You could find one answer to that question in Elm[1], and indeed it does look a lot like React. Although it generally handles exceptions by never letting them happen in the first place :)

[1] http://elm-lang.org/

Yep. React has to reinvent the wheel everywhere at the component boundaries. For example, one could see <Foo /> (which is really {type: Foo}) as a “reinvented” Foo() function call. Or see this.state as “reinvented” local variables, and this.props as arguments.

I think it’s expected that, as React gets more expressive (there are other features in the pipeline), it will unfortunately have to provide its own way to express these because it goes more into the language territory. But of course we’ll try our best to make these things look familiar in JS.

QML [0] was an attempt to do that. I would say it was a very successful attempt in terms of quality of the final product. It's probably the only UI toolkit that I enjoyed using so far.

[0] https://en.wikipedia.org/wiki/QML#Syntax.2C_semantics

    > It makes me wonder what a UI language/system
    > would look like if it were designed from the
    > ground up to be declarative

I think most people have seen XSLT only in trying to do simple transformations, without getting properly under its skin. Personally I've written a bunch of stuff in it -- a testing suite, graph traversal algorithms -- that make you appreciate it's absolutely a functional declarative language.