Question

我正在学习JavaScript并遇到此问题。基本上我要检查无效的信用卡号

// 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]

此算法（Luhn算法）可以访问信用卡的有效性：

function validateCred(card_number){
let sum = card_number[card_number.length-1];
let flag = 1;
for (i = card_number.length-2; i >= 0; i--){
    if (flag % 2 !== 0){
        card_number[i] *= 2;
        if (card_number[i] > 9){
            card_number[i] -= 9;
        }
    }
    sum += card_number[i];
    flag++;
}

if (sum % 10 === 0){
    return true;
} else {
    return false;
}
}

我必须创建一个包含所有无效卡的数组：

function findInvalidCards(numbers){
    let invalid_array = [];
    for (i = 0; i < numbers.length; i++){
        if (!validateCred(numbers[i])){
            invalid_array.push(numbers[i]);
        }
    }
    return invalid_array;
}

当我调用findInValidCards函数时，它引发了heap out of memory错误，我尝试遵循this link的解决方案并将使用内存提高到8gb，但问题仍然存在。调试之后，我发现这行invalid_array.push(numbers[i])实际上是将undefined变量附加到数组，而不是我想要的元素。可能导致此问题的原因是什么？

Answer 1

就像Nina在评论中所说的那样，每次编写for循环时，都应该用i来定义let，否则将出现不可预测的行为

但是，您在validateCred函数中还遇到了一个问题，即您在检查原始数组时对其进行了突变-您可以简单地使用let clone = card_number.slice(0);克隆输入数组，然后引用{{1} }进行支票

此外，您可以使用.filter()来简化clone，例如：

findInvalidCards

function findInvalidCards(numbers) {
  return numbers.filter(x => !validateCred(x));
}

Answer 2

如果不使用i或var来定义let变量，则将其定义为全局变量。因此，当它从findInvalidCards函数开始时，i的值为零，但是当它访问validateCred函数时，i值就会改变。因此，当它从validateCred函数结束时， i的值将为-1，它将尝试在findInvalidCards中将其递增以进行循环，而i的值将为零。这将一遍又一遍地发生，在无限循环中导致内存异常，一切崩溃。

我已经调试了您的代码，所以我知道代码的运行方式。：）

  function findInvalidCards(numbers){
        let invalid_array = [];
        //make i local variable by defining it let or var, otherwise it will be global
        for (var i = 0; i < numbers.length; i++){
            if (!validateCred(numbers[i])){
                invalid_array.push(numbers[i]);
            }
        }
        return invalid_array;
    }

function validateCred(card_number){
    let sum = card_number[card_number.length-1];
    let flag = 1;
    //make i local variable by defining it let or var, otherwise it will be global
    for (var i = card_number.length-2; i >= 0; i--){
        if (flag % 2 !== 0){
            card_number[i] *= 2;
            if (card_number[i] > 9){
                card_number[i] -= 9;
            }
        }
        sum += card_number[i];
        flag++;
    }

    if (sum % 10 === 0){
        return true;
    } else {
        return false;
    }
}

数组不推送预期元素

2 个答案: