I did look at including JSDoc comments in the .js files to define types and function signatures, from which I could then autogenerate TS documentation files. But the results were a mess, and they ruined the existing documentation. Given that documenting the code in a way that allows me to autogenerate doc files (in a format that I like) is paramount, I abandoned that idea.

Also, the library's structure just doesn't sit well with my limited understanding of TS and TS definitions. I got the impression from the TS docs that the TS developers really like JS classes, and are not that keen on ES6 modules - which is unfortunate because my library makes heavy use of prototypes, modified by mixin functions.

So I hand-wrote a single definitions file in a way that matched as closely as possible the library's structure and preferences. Hopefully that file is enough to give developers some useful tips in their preferred IDE when they use the library in their projects. But I've only tested this in Sublime Text.