Yes, great performance enhancements are available for *Arrays* - but this is not relevant
because as I explicitly stated, I am not suggesting anything be clarified or standardized with
respect to for..in order for Arrays.
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*.
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.
This means that the real-world, application-level impact of not preserving order is *slower*
applications.
On 3/10/2011 5:48 PM, Boris Zbarsky wrote:
On 3/10/11 8:44 PM, Charles Kendrick wrote:
It requires
browser vendors to implement order preservation, such that we don't get
the minor
optimization that's possible from not preserving order at all.
For what it's worth, not preserving order for numeric properties allows
optimizations that are
decidedly not "minor".
You can compare the performance of "fast" and "slow" arrays in Spidermonkey to
see the difference.
-Boris
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