There is a small list under "Built with Scala.js" here: https://www.scala-js.org/community/. And that's only for the public facing apps of companies who have explicitly sent a PR to the website to add themselves to the list. Other companies use Scala.js for internal tools.
It's hardly "one dude", though. Don't give me too much credit. There were two others (@gzm0 and @nicolasstucki) who helped a lot on the core. But even more than that, the reason it's so popular and adopted is mostly due to the amazing community who wrote great, relevant libraries, and communicated to the world.
It's at least a dozen people who should be credited, even if I'm currently the only one paid for this work.
