ts_singleton_5_1.ts

class Instance {
  constructor(public foo: number = 123) {}
}

let instance = new Instance;

export function getInstance() :Instance {
  return instance;
}

ts_singleton_5_2.ts

import * as Singleton from "singleton.ts";

let obj1 = Singleton.getInstance();
let obj2 = Singleton.getInstance();

obj1.foo = 456;

console.log( obj1 === obj2 );