Currently, there is no way to emit a `class` declaration from ClojureScript code.
In a JS environment that has native class support, there are certain cases with `class` that cannot be replicated with ES3/5 prototypal syntax, and require to use the environment’s native `class` and `extends` keywords.
Resolving this issue would involve two parts:
a `defclass` macro which provides syntax for declaring a name, superclass and methods
compiler support to do a second pass on the file in order to convert to ES3 if the user does not want their project to only target ES6+ environments
:language-out would control whether we immediately lower to ES3.
Another issue about ES6 classes