Any performance benefit to “locking down” JavaScript objects?

Question

JavaScript 1.8.5 (ECMAScript 5) adds some interesting methods that prevent future modifications of a passed object, with varying degrees of thoroughness:

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Answer 1

Update: Since this answer was originally written, the bug in V8 that caused this issue has been fixed. See the answer by Jan Molak for more info.

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In Google Chrome (so V8, that is), a frozen object iterates 98% slower than a regular object.

http://jsperf.com/performance-frozen-object

Test name*              ops/sec

non-frozen object    32,193,471
frozen object           592,726

Probably this is because those functions are relatively new and probably not optimized yet (but that's just my guess, I honestly don't know the reason).

Anyhow, I really do not recommed using it for performance benefits, as that apparently does not make sense.

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* The code for the test is:

var o1 = {a: 1};
var o2 = {a: 1};

Object.freeze(o2);

Test 1 (non-frozen object):

for(var key in o1);

Test 2 (frozen object):

for(var key in o2);