JS嵌套数组循环调用validateCred报Cannot read property 'length'错误

错误根源 #

你触发的TypeError: Cannot read property 'length' of undefined是findInvalidCards函数的循环逻辑错误直接导致的：

• 传入findInvalidCards的batch是一维嵌套数组，每一项就是完整的信用卡号数组，只需一层遍历即可，你额外加了第二层循环遍历单张卡号的数字，调用validateCred(array[j])时传入的是单个数字，不是数组，自然没有length属性。
• 除了这个报错外，你的validateCred函数也存在多处逻辑错误：pop会修改原数组、array.indexOf([i])写法错误、Luhn算法的计算和返回逻辑位置错误，无法正确验证卡号有效性。

修复后完整代码 #

// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9];
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6];
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5];
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6];

// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5];
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3];
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4];
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5];
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4];

// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4];
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9];
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3];
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3];
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3];

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5];

// 修复后的Luhn算法验证函数
function validateCred(cardArr) {
  // 复制原数组避免修改原数据
  const arr = [...cardArr];
  const checkDigit = arr.pop();
  let sum = 0;
  // 从右往左遍历，隔一位乘2
  for (let i = arr.length - 1; i >= 0; i--) {
    let num = arr[i];
    if ((arr.length - 1 - i) % 2 === 0) {
      num *= 2;
      if (num > 9) num -= 9;
    }
    sum += num;
  }
  sum += checkDigit;
  return sum % 10 === 0 ? 'Valid' : 'Invalid';
}

// 修复后的无效卡筛选函数
function findInvalidCards(cardsBatch) {
  const invalidCards = [];
  // 仅需一层循环遍历每个卡号数组
  for (let i = 0; i < cardsBatch.length; i++) {
    const currentCard = cardsBatch[i];
    const validateResult = validateCred(currentCard);
    if (validateResult === 'Invalid') {
      invalidCards.push(currentCard);
    }
  }
  return invalidCards;
}

// 测试
console.log(validateCred(invalid2)) // 输出 Invalid
console.log(findInvalidCards(batch)) // 输出所有无效卡号数组

内容的提问来源于stack exchange，提问作者omarfarah