After reading this article: https://v8.dev/blog/elements-kinds. I was wondering if some of the arrays that are created in my code are packed or holey. Is there any way to check this at runtime in a browser environment(specifically Chrome)?
I am looking for something like a %DebugPrint() that works on Chrome.
Maybe there are some other clues that I can look for. For example, some info that is captured in heap snapshots, etc.
(V8 developer here.)
As far as I'm aware, Chrome (DevTools) does not expose arrays' "elements kind".
And that's probably okay, because the performance difference between "packed" and "holey" elements is very small. Essentially, it only shows up in microbenchmarks. The typical benefit of a packed array is that two machine instructions can be avoided that would otherwise have to happen. If you're looking at a one-line hot loop body that compiles to maybe a dozen machine instructions, then saving two of them can be measurable. If you're looking at a real-world app where hundreds of kilobytes of code contribute to overall performance, saving two machine instructions here and there isn't going to matter.
I understand that you may be curious; but as far as tangible optimizations go, there are much more impactful ways to spend your time. Talking about elements kinds is pretty much a "for your curiosity, here are some of the lengths to which JS engines go to squeeze every last bit of performance out of JavaScript" story; it is not meant to be important performance advice that most developers should be aware of.