Sure, replacing a legacy Coffeescript + jQuery app with pure Scala.js. Implementing core functionality of various jQuery plugins (Datatables, Validation, FancyBox, Bootstrap Date/Time pickers, etc.) in Scala.js. Payload is less than 50% of previous version's app bundle. You can of course pull in client-side libs as you like, but for this project it's been really nice to strip out the bloat.

Having Scala's type system on both client and server is pretty surreal, not to mention full IDE support -- the entire world of javascript just appears as you type ;-)

Well, for one, the world's 3rd biggest software company, SAP. See http://event.scaladays.org/scaladays-cph-2017#!#schedulePopu... - quote: "The application development stack we are building embraces Scala all over the place – including the development of user interfaces for which Scala.js is utilized to provide a type-safe interface to SAP's own JavaScript UI library SAP UI5."

Yes, we do, and we love it.

If you know Scala, you can mostly forget about Javascript and just code everything in Scala both on server and client side, and everything just works magically (using the same data types is PURE PINK UNICORN AND RAINBOW BLISS). If you don't know Scala, your mileage may vary, but I'd learn a bit of Scala just to experience that.

Yes, for quite a few projects.

For a number of them I used scala-js-react, though very recently (as of about two weeks ago) I've been playing around with my own (smaller, less opinionated) virtual dom library. http://www.wbillingsley.com/veautiful/

yes, several personal stuff, some internal facing business apps , and few public facing I did as contractor.

It's a whole different world than anything else in frontend. The libraries from scala are immense.

We use Scala.JS in production, and so far we haven't had a single issue with it. Cross-JS/JVM projects have hairy .sbt files though.

yes, I've one big project in it. Currently working with: ui -> scalatags, serialisation -> upickle.