[NightMKoder]

Java the language? Very likely not. As proof - a majority of Clojure runs in JavaScript without any code changes (via ClojureScript). That said exceptions tend to look like Java classes, so you’ll definitely see Java bits.

Java the JVM? You _probably_ don’t need to know it to get started, but you’ll have to get familiar with JVM deployment, dependency management, packaging, JVM memory settings, etc if you want to run something outside your dev machine. Getting to 90% here is pretty easy, but the last 10% (to me at least) tends to feel a lot more difficult that other languages.

As a small pro-tip: use jstack. I wish every language came with a jstack. It just dumps the stack traces of all threads of a program by pid.

[eyelidlessness]

My experience with ClojureScript is you absolutely have to know the host environment because you will encounter type errors and the maintainers have negative interest in making them clear to users (as in flatly refused offers to contribute changes to make those errors easier to understand).

[futharkshill]

There is nothing worse than library or language maintainers who do not understand that "pure" error messages are absolute hell. If 99.99 % of the time a user should simply write x instead of y, the message should absolutely state that if possible.

[eyelidlessness]

Amusingly to me, this is what drove me to TypeScript. “Don’t do that” be damned, I’ll get my useful errors from the compiler.