Simplest/Cleanest way to implement singleton in JavaScript?

Question

What is the simplest/cleanest way to implement singleton pattern in JavaScript?

Answer 1

I believe this is the simplest/cleanest and most intuitive way though it requires ES7:

export default class Singleton {

  static instance;

  constructor(){
    if(instance){
      return instance;
    }

    this.state = "duke";
    this.instance = this;
  }

}

The source code is from: adam-bien.com