singletons

singletons.js

// without closure
function MyClass(){
    if (!MyClass.instance) MyClass.instance = this;
    else return MyClass.instance;
}
var a = new MyClass,
    b = new MyClass;
a === b; // true

// with closure (from essential js patterns book)
var SingletonTester = (function()
{
  //args: an object containing arguments for the singleton
  function Singleton(args) {
   //set args variable to args passed or empty object if none provided.
    var args = args || {};
    //set the name parameter
    this.name = 'SingletonTester';
    //set the value of pointX
    this.pointX = args.pointX || 6; //get parameter from arguments or set default
    //set the value of pointY
    this.pointY = args.pointY || 10;  
  }
   
 //this is our instance holder
  var instance;
 //this is an emulation of static variables and methods
  var _static =
  {
    name: 'SingletonTester',
   //This is a method for getting an instance
   //It returns a singleton instance of a singleton object
    getInstance: function (args) {
      if (instance === undefined) {
        instance = new Singleton(args);
      }
      return instance;
    }
  };
  return _static;
})();
 
var singletonTest = SingletonTester.getInstance({pointX: 5});
console.log(singletonTest.pointX); // outputs 5