Include optional params in fetch function

[yawaramin]

I've come to believe that JavaScript's 'options object' function parameter pattern is a poor-man's optional parameter implementation. The fetch function is a perfect example of this. I would like to wrap it in a function that actually accepts optional parameters and converts them into the requestInit type. This would be a backward-compatible change and look like this:

(* Fetch.ml *)
...
external fetchWithInit : string -> requestInit -> response Js.Promise.t = "fetch" [@@bs.val]
let fetch
  ?method_
  ?headers
  ?body
  ?referrer
  ?referrerPolicy
  ?mode
  ?credentials
  ?cache
  ?redirect
  ?integrity
  ?keepalive
  resource =
  fetchWithInit
    resource
    (RequestInit.make
      ?method_
      ?headers
      ?body
      ?referrer
      ?referrerPolicy
      ?mode
      ?credentials
      ?cache
      ?redirect
      ?integrity
      ?keepalive
      ())

Now callers will be able to use fetch ~method_:Post "http://example.com", instead of fetchWithInit "http://example.com" (RequestInit.make ~method_:Post ()).

[glennsl]

Hmm, yeah. The original objective for this was to create a set of bindings that were as thin as possible while still being sound, and then have others build libraries on top of that, like re:fetch. But since that hasn't happened and people just use this instead despite the horrible UX, we might as well add some convenience like this.

Now that @bs.string seems to work correctly with polyvariants it might also be possible to actually make these bindings as thin as originally intended, since most of the generated code is just marshaling. Perhaps make one module that compiles to almost nothing, and another that adds a bit of convenience, and weight, like this.

[yawaramin]

OK, in that case I'd like to propose making a new Fetch.Raw module that has a 'zero-cost' style, and making the default Fetch module have the convenient wrapper over that. Imho it's more important to provide a friendly UX, especially for newcomers and the (probably large) set of people who don't really care about the added weight. If this is agreeable, I'm happy to work on a PR.

[glennsl]

Sounds great. Go for it! 😄

[lessp]

Talking about Refetch which I'd completely missed, perhaps some kind of RFC might be an idea to also try to make a unified API and library which could be used for Native and BS?

I feel as this is a big part, and from lurking it looks like there's some effort going on in a few different places (apart from Refetch):

https://github.com/anuragsoni/fetch/
https://github.com/aantron/repromise
https://github.com/revery-ui/revery-fetch/