Singleton_Pattern_Blueprint.js

// Singleton Pattern
// Inspired by: https://addyosmani.com/resources/essentialjsdesignpatterns/book/#singletonpatternjavascript

var mySingleton = (function () {
 
  // Instance stores a reference to the Singleton
  let instance;
 
  function init() {
 
    // Singleton
 
    // Private methods and variables
    function privateMethod(){
        console.log( "I am private" );
    }
 
    const privateVariable = "Im also private";
 
    const privateRandomNumber = Math.random();
 
    const publicAPI = {
 
      // Public methods and variables
      publicMethod: function () {
        console.log( "The public can see me!" );
      },
 
      publicProperty: "I am also public",
 
      getRandomNumber: function() {
        return privateRandomNumber;
      }
 
    };
    
    return publicAPI;
 
  };
 
  const mySingletonPublicAPI = {
 
    // Get the Singleton instance if one exists
    // or create one if it doesn't
    getInstance: function () {
 
      if ( !instance ) {
        instance = init();
      }
 
      return instance;
    }
 
  };
  
  return mySingletonPublicAPI;
 
})();

// Usage:
var singleA = mySingleton.getInstance();
var singleB = mySingleton.getInstance();
console.log( singleA.getRandomNumber() === singleB.getRandomNumber() ); // true