The MooTools JavaScript

copy(function() {
  
  // Keep reference to the original Class
  var klass = Class;
  
  // Redefine class ("that's deep")
  Class = function(name, params, context) {
    // Find out if this is namespaced or the original method
    var namespaced = (arguments.length > 1);
    
    // Add the class name to the param list
    if(namespaced) params.$name = name;
    
    // Create and get the original class
    var original = new klass(namespaced ? params : name);
    
    // If namespaced, set class into namespace
    if(namespaced) Object.place(name, original, context);
    
    // Return this newly created class!
    return original;
  };
  
})();

copy// Create a namespaced class
var myClass = new Class("davidwalsh.ui.Slider", {
  initialize: function() { 
    // Do stuff!
  },
  doSomething: function(){}
});
// myClass === davidwalsh.ui.Slider!

// Create an instance of the class
var myInstance = new davidwalsh.ui.Slider({
  // props
});

// Get the name of the declared class
var instanceClassName = myInstance.$name; // equals "davidwalsh.ui.Slider"