Forum

Methodology

Toolbox

Platform

Community

bem-naming

About

This tool allows getting information about BEM entity using string as well as forming string representation based on naming object.

Install

$ npm install --save bem-naming

Usage

var bemNaming = require('bem-naming');

bemNaming.parse('button__text'); // { block: 'button', elem: 'text' }

bemNaming.stringify({ block: 'button', modName: 'checked' }); // button_checked

Table of Contents

String representation

To define BEM entities we often use a special string format that allows us 100% define what entity exactly is represented.

According to original BEM-naming convention it looks like the following:

'block[_block-mod-name[_block-mod-val]][__elem-name[_elem-mod-name[_elem-mod-val]]]'

(Parameters within square brackets are optional)

  • Block — block-name.
  • Block's modifier in key-value format — block-name_mod-name_mod-val.
  • Block's boolean modifier — block-name_mod.
  • Block's element — block-name__elem-name.
  • Element's modifier in key-value format — block-name__elem-name_mod-name_mod-val.
  • Element's boolean modifier — block-name__elem_mod.

Object representation of BEM entity

BEM entities can be defined with a help of JS object with the following fields:

  • block — a block name. The field is required because only a block exists as an independent BEM entity
  • elem — an element name.
  • modName — a modifier name.
  • modVal — a modifier value.

The modifier consists of a pair of fields modName and modVal. This means that the field modVal without modName has no meaning.

Example:

// The block modifier
{
    block: 'block',
    modName: 'mod',
    modVal: 'val'
}

// Not valid BEM-notation
{
    block: 'block',
    modVal: 'val'
}

To describe the boolean modifier field modVal must be specified as true.

Example:

// Boolean modifier of a block
{
    block: 'block',
    modName: 'mod',
    modVal: true
}

// Shorthand for the boolean modifier of a block
{
    block: 'block',
    modName: 'mod'
}

// Not valid BEM-notation
{
    block: 'block',
    modName: 'mod',
    modVal: false
}

API

validate(str)

Checks a string to be valid BEM notation.

Example:

bemNaming.validate('block-name');  // true
bemNaming.validate('^*^');         // false

parse(str)

It parses string into naming object.

Example:

bemNaming.parse('block__elem_mod_val');  // { block: 'block', elem: 'elem',
                                         //   modName: 'mod', modVal: 'val' }

stringify(obj)

It forms a string according to naming object.

Example:

bemNaming.stringify({
    block: 'block', elem: 'elem',
    modName: 'mod', modVal: 'val'
}); // 'block__elem_mod_val'

typeOf(str)

Returns a string indicating the type of the BEM entity.

Example:

bemNaming.typeOf('block');             // block
bemNaming.typeOf('block_mod');         // blockMod
bemNaming.typeOf('block__elem');       // elem
bemNaming.typeOf('block__elem_mod');   // elemMod

typeOf(obj)

Returns a string indicating the type of the BEM entity.

Example:

bemNaming.typeOf({ block: 'block' });                               // block
bemNaming.typeOf({ block: 'block', modName: 'mod' });               // blockMod
bemNaming.typeOf({ block: 'block', elem: 'elem' });                 // elem
bemNaming.typeOf({ block: 'block', elem: 'elem', modName: 'mod' }); // elemMod

isBlock(str)

Checks whether string is a block.

Example:

bemNaming.isBlock('block-name');   // true
bemNaming.isBlock('block__elem');  // false

isBlock(obj)

Checks whether naming object is a block.

Example:

bemNaming.isBlock({ block: 'block-name' });           // true
bemNaming.isBlock({ block: 'block', elem: 'elem' });  // false

isBlockMod(str)

Checks whether string is modifier of a block.

Example:

bemNaming.isBlockMod('block_mod');        // true
bemNaming.isBlockMod('block__elem_mod');  // false

isBlockMod(obj)

Checks whether naming object is modifier of a block.

Example:

bemNaming.isBlockMod({ block: 'block',
    modName: 'mod', modVal: true });  // true

bemNaming.isBlockMod({ block: 'block', elem: 'elem',
    modName: 'mod', modVal: true });  // false

isElem(str)

Checks whether string is element of a block.

Example:

bemNaming.isElem('block__elem');  // true
bemNaming.isElem('block-name');   // false

isElem(obj)

Checks whether naming object is element of a block.

Example:

bemNaming.isElem({ block: 'block', elem: 'elem' });  // true
bemNaming.isElem({ block: 'block-name' });           // false

isElemMod(str)

Checks whether string is modifier of an element.

Example:

bemNaming.isElemMod('block__elem_mod');  // true
bemNaming.isElemMod('block__elem');      // false

isElemMod(obj)

Checks whether naming object is modifier of an element.

Example:

bemNaming.isElemMod({ block: 'block', elem: 'elem',
    modName: 'mod', modVal: true });  // true

bemNaming.isElemMod({ block: 'block',
    modName: 'mod', modVal: true});   // false

elemDelim

String to separate elem from block.

modDelim

String to separate modifiers from blocks and elements.

modValDelim

String to separate value of modifier from name of modifier.

Common misconceptions

BEM methodology involves the use of flat structure inside a block. It means that BEM entity can not be represented as an element of the other element and the following string representation will be invalid:

'block__some-elem__sub-elem'

Also there is no such BEM entity as a modifier and an element modifier simultaneously so the following string representation will be invalid:

'block_block-mod-name_block-mod-val__elem-name_elem-mod-name_elem-mod-val'

Custom naming convention

Use bemNaming function to create instance to manage naming of your own naming convention.

Example:

var myNaming = bemNaming({
    elem: '-',
    mod: { name: '--', val: '_' }
    wordPattern: '[a-zA-Z0-9]+'   // because element and modifier's separators include
});                               // hyphen in it, we need to exclude it from block,
                                  // element and modifier's name

myNaming.parse('block--mod_val'); // { block: 'block',
                                  //   modName: 'mod', modVal: 'val' }

myNaming.stringify({              // 'blockName-elemName--boolElemMod'
    block: 'blockName',
    elem: 'elemName',
    modName: 'boolElemMod'
});

bemNaming({ elem, mod, wordPattern })

elem

Type: String

Default: __

Separates element's name from block

mod

Type: String, { name: String, val: String }

Default: _

Separates modifiers from blocks and elements.

This option can take object with following fields:

  • name — separates name of modifier from blocks and elements.

    Default as _.

  • val — separates value of modifier from name of modifier.

    Default as the value of the name.

wordPattern

Type: String

Default: [a-z0-9]+(?:-[a-z0-9]+)*

Defines which symbols can be used for block, element and modifier's names.

Convention by Harry Roberts

According to this convention elements are delimited with two underscores (__), modifiers are delimited by two hyphens (--), and values of modifiers are delimited by one underscore (_).

Read more in the Guidelines.

Example:

var twoDashes = bemNaming('two-dashes');

twoDashes.parse('block__elem');    // { block: 'block', elem: 'elem' }
twoDashes.parse('block--mod_val'); // { block: 'block',
                                   //   modName: 'mod', modVal: 'val' }

twoDashes.stringify({              // 'block__elem--mod'
    block: 'block',
    elem: 'elem',
    modName: 'mod'
});

License

Code and documentation copyright 2014 YANDEX LLC. Code released under the Mozilla Public License 2.0.

If you notice a mistake or want something to supplement the article, you can always write to us at GitHub, or correct an article using prose.io.