为什么 push 方法比通过 Javascript 中的数组索引放置值慢得多 [英] Why push method is significantly slower than putting values via array indices in Javascript

问题描述

我很不明白为什么要进行此测试:

.

除此之外，对 push 的方法调用可能会有一些开销，与使用 for 循环的索引相比，确定当前数组长度可能需要更多时间.

通常有没有理由不使用push - 该方法正是为了该操作并使某些代码更易于阅读.虽然有些人认为一个版本比另一个版本更快，但两者都在浏览器中进行了同样的优化.请参阅 为什么 array.push 有时比 array[n] 快 =值? 和 在添加到数组时使用 push 方法或 .length? - 结果差异如此之大，以至于其实无关.使用更容易理解的内容.

I pretty don't understand why this test :

http://jsperf.com/push-method-vs-setting-via-key

Shows that

 a.push(Math.random());

is over ten times slower than

 a[i] = Math.random();

Could you explain why this is the case ? What magic "push" do that make it so slow ? (or so slow compared to other valid method of doing that).

EDIT

NOTE: The push test is biased. I increase size of the array every iteration! Read carefully accepted answer!

解决方案

Could you explain why this is the case?

Because your test is flawed. The push does always append to the existing a array making it much larger, while the second test does only use the first 1000 indices. Using the setup is not enough here, you would have to reset the a array before every for-loop: http://jsperf.com/push-method-vs-setting-via-key/3.

Apart from that, the method call to push might have a little overhead, and determining the current array length might need additional time compared to using the index of the for-loop.

Usually there is no reason not to use push - the method is there for exactly that operation and makes some code easier to read. While a few people think one version is faster than the other, both are equally optimized in browsers. See Why is array.push sometimes faster than array[n] = value? and Using the push method or .length when adding to array? - results vary so wide that it's actually irrelevant. Use what is better to understand.

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