Not really a "must", it really depends on what one wants to do. Low-level stuff (firmware, OSs), machine learning, data analysis, DBA, etc, are just some of the fields where JavaScript is almost completely unheard of.
From the platforms where JavaScript is actually used, the only one where it's a "must" is frontend web, for obvious reasons*. In web backend there are many alternatives and, in mobile, JS plays second fiddle to Java and Objective c/swift.
The desktop is a funny story, Gnome shell has been around for a lot longer than electron, and it's a better example of how well js can perform. That said, JS is still a rare presence there; could become more popular, though.
*And even there, transpilers are a thing, making supersets of JS viable options. WebAssembly can potentially make any other language an alternative as well.