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
• bigint
• bool
• date
• error
• func
• nil
• number
• object
• promise
• promiseLike
• regex
• string
• symbol
• undef

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<unknown>

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<unknown>

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