为什么push方法比在Javascript中通过数组索引放置值要慢得多 [英] Why push method is significantly slower than putting values via array indices in Javascript

问题描述

我很不明白为什么这个测试：

。

除此之外，调用 push 的方法可能有与使用for循环的索引相比，确定当前数组长度可能需要额外的时间。

通常有没有理由不使用 push - 该方法可以完全实现该操作，并使一些代码更容易阅读。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同样优化。请参阅为什么array.push有时比array [n] =更快=值？和在添加到阵列时使用push方法或.length？ - 结果变化如此之大以至于实际上无关紧要。 使用更好的理解。

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.

这篇关于为什么push方法比在Javascript中通过数组索引放置值要慢得多的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！