I'd have to be pretty carefully persuaded that someone who wrote infrastructure tools in JS makes decent design decisions.

People use the tools they have. When you want to build an infrastructure tool, you won't (or shouldn't) start with "how to write rust".

Getting to the finish line matters more than using the absolute best fit so to speak.

Same goes for orgs that have a lot of JS talent but no Rust for example.

It's not an advocacy for rust but a fairly introductory level shell script would likely be a very sophisticated JavaScript program.

I've seen such efforts and they tend to be extremely complicated and not really doing much.

I don't assume rational agency but instead that many people make poor decisions.

If they add Typescript and primarily stick to wrappers around C libraries and calling out to other binaries it could be okay.

The core language is okay enough, not my favorite but it works. It's the surrounding ecosystem that's a pain.

I would have to think really hard if someone asked me if I'd rather have all the infra scripts written in Perl or TS. TS is more likely to break, but easier to read and fix. The odds of Perl breaking are slim, but it is a fucking nightmare to fix. I'm pretty sure I'd rather have Perl than JS, though. JS without a type system is rough, to me at least.

These rewrites are fantastic for performance of build tools, but add complexity and churn when the base language, usually Javascript or Typescript, was already memory safe anyways. I'm hesitant to depend on most of this newer tooling for a while when existing Javascript-based alternatives exist.

Not having proper static typing (and weak typing on top of that) in any medium-large project I think adds much more problems and complexity. JS is simply a bad language design-wise with TS being an improvement but still having the original sins of JS in it.

Performance is key. The performance differential of biome compared to prettier or eslint, for any monorepo of decent size, is a few orders of magnitude, for tools that should ideally be run on every file save.

While I don't see a sense in doing that versus managed compiled languages, as it isn't a kernel driver or game engine performance level, eventually I will get an excuse to use Rust at work exactly because of those rewrites.

Everything in JS gets rebuilt until they are no longer in JS.