没有继承属性的for-in与Object.keys forEach [英] for-in vs Object.keys forEach without inherited properties

问题描述

我正在查看具有普通对象的Object.keys + forEach与for-in的性能基准.

I was looking at a perf benchmark of Object.keys + forEach vs for-in with normal objects.

此基准表明Object.keys + forEach是比for-in方法慢62％.但是，如果您不想获得继承的属性，该怎么办? for-in包括所有非本地继承的对象，因此我们必须使用 hasOwnProperty 进行检查.

This benchmark shows that Object.keys + forEach is 62% slower than the for-in approach. But what if you don't want to get the inherited properties? for-in includes all non-native inherited objects, so we'll have to use hasOwnProperty to check.

我尝试制作另一个 在此处进行基准测试 正是这样做的.但是，现在for-in方法比Object.keys + forEach慢 41％.

I tried to make another benchmark here doing exactly that. But now the for-in approach is 41% slower than Object.keys + forEach.

更新

以上测试是在Chrome中完成的.再次进行了测试，但是使用Safari，结果却有所不同:Object.keys(..).forEach(..) 34% slower，很奇怪.

The above test was done in Chrome. Tested it again but with Safari and I'm getting different results: Object.keys(..).forEach(..) 34% slower, odd.

注意:我进行基准测试的原因是要检查 Node.js 的情况.

问题:

• Chrome 的jsperf结果对 Node.js 是否有意义?
• 发生了什么事，单一条件如何使for-in方法比 Chrome 中的Object.keys + forEach慢 41％?

• Are the jsperf result for Chrome considerable for Node.js?
• What happened, how come a single conditional made the for-in approach 41% slower than Object.keys + forEach in Chrome?

推荐答案

node.js使用V8，尽管我认为它与Chrome当前版本不同，但我认为它很好地表明了节点在该主题上的性能

node.js uses V8, although I guess it's not the same as the current version in Chrome, but I guess it's a good indicator of node's performances on the subject.

其次，您使用的是forEach，它在开发时非常方便，但每次迭代都会添加一个回调，这是一个(相对)冗长的任务.因此，如果您对表演感兴趣，为什么不只使用普通的for循环呢?

Secondarily, you're using forEach, which is quite handy when developing but adds a callback for every iteration, and that's a (relatively) lenghty task. So, if you're interested in performances, why don't you just use a normal for loop?

for (var i = 0, keys = Object.keys(object); i < keys.length; i++) {
    // ...
}

这将产生您可以获得的最佳性能，同时也解决了Safari中的速度问题.

This yields the best performances you can get, solving your speed problems in Safari too.

简而言之:不是条件，而是对hasOwnProperty的调用才有所不同.您每次迭代都在执行一个函数调用，所以这就是for...in变慢的原因.

In short: it's not the conditional, it's the call to hasOwnProperty that makes a difference. You're doing a function call at every iteration, so that's why for...in becomes slower.

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