SvelteKit 3.0 puts a Node, TypeScript and Vite upgrade ahead of the framework migration

The checklist behind this account was written by a dev.to author who read the release announcement, the release-candidate post and the full migration guide end to end ^[14]. "I have not yet run this migration on a production app, so this is not a war story," the author wrote ^[13].

The guide sets five version floors ^[2][1]. The TypeScript floor is the one most likely to wait on someone else. The author expects it to catch teams that pinned TypeScript 5 for plugin compatibility ^[4]. The Vite step is the one I would ship by itself, because 8.0.12 is the release that bundles stable Rolldown v1 ^[3]. A build that breaks after Vite and SvelteKit move in the same branch has two suspects.

The guide wants teams on the most recent 2.x release before the jump, for its deprecation warnings ^[5]. The post does not say whether that release runs on Vite 8 and vite-plugin-svelte 7. If it does, the work splits into three deploys:

1. Move to the latest 2.x and clear every deprecation warning it prints ^[5]. 2. Raise Node, TypeScript, Svelte, Vite and the Svelte Vite plugin to the 3.0 floors while still on 2.x ^[2]. 3. Upgrade to SvelteKit 3.0 and work through the breaking changes ^[1].

If it does not, steps 2 and 3 become one branch, and the two suspects come back.

The release-candidate post gives a sound reason for the config move. The Vite plugin used to resolve the SvelteKit config through an async process that could not start until the entire Vite config was resolved, because tools like Vitest can run from a working directory that is not the project root ^[7]. Options passed straight to the sveltekit() call are available to the plugin at once ^[7]. The author put it more briefly: "why were we maintaining two config files for one project?" ^[15]. Three options go in the move. preloadStrategy is deleted because modulepreload is now supported everywhere, prerender.origin becomes paths.origin, and csrf.checkOrigin becomes csrf.trustedOrigins ^[8].

The import change is where the hours go. #lib is a Node subpath import that Vite and TypeScript resolve natively, so it follows Node's rules instead of a SvelteKit-generated alias ^[9]. Node and TypeScript require subpath imports to be unambiguous. An import of #lib/foo fails and has to be written #lib/foo.ts or #lib/foo/index.ts ^[10]. According to the post, the migration script handles most of the rename, but the author tells readers to check the extension rule before trusting the script's output ^[9][10].

The last two items are smaller. tsconfig.json now extends $app/tsconfig, a generated file in node_modules, in place of ./.svelte-kit/tsconfig.json ^[11]. The release-candidate post says most custom compilerOptions can likely be deleted, and that include and exclude should be set explicitly, with exclude covering the service worker ^[11]. That service worker also loses the $service-worker module and imports from $app/env, $app/paths and the new $app/manifest instead ^[12].