Qt Promise VS last fn as arg

qt-promise.md

I've found it quite "disturbing" in 2026 there are APIs that wouldn't use Promise and accept a last argument as function to retrieve data, see: https://doc.qt.io/qt-6/qtwebchannel-javascript.html#interacting-with-qobjects

Here an easy way to workaround that, where equality of the method is preserved and things would look more modern or easier to reason about.

const { apply } = Reflect;
const { create } = Object;

const wm = new WeakMap;

const promise = fn => function (...args) {
  return new Promise((res, rej) => {
    args.push(res);
    try {
      apply(fn, this, args);
    }
    catch (err) {
      rej(err);
    }
  });
};

const handler = {
  get(target, prop) {
    const value = target[prop];
    if (typeof value === 'function') {
      const fns = wm.get(target);
      return fns[prop] ?? (fns[prop] = promise(value));
    }
    return value;
  },
};

const qtProxy = target => {
  if (!wm.has(target)) wm.set(target, create(null));
  return new Proxy(target, handler);
};

Using qtProxy(qtReference) would return a proxy able to provide methods that could be simply awaited when needed.

Use the classic method(1, 2, 3).then(result => { ... }) instead when/if awaiting is not desired.

// example
const foo = qtProxy(channel.objects.foo);
const result = await foo.myMethod(arg1, arg2);
console.log(result); // 'done'