How to generate swagger API doc from TypeScript based Express app?
I would recommend that you use a library that handles everything for you such as tsoa which can easily generate Swagger/OpenAPI documents from your TypeScript types. It also does the runtime validation for you so that you know the request actually is the type that TypeScript says it should be. The readme contains all of the setup information that you would need to start using it. It's compatible with express, hapi, koa, and more:
https://github.com/lukeautry/tsoa
(Full Transparency: I am one of the maintainers of tsoa. But I was first a consumer of tsoa and I find it to be a great product... that's why I asked to help maintain it! :) )