Could these very same arguments not be applied to Javascript itself? JS is "transpiled" to bytecode, a language with vastly different semantics and a totally different ecosystem. It end up being wildly inefficient, but consumers don't seem to mind.
The description of Dart is also wrong. My understanding is that they are aiming at REPLACING JS in the browser, not compile to it. Compilation to JS is a stopgap to make the language useful while it's left unimplemented in Google's very own browser (A fact that never ceases to entertain me). The next web language shouldn't compile to JS, it should replace JS.
As JS becomes the asm of the web, TypeScript is going to become the C of the web. Just enough abstraction to make it possible to write, but still not enough to tank performance.
For what it's worth, almost no one on the Dart team ever believed that Dart would "replace" JavaScript. The memo that claimed that wasn't written by anyone on the Dart team.
The description of Dart is also wrong. My understanding is that they are aiming at REPLACING JS in the browser, not compile to it. Compilation to JS is a stopgap to make the language useful while it's left unimplemented in Google's very own browser (A fact that never ceases to entertain me). The next web language shouldn't compile to JS, it should replace JS.
As JS becomes the asm of the web, TypeScript is going to become the C of the web. Just enough abstraction to make it possible to write, but still not enough to tank performance.