README.md
1 # kind-of [](https://www.npmjs.com/package/kind-of) [](https://npmjs.org/package/kind-of) [](https://npmjs.org/package/kind-of) [](https://travis-ci.org/jonschlinkert/kind-of) 2 3 > Get the native type of a value. 4 5 Please consider following this project's author, [Jon Schlinkert](https://github.com/jonschlinkert), and consider starring the project to show your :heart: and support. 6 7 ## Install 8 9 Install with [npm](https://www.npmjs.com/): 10 11 ```sh 12 $ npm install --save kind-of 13 ``` 14 15 Install with [bower](https://bower.io/) 16 17 ```sh 18 $ bower install kind-of --save 19 ``` 20 21 ## Why use this? 22 23 1. [it's fast](#benchmarks) | [optimizations](#optimizations) 24 2. [better type checking](#better-type-checking) 25 26 ## Usage 27 28 > es5, browser and es6 ready 29 30 ```js 31 var kindOf = require('kind-of'); 32 33 kindOf(undefined); 34 //=> 'undefined' 35 36 kindOf(null); 37 //=> 'null' 38 39 kindOf(true); 40 //=> 'boolean' 41 42 kindOf(false); 43 //=> 'boolean' 44 45 kindOf(new Boolean(true)); 46 //=> 'boolean' 47 48 kindOf(new Buffer('')); 49 //=> 'buffer' 50 51 kindOf(42); 52 //=> 'number' 53 54 kindOf(new Number(42)); 55 //=> 'number' 56 57 kindOf('str'); 58 //=> 'string' 59 60 kindOf(new String('str')); 61 //=> 'string' 62 63 kindOf(arguments); 64 //=> 'arguments' 65 66 kindOf({}); 67 //=> 'object' 68 69 kindOf(Object.create(null)); 70 //=> 'object' 71 72 kindOf(new Test()); 73 //=> 'object' 74 75 kindOf(new Date()); 76 //=> 'date' 77 78 kindOf([]); 79 //=> 'array' 80 81 kindOf([1, 2, 3]); 82 //=> 'array' 83 84 kindOf(new Array()); 85 //=> 'array' 86 87 kindOf(/foo/); 88 //=> 'regexp' 89 90 kindOf(new RegExp('foo')); 91 //=> 'regexp' 92 93 kindOf(function () {}); 94 //=> 'function' 95 96 kindOf(function * () {}); 97 //=> 'function' 98 99 kindOf(new Function()); 100 //=> 'function' 101 102 kindOf(new Map()); 103 //=> 'map' 104 105 kindOf(new WeakMap()); 106 //=> 'weakmap' 107 108 kindOf(new Set()); 109 //=> 'set' 110 111 kindOf(new WeakSet()); 112 //=> 'weakset' 113 114 kindOf(Symbol('str')); 115 //=> 'symbol' 116 117 kindOf(new Int8Array()); 118 //=> 'int8array' 119 120 kindOf(new Uint8Array()); 121 //=> 'uint8array' 122 123 kindOf(new Uint8ClampedArray()); 124 //=> 'uint8clampedarray' 125 126 kindOf(new Int16Array()); 127 //=> 'int16array' 128 129 kindOf(new Uint16Array()); 130 //=> 'uint16array' 131 132 kindOf(new Int32Array()); 133 //=> 'int32array' 134 135 kindOf(new Uint32Array()); 136 //=> 'uint32array' 137 138 kindOf(new Float32Array()); 139 //=> 'float32array' 140 141 kindOf(new Float64Array()); 142 //=> 'float64array' 143 ``` 144 145 ## Release history 146 147 ### v4.0.0 148 149 **Added** 150 151 * `promise` support 152 153 ### v5.0.0 154 155 **Added** 156 157 * `Set Iterator` and `Map Iterator` support 158 159 **Fixed** 160 161 * Now returns `generatorfunction` for generator functions 162 163 ## Benchmarks 164 165 Benchmarked against [typeof](http://github.com/CodingFu/typeof) and [type-of](https://github.com/ForbesLindesay/type-of). 166 Note that performaces is slower for es6 features `Map`, `WeakMap`, `Set` and `WeakSet`. 167 168 ```bash 169 #1: array 170 current x 23,329,397 ops/sec ±0.82% (94 runs sampled) 171 lib-type-of x 4,170,273 ops/sec ±0.55% (94 runs sampled) 172 lib-typeof x 9,686,935 ops/sec ±0.59% (98 runs sampled) 173 174 #2: boolean 175 current x 27,197,115 ops/sec ±0.85% (94 runs sampled) 176 lib-type-of x 3,145,791 ops/sec ±0.73% (97 runs sampled) 177 lib-typeof x 9,199,562 ops/sec ±0.44% (99 runs sampled) 178 179 #3: date 180 current x 20,190,117 ops/sec ±0.86% (92 runs sampled) 181 lib-type-of x 5,166,970 ops/sec ±0.74% (94 runs sampled) 182 lib-typeof x 9,610,821 ops/sec ±0.50% (96 runs sampled) 183 184 #4: function 185 current x 23,855,460 ops/sec ±0.60% (97 runs sampled) 186 lib-type-of x 5,667,740 ops/sec ±0.54% (100 runs sampled) 187 lib-typeof x 10,010,644 ops/sec ±0.44% (100 runs sampled) 188 189 #5: null 190 current x 27,061,047 ops/sec ±0.97% (96 runs sampled) 191 lib-type-of x 13,965,573 ops/sec ±0.62% (97 runs sampled) 192 lib-typeof x 8,460,194 ops/sec ±0.61% (97 runs sampled) 193 194 #6: number 195 current x 25,075,682 ops/sec ±0.53% (99 runs sampled) 196 lib-type-of x 2,266,405 ops/sec ±0.41% (98 runs sampled) 197 lib-typeof x 9,821,481 ops/sec ±0.45% (99 runs sampled) 198 199 #7: object 200 current x 3,348,980 ops/sec ±0.49% (99 runs sampled) 201 lib-type-of x 3,245,138 ops/sec ±0.60% (94 runs sampled) 202 lib-typeof x 9,262,952 ops/sec ±0.59% (99 runs sampled) 203 204 #8: regex 205 current x 21,284,827 ops/sec ±0.72% (96 runs sampled) 206 lib-type-of x 4,689,241 ops/sec ±0.43% (100 runs sampled) 207 lib-typeof x 8,957,593 ops/sec ±0.62% (98 runs sampled) 208 209 #9: string 210 current x 25,379,234 ops/sec ±0.58% (96 runs sampled) 211 lib-type-of x 3,635,148 ops/sec ±0.76% (93 runs sampled) 212 lib-typeof x 9,494,134 ops/sec ±0.49% (98 runs sampled) 213 214 #10: undef 215 current x 27,459,221 ops/sec ±1.01% (93 runs sampled) 216 lib-type-of x 14,360,433 ops/sec ±0.52% (99 runs sampled) 217 lib-typeof x 23,202,868 ops/sec ±0.59% (94 runs sampled) 218 219 ``` 220 221 ## Optimizations 222 223 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: 224 225 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. 226 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. 227 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'` 228 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. 229 230 ## Better type checking 231 232 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: 233 234 ### [typeof](https://github.com/CodingFu/typeof) lib 235 236 Incorrectly tests instances of custom constructors (pretty common): 237 238 ```js 239 var typeOf = require('typeof'); 240 function Test() {} 241 console.log(typeOf(new Test())); 242 //=> 'test' 243 ``` 244 245 Returns `object` instead of `arguments`: 246 247 ```js 248 function foo() { 249 console.log(typeOf(arguments)) //=> 'object' 250 } 251 foo(); 252 ``` 253 254 ### [type-of](https://github.com/ForbesLindesay/type-of) lib 255 256 Incorrectly returns `object` for generator functions, buffers, `Map`, `Set`, `WeakMap` and `WeakSet`: 257 258 ```js 259 function * foo() {} 260 console.log(typeOf(foo)); 261 //=> 'object' 262 console.log(typeOf(new Buffer(''))); 263 //=> 'object' 264 console.log(typeOf(new Map())); 265 //=> 'object' 266 console.log(typeOf(new Set())); 267 //=> 'object' 268 console.log(typeOf(new WeakMap())); 269 //=> 'object' 270 console.log(typeOf(new WeakSet())); 271 //=> 'object' 272 ``` 273 274 ## About 275 276 <details> 277 <summary><strong>Contributing</strong></summary> 278 279 Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new). 280 281 <details> 282 283 <details> 284 <summary><strong>Running Tests</strong></summary> 285 286 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: 287 288 ```sh 289 $ npm install && npm test 290 ``` 291 292 <details> 293 294 <details> 295 <summary><strong>Building docs</strong></summary> 296 297 _(This project's readme.md is generated by [verb](https://github.com/verbose/verb-generate-readme), please don't edit the readme directly. Any changes to the readme must be made in the [.verb.md](.verb.md) readme template.)_ 298 299 To generate the readme, run the following command: 300 301 ```sh 302 $ npm install -g verbose/verb#dev verb-generate-readme && verb 303 ``` 304 305 <details> 306 307 ### Related projects 308 309 You might also be interested in these projects: 310 311 * [is-glob](https://www.npmjs.com/package/is-glob): Returns `true` if the given string looks like a glob pattern or an extglob pattern… [more](https://github.com/jonschlinkert/is-glob) | [homepage](https://github.com/jonschlinkert/is-glob "Returns `true` if the given string looks like a glob pattern or an extglob pattern. This makes it easy to create code that only uses external modules like node-glob when necessary, resulting in much faster code execution and initialization time, and a bet") 312 * [is-number](https://www.npmjs.com/package/is-number): Returns true if the value is a number. comprehensive tests. | [homepage](https://github.com/jonschlinkert/is-number "Returns true if the value is a number. comprehensive tests.") 313 * [is-primitive](https://www.npmjs.com/package/is-primitive): Returns `true` if the value is a primitive. | [homepage](https://github.com/jonschlinkert/is-primitive "Returns `true` if the value is a primitive. ") 314 315 ### Contributors 316 317 | **Commits** | **Contributor** | 318 | --- | --- | 319 | 82 | [jonschlinkert](https://github.com/jonschlinkert) | 320 | 3 | [aretecode](https://github.com/aretecode) | 321 | 2 | [miguelmota](https://github.com/miguelmota) | 322 | 1 | [dtothefp](https://github.com/dtothefp) | 323 | 1 | [ksheedlo](https://github.com/ksheedlo) | 324 | 1 | [pdehaan](https://github.com/pdehaan) | 325 | 1 | [laggingreflex](https://github.com/laggingreflex) | 326 | 1 | [charlike](https://github.com/charlike) | 327 328 ### Author 329 330 **Jon Schlinkert** 331 332 * [github/jonschlinkert](https://github.com/jonschlinkert) 333 * [twitter/jonschlinkert](https://twitter.com/jonschlinkert) 334 335 ### License 336 337 Copyright © 2017, [Jon Schlinkert](https://github.com/jonschlinkert). 338 Released under the [MIT License](LICENSE). 339 340 *** 341 342 _This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.6.0, on October 13, 2017._