• Strong type system thanks to the type inference which will save you many headaches. Since types are inferred, you aren't forced to type out the types the whole time, so a sleek syntax + type safety.
• everything that's available in the Java world you can immediately use in Kotlin without the Java boilerplate - want to generate PDFs, simply throw in Apache FOP, want to generate Excel Spreadsheets, simply throw in Apache POI, etc; the ecosystem is huge and very well maintained
• proper multithreading
• Co-Routines which IMO is much easier and cleaner to use than ES6's Promises
• The language is very well designed and I haven't encountered any gotchas unlike JS where you have to tread carefully the whole time
• and if you really want to, you can compile the Kotlin to JS that you can run on NodeJS or just use KotlinJS in the browser.
• Kotlin Native will in the future allow you to run Kotlin without the JVM
• While you're at it, you can do Android native in the same language and there are plans for better iOS support via Kotlin Native.
• Kotlin might replace your bash scripts in the future - one language that does it all!
• The Kotlin standard lib has almost everything you need for general dev, so no need for external helper libraries to do String padding, and so forth.
• You get both Object Orientated and Functional benefits in Kotlin since they took the best features from a large number of languages and simply copied plus improved it instead of re-inventing the wheel.
• null safety is probably a huge advantage over JS.
• In terms of churn, I get a lot of work done since I switched to Kotlin a year ago and it's high quality code that just works.

If you already know JS quite well and you don't have Java experience, by all means, use NodeJS. If you're open for new things, especially coming from a Java background, give Kotlin a try, it's the best thing since sliced Kake.

A fullstack developer may prefer the same language on the server and client. In this case Node.js and some JS tech on the client.

Imho, Node.JS is a lot simpler to use.

• It uses JS, which you should already know if you are a web-dev. Kotlin is a new language to learn.
• Node.JS is one executable you can ship. You will literally have portable software. Kotlin needs the JVM, so you will have to install that and lots of updates later on, because that platform is so extensive and central
• NPM has one of the fastest growing module count overall. You will find lots of useful and powerful modules. Keep in mind, that they might also be very bug-riddled and not quite battle-tested

So, for less critical applications, Node.JS is very easy to use over the whole life-circle. If you need to build something mission-critical, you might want to go back to the Java giant and Kotlin.