@reventlessdev/rescript-web

ReScript bindings for the WHATWG web globals: fetch, WebSocket, timers and base64.

Why this exists, and where the line is

These are ambient globals, not node:* imports. Everything here works unchanged in a browser and in Node 18+ (WebSocket from 21). That is the whole distinction from rescript-node, which binds imported Node modules and is server-only by construction.

The split matters in practice because the same two APIs are needed on both sides of Reventless: the browser client subscribes to AppSync Events over WebSocket and talks to the API over fetch, and server-side scripts do the same things against the same endpoints.

Design note

The surface is driven by call sites, not by the specification.

reventless-ui already had a bindings/Fetch.res. It modelled method as [#get | #post] and carried no body field at all, so nine other files bypassed it and hand-rolled their own @val external fetch. A binding that cannot express what callers do does not reduce duplication — it becomes one more variant to maintain.

So this package binds what the real consumers need (arbitrary method strings, dict<string> headers, an optional body that is sometimes binary, an abort signal, and ok/status/text/json) and deliberately omits what nothing uses. Add to it when a consumer appears, not in anticipation of one.

Usage

open Web

let res = await Fetch.fetch(
  url,
  {
    method: "POST",
    headers: Dict.fromArray([("content-type", "application/json")]),
    body: Fetch.Body.string(payload),
  },
)
if res->Fetch.ok {
  let json = await res->Fetch.json
  // …
}

let ws = Socket.make(url, ["my-protocol"])
ws->Socket.setOnOpen(() => ws->Socket.send(`{"type":"hello"}`))
ws->Socket.setOnMessage(evt => Console.log(evt.data))
ws->Socket.setOnClose(evt => Console.log2("closed", evt.code))

Build

pnpm run build     # rescript build