kind

Type checking differently

Install

Download the CJS, ESM, UMD versions or install via NPM:

npm install @ryanmorr/kind

Usage

Rather than relying on the common "is" functions such as isArray, isString, etc., kind uses type constants to create a versatile approach that supports type assertions, identification, and customization:

import { kind, KIND_STRING, KIND_NULL, KIND_UNDEFINED } from '@ryanmorr/kind';

// Assert a type match
kind('foo', KIND_STRING); //=> true

// Assert at least one match from a group of types
kind(null, [KIND_NULL, KIND_UNDEFINED]); //=> true

// Identify a type
kind(123); //=> KIND_NUMBER

You can define a custom type via def, providing a function to detect that type (must return a boolean):

import { def, kind, KIND_FUNCTION } from '@ryanmorr/kind';

const fn = async () => 1;

// Define a custom type for async functions
const KIND_ASYNC_FUNCTION = def((obj) => {}.toString.call(obj) == '[object AsyncFunction]');

// Will return true for the new type
kind(fn, KIND_ASYNC_FUNCTION); //=> true

// Will still return true for any other matching type
kind(fn, KIND_FUNCTION); //=> true

// When identifying an object type, custom types are always tested first
kind(fn); //=> KIND_ASYNC_FUNCTION

You can also define type groups by providing an array of sub-types:

import { def, kind, KIND_STRING, KIND_NUMBER, KIND_BOOLEAN } from '@ryanmorr/kind';

// Define a custom group type
const KIND_PRIMITIVE = def([KIND_STRING, KIND_NUMBER, KIND_BOOLEAN]);

// Will return true if the object matches at least one of the sub-types
kind(123, KIND_PRIMITIVE); //=> true
kind('foo', KIND_PRIMITIVE); //=> true
kind(false, KIND_PRIMITIVE); //=> true

// Group types will never be identified as an object type
kind(789); //=> KIND_NUMBER

Default Types

Kind comes with the following built-in default types:

• KIND_NULL
• KIND_UNDEFINED
• KIND_STRING
• KIND_BOOLEAN
• KIND_NAN
• KIND_NUMBER
• KIND_SYMBOL
• KIND_PLAIN_OBJECT
• KIND_OBJECT
• KIND_ARRAY
• KIND_FUNCTION
• KIND_SET
• KIND_WEAK_SET
• KIND_MAP
• KIND_WEAK_MAP
• KIND_ITERABLE
• KIND_REGEXP
• KIND_DATE
• KIND_ERROR
• KIND_PROMISE
• KIND_GLOBAL
• KIND_UNKNOWN

License

This project is dedicated to the public domain as described by the Unlicense.