Example of how to properly create a Singleton in Typescript / Javascript

singleton.ts

import * as shortid from "shortid";
import { Type as RealType } from "@tokilabs/lang";
import { Class } from "./modeling/class";
import { Type } from "./modeling/type";

function Singleton<T>(value: T, name?: string): T {
  name = name || shortid.generate();

  const SYMBOL = Symbol.for(name);

  // check if the global object has this symbol
  // add it if it does not have the symbol yet
  // ------------------------------------------
  const globalSymbols = Object.getOwnPropertySymbols(global);

  if (!(globalSymbols.indexOf(SYMBOL) > -1)) {
    global[SYMBOL] = value;
  }

  // define the singleton API
  // ------------------------

  const singleton: {
    instance: T;
  } = <any>{};

  Object.defineProperty(singleton, "instance", {
    get: () => {
      return global[SYMBOL];
    },
  });

  // ensure the API is never changed
  // -------------------------------

  Object.freeze(singleton);

  return singleton.instance;
}

export const ClassRegistry = Singleton(
  new Map<RealType, Class>(),
  "disl.CLASS_REGISTRY"
);
export const TypeRegistry = Singleton(
  new Map<string | RealType, Type>(),
  "disl.TYPE_REGISTRY"
);