Conditional ClassName in React

If we would be only using JavaScript, it would be possible to create a conditional React className attribute this way:

const Box = ({ status, children }) => {
  let classNames = ['box'];

  if (status === 'INFO') {
    classNames.push('box-info');
  }

  if (status === 'WARNING') {
    classNames.push('box-warning');
  }

  if (status === 'ERROR') {
    classNames.push('box-error');
  }

  return (
    <div className={classNames.join(' ')}>
      {children}
    </div>
  );
}

Fortunately, there is one neat helper library for conditional classnames in React: clsx:

import cs from 'clsx';

const Box = ({ status, children }) => {
  const classNames = cs('box', {
    'box-info': status === 'INFO',
    'box-warning': status === 'WARNING',
    'box-error': status === 'ERROR',
  });

  return (
    <div className={classNames}>
      {children}
    </div>
  );
}

It works perfectly with CSS modules too:

import cs from 'clsx';

import styles from './style.css';

const Box = ({ status, children }) => {
  const classNames = cs('box', {
    [styles.boxInfo]: status === 'INFO',
    [styles.boxWarning]: status === 'WARNING',
    [styles.boxError]: status === 'ERROR',
  });

  return (
    <div className={classNames}>
      {children}
    </div>
  );
}

And could also be used for optional classNames in Styled Components.