Kind.js

A precise typechecker for JavaScript

Description

kind() returns a useful name for a variable's type. It breaks down objects into more precise terms: array, null, element, etc.

Examples:

Input	typeof	kind
[1, 2, 3]	"object"	"array"
null	"object"	"null"
new Promise(() => null)	"object"	"promise"
document.getElementById('id')	"object"	"element"
document.getElementsByTagName('div')	"object"	"nodelist"
document.createTextNode('')	"object"	"node"
new Date()	"object"	"date"
{}	"object"	"object" (if no special type was detected — see full list below)

Install

yarn: yarn add kindjs

npm: npm install kindjs

Usage

import kind from 'kindjs';

kind(['hello', 'world']);
//=> 'array'

Basic

// Objects that aren't *really* objects
kind(null);       // "null"
kind([1, 2, 3]);  // "array"
kind(arguments);  // "arraylike"
kind(new Date()); // "date"
kind(document.getElementById('id'));        // "element"
kind(document.getElementsByTagName('div')); // "nodelist"

// This one's actually just an object
kind({});         // "object"

// Also works on standard types
kind("text");     // "string"
kind(2);          // "number"
kind(alert);      // "function"

"Deep" option

You may add a second, boolean parameter to tell kind to perform a deeper test for some types. For example, instead of "number" it could return "integer" or "float".

kind(1);          // "number"
kind(1, true);    // "integer"

kind(1.21);       // "number"
kind(1.21, true); // "float"

kind(evt);        // "event"
kind(evt, true);  // "mouseevent" (i.e. if the event was a click)

A complete list is noted below

Supported types

• All standard types normally returned by typeof:
  • function, undefined, boolean, symbol
  • string
    • Deep option returns either string or emptystring
  • number
    • Deep option returns either integer or float
• array
• arraylike
  • A non-array object with a .length property
• null
• element
• node
  • Deep options from this list (e.g. text, comment)
• nodelist
• event
  • Deep options from this list (e.g. mouseevent, keyboardevent)
• regexp
• date
• error
• errorevent
• math
• promise
• set
• url (i.e. an instance of the URL() constructor)
• urlsearchparams
• map

Features

• Works with any type, not just objects
• Always returns a simple lowercase string, just like the native typeof
• TypeScript support
• Handles undefined or undeclared variables
• Optimized to check for the most common types first
• Excellent browser support, including many very old browsers
  • IE 6+ (and maybe older)
  • Chrome
  • Firefox
  • Safari
  • Android 1+
  • Opera (pre-Blink)
  • Netscape 4 (in theory!)
  • Probably anything that runs JavaScript and supports regular expressions