--- a/build.sc	Sat Dec 26 20:15:08 2020 +0100
+++ b/build.sc	Sat Dec 26 21:46:29 2020 +0100
@@ -141,4 +141,25 @@
   ()
 }
 
+object extras extends Module {
+
+  class JvmModule(val crossScalaVersion: String) extends Common
+  class JsModule(val crossScalaVersion: String, crossJSVersion: String)
+    extends ScalaJSModule with Common {
+
+    override def scalaJSVersion: Target[String] = crossJSVersion
+
+    override def millSourcePath = super.millSourcePath / os.up
+  }
+
+  object jvm extends Cross[JvmModule](V.scala211, V.scala212, V.scala213)
+  object js extends Cross[JsModule](
+    V.scala211 -> V.scalaJs06,
+    V.scala212 -> V.scalaJs06,
+    V.scala212 -> V.scalaJs,
+    V.scala213 -> V.scalaJs06,
+    V.scala213 -> V.scalaJs
+  )
+
+}
 // vim: et ts=2 sw=2 syn=scala