Violations of internal method invariants?

Jason Orendorff jason.orendorff at gmail.com
Thu Jul 31 06:26:22 PDT 2014


On Thu, Jul 31, 2014 at 1:23 AM, Boris Zbarsky <bzbarsky at mit.edu> wrote:
> And the Web IDL spec has yet another approach to this whole thing: It simply
> coerces "configurable" to true in its custom [[DefineOwnProperty]] for these
> sorts of objects (but keeps effectively separate namespaces).

Interesting. This approach doesn't seem quite kosher.

ES6 lists some invariants here that apply to all objects, even host objects:
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-invariants-of-the-essential-internal-methods

There's not a rule that says flat-out, "If Desc.[[Configurable]] is
false and [[DefineOwnProperty]](P, Desc) returns true, that counts as
'observing' the property P as a non-configurable property on the
target." but if you take that as read, what WebIDL is doing here is
banned.

Note that steps 14-22 of 9.5.6 (Proxy#[[DefineOwnProperty]]) do some
checks which enforce this rule.
http://people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-defineownproperty-p-desc

Tom, can the prose be improved? What's the intent?

-j


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