Despite being javascript an object oriented language, it doesn't use classes. Infact JavaScript is prototype based, not class based.
With javascript you can define and create your custom objects in many ways.

Direct Instance:

var o = new Object();
o.fName = "John";
o.lName = "Smith";
o.getFullName = function(){ return this.fName + " " + this.lName; };

The example above creates a new object's instance and adds two properties and one method. More...