Question

I use the following Singleton pattern in JavaScript:

  var exampleClass =(function(){ 
                        //private
                        var a ="test"; 
                        function PrivateMethod()
                        {
                            return a;
                        }
                        //public
                        return{  
                            Test: function() { 
                                   alert(PrivateMethod()); 
                                  } 
                        }
                      })(); 

As I read through StackOverflow I see a lot of other implementations of Singleton and I start to doubt if I couldn’t make mine better.
I hope someone can tell me what’s right or wrong about doing it this way.

Answer 1

It depends what you want to achieve as the different implementations will have different benefits and limitations.

The simplest implementation is just an object literal:

var singleton = {
    property: "foo",
    method: function() {
        alert('bar');
    }
}

The implementation you mention in the question allows public and private methods by encapsulating the methods in a closure and returning what should be exposed.

Here is an alternative which similarly would allow public and private methods and is more extensible:

function MySingletonClass() {

  if ( arguments.callee._singletonInstance )
    return arguments.callee._singletonInstance;
  arguments.callee._singletonInstance = this;

  this.Foo = function() {
    // ...
  }
}

var a = new MySingletonClass()
var b = MySingletonClass()
Print( a === b ); // prints: true