One more DOM classname string builder if you not enough yet 😁
It is lightweight, fast and has no dependencies!
Designed to be fastest full-feature drop-in replacement for classnames package.

Install it via npm or yarn

npm i cnbuilder
# OR
yarn add cnbuilder

Use it wherever and however you want - node.js or webpack, CJS or ESM modules!

INSTALLATION NOTE:
This lib is written in ES6+ and delivering with both, transpiled and untranspiled versions:

• main field of package.json is pointing to transpiled ES3-compatible version with CJS modules resolution;
• module field is pointing to transpiled ES3-compatible version with ES modules resolution;
• esnext field is pointing to the ES6+ version with ES modules resolution;

Depending on your targets you may have to use Webpack and/or Babel to pull untranspiled version of package.
See some tips on wiring thing up: https://2ality.com/2017/06/pkg-esnext.html

Use it wherever and however you want - node.js or webpack, CJS or ESM modules!

var cnb = require("cnbuilder");

cnb("cnbuilder", { is: true }, ["awesome!"]); // => 'cnbuilder is awesome!'

import cnb from "cnbuilder";

cnb("works", { with: true }, ["ESM!"]); // => 'works with ESM!'

Why

cnbuilder is designed to be as lightweight and fast as possible, without loosing the functionality (jorgebucaran/classcat is faster in some cases but less handy because does not allow to pass variable count of arguments). It is written with power of TypeScript and it's API is fully compatible with JedWatson/classnames, so it wont be anyhow hard to migrate if you're already using classnames package.

Usage

As already said - API is the same with classnames pkg, and due to my laziness - i'll just copy-past their usage documentation (with small additions)😅😱

The cnb function takes any number of arguments which can be a string, array or object. Any other input will be ignored. The argument 'foo' is short for { foo: true } or ['foo']. If the value associated with a given key is falsy, that key won't be included in the output.

cnb("foo", "bar"); // => 'foo bar'
cnb("foo", { bar: true }); // => 'foo bar'
cnb({ "foo-bar": true }); // => 'foo-bar'
cnb({ "foo-bar": false }); // => ''
cnb({ foo: true }, { bar: true }); // => 'foo bar'
cnb({ foo: true, bar: true }); // => 'foo bar'

// lots of arguments of various types
cnb("foo", { bar: true, duck: false }, "baz", { quux: true }); // => 'foo bar baz quux'

// other falsy values are just ignored
cnb(null, false, "bar", undefined, 0, 1, { baz: null }, ""); // => 'bar 1'

Arrays will be recursively flattened as per the rules above:

var arr = ["b", { c: true, d: false }];
cnb("a", arr); // => 'a b c'

BUT! there are two additions, comparing to classnames result generation:

• it does not generate useless spaces:

  classnames("test", [], { a: false }); // => "test " (5 chars with space at the end)
  cnb("test", [], { a: false }); // => "test" (just 4 chars)

• it skips fully numeric classnames, due to classnames starting with digit are illegal, but it can't skip strings starting with digit, cause it would impact the performance, so that part is left for the end developer

  classnames(321, "1stPlace"); // => "321 1stPlace"
  cnb(321, "1stPlace"); // => "1stPlace"

Dynamic class names with ES2015

If you're in an environment that supports computed keys (available in ES2015 and Babel) you can use dynamic class names:

let buttonType = "primary";
cnb({ [`btn-${buttonType}`]: true });

Polyfills needed to support older browsers

Array.isArray: see MDN for details about unsupported older browsers (e.g. <= IE8) and a simple polyfill.

Performance (recent benchmarks results)

benchmarks ran on 3.4GHz Core i7 CPU width 16GB DDR4 RAM

yarn && yarn build && cd ./benchmark && yarn && yarn start

# strings
cnbuilder x 9,269,882 ops/sec ±0.40% (96 runs sampled)
classcat x 8,420,286 ops/sec ±1.17% (95 runs sampled)
classnames x 2,981,605 ops/sec ±0.39% (93 runs sampled)
clsx x 7,922,417 ops/sec ±0.25% (93 runs sampled)

# objects
cnbuilder x 7,270,064 ops/sec ±0.65% (95 runs sampled)
classcat x 7,484,998 ops/sec ±0.70% (95 runs sampled)
classnames x 2,731,604 ops/sec ±0.45% (95 runs sampled)
clsx x 5,370,626 ops/sec ±0.44% (96 runs sampled)

# arrays
cnbuilder x 7,092,002 ops/sec ±0.42% (94 runs sampled)
classcat x 6,818,053 ops/sec ±0.29% (92 runs sampled)
classnames x 1,676,201 ops/sec ±0.27% (96 runs sampled)
clsx x 6,083,849 ops/sec ±0.22% (94 runs sampled)

# nested arrays
cnbuilder x 5,828,441 ops/sec ±0.39% (96 runs sampled)
classcat x 5,609,506 ops/sec ±0.25% (96 runs sampled)
classnames x 1,076,019 ops/sec ±0.45% (91 runs sampled)
clsx x 4,910,528 ops/sec ±0.19% (96 runs sampled)

# objects nested in arrays
cnbuilder x 5,652,700 ops/sec ±0.83% (95 runs sampled)
classcat x 5,756,021 ops/sec ±0.73% (96 runs sampled)
classnames x 1,599,139 ops/sec ±0.27% (95 runs sampled)
clsx x 4,677,370 ops/sec ±0.57% (95 runs sampled)

# mixed
cnbuilder x 6,000,100 ops/sec ±0.74% (94 runs sampled)
classcat x 6,028,224 ops/sec ±0.31% (94 runs sampled)
classnames x 1,971,724 ops/sec ±0.30% (93 runs sampled)
clsx x 4,922,858 ops/sec ±0.35% (94 runs sampled)

# mixed with wrong data
cnbuilder x 1,915,258 ops/sec ±0.71% (95 runs sampled)
classcat x 1,550,198 ops/sec ±0.38% (94 runs sampled)
classnames x 1,032,770 ops/sec ±0.50% (91 runs sampled)
clsx x 1,732,645 ops/sec ±0.75% (92 runs sampled)