Comment by esprehn

That's also possible in JS with __proto__. The prototypes of the classes in the chain can be mutated at runtime too. How to handle these cases is well understood for JITs though and python could do the same.

See also the warning here:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

And this related article:

https://mathiasbynens.be/notes/prototypes