Shameless self promotion, I did exactly that, blog post explains it: https://chrisfrew.in/blog/converting-a-large-project-from-javascript-to-typescript/ https:

Shameless self promotion, I did exactly that, blog post explains it: https://chrisfrew.in/blog/converting-a-large-project-from-javascript-to-typescript/ https://chrisfrew.in/blog/converting-a-large-project-from-ja... This method does have some caveats, but can get your a sort of starting point using TypeScript for any sized JavaScript project.