This is valid code, but I'd use an interface to make this more readable. Here's an example:

@JS()
@staticInterop
class JSError {}

extension on JSError {
  external String? get name;
  external String? get message;
  external String? get code;
} 

which would let you write simpler code like:

if (e.name == 'FirebaseError')

return r.code ?? ''

and so forth. You may not have access to extension types since that will require >=3.3, but it's even more concise with one:

extension type Error(JSObject e) {
  external String? get name;
  external String? get message;
  external String? get code;
}

Thanks I've updated this as well.
We don't have access to Dart 3.3 yet, but I'll keep in mind to revisit this once Flutter supports it

Once AppJsImpl is moved to an extension type that implements JSObject, this can be JSArray<AppJsImpl>, and a cast won't be needed above, but for now this is the best alternative. :/

I'm surprised this works without a toJS as this returns a JSAny? iirc. Should this be globalContext.getProperty<JSString?>('flutterfire_web_sdk_version'.toJS)?.toDart? Or perhaps more concisely, (globalContext['flutterfire_web_sdk_version'] as JSString?)?.toDart?

Good catch, surprinsinlgy, declaring it in a variable triggered an analyzer error that wasn't triggered using ??
I've updated with your version