JavaScript数组迭代 - MDN示例 [英] JavaScript array iteration - MDN example

问题描述

  
 
在MDN网站上阅读JavaScript的重新介绍， for（var i = 0，item; item = a [i ++];）{
 //用
做一些事情} 
  

其中a []是一个正在循环的数组。

我对item将在第一次迭代。当i = 0且item最初是未定义的，那么当它被赋值为[i ++]时，迭代不会从i = 1开始，这意味着迭代将从a [ ]数组 - > a [1]，完全跳过第一个元素a [0]？

解决方案

i ++ 是post 增量操作符，这意味着它通过 1增加 i / code>但计算为旧（非递增）值。



 > i = 0 
 0 
> i ++ 
 0 
>我
 1 
  




I was reading the re-introduction to JavaScript on the MDN website and came across this example in the Array section:

for (var i = 0, item; item = a[i++];){
   // Do something with item
}

Where "a[]" is an array being looped over.

I am confused about the value that "item" will have in its first iteration. As i=0 and item is at first undefined, then when it is assigned the value of a[i++] wouldn't the iteration start from i=1, which would mean that the iteration would start from the second element in the a[] array -> a[1], skipping over the first element a[0] entirely?

解决方案

i++ is the post increment operator, which means that it increments i by 1 but evaluates to the old (non-incremented) value.

> i = 0
  0
> i++
  0
> i
  1

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