Typescript support
Summary
In order to get benefit of typing in javascript, we need to setup the recent typescript support for svelte.
Ref: https://svelte.dev/blog/svelte-and-typescript
There is also a section about typescript support for existing projects: https://svelte.dev/blog/svelte-and-typescript#Adding_TypeScript_to_an_existing_project
Note: As the project is new, this issue should be resolved first to make the integration simpler.