Here is another test case, with [[GetOwnPropertyDescriptor]]:
```js
var target = Object.seal({x: 2});
var proxy = new Proxy(target, {
getOwnPropertyDescriptor(o, p) {
var d = Reflect.getOwnPropertyDescriptor(o, p)
if (d && 'writable' in d)
d.writable = false
return d
}
});
Object.getOwnPropertyDescriptor(proxy, 'x'); // { value: 2, writable: false,
configurable: false }
Object.defineProperty(proxy, 'x', { value: 3 })
Object.getOwnPropertyDescriptor(proxy, 'x'); // { value: 3, writable: false,
configurable: false }
```
IMHO, the most robust fix is the following: Both the [[DefineOwnProperty]] and
the [[GetOwnPropertyDescriptor]] contain the following check:
* If IsCompatiblePropertyDescriptor(extensibleTarget, resultDesc, targetDesc)
is false, throw a TypeError exception.
I think there should be also the following check (except when targetDesc is
undefined, in which case another appropriate check is used):
* If IsCompatiblePropertyDescriptor(extensibleTarget, targetDesc, resultDesc)
is false, throw a TypeError exception.
That would replace the weaker adhoc check about the [[Configurable]] attribute
(search for settingConfigFalse) in those algorithms.
(Alternatively, in order to avoid double checks, define an
AreBothWaysCompatiblePropertyDescriptors(extensibleTarget, desc1, desc2)
abstract operation.)
—Claude
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