ts_singleton_1.ts

class Singleton {

  protected static _instance :Singleton;
  
  protected foo :number = 123;
  
  constructor() {
    if (Singleton._instance) {
        throw new Error("Instantiation failed: "+
                        "use Singleton.getInstance() instead of new.");
    }
    Singleton._instance = this;
  }

  public static getInstance() :Singleton {
    if (Singleton._instance) {
      return Singleton._instance;
    }
    return Singleton._instance = new Singleton;
  }
}