Singleton Design Pattern in JavaScript

singleton.js

const singleton = (() => {
  // Instance stores a reference to the Singleton
  let instance;

  const init = () => {
    // Private methods and variables
    const privateMethod = () => {
      console.log('Private function');
    };
    const privateVariable = 'Private variable';
    const privateRandomNumber = Math.random();

    return {
      // Public methods and constiables
      publicVariable: 'Public variable',
      publicMethod: () => {
        console.log('Public function');
      },
      getRandomNumber: () => {
        return privateRandomNumber;
      }
    };
  };

  return {
    // Get the Singleton instance if one exists
    // or create one if it doesn't
    getInstance: () => {
      if (!instance) {
        instance = init();
      }

      return instance;
    }
  };
})();

const singletonA = singleton.getInstance();
const singletonB = singleton.getInstance();

console.log('Singleton A:', singletonA.getRandomNumber());
console.log('Singleton B:', singletonB.getRandomNumber());
console.log('isSingleton:', singletonA.getRandomNumber() === singletonB.getRandomNumber()); // isSingleton: true