Loyal Opposition to Const, Private, Freeze, Non-Configurable, Non-Writable...

And JavaScript is one of the *most* dynamic of the mainstream programming languages. Not only can you can pass any object to any function, but you can call a method with any number of arguments, easily modify the prototypes of other objects, introspect on any object's properties with a simple loop, replace any member function with a wrapped version, attach new properties to any object ... the list goes on.