# Credit card checker

Hi , I am trying to understand this project at my own, I really feel stupid, but I am stuck in the step 4. I created the first function and now I am trying to recall it in the second function. But it seems I can’t use methods

``````// 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]

function validateCred(Array) {
var x = Array.pop();
Array.reverse();
for (var i = 0; i < Array.length; i++) {
if ((i % 2) === 0) {
(Array[i] *= 2);
}
if (Array[i] >= 10) {
Array[i] -= 9;
}
}
Array.push(x);
var total = 0;
for (var i  = 0; i < Array.length; i++) {
total  += Array[i];
}
if ((total % 10) === 0) {
return true;
} else {
return false;
}
};

function findInvalidCards(Array) {
var falseCard = [];
for (i = 0; i < Array.length; i++) {
var creditCard = Array[i];
if (cardChecker(creditCard) === false) {
falseCard.push(Array[i]);
}
}
return falseCard;
};

console.log(findInvalidCards(invalid1));

``````

this is the output :

`````` var x = Array.pop();
^

TypeError: Array.pop is not a function
``````

what am I doing wrong?

Not sure why you’re using `var` instead of `let` & `const`, but that aside, the error is telling you that your variable `Array` (we don’t normally capitalize parameter/variable names) is not an array. If it were, it would have a `.pop()` method available. You can make observations of what your code is doing by adding in some `console.log()` statements. You might try:

I changed `var` with `let`& `const`, then I tried to do what you told me, and yes it prints what I was expecting. Do you think I should change all the code and don’t use methods?

When I run your code, after changing the line below to use your `validateCred` function instead of the non-existent `cardChecker` function, and add the `console.log` statement that I suggested, I get `4` printed to the console. `4` doesn’t have a `.pop()` method. `.pop()` only works with arrays. If you are getting something other than `4`, then you must have changed your code. Please paste your current code into a reply, and someone will be able to help you out.

I changed the above line to `if(validateCred(creditCard) === false) {`