Singleton Constructor

singleton.js

var MakeSingleton = function(){
  var obj;
  return function() {
    if( obj ){
      return obj;
    } else{
      obj = this;
    }
  };
};

var Singleton = MakeSingleton();
var x = new Singleton();
var y = new Singleton();
x === y;

// var x = new Singleton();
// var y = new Singleton();
// x === y => true