How to call a Dart static method from JavaScript

Question

I used dart-sass to learn and implement a Dart library used in Node.js. Everything works fine (thanks Dart Sass team!). However I would also like to call static methods in Dart classes from JavaScript.

I created JsClass.defineStaticMethods() to add them to a class in Dart but I cannot add them to self.exports.ClassName.methodName automatically. Example:

var jsClass = createJSClass('ClassName', (Object self, String value) {
  return ClassName(value);
});

jsClass.defineStaticMethods({
  'fromJson': (Object jsJson) => ClassName.fromJson(objectToMap(jsJson)),
});

I did manage to add them manually. For example:

set$ClassName(obj, v) {
  obj.ClassName = v;
  obj.ClassName.fromJson = function (jsJson) { 
    return A.ClassName_fromJson(A.objectToMap(type$.Object._as(jsJson))); 
  };
  return obj.ClassName;
}

Has anybody managed to use Dart’s js interop to add static methods to classes?

It would be great if dart-sass needed to call static methods in Dart classes - they would know how to implement it :-)