Lots of languages target JavaScript too, but only one got very popular, because ecosystem matters a lot. People are going to have to recreate the current JavaScript ecosystem for each languages, and then probably for each framework in that language.
No, not really. The only language that has mindshare in the frontend outside of JavaScript is TypeScript. Elm, CoffeeScript, Rescript and all of these are not known at all. In the JS ecosystem, Angular, React and Vue are king, but React is really fragmented with all the options (Next, etc). All of this because JavaScript is the most popular language in the world. Most other languages won't get that mindshare.
Elm doesn't have the JS ecosystem, Rust doesn't, Rescript doesn't. The thing is, when you're doing backend stuff, it's usually relatively easy to pull a library with whatever framework you're using. On the frontend, for your components, you need basically a library by framework by language.
