Basically: badly. That's the number one reason we're not trying to compile Scala.js to wasm at the moment. For wasm to get the level of JS interop that Scala.js has, it needs to integrate with JS objects, which means with the JS GC, which means basically have a GC of its own. Hence we're waiting for the wasm GC spec to take life :)
Regardless, thanks so much for the work you're doing with Scala.ks (Scala is still my main language and I'm working on removing JS from my toolbox soon).
> it needs to integrate with JS objects, which means with the JS GC
Otherwise we would have done it already.
Not good for performance, but possible in principle, and a stop-gap measure until the WASM GC lands.
Moreover, typical Scala.js code constructs cyclic dependencies between Scala objects and JS objects routinely. If Scala.js has its own GC, you'll have to manage those cyclic heap references, which will involve weak maps and other trickery so complicated that we would most likely lose all the performance that wasm would otherwise bring us.
It's just not worth it.