Can you link to where that is being discussed? I hadn't heard that int64 was being added. My google-fu has failed to turn up anything. int64 would be very useful for long types in ScalaJs. They run really slow because they have to be emulated with the whole split it into smaller parts stuff. Lots of jvm targetting code I have ported at work was written with the "just use a long, it's not much slower than an int" thought process, true on the JVM, not true in JS.