SameValueZero comparator and compatibility

Andrea Giammarchi andrea.giammarchi at
Tue Jan 21 14:09:48 PST 2014

I wish there was an answer to that too ... if implementors are confused,
how could developers even think about contributing there?

I have expressed already my wishes for a "Test Driven Development" of JS
specs/features but I find myself unable to help.

Any hint would be appreciated. Thanks

On Tue, Jan 21, 2014 at 10:03 AM, Mark S. Miller <erights at> wrote:

> The most reliable way to get the implementations to conform is to
> contribute a test262 test.
> As for how to contribute a test262 test, I am still confused about the
> situation and leave it for others to comment.
> On Tue, Jan 21, 2014 at 9:58 AM, Brandon Benvie <bbenvie at>wrote:
>> The implementations of Maps and Sets in the wild that I am aware of
>> (IE11, SpiderMonkey, and V8 behind a flag) all currently use SameValue as
>> comparator while the spec calls for SameValueZero. It seems like either the
>> implementations need to update (quickly) to match the spec. before too much
>> code depends on this, or the spec should be changed to match the
>> implementation reality.
>> This discrepancy has the potential to make for some hard to trace bugs,
>> due to the otherwise near-invisibility of the -0/0 difference. Regardless
>> of the merits of each comparator, I think at this point it's more important
>> that everyone (implementers + spec.) is following the same marching orders.
>> _______________________________________________
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> --
>     Cheers,
>     --MarkM
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