Not even reviewing the code can prove that any property is inaccessible, when its name could be constructed anywhere at runtime and used via object[propName]. W

Not even reviewing the code can prove that any property is inaccessible, when its name could be constructed anywhere at runtime and used via object[propName]. Without actual language and runtime enforcement, there are almost no pervasive changes safe enough to make without the kind of thorough regression testing most teams aren't prepared to do. Which is not to say they don't do it anyway, and sometimes get lucky.