I've been working with Scala.js for several years and I have no idea why JDG chose those four bullet points as important weaknesses of Scala.js. Those weaknesses seem overstated, they just aren't the things I had to ever worry about, even when I was new to Scala / Scala.js. Like, I'm not good at sbt in general, but I never had problems with Scala.js build setup, even when I started cross-publishing libraries for Scala and Scala.js