What are the approaches to include polyfills in your `create-react-app`?

There are approaches to include polyfills in create-react-app,

1. Manual import from core-js:

   Create a file called (something like) polyfills.js and import it into root index.js file. Run npm install core-js or yarn add core-js and import your specific required features.

   import 'core-js/fn/array/find';
   import 'core-js/fn/array/includes';
   import 'core-js/fn/number/is-nan';

2. Using Polyfill service:

   Use the polyfill.io CDN to retrieve custom, browser-specific polyfills by adding this line to index.html:

   <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=default,Array.prototype.includes"></script>

   In the above script we had to explicitly request the Array.prototype.includes feature as it is not included in the default feature set.