Singleton in TypeScript

singleton.ts

const instanceMap: {[key:string]: any} = {};

export function Singleton<T>(instanceName:string, InstanceConstructor: new () => T):T {
  if (typeof instanceMap[instanceName] === 'undefined') {
    instanceMap[instanceName] = new InstanceConstructor();
  }
  return <T>instanceMap[instanceName];
}

export default Singleton;