A 10x Faster TypeScript

tl;dr — Rust would be great for a rewrite, but Go makes way more sense for a port. After the dust settles, I hope people focus on the outcomes, not the language choice.

I was very surprised to see that the TypeScript team didn’t choose Rust, not just because it seemed like an obvious technical choice but because the whole ecosystem is clearly converging on Rust _right now_ and has been for a while. I write Rust for my day job and I absolutely love Rust. TypeScript will always have such a special place in my heart but for years now, when I can use Rust.. I use Rust. But it makes a lot of sense to pick Go.

The key “reading between the lines” from the announcement is that they’re doing a port not a rewrite. That’s a very big difference on a complex project with 100-man-years poured into it.

Places where Go is a better fit than Rust when porting JavaScript:

- Go, like JavaScript and unlike Rust, is garbage collected. The TypeScript compiler relies on garbage collection in multiple places, and there are probably more that do but no one realizes it. It would be dangerous and very risky to attempt to unwind all of that. If it were a Rust rewrite, this problem goes away, but they’re not doing a rewrite.

- Rust is so stupidly hard. I repeat, I love Rust. Love it. But damn. Sometimes it feels like the Rust language actively makes decisions that demolish the DX of the 99.99% use-case if there’s a 0.001% use-case that would be slightly more correct. Go is such a dream compared to Rust in this respect. I know people that more-or-less learned Go in a weekend and are writing it professionally daily. I also know people that have been writing Rust every day professionally for years and say they still feel like noobs. It’s undeniable what a difference this makes on productivity for some teams.

Places where Go is just as good a fit as Rust:

- Go and Rust both have great parallelism/concurrency support. Go supports both shared memory (with explicit synchronization) and message-passing concurrency (via goroutines & channels). In JavaScript, multi-threading requires IPC with WebWorkers, making Go’s concurrency model a smoother fit for porting a JS-heavy codebase that assumes implicit shared state. Rust enforces strict ownership rules that disallows shared state, or we can at least say makes it a lot harder (by design, admittedly).

- Go and Rust both have great tooling. Sure, there are so many Rust JavaScript tools, but esbuild definitively proves that Go tooling can work. Heck, the TypeScript project itself uses esbuild today.

- Go and Rust are both memory safe.

- Go and Rust have lots of “zero (or near zero) cost abstractions” in their language surface. The current TypeScript compiler codebase makes great use of TypeScript enums for bit fiddling and packing boolean flags into a single int32. It sucks to deal with (especially with a Node debugger attached to the TypeScript typechecker). While Go structs are not literally zero cost, they’re going to be SO MUCH nicer than JavaScript objects for a use-case like this that’s so common in the current codebase. I think Rust sorta wins when it comes to plentiful abstractions, but Go has more than enough to make a huge impact.

Places where Rust wins:

- the Rust type system. no contest. In fairness, Go doesn’t try to have a fancy type system. It makes up for a lot of the DX I complained about above. When you get an error that something won’t compile, but only when targeting Windows because Rust understands the difference in file permissions… wow. But clearly, what Go has is good enough.

- so many new tools (basically, all of them that are not also in JS) are being done in Rust now. The alignment on this would have been cool. But hey, maybe this will force the bindings to be high-quality which benefits lots of other languages too (Zig type emitter, anyone?!).

By this time next week when the shock wears off, I just really hope what people focus on is that our TypeScript type checking is about to get 10 times faster. That’s such a big deal. I can’t even put it into words. I hope the TypeScript team is ready to be bombarded by people trying to use this TODAY despite them saying it’s just a preview, because there are some companies that are absolutely desperate to improve their editor perf and un-bottleneck their CI. I hope people recognize what a big move this is by the TypeScript team to set the project up for success for the next dozen years. Fully ejecting from being a self-hosted language is a BIG and unprecedented move!

What? And how? And how would that help in Go which has a completely different garbage collection mechanism?

"To meet those goals, we’ve begun work on a native port of the TypeScript compiler and tools. The native implementation will drastically improve editor startup, reduce most build times by 10x, and substantially reduce memory usage."

It's hard to tell if there will even be a runtime that somehow uses TS types to optimize even further (e.g. by proving that a function diverges) but to my knowledge they currently don't and I don't think there's any in the works (or if that's even possible while maintaining runtime soundness, considering you can "lie" to TS by casting to `unknown` and then back to any other type).