catstodon/app/javascript/mastodon/components/icon_with_badge.tsx

import React from 'react';
import { Icon } from './icon';

const formatNumber = (num: number): number | string => num > 40 ? '40+' : num;

type Props = {
  id: string;
  count: number;
  issueBadge: boolean;
  className: string;
}
const IconWithBadge: React.FC<Props> = ({ id, count, issueBadge, className }) => (
  <i className='icon-with-badge'>
    <Icon id={id} fixedWidth className={className} />
    {count > 0 && <i className='icon-with-badge__badge'>{formatNumber(count)}</i>}
    {issueBadge && <i className='icon-with-badge__issue-badge' />}
  </i>
);

export default IconWithBadge;