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:

• Object.preventExtensions(obj)
• Object.seal(obj)
• Object.freeze(obj)

Presumably the main point of these is to catch mistakes: if you know that you don't want to modify an object after a certain point, you can lock it down so that an error will be thrown if you inadvertently try to modify it later. (Providing you've done "use strict"; that is.)

My question: in modern JS engines such as V8, is there any performance benefit (eg, faster property look-ups, reduced memory footprint) in locking down objects using the above methods?

(See also John Resig's nice explanation – doesn't mention performance, though.)

Answer 1

There's been no difference in performance since at least Chrome 47.0.2526.80 (64-bit).

Testing in Chrome 6.0.3359 on Mac OS 10.13.4 ----------------------------------------------- Test               Ops/sec non-frozen object  106,825,468  ±1.08%  fastest frozen object      106,176,323  ±1.04%  fastest 

Performance test (available at http://jsperf.com/performance-frozen-object):

  const o1 = {a: 1};   const o2 = {a: 1};    Object.freeze(o2);    // Non-frozen object:   for(var key in o1);    // Frozen object:   for(var key in o2); 

Update 30.10.2019: There's no difference in performance on Chrome 78.0.3904 (64-bit)

Update 17.09.2019: There's no difference in performance on Chrome 76.0.3809 (64-bit)

Update 03.05.2018: There's no difference in performance on Chrome 66.0.3359 (64-bit)

Update 06.03.2017: There's no difference in performance on Chrome 56.0.2924 (64-bit)

Update 13.12.2015: There's no difference in performance on Chrome 47.0.2526.80 (64-bit)

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With Chrome 34, a frozen object performs slightly better than a non-frozen one in @pimvdb's test case (results below). The difference, however doesn't seem to be large enough to justify using this technique for performance benefits.

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

Testing in Chrome 34.0.1847.116 on OS X 10.9.2 ---------------------------------------------- Test               Ops/sec non-frozen object  105,250,353  ±0.41%  3% slower frozen object      108,188,527  ±0.55%  fastest 

Running @kangax's test cases shows that both versions of the object perform pretty much the same:

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

Testing in Chrome 34.0.1847.116 on OS X 10.9.2 ---------------------------------------------- Test               Ops/sec non-frozen object  832,133,923  ±0.26%  fastest frozen object      832,501,726  ±0.28%  fastest 

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

Testing in Chrome 34.0.1847.116 on OS X 10.9.2 ---------------------------------------------- Test               Ops/sec non-frozen object  378,464,917  ±0.42%  fastest frozen object      378,705,082  ±0.24%  fastest