I'm trying to create an instance of a dart class in js

Here is my dart code:

main() {
  js.context["project"] = js.JsObject.jsify({
    "Thing": Thing
  });
}

When I call new project.Thing() in js I get the following error:

Uncaught TypeError: project.Thing is not a constructor

project.Thing:

How do I call the constructor of a DartObject?