Javascript:为什么对数组使用 for 循环而不是 for-in 循环？

Question

我一直在阅读 Stoyan Stefanov 的《面向对象的 Javascript》，有一次他写道:

The for-in loop is used to iterate over the element of an array (or an object, as we'll see later). This is it's only use; it can not be used as a general-purpose repetition mechanism that replaces for or while. Let's see an example of using a for-in to loop through the elements of an array. But bear in mind that this is for informational purposes only, as for-in is mostly suitable for objects, and the regular for loop should be used for arrrays.

我过去在迭代数组元素时一直使用 for 循环，我通常看到的是 for 循环而不是 for-in 循环用于此目的，但是“常规 for 循环应该用于数组”的原因是什么？

Answer 1

对数组使用常规 for 循环的原因是它将迭代限制为索引值。

如果您使用 for-in 循环，它将遍历对象的所有属性(数组是对象)，如果您将任意属性附加到数组，可能会给您带来意想不到的结果没有数字索引。