[ufo]

I wasn't talking about manually adding in the assertions into the library code. The idea is that you would take the type declarations that people are already writing and have the Typescript runtime add some sanity checks to verify that they are correct. TS doesnt do that because it insist on not including any extra runtime code so if there is a error in a type declaration that problem might go undetected or onyly cause an exception in a different part of the code.

I can see that library versioning would be annoying but I think its more of a ecossystem problem then a technical one.