Conflict on Enumerable: false

If Enumerable is false:

• It will break current behavior of JSON.stringify(), for ... in, Object.keys(), Object.values(), and Object.entries() on errors with "manualy" set code properties.
• It will limit one of the key advantage (in my opinion) of this code property as it won't be propagated in logs by default (the error message only is propagated because developers painfuly learned to extract it manually instead of relying on default JSON stringify behavior)

We may have a look on how the code property is used in the mentioned libraries, but it is impossible to know how it is used by those library consumers worlwide, not even talking about application level defined code properties

Even if the purpose is good, I do think it is very ambitious to try add constraints on a such commonly used Error property name and probably incompatible with the W3C mantra "Don't break the Web", maybe another property name would be more appropriate

Conflict

Current behavior

const err = new Error('foo')
err.code = 'ERR_FOO' 
// or const err = Object.assign(new Error('foo'), { code: 'ERR_FOO' })
JSON.stringify(err) // '{"code":"ERR_FOO"}'

Behavior with Enumerable false

const err = new Error('foo')
Object.defineProperty(err, 'code', { value: 'ERR_FOO', enumerable: false })
JSON.stringify(err) // '{}'

No files or tests are named. Start with the current and proposed JSON.stringify(), for...in, Object.keys(), Object.values(), and Object.entries() examples in the issue, then review the compatibility concern and define an agreed resolution for the property's enumerability; done requires a documented proposal decision.