TypeScript Go support (at least in CLI)

[notramo]

Description

JSX support has been recently implemented in the Go implementation of TypeScript.

The new Go implementation is a lot faster (10 times faster in some projects), and uses ~half the memory as the JS implementation.

It seems that this new version has enough features for a fast CLI svelte-check command. LSP support is lacking at the moment, but an optional svelte-check config option would be really useful.

Proposed solution

Add a command line option to svelte-check that enables the use of tsgo tsc … instead of tsc.

Alternatives

None. This seems a quite simple change, with the most obvious solution being a CLI option. Other solutions seem a lot more complicated.

Additional Information, eg. Screenshots

No response

[jasonlyu123]

No. It's not a simple change. svelte-check does not call tsc by the command. It used low-level typescript API that is about to be rewritten in typescript go. This is definitely on the radar but not anytime soon.

[KieranP]

The first Typescript Native Previews just released, and with it a very early version of the APIs:

• https://devblogs.microsoft.com/typescript/announcing-typescript-native-previews/#api-progress
• Scaffold IPC-based API microsoft/typescript-go#711

I understand that it won't be anywhere ready for use by Svelte, but it might be a good time for the Svelte language-tools team/contributors to give the TS team feedback so that APIs support what Svelte needs from day one.

[jasonlyu123]

To keep the expectation in check, TypeScript mentioned a while ago that the TypeScript API library is expected to be released after TypeScript 7 is released. So this most likely won't be available on day one.

[Kae7in]

Really looking forward to this, especially in our SvelteKit app where we have ~370K LoC in .svelte files and svelte-check takes about 54s :(

[pheuter]

Some significant recent movement: https://devblogs.microsoft.com/typescript/progress-on-typescript-7-december-2025/

[jasonlyu123]

Yeah. The TypeScript team is very committed to it and plans to stop active development on the old codebase. The API we need, however, is still pretty much the same since my last update. The main problem is that there is no way for us to alter the module resolution to resolve Svelte files.

[astralhpi]

For those looking for a faster alternative until svelte-check gets tsgo support, I made a tool using svelte2tsx + tsgo: svelte-fast-check (https://github.com/astralhpi/svelte-fast-check)
It only does type checking (no other diagnostics). In my project (~280 Svelte + 740 TS files), it runs in 2-3s vs 14s for svelte-check, or 0.6s with --incremental in warm state.

[pheuter]

@astralhpi that's awesome, i've also been working on a similar project that built a custom parser and compiler in Rust to quickly compile .svelte -> .tsx and run tsgo on the entire codebase. it can do diagnostics beyond type checking, including svelte-specific diagnostics:

https://svelte-check-rs.vercel.app/

[astralhpi]

@pheuter Nice! Keeping a custom parser in sync with Svelte updates is no small feat. Best of luck with the project!

[auvred]

Here is another take on this problem: https://github.com/auvred/golar. It also uses the official svelte2tsx, so there should be no loss in type-checking functionality. Also, instead of writing generated files to /tmp, Golar extends typescript-go to work with .svelte files directly. LSP support is planned as well!

[jasonlyu123]

I also did a prototype of LSP tsgo integration. It needs some changes to the tsgo codebase. Hope the change would be something the TypeScript team could adopt as an API. So we won't need to patch tsgo and publish a new binary.

[jasonlyu123]

svelte-check currently has --tsgo and --tsgo-experimental-api flags for supporting TypeScript Go. You need to install @typescript/native-preview in your project to use it. TypeScript 7 RC isn't supported yet. --tsgo calls tsgo by command. It's slightly faster than --tsgo-experimental-api but has some limitations. --tsgo-experimental-api uses experimental api, which might break when you update @typescript/native-preview.

Some of the api and workaround --tsgo-experimental-api currently used aren't available in LSP. So the editor integration still has to wait for a while.