bem-names

bemNames

Advanced generator of BEM class names. bemNames can follow any BEM naming convention and allow easy transition between any of them. It also supports a transition between classic classnames as well as css-Modules.

Install

yarn add bem-names
npm install bem-names --save

<script src="https://cdn.jsdelivr.net/npm/bem-names/dist/bem-names.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bem-names/dist/bem-names.js"></script>

Basic usage

The bemNames function takes any number of arguments, which can be a string, array or object. The first two arguments must be strings and are treated accordingly as the name of the block and the element. In the default configuration, the modifiers must be wrapped with [] or {}, in order to maintain clarity of what is a block, element or modifier. This and many other behaviours can be changed, check advanced usage.

import bemNames from 'bem-names';

bemNames('block');
// 'block'
bemNames('block', ['mod']);
// 'block block--mod'
bemNames('block', 'element', ['mod']);
// 'block__element block__element--mod'
bemNames('block', 'element', { mod2: true, mod3: false });
// 'block__element block__element--mod2'

With factory:

import { bemNamesFactory } from 'bem-names';

const bem = bemNamesFactory('block');

bem();
// 'block'
bem(['mod']);
// 'block block--mod'
bem('element', ['mod']);
// 'block__element block__element--mod'
bem('element', { mod2: true, mod3: false });
// 'block__element block__element--mod2'

With secondary API:

import bemNames from 'bem-names';

const bem =  bemNames.factory(
  'block'
  { stringModifiers: 'passThrough' },
);

bem(['blue'], 'extra-class');
// 'block block--blue extra-class'

bemNames.custom({ state: { blue: 'is-blue' } }, 'block', ['blue']);
// 'block is-blue'

Motivation

When I tried to add a BEM-like styled component react-select to project with different BEM-naming conventions I've encounter two obstacles:

• There was a class name collision with existing components
• The component followed different class naming convention, and did not fit with existing scss helper functions.

To work with these kind of components you need to accept their global namespace presents and/or wrap with dummy element just for styling.

Ideal solution would be if the component had an option to pass a class name generator (sample code), and this is where I've decided to start. My first step was writing this generator, with option to transitions to css-modules in the near future, and this is what this library is all about.

Other projects

There are many great generators of BEM-like class names. But none of them can be used as a generic generator covering various conventions. Below are several projects I've tested.

• bem-classname Very basic generator covering single convention.

• bem-classnames Basic generator covering single convention with troublesome need of setting up configuration for every component. The slowest of presented here.

• b_ Very fast generator allowing basic configuration but limited in BEM-flexibility.

• bem-cn Versatile BEM class name generator. Does not have flexible API allowing to apply other conventions. Personally prefer API similar to "classic" classnames.

• classnames Good class name generator but without support form BEM-like naming convention. :]

Performance

I've performed some performance tests. Each packaged received same parameters, and bemNames was configured to match output for each of the packages.

Implementation with de-duplication was about 18% slower.

	10K	bemNames
b_	2ms	12ms
bem-classname	13ms	11ms
bem-classanmes	101ms	13ms
bem-cn	23ms	26ms
classnames	3ms	7ms

Advanced usage

bemNames was create with castomization in mind. Configuration object is merged with the default configuration so there is no need to specify all of the options every time.

import { customBemNames } from 'bem-names';

const config = {
  separators: { element: '-' },
  states = { mod1: 'is-mod1' },
};

customBemNames(config, 'block', 'element', ['mod1']);
// 'block-element is-mod1'

The customBemNames is created for in-line usage, for more generic approuch there is bemNamesFactory.

import { bemNamesFactory } from 'bem-names';

const config = {
  separators: { element: '-' },
  states = { mod1: 'is-mod1' },
};

const bem = bemNamesFactory('block', config);

bem('element', ['mod1']);
// 'block-element is-mod1'

Secondary API

//bemNames.factory = bemNamesFactory;
//bemNames.custom = customBemNames;
//bemNames.StringModifiers = StringModifiers;
//bemNames.StylesPolicy = StylesPolicy;

const config = {
  separators: { element: '-' },
  states = { mod1: 'is-mod1' },
};

bemNames.custom(config, 'block', 'element', ['mod1']);
// 'block-element is-mod1'

const bem = bemNames.factory('block', config);
bem('element', ['mod1']);
// 'block-element is-mod1'

Config object

const defaultConfig = {

  /**
  * When set to false generator will behave
  * like "classic" classnames, also will not use these configuration options::
  * seperators, states, keyValue, stringModifiers, parseModifier.
  */
  bemLike: true,

  separators: { element: '__', modifier: '--', keyValue: '-' },

  /**
  * This configuration option is handled in the default parseModifier. If
  * a modifier will match a key from this object, then instead returning
  * bemName conjuction with modifier, the parser will return appropriate value.
  */
  states: {},

  joinWith: ' ',

  /**
  * When set to true, modifiers from objects will be combined with its
  * values, unless value is type of boolean.
  */
  keyValue: false,

  /**
  * This defines how to handle modifiers not wrap with [] or {}.
  */
  stringModifiers: StringModifiers.WARN,

  /**
  * This function is generating modifier strings. The default implementation is
  * replaces modifiers with values from states and if modifier is not defined
  * in states object then returns bemName joined with the modifier.
  *
  * (config:object, bemName:str, modifier:str) => string
  */
  parseModifier: defaultParseModifier,

  /**
  * This configuration option allows to apply css-modules, just set here object
  * import from styles file.
  */
  styles: undefined,

  /**
  * Determines what to do when given modifer is missing in styles definitions.
  */
  stylesPolicy: StylesPolicy.WARN,
};

export const StringModifiers = {

  /**
  * Prints warning and ignores modifiers not wrapped with [] or {}.
  */
  WARN: 'warn',

  /**
  * Allows modifiers not wrapped with [] or {}.
  */
  ALLOW: 'allow',

  /**
  * Modifiers not wrapped with [] or {} are not parsed and are joined at the end of
  * the generated string.
  */
  PASS_THROUGH: 'passThrough',
};

export const StylesPolicy = {

  /**
  * Prints warning for missing class name definitios in style objects.
  */
  WARN: 'warn',

  /**
  * Ignores class names not defined in style objects.
  */
  IGNORE: 'ignore',
};

Sample configurations

emulate classNames like behaviour

import { customBemNames } from 'bem-names';

const cn = (...args) => customBemNames({ bemLike: false }, ...args);

cn(['block', 'element'], { mod1: false }, ['mod2'], 'mod3');
// 'block element mod2 mod3'

BEM with regular classes

import { bemNamesFactory, StringModifiers } from 'bem-names';

const config = {
  stringModifiers: StringModifiers.PASS_THROUGH,
};

const bem = bemNamesFactory('block', config);

bem('element', { mod1: true }, 'mod3');
// 'block__element block__element--mod1 mod3'
bem('element', 'mod3');
// 'block__element mod3'
bem('hmmm');
// 'block__hmmm'

BEM with states

import { bemNamesFactory } from 'bem-names';

const config = {
  states = { disabled: 'is-disable', values: 'has-values' },
};

const bem = bemNamesFactory('block', config);

bem({ disabled: true, mod: true });
// 'block is-disabled block--mod'

BEM with keyValues

import { bemNamesFactory } from 'bem-names';

const config = {
  keyValue = true,
};

const bem = bemNamesFactory('block', config);

bem({ disabled: true, mod: false, key: 'value' });
// 'block block--disabled block--key-value'

css-modules

import { bemNamesFactory } from 'bem-names';

const config = {
  styles: { block: '123', 'block--disabled': 234 },
};

const bem = bemNamesFactory('block', config);

cn('block', { disabled: true, mod: false });
// '123 234'

cn('block', { disabled: true, key: 'value' });
// '123 234'
// console: 'Key "key" is missing in styles'