I'm working on a similar thing, tho I don't intend to extract it into a library (yet). I was inspired by Gary Bernhardt's blog post [1] and video [2].

I have an endpoints.ts file, shared between client/server, which has something like:

  export type Endpoints = {
    createProduct: {
      path: '/api/products.json';
      method: 'POST';
      clientSends: { name: string };
      serverResponds: ProductJSON;
    };
  }

The client can do `makeRequest('createProduct', ...)` and the Express server can use `registerEndpoint('createProduct', ...)` which must adhere to the schema defined above.

TypeScript's structural typing helps a lot here.

Of course, I can "lose" typing through things like raw SQL queries (working on a mini db helper library to help with that), but so I'll have to validate that the endpoints return what they say they do through tests (probs using io-ts).

I'm just getting started (coming from Rails). Not sure what the "correct" way to do this is, but my approach works so far. Would also be nice to have a generic way to create REST endpoints for a given resource, but meh.

[1]: https://www.executeprogram.com/blog/porting-to-typescript-so...

[2]: https://www.youtube.com/watch?v=GrnBXhsr0ng