Unlikely, because Scala.js already has the reductions that are brought on the JVM only in 2.12. Scala.js has been emitting tiny wrappers around JS closures for

Unlikely, because Scala.js already has the reductions that are brought on the JVM only in 2.12. Scala.js has been emitting tiny wrappers around JS closures for more than 2 years. (and no, that's not because of Closure; it's because of our own compiler and optimizer) The overhaul of collections is, in part, supposed to be more friendly to Scala.js and in particular code size of small applications.