@infinity-msfs/rescript-instrument

Pure ReScript API for registering MSFS BaseInstrument subclasses.

ReScript cannot emit ES6 class extends syntax with working super calls, which is the one thing BaseInstrument requires. This library isolates that concern into a ~50-line JS shim (instrumentShell.mjs) behind a small typed ReScript API. Everything else about your gauge stays in ReScript.

Usage

let relay: ref<option<MyRelay.t>> = ref(None)

Instrument.define(
  "my-gauge-instrument",
  {
    templateID: "MyGaugeTemplate",
    onConnected: _self => {
      let r = MyRelay.make()
      MyRelay.init(r)
      relay := Some(r)
    },
    onDisconnected: _self => {
      relay.contents->Option.forEach(MyRelay.destroy)
      relay := None
    },
  },
)

API

type instance

Opaque handle for the BaseInstrument this reference. Treat it as a key for per-instance state (e.g. in a WeakMap).

type spec

type spec = {
  templateID: string,
  onConnected?: instance => unit,
  onDisconnected?: instance => unit,
  onUpdate?: instance => unit,
}

• templateID — the HTML template identifier MSFS looks up.
• onConnected — runs after super.connectedCallback().
• onDisconnected — runs before super.disconnectedCallback().
• onUpdate — runs after super.Update() every sim tick.

Instrument.define(name, spec): unit

Registers the subclass with MSFS. Call once at module load.