However, in my experience, once a code base is big enough, you can open almost any file and find documentation that's out of date, incorrectly copy-pasted, or some other major issue. TS, on the other hand, at least forces you to stay correct, which is ultimately what convinced me to switch.

Which are a form of type annotations. Case in point: the typescript compiler can actually parse those, in .js files, and yield appropriate warnings on errors. See the //@ts-check annotation.