Instead of deprecating it, could we just alias it to Function.prototype.call.bind(String.prototype.codePointAt) and note that it's there for legacy reasons in the docs?

it is actually undocumented and is not supposed to be used anyway. Unfortunately we have a lot of private not underscored stuff

If it's undocumented, isn't is subject to disappearing at any time? (I realize someone could be using it)

FWIW, I agree with @vkurchatkin. I believe the reason it was exported was so it could be unit-tested in the test suite.

I guess that would a bit irresponsible. People use repl to discover stuff. We need a roadmap to avoid these in the future

Yes people use the repl and other reads the code to find and use undocumented apis. I've done it myself, but I do not expect that code to work between versions.