(2) Chrome ends up with 90%+ market share, so it doesn't matter that I'm bad in all the other browsers. But I can't see this happening as long as e.g. iOS is around and relevant.
(3) I have the resources to write both a Dart version for Chrome and a CoffeeScript version for older browsers. At this point, Google has strictly made my life harder than it would have been otherwise.
I do want to give Dart a fair shake, but I'm having a hard time seeing how it could realistically succeed.
But will it, though? Sure, "Hello, World" transpiles to 17,000 lines of code, but I'd want to see some actual benchmarks of actual code to see what kind of performance hit that implies, before deciding against Dart on that basis.
And then there's the whole python argument about developer time being more valuable, and most applications these days not being performance constrained, etc, that could possibly apply here, as well.
See Objective-J / Cappuccino which chose to eat the very real overhead messaging in order to gain expressiveness. How many JS apps are as responsive / elegant as 280 North Slides?
Is this a typo, tongue-in-cheek, or a technical term I don't know? I've only heard of "syntactic sugar" myself.
I think you are correct here. But there is still something very worrying about what Dart compiles into. It isn't just the amount of code, which is what most people are discussing. It's the content too.
The content of the code makes it look like much of that code will be run all the time. In other words, it isn't just some library functions that are called rarely, it is stuff that will end up being called from your inner loops. I might be wrong here, but that's what the code suggests to me.
In that respect, the Dart compiler looks different from both CoffeeScript and Emscripten. CoffeeScript by design compiles into straightforward JS, and Emscripten manages to compile into mostly-straightforward JS as well, which is why it has decent performance. But what Dart compiles into looks like it would not run very fast on most JS engines. It might run fast on Chrome, if they tune its inlining and other capabilities for Dart-like code, but I doubt that would hold anywhere else.
Again, though, I have not profiled the generated code, I just took a look at it, so I might be wrong.