Object extending in JavaScript is done with the prototype property, and in most cases simple prototype reassignment is sufficient for creating classes. But when you are developing a more complex application, you code quickly becomes ugly, because the syntax for creating prototypal chains is definitely not friendly.
All popular frameworks, except jQuery have their own way of creating classes, but personally, I think that they sometimes use unnatural and unnecessary code to achieve this. For example, here is the way how using prototypejs you are meant to call a super class method:
