If the idea is "Hey, let's use a framework good for beginners and hack together projects", OP should just extend their Javascript knowledge into Nodejs--and there's nothing wrong with that.
"By learning Java, you're already getting some good CS fundamentals."
This is wrong. If you are trying to learn CS fundamentals, learn Scheme or Clojure or some other functional language. Java in practice is basically plumbing together large frameworks built by people smarter than you who probably worked at Sun fifteen years ago--and who often got things wrong. Java in theory is ramming OOP design down your throat, and still exposing enough implementation details of the runtime that you can't ignore them.
Java is a not a good way to learn CS fundamentals.
if you want to make programming into a career, you don't need to learn C.
This is only true if you want to be a blub programmer and punch the clock and basically just farm code in enterprise. Learning C is essential (barring learning assembly) to getting access to great swathes of performance-critical environments, tracking down weird bugs, and generally understanding what you machine is doing.
Times change. A lot of (what I would consider) interesting jobs only require web languages, which are high-level, messy, and abstract away a huge amount of underlying complexity (many would say too much).
I'm telling him/her how things are, not how we want them to be. Only a small fraction of being can be great engineers. The rest of the millions of developers out there are writing sloppy blub code on top of an opinionated framework.
If you are trying to learn CS fundamentals, learn Scheme or Clojure or some other functional language.
I don't think we're using the same definition of "fundamentals". I was talking about things as simple as writing code, compiling, debugging, and googling (the most important skill of a programmer).
S/he'd also be learning OOP, which dwarfs FP in the web development world[1]. I actually don't think I've ever heard of a popular web framework that was written functionally, though I should also mention that I think the practical differences between FP and well-written OO are exaggerated. They aren't mutually exclusive, and OO doesn't imply mutability.
1. http://lifehacker.com/the-top-programming-languages-ranked-b...
By learning Java, you're already getting some good CS fundamentals. It probably wouldn't help you that much to learn C on top of that.
I'll leave you with this: if you want to make programming into a career, you don't need to learn C. If you want to study programming as a researcher or teach it, you should learn C.
Being 15, you don't know what you want to do though, so I'd suggest just doing what you find fun for now and worry about the rest of it later.