Correct way of doing initializing one instance

gistfile1.js

var TestClass = Class.create({
  initialize: function(){
    //fancy stuff here
  }
});

document.observe("dom:loaded", function(){ new TestClass(); });

// or
(function(){
  var TestClass = Class.create({
    initialize: function(){
      //fancy stuff here
    }
  });
  
  new TestClass();
})();