is-js

A small library for identifying Javascript types.

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Readme

is.js
A collection of user-defined type guards to handle some of Javascript's less-than-ideal behavior.

Installing

$ npm install is-js
$ yarn add is-js

Usage

array

array(arg): arg is any
Determines if the argument is an array.
remarks Defaults to the native Array.isArray method, if present.

Parameters

| Name | Type | | :------ | :------ | | arg | any |

Returns

arg is any
true if the given argument is an array

bigint

bigint(value): boolean
Determines if the argument is a BigInt
remarks This method does not support polyfilled BigInt implementations; please defer to the library in use to determine the type of an unknown argument.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

boolean
true if the given argument is a native BigInt

bool

bool(value): value is boolean
Determines if the argument is a boolean

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is boolean
true if the given argument is a boolean

date

date(value): value is Date
Determines if the argument is a date.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Date
true if the given argument is a date

error

error(value): value is Error
Determines if the argument is an error.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Error
true if the given argument is an error

func

func(value): value is Function
Determines if the argument is a function.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Function
true if the given argument is a function

nil

nil(value): value is null
Determines if the argument is null

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is null
true if the given argument is null

number

number(value): value is number
Determines if the argument is a number

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is number
true if the given argument is a number

object

object(value): value is Object
Determines if the argument is an object.
remarks Nearly everything in Javascript is an object; this method discerns between native primitives (e.g. true, 3, some text) and their object-wrapped variants (Boolean, Number, String)

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Object
true if the given argument is an object

promise

promise(value): value is Promise
Determines if the argument is a native promise.
remarks Some libraries and frameworks still include their own polyfilled Promises, in which case this method is unreliable. If you are using such a library, please defer to the provided Promise implementation or use promiseLike

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Promise
true if the given argument is a string

promiseLike

promiseLike(value): value is Object
Determines if the argument conforms to the minimal interface of a Promise; that is, it has a method named then.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Object
true if the given argument conforms to the Promise interface

regex

regex(value): value is RegExp
Determines if the argument is a regular expression.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is RegExp
true if the given argument is a regular expression

string

string(value): value is string
Determines if the argument is a string.

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is string
true if the given argument is a string

symbol

symbol(value): value is Symbol
Determines if the argument is a symbol

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is Symbol
true if the given argument is a symbol

undef

undef(value): value is undefined
Determines if the argument is undefined

Parameters

| Name | Type | Description | | :------ | :------ | :------ | | value | unknown | Value in question |

Returns

value is undefined
true if the given argument is undefined