What are the approaches to include polyfills in your 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.