ES6 has a way to name functions with Symbols, and Symbols with the same name are not equal. It's not used often but I've seen it used to give a secret back entrance to an object. Like a very limited version of friend functions/classes.

If the symbol is not exposed, then you can't get anywhere in the neighborhood of calling it accidentally. I think if you do enough object introspection you can still get the function handle, but you could never mistake the resulting code for being anything other than farm fresh, Grade-A Cheese.