The source-code linked is only 279 lines of Scala code, including blanks and comments and the code is very readable [1]. However, it is using Scala's standard library, which is somewhere at 16.5 MB - 18.5 MB, depending on version. That the minified code is 209 KB (50 KB gzipped), I find that awesome, as it means that the compression / tree shaking done is pretty aggressive, much better than what people can do by hand. Under the hood Scala.js does optimizations of its own, before passing the result to Google's Closure compiler in advanced mode.

https://github.com/lihaoyi/workbench-example-app/blob/ray-tr...