for循环行为"TypeError:无法读取未定义的属性'length'" [英] for loop behavior "TypeError: Cannot read property 'length' of undefined"

问题描述

对于已经问过的此类问题，我没有找到答案.我不明白，为什么当我的for循环包含此条件

I don't find an answer in the replies to this kind of question already been asked. I don't understand, why console throws this error "TypeError: Cannot read property 'length' of undefined" , when my for-Loop contains this condition

  for (let i = 0; i <= res.length; i++) {
    arr.push(res[i].length);
  }

没有等号.

我不明白为什么.我以为设置i = 1会起作用.但事实并非如此.谁能解释，为什么在给出条件时出现错误

I don't get why. I thought setting i=1 would work. But it does not. Could anyone explain please, why I get the error when given the condition

i>**=**res.length; (with equal sign)

完整代码

function findLongestWordLength(str) {
  var arr = [];
  var res = str.split(" ");
  for (let i = 1; i < res.length; i++) {
    arr.push(res[i].length);
  }

  return Math.max(...arr);
}

findLongestWordLength("May the force be with you");

谢谢你，新年快乐.

推荐答案

因为数组的索引始终为长度-1.

您可以说.假设您的数组长度为2

You can say. Suppose you have the array of length 2

const ar = ["a"，"b"]

，如果您检查此数组的长度，它将显示 2 ，但此数组的最大索引仅为 1 .

and if you check the length of this array it will show 2 but the max index of this array is 1 only.

因此，当您遍历数组的长度时，它会上升到索引2，而 res [2] 是 undefined

So when you loop through the length of the array then it goes up to index 2 and res[2] is undefined

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