Mobx: toJS does not deeply convert to POJO when top level object isObservable === false

[capaj]

this tape test reproduces the behaviour that surprised me:

test("toJS toplevel not observable", t => {
    const a = mobx.observable({ x: null, y: 3 });
    const arr =[a]
    const res = mobx.toJS(arr);
    t.equal(mobx.isObservable(res[0]), false);
    t.end();
})

I think we should always traverse the whole object when doing toJS() even if the top level object is not observable. This is the behaviour that would match it's counterpart- observable which always makes everything observable.

What do you think @mweststrate ? Can I prepare another PR?

[jeffijoe]

Having the same issue I believe (v2.7.0)

[urugator]

observable which always makes everything observable.

Actually that isn't entirely true ... if the object is observable already, it's not traversed.
So toJS behavior is somehow complementary to this - if the object isn't observable already, it's not traversed:

const Mobx = require("mobx");
const ob = Mobx.observable({
  arr: Mobx.asReference([])
});
console.log(Mobx.isObservable(ob.arr)); // false
Mobx.observable(ob);
console.log(Mobx.isObservable(ob.arr)); // still false

const nonOb = {
  arr: Mobx.observable([])
};  
console.log(!Mobx.isObservable(nonOb.arr)); // false
Mobx.toJS(nonOb)
console.log(!Mobx.isObservable(nonOb.arr)); // still false
// read !Mobx.isObservable as isJS()

EDIT:
Maybe Mobx could support implementing:
[mobx.Symbol.observable] (following TC39 Observables syntax)
and
[mobx.Symbol.toJS]
they would be used by observable/toJS during conversion if defined.

[capaj]

@urugator good point. Haven't thought of that.

[mweststrate]

@capaj the behavior has changed in 2.7 indeed, as toJS only walks the observable parts of a tree, until something is non-observable. This fixes issues related to accidentally trying to clone referred concepts, see e.g. #377 and several other issues as well. A generic clone function is not really the domain of MobX, but rather should lodash be used for such problems (in combination with toJS for example).

@jeffijoe toJS_legacy can be used in 2.7 to get the old behavior still.