Creating Singleton objects with JavaScript

javascript_prototype_singleton_objects.js

// Defining constructor function
function SingletonObject() {
  // TODO: Add your own initialization code here
  this._message  = 'Hello Prototype World!';
};

// Current instance property
SingletonObject._instance = null;

SingletonObject.getInstance = function() {
  if (SingletonObject._instance === null) {
    SingletonObject._instance = new SingletonObject();
  }
  return SingletonObject._instance;
}

// Defining instance functions

SingletonObject.prototype.sayHello = function(message) {
  alert(this.message);
};

SingletonObject.prototype.setMessage = function(message) {
  this.message = message;
};
 
// Set message to a singleton object
SingletonObject.getInstance().setMessage('Singleton Message');

// Say hello twice from the same instance:
SingletonObject.getInstance().sayHello();
SingletonObject.getInstance().sayHello();