If you are familiar with design patterns then, you may also know about Singleton Pattern. It is used to restrict creation of multiple instance of a class or a class will have only one instance.

function MyClass()	{
	if (MyClass.caller.toString() != MyClass.getInstance)	{
		throw new Error("Initialization not allowed");
	}
	this.someProperty = "some value";
}
MyClass._instance = null;
MyClass.getInstance = function()	{
	if (MyClass._instance == null)
		this._instance = new MyClass();
	return this._instance;
}

var c = MyClass.getInstance();

fireunit.compare("some value", c.someProperty, "this should pass");
c.someProperty = "aa";
//try to create another instance
var d = MyClass.getInstance();
fireunit.compare("aa", d.someProperty, "new value - this should pass");
fireunit.testDone();

Here is the output of the code:

Hope this will help you