kind-of

What is kind-of?

The kind-of npm package is a utility library that allows developers to check the type of a given value in JavaScript. It provides a simple API to determine whether a value is a string, number, array, object, function, and other JavaScript types. This can be particularly useful for type checking and validation in applications where type safety is important.

What are kind-of's main functionalities?

Type checking for primitives

This feature allows you to check the type of primitive values such as numbers, strings, and booleans.

"use strict"; const kindOf = require('kind-of'); console.log(kindOf(1)); // 'number' console.log(kindOf('hello')); // 'string' console.log(kindOf(true)); // 'boolean'

Type checking for objects

This feature allows you to check the type of object-based values such as plain objects, arrays, and regular expressions.

"use strict"; const kindOf = require('kind-of'); console.log(kindOf({})); // 'object' console.log(kindOf([])); // 'array' console.log(kindOf(/foo/)); // 'regexp'

Type checking for functions and undefined

This feature allows you to check the type of functions and the undefined value.

"use strict"; const kindOf = require('kind-of'); console.log(kindOf(function () {})); // 'function' console.log(kindOf(undefined)); // 'undefined'

Type checking for null and dates

This feature allows you to check the type of null values and date objects.

"use strict"; const kindOf = require('kind-of'); console.log(kindOf(null)); // 'null' console.log(kindOf(new Date())); // 'date'

Other packages similar to kind-of

type-check

The 'type-check' package offers a similar functionality to 'kind-of' by allowing type assertions and checks. It provides a mini language to specify the types of values and can validate against those specifications.

is

The 'is' package is another utility library that provides type checking functions. It has a wider range of type checks available, including checks for specific JavaScript environments like the browser or Node.js.

check-types

The 'check-types' package provides a set of predicates for type checking. It has a fluent API and includes additional checks for min/max values, empty strings, and arrays, which are not directly available in 'kind-of'.

README

kind-of

Get the native type of a value.

Please consider following this project's author, Jon Schlinkert, and consider starring the project to show your :heart: and support.

Install

Install with npm:

$ npm install --save kind-of

Install with bower

$ bower install kind-of --save

Why use this?

1. it's fast | optimizations
2. better type checking

Usage

es5, browser and es6 ready

var kindOf = require('kind-of');

kindOf(undefined);
//=> 'undefined'

kindOf(null);
//=> 'null'

kindOf(true);
//=> 'boolean'

kindOf(false);
//=> 'boolean'

kindOf(new Boolean(true));
//=> 'boolean'

kindOf(new Buffer(''));
//=> 'buffer'

kindOf(42);
//=> 'number'

kindOf(new Number(42));
//=> 'number'

kindOf('str');
//=> 'string'

kindOf(new String('str'));
//=> 'string'

kindOf(arguments);
//=> 'arguments'

kindOf({});
//=> 'object'

kindOf(Object.create(null));
//=> 'object'

kindOf(new Test());
//=> 'object'

kindOf(new Date());
//=> 'date'

kindOf([]);
//=> 'array'

kindOf([1, 2, 3]);
//=> 'array'

kindOf(new Array());
//=> 'array'

kindOf(/foo/);
//=> 'regexp'

kindOf(new RegExp('foo'));
//=> 'regexp'

kindOf(function () {});
//=> 'function'

kindOf(function * () {});
//=> 'function'

kindOf(new Function());
//=> 'function'

kindOf(new Map());
//=> 'map'

kindOf(new WeakMap());
//=> 'weakmap'

kindOf(new Set());
//=> 'set'

kindOf(new WeakSet());
//=> 'weakset'

kindOf(Symbol('str'));
//=> 'symbol'

kindOf(new Int8Array());
//=> 'int8array'

kindOf(new Uint8Array());
//=> 'uint8array'

kindOf(new Uint8ClampedArray());
//=> 'uint8clampedarray'

kindOf(new Int16Array());
//=> 'int16array'

kindOf(new Uint16Array());
//=> 'uint16array'

kindOf(new Int32Array());
//=> 'int32array'

kindOf(new Uint32Array());
//=> 'uint32array'

kindOf(new Float32Array());
//=> 'float32array'

kindOf(new Float64Array());
//=> 'float64array'

Release history

v4.0.0

Added

• promise support

v5.0.0

Added

• Set Iterator and Map Iterator support

Fixed

• Now returns generatorfunction for generator functions

Benchmarks

Benchmarked against typeof and type-of. Note that performaces is slower for es6 features Map, WeakMap, Set and WeakSet.

#1: array
  current x 23,329,397 ops/sec ±0.82% (94 runs sampled)
  lib-type-of x 4,170,273 ops/sec ±0.55% (94 runs sampled)
  lib-typeof x 9,686,935 ops/sec ±0.59% (98 runs sampled)

#2: boolean
  current x 27,197,115 ops/sec ±0.85% (94 runs sampled)
  lib-type-of x 3,145,791 ops/sec ±0.73% (97 runs sampled)
  lib-typeof x 9,199,562 ops/sec ±0.44% (99 runs sampled)

#3: date
  current x 20,190,117 ops/sec ±0.86% (92 runs sampled)
  lib-type-of x 5,166,970 ops/sec ±0.74% (94 runs sampled)
  lib-typeof x 9,610,821 ops/sec ±0.50% (96 runs sampled)

#4: function
  current x 23,855,460 ops/sec ±0.60% (97 runs sampled)
  lib-type-of x 5,667,740 ops/sec ±0.54% (100 runs sampled)
  lib-typeof x 10,010,644 ops/sec ±0.44% (100 runs sampled)

#5: null
  current x 27,061,047 ops/sec ±0.97% (96 runs sampled)
  lib-type-of x 13,965,573 ops/sec ±0.62% (97 runs sampled)
  lib-typeof x 8,460,194 ops/sec ±0.61% (97 runs sampled)

#6: number
  current x 25,075,682 ops/sec ±0.53% (99 runs sampled)
  lib-type-of x 2,266,405 ops/sec ±0.41% (98 runs sampled)
  lib-typeof x 9,821,481 ops/sec ±0.45% (99 runs sampled)

#7: object
  current x 3,348,980 ops/sec ±0.49% (99 runs sampled)
  lib-type-of x 3,245,138 ops/sec ±0.60% (94 runs sampled)
  lib-typeof x 9,262,952 ops/sec ±0.59% (99 runs sampled)

#8: regex
  current x 21,284,827 ops/sec ±0.72% (96 runs sampled)
  lib-type-of x 4,689,241 ops/sec ±0.43% (100 runs sampled)
  lib-typeof x 8,957,593 ops/sec ±0.62% (98 runs sampled)

#9: string
  current x 25,379,234 ops/sec ±0.58% (96 runs sampled)
  lib-type-of x 3,635,148 ops/sec ±0.76% (93 runs sampled)
  lib-typeof x 9,494,134 ops/sec ±0.49% (98 runs sampled)

#10: undef
  current x 27,459,221 ops/sec ±1.01% (93 runs sampled)
  lib-type-of x 14,360,433 ops/sec ±0.52% (99 runs sampled)
  lib-typeof x 23,202,868 ops/sec ±0.59% (94 runs sampled)

Optimizations

In 7 out of 8 cases, this library is 2x-10x faster than other top libraries included in the benchmarks. There are a few things that lead to this performance advantage, none of them hard and fast rules, but all of them simple and repeatable in almost any code library:

1. Optimize around the fastest and most common use cases first. Of course, this will change from project-to-project, but I took some time to understand how and why typeof checks were being used in my own libraries and other libraries I use a lot.
2. Optimize around bottlenecks - In other words, the order in which conditionals are implemented is significant, because each check is only as fast as the failing checks that came before it. Here, the biggest bottleneck by far is checking for plain objects (an object that was created by the Object constructor). I opted to make this check happen by process of elimination rather than brute force up front (e.g. by using something like val.constructor.name), so that every other type check would not be penalized it.
3. Don't do uneccessary processing - why do .slice(8, -1).toLowerCase(); just to get the word regex? It's much faster to do if (type === '[object RegExp]') return 'regex'
4. There is no reason to make the code in a microlib as terse as possible, just to win points for making it shorter. It's always better to favor performant code over terse code. You will always only be using a single require() statement to use the library anyway, regardless of how the code is written.

Better type checking

kind-of is more correct than other type checking libs I've looked at. For example, here are some differing results from other popular libs:

typeof lib

Incorrectly tests instances of custom constructors (pretty common):

var typeOf = require('typeof');
function Test() {}
console.log(typeOf(new Test()));
//=> 'test'

Returns object instead of arguments:

function foo() {
  console.log(typeOf(arguments)) //=> 'object'
}
foo();

type-of lib

Incorrectly returns object for generator functions, buffers, Map, Set, WeakMap and WeakSet:

function * foo() {}
console.log(typeOf(foo));
//=> 'object'
console.log(typeOf(new Buffer('')));
//=> 'object'
console.log(typeOf(new Map()));
//=> 'object'
console.log(typeOf(new Set()));
//=> 'object'
console.log(typeOf(new WeakMap()));
//=> 'object'
console.log(typeOf(new WeakSet()));
//=> 'object'

About

Contributing

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.

Running Tests

Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:

$ npm install && npm test

Building docs

(This project's readme.md is generated by verb, please don't edit the readme directly. Any changes to the readme must be made in the .verb.md readme template.)

To generate the readme, run the following command:

$ npm install -g verbose/verb#dev verb-generate-readme && verb

Related projects

You might also be interested in these projects:

• is-glob: Returns true if the given string looks like a glob pattern or an extglob pattern… more | homepage
• is-number: Returns true if the value is a number. comprehensive tests. | homepage
• is-primitive: Returns true if the value is a primitive. | homepage

Contributors

Commits	Contributor
82	jonschlinkert
3	aretecode
2	miguelmota
1	dtothefp
1	ksheedlo
1	pdehaan
1	laggingreflex
1	charlike

Author

Jon Schlinkert

• github/jonschlinkert
• twitter/jonschlinkert

License

Copyright © 2017, Jon Schlinkert. Released under the MIT License.

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This file was generated by verb-generate-readme, v0.6.0, on October 13, 2017.

Changelog

[5.1.0] - 2017-10-13

Added

• Merge pull request #15 from aretecode/patch-1
• adds support and tests for string & array iterators

Changed

• updates benchmarks