javascript singleton question

Question

I just read a few threads on the discussion of singleton design in javascript. I\'m 100% new to the Design Pattern stuff but as I see since a Singleton by definition won\'t

Answer 1

The singleton pattern is implemented by creating a class with a method that creates a new instance of the class if one does not exist. If an instance already exists, it simply returns a reference to that object. 1

(function (global) {

     var singleton;

     function Singleton () {
         // singleton does have a constructor that should only be used once    
         this.foo = "bar";
         delete Singleton; // disappear the constructor if you want
     }

     global.singleton = function () {
         return singleton || (singleton = new Singleton());
     };

})(window);

var s = singleton();
console.log(s.foo);

var y = singleton();
y.foo = "foo";
console.log(s.foo);

You don't just declare the singleton as an object because that instantiates it, it doesn't declare it. It also doesn't provide a mechanism for code that doesn't know about a previous reference to the singleton to retrieve it. The singleton is not the object/class that is returned by the singleton, it's a structure. This is similar to how closured variables are not closures, the function scope providing the closure is the closure.