[gedy]

Since webpack does dead code elimination as well, wondering if that all needs to be a problem solved in Scala.js?

[sjrd]

Scala.js does a much better dce than Webpack, or any other JavaScript optimizer (including Closure). It does it at the method level (not top-level function/class level), and can also leverage the type system to do a better job at it. So yes, it needs to be solved at the Scala.js level.

Scala.js also performs whole-program optimizations of the code, besides "simple" dead cole elimination.