The author might assume it, but I think it needs to be explicitly stated. Tools like this are often sold as "You don't need to know X because you can now code in Y and translate automatically to X!" That never works out though because there are always leaky abstractions. (For this project, just take a look at the Attributes docs to see how leaky the abstractions are.)

I've had to work with a bunch of C, C++, Java, Perl, and C# developers who were good at backend stuff and just started to learn HTML, CSS, and Javascript, and they're mostly pretty awful at it until they give in and dedicate themselves to the frontend web developer platform and environment. Prior to that they'd grasp at tools like this one that seem to offer hope that they won't have to learn that nasty javascript.

I'm coming at it from a different perspective. I can't worry about what other programmers do. I need tools. I love JS but the tools for it could be better. I'm hoping C#->JS will be a great addition to the toolbox.