Worked with some Elm in the past weeks, compiling back to Js to make some apps. What I was really amazed of is the compiler, it's blazing fast and really error friendly, they really did a great job creating this.
Moreover, the fact that it is a compiled language speed up your developments, you don't need to refresh and check the browser to see it's working, if it passes the compiler it has a high chance of working once in the browser.
The last thing I really like is Signals, it enable the app to be reactive to user's actions and make things a lot more interesting.