JavaScript for ... in vs for [英] JavaScript for...in vs for

问题描述

你认为for in和for循环有很大的不同吗？您更喜欢使用什么样的for以及为什么？

Do you think there is a big difference in for...in and for loops? What kind of "for" do you prefer to use and why?

假设我们有一组关联数组：

Let's say we have an array of associative arrays:

var myArray = [{'key': 'value'}, {'key': 'value1'}];

所以我们可以迭代：

for (var i = 0; i < myArray.length; i++)

并且：

for (var i in myArray)

我没有看到很大的区别。是否存在任何性能问题？

I don't see a big difference. Are there any performance issues?

推荐答案

选择应基于最能理解的习语。

The choice should be based on the which idiom is best understood.

使用以下函数迭代数组：

An array is iterated using:

for (var i = 0; i < a.length; i++)
   //do stuff with a[i]

一个对象是用作关联数组的方法是使用：

An object being used as an associative array is iterated using:

for (var key in o)
  //do stuff with o[key]

除非你有惊天动地的原因，否则请坚持既定的使用模式。

Unless you have earth shattering reasons, stick to the established pattern of usage.

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