Boris, this is why I also took care to mention that for..in iteration on Arrays should remain
unordered, so that developers doing relatively obscure things like crypto evoting in JavaScript
(the use case in the first bug) still have access to a dense-array implementation.
Best of both worlds: Object does what you would expect, Array has optimizations for obscure use
cases.
Last point below.
----------
== Objections and counter-arguments
1. Array for..in iteration order has always been inconsistent across browsers
Yes, this is true. I am proposing only that Object preserves insertion order,
not Array.
No developers or sites rely on Array for..in iteration order, since it was
never consistent.
If Array for..in iteration continues to be unordered, any developer that cares
about the tiny
performance difference can use an Array to store non-numeric property/value
pairs.
-----------
On 3/10/2011 6:11 PM, Boris Zbarsky wrote:
On 3/10/11 9:00 PM, Charles Kendrick wrote:
People use Objects as classes, instances, "associative arrays" / Maps,
etc. Numeric keys are a tiny minority and there would be no measurable
performance gains for special treatment of such keys *on Object*.
You may want to read <https://bugzilla.mozilla.org/show_bug.cgi?id=594655> and
<https://bugzilla.mozilla.org/show_bug.cgi?id=611423>. People are running into
performance
issues due to lack of such special treatment today.
Now maybe these people are just doing dumb things they shouldn't be doing, but
that doesn't
make the performance differences observed on those tests "not measurable".
However because frameworks have to deal with all possible keys, we end
up with a much, much more expensive data structure that has to be used
just because numeric keys are being treated specially.
I agree this is an issue. I just think you're underestimating the performance
drag of
preserving numeric property order for vanilla Objects.
-Boris
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