A simple way to implement protected

For completeness the following is how I think protected fields would look (ignoring exact naming) if done in userland with the current GitHub - tc39/proposal-decorators: Decorators for ES6 classes

@protectedFields
class X extends Y {
  @protect accessor #field1;
 
  @protect accessor #field2;
}

With the above decorators making use of the techniques already demonstrated in this thread so far.