Js was not born with a rich ecosystem of libraries, its perfect compatibility with Scala meant that it had the potential to support many of the libraries that are common in the Scala ecosystem. With its strong compatibility with the original Scala language, and the ability to easily write cross-platform code that runs on both the client and the server, Scala. While Scala's syntax can be cryptic and infuriating at times, I want to love it, there is a beauty in the syntax and language constructs that Scala provides (after accepting the grey hairs). Also to add to what others have said, FP is top notch in Scala if you care about that, and the ability to mix and match parts of the Java ecosystem and let Scala do its heavy lifting makes it really powerful compared to other languages.
My final conclusion from being exposed to Scala as a RESTful backend server is that if you haven't experienced what Scala has to offer, then I wholeheartedly suggest you do. I've read before that Twitter has moved some things away from Scala and Linked-In has moved completely away from Scala. As expected, Scala has the if-else and while control structures common in most programming languages. But enough praise for Scala, let's get to the differences in the experience of writing a backend in Scala vs.
Linked-In. And I think it's those constructs, combined with the strongly typed system, that attracts me to Scala as a backend, and makes Scala a very compelling alternative to Node. If you've decided that you like the performance features of the JVM but are hesitant about Scala as a language for various reasons (e.g. Scala developers are rare and expensive), then perhaps the most pragmatic thing to do is to go with Java.