I remember you, of course.

The book is not published yet, but interestingly enough, it was announced just today on the publisher’s website:
http://www.packtpub.com/object-oriented-javascript-applications-libraries/book

Best regards!

I had a chance to interview with you for summer internship at Santa Monica Office.

You were talking about writing a book on object oriented javascript !! Whens it coming out ? I have a keen interest in JavaScript..

But it’s true that keeping the reference as a property of the constructor function makes it available for modification.

I’ll play around you your idea of keeping the reference private but still be able to just say:
new Sungle(), new Single() and they both point to the same object.

In Singleton2, the instance property lives on the constructor, and as such is externally modifiable which breaks encapsulation. If you’re interested in more detail, email me, but for the moment, you might want to consider the following:

/**
 * toSingleton, transforms javascript classes into singletons
 * @copyright David Foley 2007
 * free as in beer!
 */

function MyClass ()
{
	var _value = null;
	this.setValue = function (value) {
		_value = value;
	};
	this.getValue = function () {
		return _value;
	};
};

/**
 *	@param {Function} Class, the class to transform into a singleton
 *@return {Object} an object with one method, getInstance, which returns an instance of Class
 */

function toSingleton (Class)
{
	// return the results of an anonymours function
	return (function(){
		// variable instance exists in this closure
		// private and cannot be modified externally
		var  instance = null;
		// the following object literal is returned
		// as the final result of the toSingleton transformation
		// it can access the variable 'instance', but
		// nothing else can, in keeping with priniciple
		// of encapsulation
		return {
			getInstance: function()
			{
				if( instance == null) instance = new Class();
				return instance;
			}
		};
	})();
};

// overwrite MyClass with the result of the toSingleton transformation
MyClass = toSingleton(MyClass);

// show it works
MySingletonReference = MyClass.getInstance();
MyClass.getInstance().setValue("1");
alert(MySingletonReference.getValue());
MySingletonReference.setValue("2");
alert(MyClass.getInstance().getValue());
alert(MySingletonReference.getValue() == MyClass.getInstance().getValue());