BEM composer

A easy BEM classname tool for React, styled-components, linaria. Recommend using with classnames.

Install

npm

npm i bem-composer

yarn

yarn add bem-composer

API

Output

import { bem } from 'bem-composer';

// create a `button` block
const b = bem('button');

console.log(b.toString()); // 'button'
// shortcut for .toString()
console.log(b()); // 'button'
console.log(b.toSelector()); // '.button'

// create a `icon` element based on `b` block
const e = b('icon');

console.log(e.toString()); // 'button--icon'
// shortcut for .toString()
console.log(e()); // 'button--icon'
console.log(e.toSelector()); // '.button--icon'
console.log(e.toSuffix()); // '--icon'
console.log(e.toParentSelector()); // '&--icon'

// create a modifier based on `e` element
const m = e('active');

console.log(m.toString()); // 'button--icon__active'
// shortcut for .toString()
console.log(m().toString()); // 'button--icon__active'
console.log(m.toSelector().toString()); // '.button--icon__active'
console.log(m.toSuffix().toString()); // '__active'
console.log(m.toParentSelector().toString()); // '&__active'
// get suffix with element
console.log(m.toSuffix(true).toString()); // '--icon__active'
// get parent selector with element
console.log(m.toParentSelector(true).toString()); // '&--icon__active'

// multiple modifiers support
console.log(m('large')({
  name: 'rounded',
  value: true
}).toString()); // 'button--icon__active_large_rounded'

// create a modifier with value
const mv = e({
  name: 'active',
  value: 'hover'
});
console.log(mv.toString()); // 'button--icon__active-hover'

// modifier with condition
console.log(e({
  'active',
  value: false
}).toString()) // 'button--icon'
console.log(e({
  'active',
  value: true
}).toString()) // 'button--icon__active'

// block with modifier
console.log(b('', 'active').toString()); // 'button_active'

Configure delimiters

import { configure, DefaultBEMDelimiters } from 'bem-composer';

// Configure BEM constructor with custom delimiters.
const cbem = configure({
  prefix: 'bem-',
  element: '__',
  modifier: '~~',
  modifierValue: '~'
});

console.log(
  cbem('block', 'icon', {
    name: 'active',
    value: 'hover'
  }).toString()
); // bem-block__icon~~active~hover

Curried API

Provide a curried API to easily create elements and modifiers.

import { bem } from 'bem-composer';

console.log(bem('button', 'icon').toString()); // button--icon
console.log(bem('button')('icon').toString()); // button--icon
console.log(bem('button', 'icon', 'active').toString()); // 'button--icon__active'
console.log(bem('button')('icon', 'active').toString()); // 'button--icon__active'
console.log(bem('button', 'icon')('active').toString()); // 'button--icon__active'

BEM Constructor type definition

function bem(blockName: string): BEMBlock;
function bem(blockName: string, elementName: string): BEMElement;
function bem(
  blockName: string,
  elementName: string,
  modifierValue: BEMModifierValue
): BEMModifier;

export type BEMModifierValue =
  | {
      name: string;
      value?: string | boolean;
    }
  | string;

export interface BEMBlock {
  (): string; // shortcut for toString()
  (elementName: string): BEMElement;
  (
    elementName: undefined | string,
    modifierValue: BEMModifierValue
  ): BEMModifier;
  toString: () => string; // Return classname
  toSelector: () => string; // Return classname selector
}

export interface BEMElement {
  (): string; // shortcut for toString()
  (modifierValue: BEMModifierValue): BEMModifier;
  toString: () => string;
  toSelector: () => string;
  toSuffix: () => string;
  toParentSelector: () => string;
}

export interface BEMModifier {
  (): string;
  (modifierValue: BEMModifierValue): BEMModifier; // modifier chain, for multiple modifiers support
  toString: () => string;
  toSelector: () => string;
  toSuffix: (withElement?: boolean) => string;
  toParentSelector: (withElement?: boolean) => string;
}

React

import React from 'react';
import { bem } from 'bem-composer';
import classNames from 'classnames';

const b = bem('button');
const e = b('icon');
const m = e('active');

export default function Button(props) {
  const { active } = props;
  return (
    <button
      classname={classNames([
        b(), // 'button'
        b('', {
          name: 'active',
          value: active
        }) // button__active
      ])}
    >
      <img
        classname={classNames([
          e(), // 'button-icon'
          e({
            name: 'active',
            value: active
          }), // active === true ? 'button--icon__active' : 'button--icon'
          e('primary') // 'button--icon__primary'
        ])}
      />
    </button>
  );
}

Styled-components & Linaria

import styled from 'styled-components';

const b = bem('button');
const e = b('icon');
const m = e('active');

export const StyledButton = styled.button`
  /* .button */
  ${b.toSelector()} {
    border: 1px solid red;
    outline: none;
  }

  /* &--icon */
  ${e.toParentSelector()} {
    width: 20px;
    height: 20px;

    /* &__active */
    ${m.toParentSelector()} {
      opacity: 0.5;
    }
  }
`;

---

Trouble shooting

Multiple elements support

As we don't want BEM classname to be too complicated, multiple elements is not provided by this library, but you can do some workaround like this:

bem('block', 'e1--e2--e3').toString();