SameValueZero comparator and compatibility

Mark S. Miller erights at
Tue Jan 21 10:03:40 PST 2014

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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