjectLoose()
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
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: falseFeatures
- ✅ 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.).
Behaviour
- ✅
isObjectLoose({})→true - ✅
isObjectLoose([])→true - ✅
isObjectLoose(() => {})→true - ❌
isObjectLoose(null)→false
When to use
- Use
isObjectStrictwhen you need a strict check for plain objects. - Use
isObjectLooseif 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
function isObjectLoose(value): value is object;Defined in: main.ts:301
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is object
Call Signature
function isObjectLoose(value): boolean;Defined in: main.ts:306
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isObjectPlain()
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
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<string, unknown>
console.log(value.foo);
}See
- https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global\_Objects/Object/toString
- https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global\_Objects/Object/getPrototypeOf
Call Signature
function isObjectPlain(value): value is Record<string, unknown>;Defined in: main.ts:185
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is Record<string, unknown>
Call Signature
function isObjectPlain(value): boolean;Defined in: main.ts:190
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isObjectStrict()
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
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: falseFeatures
- ✅ 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.
Behaviour
- ✅
isObjectStrict({})→true - ❌
isObjectStrict([])→false - ❌
isObjectStrict(() => {})→false - ✅
isObjectStrict(Object.create(null))→true
When to use
- Use
isObjectStrictwhen you need a strict check for plain objects. - Use
isObjectLooseif you need to check if a value is an object-like structure, including functions.
Call Signature
function isObjectStrict(value): value is Record<string, unknown>;Defined in: main.ts:236
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is Record<string, unknown>
Call Signature
function isObjectStrict(value): boolean;Defined in: main.ts:243
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isString()
Checks if the given value is a string.
Param
The value to check.
Call Signature
function isString(value): value is string;Defined in: main.ts:5
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is string
Call Signature
function isString(value): boolean;Defined in: main.ts:10
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
isUndefined()
Checks if the given value is undefined.
Param
The value to check.
Call Signature
function isUndefined(value): value is undefined;Defined in: main.ts:125
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
value is undefined
Call Signature
function isUndefined(value): boolean;Defined in: main.ts:130
Parameters
| Parameter | Type |
|---|---|
value |
unknown |
Returns
boolean
Development
// Build
$ npm run build
// Run dev
$ npm run dev
// Test
$ npm testContributing
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.
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