I find compilation of statically typed languages to JS, as in Scala.js, worthwhile in principle, for the reasons that Haoyi argued so well in a blog post a while back [1]. But there's one major reason I would be reluctant to use Scala.js: runtime footprint. 45 KB gzipped (the number given on scala-js.org) is pretty heavy. Is that an inevitable trade-off for the power of Scala, or is there still more work that can be done to bring that down?
[1]: http://www.lihaoyi.com/post/FromfirstprinciplesWhyIbetonScal...