When this is happening?

While using the library with react app, it gives the polyfills error.

What is the Error?

BREAKING CHANGE:
webpack < 5 used to include polyfills for node.js core modules by default.
This is no longer the case. Verify if you need this module and configure a polyfill for it.

If you want to include a polyfill, you need to:
- add a fallback 'resolve.fallback: { "querystring": require.resolve("querystring-es3") }'
- install 'querystring-es3'
If you don't want to include a polyfill, you can use an empty module like this:
resolve.fallback: { "querystring": false }

Solution:

If targeting modern environments, we can replace querystring with the standard URLSearchParams API, which provides similar functionality for parsing and formatting query strings.
For example:

Replace:

const querystring = require("querystring");
let config = querystring.parse(parsedUrl.query);

With:

let config = Object.fromEntries(new URLSearchParams(parsedUrl.query));