How to define Singleton in TypeScript

Question

What is the best and most convenient way to implement a Singleton pattern for a class in TypeScript? (Both with and without lazy initialisation).

Answer 1

namespace MySingleton {
  interface IMySingleton {
      doSomething(): void;
  }
  class MySingleton implements IMySingleton {
      private usePrivate() { }
      doSomething() {
          this.usePrivate();
      }
  }
  export var Instance: IMySingleton = new MySingleton();
}

This way we can apply an interface, unlike in Ryan Cavanaugh's accepted answer.

Answer 2

This is a typescript decorator checking if multiple instances were accidentaly created against a service class that is designed to be singleton:

https://www.npmjs.com/package/singleton-checker