[javascript] Getters \ setters for dummies

I think the first article you link to states it pretty clearly:

The obvious advantage to writing JavaScript in this manner is that you can use it obscure values that you don't want the user to directly access.

The goal here is to encapsulate and abstract away the fields by only allowing access to them thru a get() or set() method. This way, you can store the field/data internally in whichever way you want, but outside components are only away of your published interface. This allows you to make internal changes without changing external interfaces, to do some validation or error-checking within the set() method, etc.