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2.0.1 • Public • Published

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React components bound to class names. As simple as that. Without tagged template literals.

What it does

  • Create component bound to one or more class name
  • Apply class names based on boolean props, referred to as variants
  • Offers shortcut members to wrap intrinsic elements such as classBound.blockquote('my-blockquote')
  • Extend existing class bound components with the modifiers extend, as, withVariants and withOptions
  • Strong TypeScript support: Allowed props restricted to those of the composed component and variant flags

Use babel-plugin-class-bound-components to benefit from:

  • Automatic inferring of display names like you're used to with regular React functional components
  • Backwards compatibility with browsers not supporting ES6 Proxy, but still being able to use the classBound[JSX.IntrinsicElement]() shorthand (e.g., classBound.button('foo') instead of classBound('foo', null, null, 'button'))

Why not styled-components

While CSS-in-JS approaches like styled-components have gained a lot of attention in the last couple of years you might be in a position where you can't or don't want to move to CSS-in-JS

  • You might be using an external CSS library like Bootstrap
  • You might be converting an old codebase to React and just want to focus on component functionality instead of also migrating all of your CSS to CSS-in-JS
  • You might as well just not like CSS-in-JS

Still, you might want to have React components that abstract away the internals of your style sheets, or you're even using TypeScript and want to benefit from static types for styling components instead of raw class name concatenation.

This is where class-bound-components comes into play. It allows you to bind class names, be it global class name strings or even class names generated by css-modules to be bound to components. class-bound-components enables you to introduce an abstraction layer between style sheets and component usage that can also support a future migration from CSS-in-CSS to CSS-in-JS.


import classBound from 'class-bound-components';
import './breadcrumb.css';

const Container = classBound('container');
const Breadcrumb = classBound.ol('breadcrumb');
const BreadcrumbItem = classBound.li('breadcrumb-item', { isActive: 'active' });
const BreadcrumbLink = classBound.a('breadcrumb-link');

const BreadcrumbContainer: React.FC<{ items: Item[]; activeId: number }> = ({ items, activeId }) => (
    <Breadcrumb aria-label="breadcrumb">
      {items.map(item => {
        <BreadcrumbItem key={item.id} isActive={item.id === activeId}>
          <BreadcrumbLink href={item.url} target="_blank">{item.name}</a>

const BreadcrumbButton = classBound.as(BreadcrumbLink, 'button');
const VisitableBreadcrumbLink = classBound.withVariants(BreadcrumbLink, { isVisited: 'visited' });
const CustomBreadcrumbItem = classBound.extend(BreadcrumbLink, 'custom-breadcrumb-item', { isActive: 'custom-active' });


  1. Installation
  2. API
  3. Usage with CSS Modules
  4. Display Names
  5. TypeScript Support
  6. Ref Forwarding
  7. Changelog
  8. License


# With npm
npm install --save class-bound-components

# With yarn
yarn add class-bound-components

In both cases make sure you have react as well as react-dom added to your project.


Component Creation


Creates a new ClassBoundComponent from an options object with the following properties. All options are optional.

Name Type Description
className string or string[] Classes that are applied to the base component without any condition
displayName string Display name of the component created. This appears for instance in the React devtools. When omitted it's referred to as Anonymous
variants Record<string, ClassValue>1 Object mapping the name of a variant, i.e., the name of the prop that has to be set to enable the variant, to a ClassValue that should be applied when the variant is enabled.
elementType React.ElementType<any> Type of element to use a the base for the component. May be any string recognized by ReactDOM or a custom React component. default: 'div'

1 ClassValue refers to any kind of value that can be passed into the classnames Function.

const Button = classBound({
  className: 'custom-button',
  displayName: 'Button',
  variants: { isPrimary: 'primary', isCTA: ['secondary', 'cta'] },
  elementType: 'button'

classBound[JSX.IntrinsicElement](className[, displayName[, variants]])

Alias for classBound(options) offering a member on the classBound function for all known intrinsic elements, i.e., leaf elements that are recognized by React DOM.

Note that these shortcut members make use of the JavaScript Proxy object. Using this in a browser that does not support Proxy will throw a runtime error. If you need to support such browsers, it is recommended to make use of the babel-plugin-class-bound-components, which will inline these method calls to the standard elementType argument and hence won't use Proxy anymore.

const CustomLink = classBound.a('custom-link', 'CustomLink', {
  isActive: 'active',

const CustomQuote = classBound.blockquote('custom-quote');

classBound(className[, displayName[, variants[, elementType]]])

Alias for classBoundComponent(options) containing all options defined above as positional arguments.

const Button = classBound('custom-button', 'Button', { isPrimary: 'primary' }, 'button');
const UnnamedButton = classBound('custom-button', { isPrimary: 'primary' }, 'button');

classBound(className[, variants[, elementType]])

Alias for classBoundComponent(options) omitting the displayName option which will be set to undefined when calling this signature.

const Button = classBound('custom-button', { isPrimary: 'primary' }, 'button');
Button.displayName === undefined; // Meh, not interested in `displayName`


Modifiers are functions with which clones of an existing ClassBoundComponent can be created with slight modifications. The modifiers extend, withVariants, withOptions and as are accessible as members of the classBound function. Additionally, all of them can be imported as named imports from class-bound-components

import classBound, {
} from 'class-bound-components';

classBound.extend === extend;
classBound.withVariants === withVariants;
classBound.withOptions === withOptions;
classBound.as === as;

classBound.extend(ClassBoundComponent, className[, displayName][, variants])

Extends an existing ClassBoundComponent with class names and variants so that class names and already existing variants are combined. Useful when existing class names and variant class names should persist while augmenting them with more specific classes. The displayName argument can optionally be left out.

const Button = classBound.button('button', 'Button', {
  isActive: 'button-active',

const CustomButton = classBound.extend(
    isActive: 'custom-button-active',

<CustomButton isActive />;
// renders <button className="button custom-button button-active custom-button-active" />

classBound.as(ClassBoundComponent, elementType)

Creates a copy of a ClassBoundComponent with similar options except the elementType being set to a different value

const CustomButton = classBound.button('custom-button', 'CustomButton', { isPrimary: 'primary' });

// Oops need the same styles as an `<a />` tag
const CustomLink = classBound.as(CustomButton, 'a');

<CustomLink href="https://example.com/" target="_blank" isPrimary>Click me!</CustomLink>
         // ^ awesome! TypeScript allows these <a> specific props now!

classBound.withVariants(ClassBoundComponent, mergeVariants)

Creates a copy of a ClassBoundComponent with similar options except the variants are merged with mergeVariants. While old variants that are not specified in the merge variants remain untouched, naming conflicts are resolved by preferring the variants in mergeVariants. Note that this differs from the behavior of ClassBoundComponent.extend.

// button.tsx
import './buttons.css';

const BaseButton = classBound.button('baseButton', 'BaseButton', { isPrimary: 'primary', isFlashy: 'flashy' });

// my-custom-container.tsx
import 'my-custom-container.css';

const CustomButton = classBound.withVariants(BaseButton, {
  isFlashy: 'customFlashy',

<CustomButton type="button" isPrimary isFlashy>Click me</CustomButton>
// renders <button type="button" className="baseButton primary customFlashy">Click me</button>
// note that `flashy` got removed in favor of `customFlashy`

classBound.withOptions(ClassBoundComponent, oldOptions => newOptions)

Creates a copy of a ClassBoundComponent by applying the provided function on the existing options and taking the return value of the function as the new options.

const Button = classBound.button('button', 'Button', { variantA: 'variant-a' });

const CustomButton = classBound.withOptions(Button, (options) => ({
  className: [options.className, 'fooClass', 'barClass'],
  variants: { ...options.variants, variantB: 'variant-b' },
  displayName: `Custom(${options.displayName})`,

CustomButton.displayName === 'Custom(Button)';

<CustomButton variantA variantB />;
// renders <button classNames="button fooClass barClass variantA variantB">

Usage with CSS Modules

class-bound-components is compatible with anything that produces class names as strings. This might be global styles defined in a separate CSS file but also class names that are generated by CSS modules for instance. Instead of the raw class name string you would normally pass to classBound, simply pass the modularized CSS class name generated by CSS modules.

/* button.css */

.button {
  background-color: white;
  border: 1px #ccc solid;

.isActive {
  background-color: #ccc;
// button.tsx
import classBound from 'class-bound-components';

import buttonStyles from './button.css';

export const Button = classBound.button(buttonStyles.button, {
  isActive: buttonStyles.isActive,

// renders <button className="6h3b 0e9c">Click me</button> given that CSS modules
// provides these class names for the module styles
const Container: React.FC = () => <Button isActive>Click me</Button>;

Display Names

Usually, displayNames in React benefit from the automatic assignment to Function.name when defining a functional component, which will make the component appear as the name of the function in React DevTools and Error traces.

Unfortunately, this doesn't work for components created with classBound, since these are defined in a closure. For this, all signatures of classBound can be provided with an explicit string for the displayName property of the component.

This can be omitted when using babel-plugin-class-bound-components. This babel plugin tries to infer the displayName in the fashion like Function.name would normally do and inlines these into the calls of classBound, so you don't have to repeat yourself over and over again. Read more in the transformation documentation.


class-bound-components is built in TypeScript so it supports strong static types out of the box. In particular it is aware of the props that are allowed to be passed to components, be it the passed-down props of the composed element type (e.g., the props of a <button /> element) or props introduced through custom variants. Of course types are also provided for the different signatures of the classBound function and the member functions on the components.

Ref Forwarding

class-bound-components handles ref-forwarding automatically. This means for intrinsic elements like div or img it will create a React.forwardRef component as well as in the case of passing it a forwardRef component as elementType. For other cases a regular function component is returned.

// Wrapping an intrinsic element
const CustomImage = classBound.img('custom-image');
const imageRef = React.createRef<HTMLImageElement>();
const el1 = <CustomImage ref={imageRef} />; // This works by default!

// Wrapping a ref forwarding component
const RefForwardingImage = React.forwardRef<HTMLImageElement, {}>((_, ref) => (
  <img ref={imageRef} />

const CustomRefForwardingImage = classBound(
const el2 = <CustomRefForwardingImage ref={imageRef} />; // This works as well!

// Wrapping a non ref forwarding component
const FunctionComponent: React.FC<{}> = () => <img alt="No ref here" />;
const CustomFunctionComponent = classBound(
const el3 = <CustomFunctionComponent ref={imageRef} />; // This doesn't work since `FunctionComponent` doesn't have a ref

© 2020 Jannik Portz – License


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