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@bem-react/core v2.0.1

BEM React Core

@bem-react/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 within the interface that extends IClassNameProps from '@bem-react/core' :

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

export interface IButtonProps extends IClassNameProps {
  tag?: string;

export const cnButton = cn('Button');

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 React, { FC } from 'react';

import { IButtonProps, cnButton } from './index';

export const Button: FC<IButtonProps> = ({
  tag: TagName = 'button',
}) => (
  <TagName className={cnButton({}, [className])}>

Step 3.

Set up the optional withButtonTypeLink and optional withButtonThemeAction 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 React from 'react';
import { withBemMod } from '@bem-react/core';

import { IButtonProps, cnButton } from '../index';

export interface IButtonTypeLinkProps {
  type?: 'link';

export const withButtonTypeLink = withBemMod<IButtonTypeLinkProps, IButtonProps>(cnButton(), { type: 'link' }, (Button) => (
  (props) => (
    <Button {...props} tag="a" />

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

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

import { cnButton } from '../index';

export interface IButtonThemeActionProps {
  theme?: 'action';

export const withButtonThemeAction = withBemMod<IButtonThemeActionProps>(cnButton(), { theme:  'action' });

Step 4.

Finally, in your App.tsx you need compose only necessary the variants with the basic Button. Be careful with the import order - it directly affects your CSS rules.

NOTE: If you wanna use same modifiers with different values you should use composeU for getting correctly typings.

import React, { FC } from 'react';
import { compose, composeU } from '@bem-react/core';

import { Button as ButtonPresenter } from './Components/Button/Button';
import { withButtonTypeLink } from './Components/Button/_type/Button_type_link';
import { withButtonThemeAction } from './Components/Button/_theme/Button_theme_action';
import { withButtonThemeDefault } from './Components/Button/_theme/Button_theme_default';

import './App.css';

const Button = compose(
  composeU(withButtonThemeAction, withButtonThemeDefault),

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

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

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

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

Note! The order of optional components composed onto ButtonPresenter 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 withButtonThemeAction was somewhat like

<button className={className}>{children}</button>

your JSX-component:

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

would render into HTML:

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


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

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

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