JavaScript over TypeScript for SvelteKit codebase

[hanneswidrig]

Hello, not sure if this is the correct spot to ask this question. I am curious why SvelteKit appears to written in JavaScript while Svelte itself is written in TypeScript?

[geoffrich]

Note that SvelteKit is still typed, but uses JSDoc instead of TypeScript. You can find some tweets from Rich Harris about this, but it comes down to a few reasons:

• You can still generate types from JSDoc source code and the resulting code is generally smaller than TS-compiled code (source)
• Using JS made it easier to make changes when the project was in an experimental phase (source)
• Using JSDoc types means you can run tests without adding a build step (source)

Maintainers have said in the past that Kit could go back to TypeScript after 1.0, but so far JSDoc types are working well for the project.