Singleton ES6 pattern using Symbol to ensure singularity

SingletonClass.js

// https://stackoverflow.com/a/26227662
const singleton = Symbol();
const singletonEnforcer = Symbol()

class SingletonClass {

  constructor(enforcer) {
    if(enforcer != singletonEnforcer) throw "Cannot construct singleton";
  }

  static get instance() {
    if(!this[singleton]) {
      this[singleton] = new SingletonClass(singletonEnforcer);
    }
    return this[singleton];
  }
}

export default SingletonClass;

// const instance = SingletonClass.instance;