JS as a backend is more of a joke, though. It has heartful followers, true. But it doesn't bring anything valuable to the table. I may be wrong (and happy to be corrected) but this was developed by people who learned the JS frontend stuff first and then didn't want to learn another language for the backend just as well. So they decided to make the language they already know available in the backend as well. But that's it.
Think about competitions in the backend/desktop area. For instance Go. It aims to combine the advantages you have in the most popular programming languages, while also providing stuff as core elements (e.g. packaging) that are only attached on top of other languages. Or coming from the other direction of the "cool" languages, it provides all the nice little modern features you know from other languages but also enables you to write and compile code as fast as the C codes of the ancients you always read about.
This is what real competition looks like. It provides something huge and new while also providing quality features you know from your current favorite language. If you don't bring something like that to the table people won't switch to you, at least not for serious projects. The advantage of already having educated developers on the market for the "old stuff" and having an infrastructure of libraries that solve most of the tasks at hand, is just too big to compete against without killer features.
And as I said, I may just not know the killer feature of server side JS, in which case it may be just a marketing blunder of the server JS people that can be corrected.