const file = new File(["some data"], "testfile");
const proxiedFile = new Proxy(file, {});
const formData = new FormData();
formData.append("origFile", file);
formData.append("proxiedFile", proxiedFile);

formData.get("origFile");
// File {name: "testfile", …}
formData.get("proxiedFile");
// "[object File]" <--- ???