You are mixing up the languages with the platforms.

Java doesn't let you connect to databases or any of that - the JVM does, and for any language running on it (Scala, Clojure, etc).

Java the language just gives you a certain set of syntax and semantics which can be useful to model a problem and its solution - classes, interfaces, etc.

Even if you're limited by the API of the platform - the browser - that has nothing to do with whether a different language is useful or not for your particular problem.