Never used it but it seems like a plausible project; it has Google's infinite $$$ backing it and smart people like Gilad Bracha on the team. They've built up qu

Never used it but it seems like a plausible project; it has Google's infinite $$$ backing it and smart people like Gilad Bracha on the team. They've built up quite a lot (language, tools, package-manager, IDE, ...) from scratch which is pretty impressive. As a language, it seems pleasant: somewhere around C#, a mix of JS and Java, less "powerful" (or less "crazy" depending on how you look at it) than Scala. I think I personally prefer Scala, but wouldn't complain too loudly if I had to use Dart/Dart instead of Javascript/PHP. On the other hand, even with Google's backing they seem to not have managed to aggregate as much of an ecosystem in the 4 years they've been available. In particular, server-side-Dart hasn't really taken off, and client-side dart doesn't seem to be that popular compared to say Coffeescript or Typescript or even Clojurescript. I think the advantage of Scala.js over dart is that we only need to build the JS side of things: there's already a pretty large server-side Scala ecosystem. There's already all the tooling and IDEs set up. There's already the community of people who already know Scala, and do not need to re-learn anything. Thus even though the Dart-JS ecosystem is probably not that much smaller than the Scala-JS ecosystem, I think Scala-JS is a lot more viable and sustainable (since it can piggy-back on all the Scala-JVM stuff) while Dart-JS and many other new-language communities have a tough struggle to gain enough critical-mass to be self-sustaining