Before Flutter | Rubber Duck Engineering | Episode #100

I'm not sure why you're being downvoted, it's a super reasonable question. Iirc the reason is that the Dart team was willing to heavily modify the language and runtime to accommodate the needs of Flutter and the V8 team wasn't. I think this is the video that talks about this: ▶ this video

Typescript is great! But doesn't get you away from running in a JS interpreter or JIT, which at least on iOS is very slow. We wrote the first 3 versions of Flutter in JS but eventually had to move off due to 10s+ startup times (we wrote a ton of JS). Once we moved to an ahead-of-time compiled language we could write as much code as we wanted and the user didn't have to compile it during launch on their device. Typescript would have that problem still today, sadly. ▶ this video is a talk where we discuss what led to modern Flutter (including 3 attempts in JS). Angular was originally in Dart is my understanding, but eventually forked into two projects. Angular Dart (which is really only still used internally at Google, mostly for Google AdWords which makes all the money) and Angular JS which is what has seen so much popularity more generally.

They've answered why Dart many times. It's a language that fits their needs, since it has JIT, AOT, compilation to JS and now WASM. Back then there weren't many languages that could do all that, and even today there aren't many. Kotlin (and other JVM languages) and TypeScript (and other compile-to-JS-only languages) are already out since they are not AOT, only JIT even now. More importantly, it was a Google language that they could mold for their own needs, not so possible if it's an outside language like TypeScript. For example, early on, they asked the Dart team to create an AOT compiler since Apple does not allow JITted code apparently (not sure how React Native gets around this then), or maybe it didn't back then, and the Dart team was able to do it successfully for the Flutter team. Try asking the TypeScript team to do the same, it's next to impossible. For what it's worth, Dart 3+ introduces more functional parts like records, patterns, and exhaustive pattern matching so you can use it in a functional style if you want once that ships. There is also fpdart, for full functional support, and for brevity of code, since Dart has the ability to generate code via macros (with build_runner), you can also use packages like functional_widget, flutter_hooks etc to achieve a very functional code style as well, React-like. This is a great podcast/video episode on how Flutter came to be, from the early days to now, and how it used JS in the beginning but it didn't serve their needs,