dts-gen

Sort of... Your maintenance burden just becomes higher as a consumer of the library because you can't rely on the compiler to tell you if something goes wrong. But if you have a good testing harness you'll probably figure that out eventually anyways. To generate typings for your library, you can start with converting from jsdoc if you have docstrings with types, or if you want to infer types at runtime during a testing suite you can use something like https://github.com/microsoft/dts-gen I've never used dts Gen but it looks promising as a starting point. But as an additional point, only the public functions and classes really need type declarations, so unless you export all of your functions that could cut down on the burden to write up the types.

Typescript has inference for "plain" JS files if you use the `--allowJS` flag. That inference is also made available more directly in dts-gen [1], which is a tool built around Typescript inferencing that produces decent first pass type definition files for a library. dts-gen may be something to try the next time you need a definition file. (Personally, I still prefer to start a new definition file by hand, but it's good to have an automated option, even if only to double-check your work.) [1] https://github.com/Microsoft/dts-gen

You can try https://github.com/Microsoft/dts-gen now.