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.

It's also how you end up with cargo cult optimizations for things that may have been solved ages ago in the VM. I've met Java devs who still insist on using StringBuilder for everything without empirical evidence.

I was indoctrinated with that in school. What, it is not true anymore?

Yes! Much has changed. Here's a good summary: https://stackoverflow.com/questions/46512888/how-is-string-c...

The change in question is JEP 280.

Don't quote me on this, but I think most String operations are compiled to StringBuilder operations automatically.

If compilers could do this even with hours of time to spend, that would be absolutely revolutionary. I program in a high level language (C#) and my whole day is usually moving things to the stack instead of the heap, devirtualizing calls, making SoA/AoS changes etc. I doubt we'll ever be in a position where compilers can make these decisions well enough. Much less jit compilers and dynamic runtimes that need to do it with time constraints.

What are you building that requires that?

A large desktop app (CAD). But the same thing has popped up in other projects: games, audio plugins, statistics, visualization... Basically anything that is CPU/Memory bound (which is most things except for basic web/database apps I find) needs careful thinking around performance.

Structure of arrays vs array of structures is in many ways identical code but a compiler can much easier optimize the former than the latter.

Totally agreed; try to do that for C++ before Java is popular. The maintenance guy would love you for the saving of time.

Optimise after. BTW, I thought it is about memory leak which is seriously not performance tuning!