gistfile1.js

// insert in core.js
JS.singleton = function(name, parent, methods) {
	var args = arguments;
	return (function(args) {
		// store instance and class in private variables
		var instance = null;
		var klass = new JS.Class(name, parent, methods);
		return {
			getInstance: function() {
				if (instance) { return instance; }
				return (instance = new klass());
			}
		};	
	})(args);
};

// test code
var A = new JS.Class("A", {
	initialize: function(name) {
		this.name = "Albert";
	}
});

var B = new JS.singleton("B", A, {
	display: function() {
		Log.Message("My name is " + this.name);
	}
});

var b = B.getInstance(); // runs A.initialize()
var b = B.getInstance(); // does not run A.initialize()
b.display(); // -> "My name is Albert"