在此循环中，++ i和i ++有区别吗? [英] Is there a difference between ++i and i++ in this loop?

问题描述

array.prototype.reduce函数位于:

The array.prototype.reduce function at: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

它具有以下循环:

for (index = 0; length > index; ++index) {
    if (this.hasOwnProperty(index)) {
      if (isValueSet) {
         value = callback(value, this[index], index, this);
      } else {
        value = this[index];
        isValueSet = true;
      }
    }
}

我认为这里的索引是先递增还是后递增都没有区别，因为它是在每次循环迭代之后完成的，但是要确定.

I don't think there is a difference whether the index is pre or post incremented here since it's done after the loop iterates each time, but want to be certain.

可以将其更改为索引+ = 1，以使其通过jslint吗?请不要争论jslint警告的优点.

Can this be changed to index += 1 so it passes jslint? Please don't debate the merits of jslint's warning.

此更改会有所不同吗?

推荐答案

i++，++i和i += 1之间的唯一区别是从表达式返回的值.请考虑以下内容:

The only difference between i++, ++i, and i += 1 is the value that's returned from the expression. Consider the following:

// Case 1:
var i = 0, r = i++;
console.log(i, r); // 1, 0

// Case 2:
var i = 0, r = ++i;
console.log(i, r); // 1, 1

// Case 3:
var i = 0, r = (i += 1);
console.log(i, r); // 1, 1

在这些情况下，i在增加后保持不变，但r不同，i += 1只是++i的详细形式.

In these cases, i remains the same after the increment, but r is different, i += 1 just being a slightly more verbose form of ++i.

在您的代码中，您根本没有使用返回值，所以不，没有区别.就个人而言，我更喜欢使用i++，除非特别需要使用其他形式之一.

In your code, you're not using the return value at all, so no, there is no difference. Personally, I prefer to use i++ unless there is a specific need to use one of the other forms.

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