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

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

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

▸ array(arg): arg is any[]

Determines if the argument is an array.

remarks Defaults to the native Array.isArray method, if present.

arg is any[]

true if the given argument is an array

▸ 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.

boolean

true if the given argument is a native BigInt

▸ bool(value): value is boolean

Determines if the argument is a boolean

value is boolean

true if the given argument is a boolean

▸ date(value): value is Date

Determines if the argument is a date.

value is Date

true if the given argument is a date

▸ error(value): value is Error

Determines if the argument is an error.

value is Error

true if the given argument is an error

▸ func(value): value is Function

Determines if the argument is a function.

value is Function

true if the given argument is a function

▸ nil(value): value is null

Determines if the argument is null

value is null

true if the given argument is null

▸ number(value): value is number

Determines if the argument is a number

value is number

true if the given argument is a number

▸ 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)

value is Object

true if the given argument is an object

▸ 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

value is Promise<unknown>

true if the given argument is a string

▸ 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.

value is Object

true if the given argument conforms to the Promise interface

▸ regex(value): value is RegExp

Determines if the argument is a regular expression.

value is RegExp

true if the given argument is a regular expression

▸ string(value): value is string

Determines if the argument is a string.

value is string

true if the given argument is a string

▸ symbol(value): value is Symbol

Determines if the argument is a symbol

value is Symbol

true if the given argument is a symbol

▸ undef(value): value is undefined

Determines if the argument is undefined

value is undefined

true if the given argument is undefined