`in` operator regression for actions

[getkey]

Bug report

• I've checked documentation and searched for existing issues
• I've made sure my project is based on the latest MST version not applicable
• Fork this code sandbox or another minimal reproduction.

Sandbox link or minimal reproduction code

https://stackblitz.com/edit/in-regression-mobx-state-tree?file=index.html

import { types } from "mobx-state-tree";

const User = types
  .model({
    name: ""
  })
  .actions(self => ({
    setName(name) {
      self.name = name;
    }
  }));

const john = User.create();
console.log("This should be true:", "setName" in john);

Describe the expected behavior

The in operator should detect actions. I've observed that the regression appeared somewhere between version 4.0.2 and 4.0.3.

Describe the observed behavior

The in operator doesn't detect actions on instances of the model.

[iChenLei]

Diff v4.0.2 with v4.0.3

Github code diff link
The main code change in packages/mobx-state-tree/src/utils.ts

- import { isObservableArray, $mobx, getAtom } from "mobx"
+ import { isObservableArray, _getGlobalState, getAtom } from "mobx"

- export const mobxShallow =
-     typeof $mobx === "string" ? { deep: false } : { deep: false, proxy: false }
+ export const mobxShallow = _getGlobalState().useProxies
+    ? { deep: false }
+     : { deep: false, proxy: false }

The $mobx in mobx6 is a Symbol

  export const $mobx = Symbol("mobx administration")

🔥 When we use modern browser which support Proxy 🔥

typeof $mobx === "string" is false in v4.0.2
_getGlobalState().useProxies is true in v4.0.3

v4.0.2 mobxShallow = { deep: false, proxy: false }

v4.0.3 mobxShallow = { deep: false }

Reproduction Example

v4.0.2 The john object is a plain object

v4.0.3 The john object is a Proxy object Proxy MDN doc

Mobx Proxy process code: mobx/packages/mobx/src/types/dynamicobject.ts

    has(target: IIsObservableObject, name: PropertyKey) {
        if (name === $mobx || name === "constructor") return true
        if (__DEV__ && globalState.trackingDerivation)
            warnAboutProxyRequirement(
                "detect new properties using the 'in' operator. Use 'has' from 'mobx' instead."
            )
        const adm = getAdm(target)
        // MWE: should `in` operator be reactive? 
        // If not, below code path will be faster / more memory efficient
        // check performance stats!
        // if (adm.values.get(name as string)) return true
        if (isStringish(name)) return adm.has_(name)
        return (name as any) in target
    }

So when we use v4.0.3 console.log('setName' in john); will print false in console....
Hope my analysis is helpful. @jamonholmgren @getkey

[airhorns]

I think this is an issue for views too, not just actions. I can confirm it only happens for me when proxies are used. Is this maybe a plain mobx bug?

[iChenLei]

@airhorns @getkey It's existing Mobx6 issue
Mobx Github discussions

[urugator]

It has nothing to do with enumerability, but should be fixed by:
mobxjs/mobx#2641

[urugator]

Should work with MobX 6.1.* (MST > 5.0.1)

[iChenLei]

https://stackblitz.com/edit/in-regression-mobx-state-tree-lng8z9

Yes, fixed by PR 2641!

[getkey]

Awesome, thanks @urugator! Closing this issue.