为什么push方法比在Javascript中通过数组索引放置值要慢得多

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 - 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。请参阅和 - 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

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！