JavaScript is ubiquitously deployed. Ubiquitous deployment comes along with ubiquitous education. Ubiquitous education leads to ubiquitous expertise. Even if you do browser front-end work in a language that compiles to JavaScript, chances are you've still learned enough about JavaScript that you can deal with errors and understand what browser development tools are telling you.
That means that there is a HUGE amount of knowledge floating around out there in the industry, in the open source community, in government, in academia... pretty much everywhere.
You can re-use that expertise when you write server-side logic in Node.