On Feb 16, 2013, at 11:57 AM, Mark S. Miller wrote:
> Allen, by "put:", did you mean "set:"?
>
aaaaarrrrrrrggg..... to much vacation.....
yes, of course, it should be "set" in which case the exception does occur as it
should in FF.
Allen
>
> On Sat, Feb 16, 2013 at 10:51 AM, Allen Wirfs-Brock <al...@wirfs-brock.com>
> wrote:
>
> On Feb 15, 2013, at 6:30 PM, Jeff Walden wrote:
>
>> Consider:
>>
>> Object.defineProperty(Object.prototype, "0", { value: 17, writable: false,
>> configurable: false });
>> [].push(42);
>>
>> Per ES5, I think this is supposed to throw a TypeError. The push should be
>> setting property "0" with Throw = true, which means that when [[CanPut]]
>> fails, a TypeError gets thrown. No engine I can test does this, I suspect
>> because everyone's mis-implemented an optimization.
>
> Right, ES5 carefully put in all those Throw = true's, to account for exactly
> those situations. Did you also test for non-writable and accessor
> properties on an actual Array instance.
>
> Did you try this on IE9/10 (I don't have copies available with me right now).
> All the other browsers had implementations of push and other Array methods
> that predate ES5, so it is conceivable that those implementations have not
> been updated to match the spec. IE9, on the other-hand, was a new
> implementation that post dates ES5 and was supposed to be following the spec.
>
> I'm shocked if Test262 doesn't include any tests for these situations. I'm
> remember including them in a list of things that needed to be tested for all
> of the Array methods that was handed off to the team that wrote the Test262
> tests.
>
>>
>> On IRC it was pointed out that
>> http://wiki.ecmascript.org/doku.php?id=strawman:fixing_override_mistake is
>> supposed to fix this: you should be able to shadow a non-writable property
>> on a prototype. Or something. But there's contention there about this not
>> actually being a mistake. (I think that contention's probably right, for
>> what it's worth, but I digress.)
>>
>> But suppose it isn't, for the moment. What then of this:
>>
>> Object.defineProperty(Object.prototype, 0, { set: function() { throw
>> "FAIL"; } });
>> [].push(42)
>>
>> I think this should throw, again because it's *setting* property "0". But
>> again, no engine I can test actually throws for this.
>>
>> My gut says this is a case where every engine attempted to optimize, and
>> optimized wrongly such that incorrect semantics resulted. The question is,
>> since no engine's following the spec, whether the spec should change, the
>> engines should change, or what. Given that indexed properties on
>> Array.prototype and Object.prototype are not something anyone sane does, I
>> tend to think changing it to [[DefineOwnProperty]] would be good. But maybe
>> the spec really should win, and everyone should change. I dunno. Please
>> sort this out! :-)
>
> Prior to ES5, implementations were doing various random things for the edge
> cases of accessor properties in arrays. ES5 now tells them what they are
> supposed to do.
>
> Note that implementation bugs aren't just in the Array methods and don't
> require access to inherited properties. I just tried the following in a
> FF18 scratch pad:
>
> var a = []
>
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
>
> */
>
> a[1]=0
> /*
> 0
> */
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
>
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
>
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
> var a = []
> Object.defineProperty(a, "1", {
>
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
>
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
>
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
>
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
>
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
>
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
>
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
>
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
>
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
> var a = []
> Object.defineProperty(a, "1", {
>
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
>
> */
>
> var a = []
> Object.defineProperty(a, "1", {
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
> */
>
>
> Note that no exception was reported on the [[Put]] to the accessor.
>
> Allen
> var a = []
> Object.defineProperty(a, "1", {
>
> get: function() {throw "get"; return "got 1"},
> put: function(v) {throw "put"+v},
> configurable: true});
>
> a[1]
> /*
> Exception: get
> */
>
> a[1]=0
> /*
> 0
>
> */
>
>
>>
>> Jeff
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss@mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
>
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>
>
>
> --
> Cheers,
> --MarkM
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