bem-helper-js

JavaScript helper for generating BEM class names with chainable API for adding modifiers and elements.

Basic Usage

import BEM from 'bem-helper-js';
 
assert.equal(BEM('my-block'), 'my-block');
assert.equal(BEM('my-block').is('active'), 'my-block my-block--active');
 
assert.equal(BEM('my-block').el('element'), 'my-block__element');
assert.equal(BEM('my-block').el('element').is('active'), 'my-block__element my-block__element--active');

Note: as of now, only one .el() can be used in the same chain and all modifiers applies to this element (even if they were added earlier in the chain).

Multiple Modifiers

import BEM from 'bem-helper-js';
 
assert.equal(BEM('my-block').is('wide').is('active'), 'my-block my-block--wide my-block--active');

Conditional Modifiers

Sometimes it's useful to decide if a modifier class should be present at runtime. The is() function takes an optional second parameter which specifies if the class should be added.

import BEM from 'bem-helper-js';
 
let isActive = true;
 
assert.equal(BEM('my-block').is('active', isActive), 'my-block my-block--active');
 
let isActive = false;
 
assert.equal(BEM('my-block').is('active', isActive), 'my-block');

Mix with non-BEM classes

import BEM from 'bem-helper-js';
 
assert.equal(BEM('my-block').is('wide').add('grid-wide'), 'my-block my-block--wide grid-wide');

Usage with React

This helper was mainly developed to make it faster to write class names in JSX with React.

A common use case is to match the CSS Block name with the JavaScript class name.

Simply pass the class instance this as the first argument to BEM() and the block name will be set to match the constructor name. This works for both ES5 and ES6 classes.

import BEM from 'bem-helper-js';
 
class MyComponent {
  render() {
    return (
      <div className={BEM(this).is('active', this.props.active)}>
        <h1 className={BEM(this).el('title')}>
          My title
        </h1>
      </div>
    );
  }
);

Assuming this.props.active is true this will output:

<div class="MyComponent MyComponent--active">
  <h1 class="MyComponent__title">My title</h1>
</div>

Collaborators

• https://github.com/ffdead
• https://github.com/filipstefansson
• https://github.com/og2t
• https://github.com/pudgereyem
• https://github.com/hjortureh