bem-cn

BEM class names generator

Friendly BEM class names generator. Great for React.

Bem-cn (aka BEM Class Name) is extra small (minified+gzipped less than 1.6Kb) and extremely simple client-side library and Node.js module.

Important! Only bem-cn@3.x+ compatible with react@16+. Please do not use version 2.x or lower. More details about the problem.

Inspired by b_.

Justification

I spent a lot of time finding BEM class name generator, that meets my needs:

• Simple usage with React
• Support modifiers without value
• Mix multiple blocks
• Friendly API

When my efforts had led to naught I've created this micro library.

Install

With Node.js:

npm i --save bem-cn
yarn add bem-cn

Works with webpack and browserify:

// CommonJS
var { block } = require('bem-cn');

// ES6
import { block } from 'bem-cn';

API

const b = block('button');

// Block
b(); // 'button'

// Element
b('icon'); // 'button__icon'

// Modifier
b({ type: 'text' });  // 'button button_type_text'
b({ onlykey: true });  // 'button button_onlykey'
b({ without: false });  // 'button'

b('icon', { name: 'check' }); // 'button__icon button__icon_name_check'

// Mix another classes
b('icon').mix('another'); // 'button__icon another'
b('icon').mix(['one', 'two']); // 'button__icon one two'

// States like in SMACSS: https://smacss.com/book/type-state
b.state({ hidden: true }); // 'button is-hidden'
b.state({ hidden: false }); // 'button'
b.state({ hidden: true, error: true }); // 'button is-hidden is-error'

// More states!
b.is({ loading: true }); // 'button is-loading'
b.has({ content: true }); // 'button has-content'

// Setup custom delimiters
import { setup } from 'bem-cn';

const block = setup({
    el: '~~',
    mod: '--',
    modValue: '-'
});

const b = block('block');

b('element'); // 'block~~element'
b({ mod: 'value' }); // 'block block--mod-value'

// Setup namespace
const block = setup({ ns: 'ns-' });

const b = block('block');

b(); // 'ns-block'
b('element'); // 'ns-block__element'
b({ mod: 'value' }); // 'ns-block ns-block_mod_value'

Try it with React

import block from 'bem-cn';
import React from 'react';
import ReactDOM from 'react-dom';

const b = block('popup');

const Popup = React.createClass({
    render() {
        const { skin, children } = this.props;

        return (
            <div className={b()}>
            	<span className={b('icon')} />
            	<div className={b('content', { skin })}>
            		{children}
            	</div>
            </div>
        );
    }
});

ReactDOM.render(<Popup skin="bright">Hello!</Popup>, target);

/*
<div class="popup">
	<span class="popup__icon"></span>
	<div class="popup__content popup__content_skin_bright">
        Hello!
	</div>
</div>
 */

Troubleshooting

Maigrate to version 3.x

@todo

PropTypes warnings

bem-cn@2.x or lower has specific chainable API. As a result, each call returns function for a further call. But most components are expecting property className as a string and using propTypes object for check this. In this case, you will see a warning. There are the couple of ways to avoid these warnings below.

#1

Use final call without arguments to get a string

<CustomComponent className={b('icon')()} />

#2

Use explicit call of method toString():

<CustomComponent className={b('icon').toString()} />

#3

Use less specific propTypes rules:

let CustomComponent = React.createClass({
    propTypes: {
        className: React.PropTypes.oneOfType([
            React.PropTypes.string,
            React.PropTypes.func
        ])
    },
    // ...
});

ES3 browsers

bem-cn is fully compatible with ES5 browsers. If you are going to support ES3 browsers than just use es5 shim.