pokemon.trade/app/javascript/packs/frontend.tsx

import React from 'react';
import {render} from 'react-dom';

document.addEventListener(
  'DOMContentLoaded',
  (): void => {
    import('./frontend/app').then(
      ({default: App}): void => {
        render(<App />, document.querySelector('main[id="app"]'));
      }
    );
  }
);