任何性能上的好处是“锁定"了虚拟机. JavaScript对象? [英] Any performance benefit to "locking down" JavaScript objects?

问题描述

JavaScript 1.8.5(ECMAScript 5)添加了一些有趣的方法，防止将来对所传递的对象进行修改，并具有不同程度的完整性:

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

大概这些要点是捕捉错误:如果您知道不想在某个点之后修改对象，则可以将其锁定，以便在无意中尝试修改时抛出错误以后再说. (证明您已经完成了"use strict";.)

我的问题:在现代JS引擎(例如V8)中，使用上述方法锁定对象是否有任何性能优势(例如，更快的属性查找，更少的内存占用)?

(另请参见约翰·雷西格的漂亮解释 –不会提及性能.)

解决方案

至少从Chrome 47.0.2526.80(64位)开始，性能一直没有差异.

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

性能测试(位于 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);

更新30.10.2019 :Chrome 78.0.3904 (64位)

的性能没有差异

更新17.09.2019 :Chrome 76.0.3809 (64位)上的性能没有差异

更新03.05.2018 :Chrome 66.0.3359 (64位)上的性能没有差异

更新06.03.2017 :Chrome 56.0.2924 (64位)

的性能没有差异

2015年12月13日更新:Chrome 47.0.2526.80 (64位)上的性能没有差异

---

使用Chrome 34，在@pimvdb的测试案例中，冻结对象的性能要比非冻结对象好一些(结果如下).但是，差异似乎还不够大，不足以证明使用此技术可获得性能上的好处.

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

运行@kangax的测试用例表明，该对象的两个版本执行的功能几乎相同:

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-性能冻结对象实例

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

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.)

解决方案

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)

---

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

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