Workaround to enable switching main entry point of Create-React-App by .env

CRASwitchEntryPointByEnv.js

// package.json 
{
   //...
   "scripts": {
      "startfirst": "REACT_APP_MAIN_COMPONENT=FirstMainComponent react-scripts start",
      "buildfrst": "REACT_APP_MAIN_COMPONENT=FirstMainComponent react-scripts build",
      "startsecond": "REACT_APP_MAIN_COMPONENT=SecondMainComponent react-scripts start",
      "buildsecond": "REACT_APP_MAIN_COMPONENT=SecondMainComponent react-scripts build",
      "test": "react-scripts test",
      "eject": "react-scripts eject"
    },
    //...
}
// src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import * as serviceWorker from './serviceWorker';
let {Suspense} = React

let appstring = './' + process.env.REACT_APP_MAIN_COMPONENT
const DynamicallyLoaded = React.lazy( () => import(`${appstring}`) )
const DynamicLoader = () => <div className='h100 w100'>
   <Suspense fallback={<div>&nbsp;</div>}>
      <DynamicallyLoaded/>
   </Suspense>
</div>

ReactDOM.render(<DynamicLoader />, document.getElementById('root'));
serviceWorker.unregister();

// src/FirstMainComponent.js
// src/SecondMainComponent.js

CRA devs did not pulled this commit which would have allowed switching main component of CRA.

Usiing React lazy loading, switching main entry point is an achievable workaround, albeit not ideal.