computed with ifavailable cause Error

[doxiaodong]

Intended outcome:
cause by Reflect.ownKeys
it is seem broken with JSON.stringify

Actual outcome:

How to reproduce the issue:
https://codesandbox.io/s/multi-selection-forked-vdjqn?file=/src/index.tsx

Versions

mobx@6.0.4
useProxies: 'ifavailable'

[urugator]

Minimal repro:

const o = observable({});
autorun(() => {
  JSON.stringify(o);
})

Possible solutions:
a) Don't warn
b) Force user to provide own toJSON or to use other means for conversion
c) When proxies are not available, add default toJSON to every observable object

[urugator]

Btw toJS has the same problem

[mweststrate]

This behavior is correct, as JSON.stringify would behave differently indeed a non proxy environment, and this error is an early warning for it. toJS should ideally not suffer from the same thing as it could default to using mobx own iteration mechanism. Feel free to file a separate issue for that.

[doxiaodong]

But same code work fine with mobx@5

[urugator]

Mobx5 required proxy support - it would not work at all in env without proxies, you had to use Mobx4 instead.
Mobx6 lets you decide - by configure({ useProxies: "ifavailable" }), you're saying - this code should work in any environment, but if available use proxies as internal implementation. So mobx will warn anytime your code would break in non-proxy env.

[doxiaodong]

Yes, Mobx4 and Mobx5 is fine with JSON.stringify , but Mobx6 with configure({ useProxies: "ifavailable" }) is not. That means it's a breaking. By the way, I think it's better to throw warn for all cases of useProxies

[mweststrate]

It's breaking because it would break if you would run this code on Internet Explorer, just as this would break on Internet Explorer if you were running this very same code with MobX5 on Internet Explorer. Please read the conversation again, it errors because you configured it to error as an early warning this will not run on older browsers. If you want the MobX 4 behavior, put it on useProxies: "never".

[urugator]

@doxiaodong In Mobx4 JSON.stringify may not work correctly - if you add or delete prop from the object it would NOT notify the computed. We don't warn in Mobx4, because the warning only works when proxies are available and Mobx4 does not have a proxy based implementation at all - so we simply don't have a way to warn in Mobx4 - but the code is still potentially broken (depends on usage).

[doxiaodong]

Thanks，I use always for proxy.