Scala.js scratches that itch for me. I rarely write frontend code, but when I do the extra IDE support given to me by IDEA for Scala.js is pretty great.
I'm a full time Scala dev though, so I'm totally biased
It is kind of surreal to look at a source file and not immediately know if it's Scala or Scala.js (like, oh wait, this is the front end).
Just finished porting a legacy 5K Coffeescript front end over to Scala.js. Having a typed front end with all the power of Scala completely transforms the browser development experience. Great stuff.
Only major drawback is generated js binaries incur a 160KB "tax", primarily due to size of Scala collections. Though, FWIW, the front end weighs in at 232KB non-gzip'd, and was able to scrap jQuery + DataTables + Modal window and Validation plugin dependencies -- shaved off about 200KB compared to previous front end.
I'm a full time Scala dev though, so I'm totally biased