index.js

import React from 'react';
import ReactDOM from 'react-dom';
import * as Sentry from '@sentry/react';
import { Integrations } from '@sentry/tracing';
import './index.css';
import App from './components/app';
import reportWebVitals from './reportWebVitals';

if(process.env.NODE_ENV === 'production' && process.env.REACT_APP_SENTRY_DSN) {
  Sentry.init({
    dsn: process.env.SENTRY_DSN,
    integrations: [new Integrations.BrowserTracing()],

    // Set tracesSampleRate to 1.0 to capture 100%
    // of transactions for performance monitoring.
    // We recommend adjusting this value in production
    tracesSampleRate: 1.0,
  });
}

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
// or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
reportWebVitals();