host.ts

// gc impl
import { flush, js_string, setMemory, spectest } from "./js_string.ts";

const { instance: { exports } } = await WebAssembly.instantiateStreaming(
  fetch(new URL("../target/wasm-gc/release/build/main/main.wasm", import.meta.url)),
  {
    js_string,
    spectest,
    js: {
      setTimeout, clearTimeout,
      setInterval, clearInterval,
      run(fn: any) {
        return fn();
      }
    },
    "moonbit:ffi": {
      make_closure(funcref: any, context: any) {
        // console.log("make_closure", funcref, context);
        return funcref.bind(null, context)
      }
    },
  }
);

const {
  run,
  _start,
  take_js_and_run,
  ["moonbit.memory"]: memory,
} = exports as any;

_start();

setMemory(memory);

run();
take_js_and_run(() => {
  console.log("call me");
});

flush();

new_ffi.mbt

fn set_timeout(cb : () -> Unit, timeout : Int) -> Int = "js" "setTimeout"

fn clear_timeout(tid : Int) -> Unit = "js" "clearTimeout"

type JsFunc

fn run_js(js_fn : JsFunc) -> Unit = "js" "run"

pub fn run() -> Unit {
  let tid = set_timeout(fn() { println("never called") }, 100)
  clear_timeout(tid)
  let _ = set_timeout(fn() { println("timeout called") }, 100)
  ()
}

pub fn take_js_and_run(func : JsFunc) -> Unit {
  run_js(func)
}