Lazy-loaded object in Typescript

lazy-load.ts

export const lazyLoaded = <Data extends object>(loadData: () => Data) => {
  let data: Data | undefined = undefined;

  const isDataKey = (
    obj: Data,
    key: string | symbol | number
  ): key is keyof Data => key in obj;

  return new Proxy<Data>({} as Data, {
    get: (_target, prop) => {
      if (typeof data === "undefined") {
        data = loadData();
      }
      if (isDataKey(data, prop)) {
        return data[prop];
      }
    },
  });
};