Comment #30 on issue 164 by charles.kendrick: Wrong order in Object
properties interation
http://code.google.com/p/v8/issues/detail?id=164
Precisely, this is an "optimization" used to score better in synthetic
benchmarks, while real-world performance will actually be degraded.
And not just performance. Say you are dynamically providing the set of
options for a drop-down list in JavaScript. Essentially all Ajax widget
kits have such an API, and usage is generally:
selectControl.setOptions({
storedValue1 : "displayValue1",
storedValue2 : "displayValue2",
storedValue3 : "displayValue3"
})
Now we're going to be telling all of customers and users "If you want to
support the Chrome browser, you must change your code to":
selectControl.setOptions(
["storedValue1",
"storedValue2",
"storedValue3"],
["displayValue1",
"displayValue2",
"displayValue3"]
})
This:
1. is awkward and unnatural, it doesn't correspond to how a list of options
is specified in HTML
2. involves *double* the number of GC-tracked objects (6 strings and 2
Arrays vs one Object and 3 Strings - slots don't GC)
3. requires code to track, store and update two objects to represent an
ordered Map instead of just one
So let's please connect the dots here - we've got several optimization
experts talking about how this provides a great speed boost *for Arrays*,
and several application developers pointing out that if it's applied *to
Objects* it breaks existing applications and will degrade performance in
the real world.
Solution: be order-preserving for Object, not order-preserving for Arrays.
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