Version: V8 version 7.1.78


`for-in` is inconsistent about whether it hits properties which are non-enumerable and shadow enumerable properties of the same name further up the prototype chain.

Compare:


```

let base = { prop: 0 };

let derived = Object.create(null, {
  prop: { enumerable: false, configurable: true, value: 0 },
});

Object.setPrototypeOf(derived, base);


for (let key in derived) {
  console.log(key);
}
```


vs


```
let base = { prop: 0 };

let derived = Object.create(base, {
  prop: { enumerable: false, configurable: true, value: 0 },
});


for (let key in derived) {
  console.log(key);
}
```


The first of these prints 'prop', the second nothing. But they're enumerating over objects with _exactly_ the same shape; the only difference is whether the object is created with its prototype already in place or has its prototype set afterwards.

It's hard to say which if either of these are wrong, since the spec text here [1] is quite difficult to interpret. But it seems very odd that they should be inconsistent.

See also (and please comment on) this open spec bug [2] about more precisely specifying the behavior of for-in, which prompted the investigation which lead me to discovering this.

[1] https://tc39.github.io/ecma262/#sec-enumerate-object-properties

[2] https://github.com/tc39/ecma262/issues/1281