by staticassertion | 2026-02-24 03:57:31+00:00
> I still think that's a training/familiarity problem more than a language issue?

But that's fine. Even if we say it's a familiarity problem, that's fine. I'm only saying that it's not reasonable to expect my skills in optimizing backend code to somehow transfer. Obviously many things are the same - reducing allocation, improving algorithmic performance, etc. But that looks very different when you go from the backend to the frontend because the languages can look very different.

> You can just as easily start with `rg \bnew\b` as you can `rg \.clone`.

That's not true though. In Rust you have to have a clone somewhere if you're allocating on the heap, or one of the pointer types like `new`. If I pass a struct around it's either cheaply moveable (ie: Copy) or I have to `clone` it. Granted, many APIs will clone "invisibly" within them, but I can always grep to find the clone.

In Javascript, things seem to allocate by default. A new object allocates. A closure allocates. Things are very implicit, you sort of are in an "allocates by default" mode with js, it seems. In Rust I can just do `[u8; n]` or whatever if I want to, I can just do `let x = "foo"` for a static string, or `let y = 5;` etc. I don't really have to question the memory layout much.

Regardless, you can just learn those rules, of course, but you have to learn them. It seems much easier to "trip onto" an allocation, so to speak, in js.

> Again, perhaps this is just a familiarity issue

I largely agree, though I think that js does a lot more allocation in its natural syntax.

> Do you treat all your backend library dependencies as black boxes as well?

No, but I don't really use frameworks in backend languages much. The heaviest dependency I use is almost always the HTTP library, which is reliably quite optimized. Frameworks impose patterns on how code is structured, which, to me, makes it much harder to reason about performance. I now have to learn the details of the framework. Perhaps the only thing close to this in Rust would be tokio.

> I've used profilers to guide building my own "frameworks" and help proven "Vanilla" approaches to other developers over frameworks in use.

I suspect that this is merely an issue of my own biased experience where I have inherited codebases with javascript that are already using frameworks.

> Maybe I'm missing what primitives you are looking for. async/await is about the same primitive in JS and Rust and there are very similar higher-level tools on top of them.

I mean, stack allocation feels like a pretty obvious one, reasoning about mutability, control over locking, the ability to `join` two futures or manage their polling myself, access to operating system threads, access to atomics, access to mutexes, access to pointers, etc. These just aren't available in javascript. async/await in js is only superficially similar to Rust.

I mean, a simple example is that I recently switched to CompactString and foldhash in Rust for a significant optimization. I used Arc to avoid expensive `.clone` calls. I preallocated vectors and reused them, I moved other work to threads, etc. I feel really comfy doing this in Rust where all of this is sort of just... first class? Like, it's not "weird" rust to do any of this. I don't have to really avoid much in the language, it's not like js where I'd have to be like "Okay, I can't write {a: 5} here because it would allocate" or something. I feel like that shouldn't be too contentious? Surely one must learn how to avoid much of javascript if they want to learn how to avoid allocations.

> To be fair, I get the impulse to want to leave it as someone else's problem.

I just reject that framing. People focus on what they focus on. Optimizing their website is not necessarily their interest.

> I feel like if you can profile and performance tune Rust you should be able to profile and performance tune JS.

I probably could but it's definitely not going to feel like second nature to me and I suspect I'd really feel like I'm fighting the language. I mean, seriously, I'd be curious, how do you deal with the fact that you can't stack allocate? I can spawn a thread in Rust and share a pointer back to the parent stack, that just seems very hard to do in javascript if not outright impossible?

> I think I'm saying that it is surprising to me that people who have developed skillsets for optimizing backend code in languages designed to be fast seem to struggle applying the same skills to a language with simpler/"slower" mechanics

Yeah I don't really see it tbh. I mean even if you say "I can do it", that's great, but how is it surprising?