Companion classes don't work in offline mode

[ebruchez]

Getting error:

baseline.js?updates=offline:462081 scala.scalajs.js.JavaScriptException: TypeError: Class constructor $b_Lorg_orbeon_xbl_Grid$GridCompanion cannot be invoked without 'new'

In offline, we use ESVersion.ES2018 for "improved regular expressions", and so our subclassing code in xforms.js fails.

[ebruchez]

If we switch all to ESVersion.ES2018, which we can do now, we only need one solution. In JavaScript, I can now do it. However our antiquated sbt-uglify is unable to process JavaScript containing classes. So I wondered whether this could be written in Scala.js, and the answer is "yes" for the subclassing (via hack), but calling super.init() causes a compiler error. See https://github.com/scala-js/scala-js/issues/4801.

So for now either:

• the Scala/Scala.js bug is fixed very quickly
• or we have to find a solution for our JavaScript function (maybe put it in a spearate JavaScript file not processed by sbt-uglify.

[ebruchez]

For now, chose JavaScript solution.