You can claim that there exists a subset of C that can be considered purely functional, and others have argued that (http://conal.net/blog/posts/the-c-language-is-purely-functio...), but the existence of standard library functions like strtok makes the general statement false.

You can claim that nodejs HTTP module forces a callback style, and that is true given the implementation, but javascript spec doesn't force you to implement an HTTP server in that fashion. As I stated in both responses, the article claims that javascript forces you to use a callback style, which is not the case. It is Node that forces you to use callbacks.