Instances of global classes not observable

Test case:

https://runkit.com/scriptspry/observer-utils-global-definitions-not-observable

---

const {observable, observe, isObservable} = require('@nx-js/observer-util');

class Counter {
    constructor() { this._count = 0 }
    increment() { this._count += 1 }
    decrement() { this._count -= 1 }
}

const c = observable(new Counter());
console.log('c', isObservable(c));

global.Counter = Counter;
const c2 = observable(new Counter());
console.log('c2', isObservable(c2));

[solkimicreb]

Hi!

That’s intended, but it is a dirty hack and it should be changed. I introduced this in the latest patch (4.1.2). The reason:

Built-in JS objects can not be wrapped with Proxies because of their ‘internal slots’. They throw an ‘Invalid Invocation’ error when you try to call their methods on the wrapping Proxy. To work around this I had to do two things.

1. Instrument stateful built-in objects - like Map and Set - with monkey patching instead of Proxies.
2. Opt-out stateless built-in objects from the Proxy wrapping, since there is not state to observe and and it would throw errors.

To do the latter I need an algorithm, which detects built-in Objects. At first I tried to maintain a list, since there or not so many standard JS built-ins. I failed to do this though, because this lib supports both NodeJS and browsers, which have a lot of different built-ins. I got issues about illegal invocation error on WebAudio objects (browser built-in) for example. Maintaining a list of all browser and NodeJS built-ins is not feasible, so I decided to do the current dirty detection. I check if the object constructor is available on the global Object, since all built-ins are global.

This should swapped with a more elegant algorithm, but I couldn’t find any. I will keep thinking about this and change it soon and I am open to any suggestions, ideas and PRs.

I hope this made the issue clear. Thanks for the issues 🙂 (I won’t be around during the weekend.)

[scriptspry]

On second thought, I don’t think that will work, It will just check for things in Window but not things like Map, Array etc. which are what need to be skipped. I have no other ideas. Perhaps posting on stackoverflow may help us.

EDIT: posted too soon. I think this might still work. Object.keys(frame.contentWindow) didn’t have Map, Array etc. but ‘Array’ in frame.contentWindow is true. So that might just work.