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I worked with Elm for 2 (or maybe 3?) years, and with Clojurescript for another 2. I recently had to decide on which of the two I would use on my next project, and it was definitely not an easy decision. Ultimately, I went with Clojurescript.

Main Clojurescript pro was re-frame[0]. Re-frame makes state handling easy and, especially importantly for performance-sensitive projects, it entirely removes the (rather common) problem of re-renders with the way its subscriptions are handled. This, plus the ability to have your entire stack in a single (amazing) language, were the tipping points to me.

While you can't achieve the same level of compile-time safety in Clojurescript, you can apply "state checks" (with Spec or any custom validation mechanism) any time your state changes. And with re-frame, it is extremely clear when your state changes, therefore you can block any invalid state from being saved and catching it as soon as it happens. Again, not the same kind of safety you have with Elm, but to me it's a good-enough trade-off.

And that's exactly what I do with my code: every time my state changes, I run a validation check on the keys that are about to change. If their value is deemed invalid, an error popup (identical to old Windows XP error popups, because why not) will appear, stating what the invalid state is and what it should be like instead, as well as which event led to this state in the first place. This check is so fast I don't even need to disable it in the production build (but instead of a popup we get a notification that an invalid state error happened).

In fact, there's this (non-mainstream) argument that runtime checks bring even more power over typing: https://www.youtube.com/watch?v=nqY4nUMfus8

TL;DR: Not an easy decision, but the truth is whichever one you pick, it will be a great choice.

[0] - https://github.com/day8/re-frame/