// Data fetching import useSwr from 'swr' // Font Awesome import { faHeartbeat } from '@fortawesome/free-solid-svg-icons' import { FontAwesomeIcon } from '@fortawesome/react-fontawesome' // Data fetching implements const fetcher = (url) => fetch(url).then((res) => res.json()) function App (props) { const { data, error } = useSwr( '/api/Fitbit/Heartrate', fetcher ) if (error) { return ( <>エラーが発生しました。 ) } else { if (!data) { return ( <>読み込み中... ) } else { return ( <>   {data.heartrate.value} ) } } } export default App;