Imagine you have come up with a novel algorithm to solve a problem, and have implemented it in, e.g., javascript, and have put its src, along with an appropriate copyright, on a publicly available code repository, e.g, bitbucket.
Can the copyright alone be enough to keep another entity (let's call it Evilsoft) from copying the algorithm or integrating it with software it produces (which might not be written in the same programming language)?
If it isn't the answer, what else is?
No, copyright absolutely does not protect anything "novel" or anything related to algorithms or generally anything functional at all.
Copyright only protects your "expressed representation of a creative work". Other people can duplicate your work with a different "expression" and not be infringing on copyright. And if there is nothing creative in your work then it's not even eligible for copyright in the first place.
For example, if you figure out how to sort an array with fewer computational steps than what anybody else is doing then that is functional code, not creative code, and anybody can reverse engineer/duplicate your sorting algorithm.
However, patents do provide the protection you're looking for. If you want to protect your fancy algorithm then apply for a patent. Patents expire an order of magnitude sooner than copyright, but they are the only means of legally protecting this type of intellectual property.
Unlike copyright, patent protection is only available if you apply for it, and it has to be approved by the relevant government department in your country (although you can start using the patented technology before approval has gone through).
