Definitely agree with "the best language for that is the one you're using everywhere else"
Where I work right now, we use the newer versions of ASP.NET that come bundled with the Razor templating engine, which uses .cshtml files. You can write C# inside the files much the same way you can write JavaScript in a JSX file, it makes creating forms and such a breeze.
Big bonus is that moving from writing server-side logic to client-side logic doesn't require much of a context switch, and you can use the same objects to represent your data on both sides. If I spend all day moving between half a dozen different languages that get compiled by a dozen different tools, it can get a little exhausting.
Razor seems to have been born out of a frustration someone had with writing
return "<div>" + model.name + "</div>";
Razor is basically a DSL for C# string concatenation, where everything not escaped with an @ is a string literal to be concatenated. This means it's fairly unopinionated about structuring code. React, on the other hand, forces you to define components- ideally, pure functions from properties to JSX (which is just sugar for JS). This means composition is the default solution to everything. Razor doesn't place nearly as much emphasis on composable components, and the mechanisms it has for doing so, like helpers or calls to RenderPartial, are clunky and worlds away from the first-class component support of React.
While it's technically possible to write Razor code with a React-style focus on composition, the syntax and architecture of viewmodels/templates actively pushes you away from doing so. In my experience, most Razor ends up like a C# translation of PHP, and I think that's really the paradigm Razor inherited. Razor has been around since 2011, which significantly predates the Cambrian explosion of clientside js frameworks, so it makes sense.
Good point that it's hard to write nice and modular views with Razor; helpers and RenderPartial are pretty clunky and overall just hard to manage. I suppose it is pretty PHP-like...
Where I work right now, we use the newer versions of ASP.NET that come bundled with the Razor templating engine, which uses .cshtml files. You can write C# inside the files much the same way you can write JavaScript in a JSX file, it makes creating forms and such a breeze.
Big bonus is that moving from writing server-side logic to client-side logic doesn't require much of a context switch, and you can use the same objects to represent your data on both sides. If I spend all day moving between half a dozen different languages that get compiled by a dozen different tools, it can get a little exhausting.