Typescript Singleton function with code splitting

singleton.ts

type Singleton = {
  done(): void;
};

type SingletonContructor = {
  new (): Singleton;
  (): Singleton;
  staticDone(): void;
};

// export functions for code splitting
export function done() {
  console.log("Singleton function");
}
export function staticDone() {
  console.log("Static function");
}

const singleton = (function () {
  let instance: Singleton;

  const Singleton = function (this: Singleton) {
    if (instance) return instance;
    instance = new.target ? this : new Singleton();
    return instance;
  } as SingletonContructor;

  Singleton.prototype.done = done;
  Singleton.staticDone = staticDone;

  return Singleton;
})();

singleton.staticDone(); // Static function
new singleton().done(); // Singleton function
const eg1 = singleton();
const eg2 = new singleton();
console.log(`eg1 === eg2 ? ${eg1 === eg2}`); // eg1 === eg2 ? true
eg1.done(); // Singleton function
eg2.done(); // Singleton function

export default singleton;