I've used gleam for a toy project in uni, and AoC
My main friction point is that the Int type maps to different concepts in erlang and js
In erlang it's a arbitrary precision Int
In js it the js number type, which is a 64bit float iirc.
Also recursion can hit limits way sooner in js.
For me, my code rarely ran in both js and erlang. But could be skillissue
Fair, but you usually don't run your project on both, unless you're writing a library.
Pick the target that makes sense for your project and stick with it :)