Javascript Type Verification Library

A small JavaScript library to help with JavaScript's data typing.

Project setup

npm i @langlois/is-a

Run your tests

npm run test

Lints and fixes files

npm run lint

Usage

import { isA } from '@langlois/is-a'

isA.array([]) // true

isA.array('[]') // false

API

Arguments

Returns true if passed a function's arguments list.

function () {
	isA.arguments(arguments) // true

	isA.arguments(arguments[0]) // false
}

Array

Returns true if passed an array.

isA.array([]) // true

Boolean

Returns true if passed a boolean.

isA.boolean(true) // true

isA.boolean(false) // true

Date

Returns true if passed a date.

const today = new Date()

isA.date(today) // true

Email

Returns true if the string passed is a valid email address.

The regex for determining if an email is valid is taken from the HTML spec.

const email = 'test@test.com'

isA.email(email) // true

Error

Returns true if passed an error.

const error = new Error()

isA.error(error) // true

Function

Returns true if passed a function.

const myFunction = () => undefined

isA.function(myFunction) // true

Map

Returns true if passed a map.

const myMap = new Map()

isA.map(myMap) // true

NaN

Returns true if passed NaN.

isA.NaN(NaN) // true

Null

Returns true if passed null.

isA.null(null) // true

Number

Returns true if passed a number, excluding NaN.

isA.number(123) // true

isA.number(NaN) // false

Numerical

Returns true if passed a number or a string representing a number, excluding NaN.

isA.numerical(23) // true

isA.numerical('23') // true

isA.numerical('-23') // true

isA.numerical(NaN) // false

Object

Returns true if passed an object.

isA.object({}) // true

Everything in JavaScript is an Object and that means that many data types return typeof x === 'object' as true as well as x instanceof Object as true. However, it isn't really useful to treat certain things as if they were objects when developing so this function will return false for the following data types:

• dates
• errors
• maps
• regExps
• sets
• weakMaps
• weakSets

isA.object(new Date()) // false
isA.object(new Error()) // false
isA.object(new Map()) // false
isA.object(/\d/) // false
isA.object(new Set()) // false
isA.object(new WeakMap()) // false
isA.object(new WeakSet()) // false

RegExp

Returns true if passed a regExp.

const myRegExp = /\d/

isA.regExp(myRegExp) // true

Set

Returns true if passed a set.

const mySet = new Set()

isA.set(mySet) //  true

String

Returns true if passed a string.

isA.string('hello, world') //  true

Symbol

Returns true if passed a symbol.

const mySymbol = Symbol()

isA.symbol(mySymbol) //  true

Undefined

Returns true if passed undefined.

isA.undefined(undefined) //  true

URI

Returns true if passed a URL instance or a string that can become a valid URL instance.

const myUrl = new URL('https://langlois.dev')

isA.uri(myUrl) //  true
isA.uri('https://langlois.dev') // true

WeakMap

Returns true if passed a weakMap.

const myWeakMap = new WeakMap()

isA.weakMap(myWeakMap) //  true

WeakSet

Returns true if passed a weakSet.

const myWeakSet = new WeakSet()

isA.weakSet(myWeakSet) //  true