docs: add a note about dual module hazard

Author: satya164

docs/pages/esm.md

@@ -126,6 +126,8 @@ To set up a dual module setup, you can follow these steps:
 
    The `default` field is the fallback entry point for both conditions. It's used for the actual JS code when the library is imported or required.
 
+> **Important:** With this approach, the ESM and CommonJS versions of the package are treated as separate modules by Node.js as they are different files, leading to [potential issues](https://nodejs.org/docs/latest-v19.x/api/packages.html#dual-package-hazard) if the package is both imported and required in the same runtime environment. If the package relies on any state that can cause issues if 2 separate instances are loaded, it's necessary to isolate the state into a separate CommonJS module that can be shared between the ESM and CommonJS builds.
+
 ## Guidelines
 
 There are still a few things to keep in mind if you want your library to be ESM-compatible: