core · npm (scoped) npm bundle size (minified + gzip)

Core package helps organize and manage components with BEM modifiers in React.


npm i -S @bem-react/core


Let's say, you have an initial App file structure as follows:


And you need to set up two optional types of buttons that will be different from the Button.tsx. (In our example those will be Button of theme 'action' and Button of type 'link')

You can handle those using @bem-react/core.

Follow the guide.

Step 1.

In your Components/Button/index.tsx, you define the type of props your button can get (including all the modifiers) within the interface that extends IClassNameProps from '@bem-react/core' :

import { IClassNameProps } from '@bem-react/core'

export interface IButtonProps extends IClassNameProps {
  text: string;

  // the following is the list of all modifiers:

  type?: 'link';
  theme?: 'action';

Step 2.

Set up the basic Button variant which will be rendered if no modifiers props are set in the parent component. Inside your Components/Button/Button.tsx:

import * as React from 'react';
import { IButtonProps } from './index';

export const Button: React.SFC<IButtonProps> = ({ text, className }) => ( 
  <div className={className}>{text}</div>

Step 3.

Set up the optional ButtonTypeLink and optional ButtonThemeAction variants that will be rendered if {type: 'link'} and/or {theme: 'action'} modifiers are set in the parent component respectively. Inside your Components/Button/ you add folders _type/ with Button_type_link.tsx file in it and _theme/ with Button_theme_action.tsx .

+   _type/
+     Button_type_link.tsx
+   _theme/
+     Button_theme_action.tsx

Set up the variants:

Note! The second parameter in withBemMod() is the condition for this component to be applied.

1. In Components/Button/_type/Button_type_link.tsx

import * as React from 'react';
import { withBemMod, ModBody } from '@bem-react/core';
import { IButtonProps } from '../index';

const ButtonLink: ModBody<IButtonProps> = (Base, { text, className }) => (

  // className === 'Button Button_type_link'

  <a className={className}>{text}</a>

export const ButtonTypeLink = withBemMod<IButtonProps>('Button', { type: 'link' }, ButtonLink);

2. In Components/Button/_theme/Button_theme_action.tsx

import { withBemMod } from '@bem-react/core';
import { IButtonProps } from '../index';

export const ButtonThemeAction = withBemMod<IButtonProps>('Button', { theme:  'action' });

Step 4.

Back in your Components/Button/index.tsx you need to compose all the variants with the basic Button. Be careful with the import order - it directly affects your CSS rules.

import { compose, IClassNameProps } from '@bem-react/core';
import { Button  as  Base } from './Button';
import { ButtonTypeLink } from './_type/Button_type_link';
import { ButtonThemeAction } from './_theme/Button_theme_action';

export interface IButtonProps extends IClassNameProps {
  text: string;
  type?: 'link';
  theme?: 'action';

export const Button = compose(

Note! The order of optional components composed onto Base is important: in case you have different layouts and need to apply several modifiers the FIRST one inside the compose method will be rendered! E.g., here:

export const Button = compose(

If your ButtonThemeAction was somewhat like

<button className={className}>{text}</button>,

your JSX-component:

<Button type="link" theme="action" text="Hello"/>

would render into HTML:

<button class="Button Button_theme_action Button_type_link">Hello</button>

Step 5.

Finally, in your App.tsx you can use these options composed all together or partially:

import * as React from 'react'
import Button from './Components/Button/Button'
import './App.css'

export const App: React.SFC = () => {
  <div className="App">
    <Button text="I'm basic" />   
    // Renders into HTML as: <div class="Button">I'm Basic</div>                                    

    <Button text="I'm type link" type="link" />    
    // Renders into HTML as: <a class="Button Button_type_link">I'm type link</a>

    <Button text="I'm theme action" theme="action" />
    // Renders into HTML as: <div class="Button Button_theme_action">I'm theme action</div>

    <Button text="I'm all together" theme="action" type="link" />
    // Renders into HTML as: <a class="Button Button_theme_action Button_type_link">I'm all together</a>


To help your debug "@bem-react/core" support development mode.

For <Button text="Hello" type="link" theme="action" /> (from the Example above), React DevTools will show:

<WithBemMod(Button)[theme:action][enabled] ...>
  <WithBemMod(Button)[type:link][enabled] ...className="Button Button_theme_action">
    <a className="Button Button_type_link Button_theme_action">Hello</a>
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