I've been a long time fan of Dart but I've recently (this week) given up on it for my purposes, which are write browser SPA's that need to run in different browsers. My sense is that after the Chrome team decided not to include the Dart VM in Chrome, Dart started looking for a new story. That story is Flutter, which is Dart running in the Dart VM on mobile devices [1] It is not Dart converted to JavaScript so it can run in any browser, despite the awesome work of the dart2js authors and the relatively new dev_compiler project [2]. The latter will be awesome when done, because the goal is to convert Dart to ES6/ES2015. However, it is my impression that Google really doesn't care that much about transpiling Dart to JavaScript. I was willing to put up with the huge file size dart2js produced, because Dart made my life easier and something better was coming. However, it's been a long time and the pace of Dart transpiling work is too slow. I converted my Dart app to TypeScript (size dropped from 650kb to 60 kb) and am happy for that, but sad that Google does not put more people on the dev_compiler team to keep long term enthusiasts like me on board. I'm sure Flutter is fantastic and will take a look when I have a need for that kind of solution. I can't really blame Google, because the JavaScript community turned it's back on Dart, but I wish they would just state the new goals and not leave us hanging.

[1] https://flutter.io/faq/ [2] https://github.com/dart-lang/dev_compiler