I'd be surprised to learn that there's any sensible optimization that the compiler/runtime can make to ensure optimal data locality. The problem is difficult enough that the entire Unity engine is being pretty much rewritten to make use of sequential memory access.
In addition, I really, really wish more JS developers actually cared to learn about optimization and about how the runtime/hardware actually works. We've "developed" the web to such a slow, buggy mess that I've given up on the idea that there's any way to fix it. I hope somebody figures out a way to start over, preferably with no scripting capability, because apparently giving people any half-baked scripting language results in them soon developing nuclear footguns with it.
Significant part of the web is fast and works just fine. Sure experience on major news and media sites sucks, but you have to realise that it's caused by their monetisation model and not a platform itself.
In addition, I really, really wish more JS developers actually cared to learn about optimization and about how the runtime/hardware actually works. We've "developed" the web to such a slow, buggy mess that I've given up on the idea that there's any way to fix it. I hope somebody figures out a way to start over, preferably with no scripting capability, because apparently giving people any half-baked scripting language results in them soon developing nuclear footguns with it.