[js_interop] Can `@JSExport` annotation be applied to not a class?

[sgrekhov]

From JSExport documentation it is not clear if enums, extension types and extensions can be annoteted with JSExport annotation or not. The following example works for me.

import 'dart:js_interop';
import 'dart:js_interop_unsafe';

@JS()
external void eval(String code);

@JSExport()
enum E {
  e0(0);

  final int id;
  const E(this.id);
}

@JSExport()
class C {
  int id = 42;
}

@JSExport()
extension type ET(C c) implements C {
}

@JSExport()
extension Ext on C {
  int extensionMethod() => 42;
}

void main() {
  var jsE = createJSInteropWrapper<E>(E.e0);
  var jsET = createJSInteropWrapper<C>(ET(C()));
  var jsC = createJSInteropWrapper<C>(C());

  globalContext["jsE"] = jsE;
  globalContext["jsET"] = jsET;
  globalContext["jsC"] = jsC;
  eval(r'''
    console.log(globalThis.jsE.id);     // 0
    console.log(globalThis.jsET.c);     // undefined
    console.log(globalThis.jsC.id);     // 42
    console.log(globalThis.jsC.extensionMethod);    // undefined
  ''');
}

@srujzs @osa1 Is the above intended and expected?

[srujzs]

It's only intended for classes and mixins (that will eventually be mixed into a class) and their instance members.

I'm not sure why the enum case works, possibly because they're classes? It isn't really intentional, but I suppose if they're a class, it's fine?

The extension type case likely works because you're just testing the behavior of the class that it's wrapping. If you had an extension type member and assumed that it would be wrapped somehow, you'd be wrong. The same applies to extensions (as we can see in the test).

[sgrekhov]

If you had an extension type member and assumed that it would be wrapped somehow, you'd be wrong.

In the code above we have a representation variable c and it is undefined in JS. Thank you for your response. I'll expect that this annotation is allowed. Closing this question as answered.