Singleton Design Pattern JavaScript

It is Creational Patterns which focus on how to instantiate an object.

Singleton Design Pattern ensure that a class has only one instance, and provides a way to access it globally.

In other words, Singletons are used to create an instance of a class if it does not exist or else return the reference of the existing one.

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var Singleton = (function() {
  var instance;

  function createInstance() {
    var object = new Object("I am the instance");
    return object;
  }

  return {
    getInstance: function() {
      if (!instance) {
        instance = createInstance();
      }
      return instance;
    }
  };
})();

function myFunc() {
  var instance1 = Singleton.getInstance();
  var instance2 = Singleton.getInstance();

  console.log(instance1 === instance2);
}

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class Singleton {
  static instance;

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

    this.state = "Singleton ES6";
    this.instance = this;
  }
}

export default Singleton;

let instance1 = new Singleton();
let instance2 = new Singleton();
console.log(instance1 === instance2);

//output: true