Took a while but I nailed it. 
Here is the code of my project. I’ll be happy to receive any feedback! GitHub - Juneik/Credit-Card-Checker
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Hello mates!
Here’s my version of the project: Github Repo - Credit card checker.
Hoping to see any review about my code. Thanks!. 
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It took around 3 hours for me to complete the task… Everything seems to work well. Here is my code. I only didn’t accomplish the last optional task (Making valid cards out of invalid ones) as I couldn’t figure out what exactly should be done…
Hi, here´s my solution:
I took notes on my process in the README file. It works, but I can still make some improvements.
One thing I’m puzzling about is the return value of findInvalidCards() returns undefined in the console.
I’m wondering if this matters, and if I could either make it not print to the console, or actualy use returned values for the idInvalidCardCompanies function.
Hi, I share my code, for all everyone who want to see it, thanks
Hi ! Here is my solution until point 6.
Your comments are welcomed ! 
// 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];
// Add your functions below:
function validateCred(array) {
let sum = 0;
for (let i=array.length-1; i>=0; i--) {
if (i%2===1) {
sum += array[i];
}
else
{
let count = array[i]*2;
if (count>9) count-=9;
sum += count;
}
}
return (sum%10 === 0) ;//? true : false;
}
console.log(validateCred(mystery5));
function findInvalidCards(array) {
return array.filter(p=>!validateCred(p));
}
const invalidcards=findInvalidCards(batch);
console.log(invalidcards);
const findCompany = array => {
switch (array[0])
{
case 3 : return "Amex (American Express)"; break;
case 4: return "Visa"; break;
case 5: return "Mastercard"; break;
case 6: return "Discover"; break;
default: return "Company not found"; break;
}
}
function idInvalidCardCompanies(array) {
const result = array.map(findCompany);
return result.reduce((a,b) => {
if (!a.includes(b)) return a + ', ' + b;
return a;
}).split(', ');
}
console.log(idInvalidCardCompanies(invalidcards));
// 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];
// Add your functions below:
function validateCard(array) {
let num = 0;
let total = 0;
let doubledNum;
for (let i = array.length -1; i>=0; i–) {
if (num % 2 === 0) {
total = total +array[i];
} else if (num % 2 != 0) {
doubledNum = array[i] * 2;
if (doubledNum > 9) {
doubledNum -= 9;
};
total += doubledNum;
}
num += 1;
}
if (total % 10 === 0 ) {
return true;
} else {
return false;
};
}
console.log(validateCard(valid1));
function findInvalidCards(arr) {
let invalidCards = ;
arr.forEach(cardNum => {
if (validateCard(cardNum)) {
} else {
invalidCards.push(cardNum);
};
});
return invalidCards;
};
findInvalidCards(batch);
function idInvalidCardCompanies(array) {
let companiesNcards = ;
let cardObject;
array.forEach(cardNmbr =>{
if (cardNmbr[0] === 3) {
cardObject = [“Amex”, cardNmbr];
companiesNcards.push(cardObject);
} else if (cardNmbr[0] === 4) {
cardObject = [“Visa”, cardNmbr];
companiesNcards.push(cardObject);
} else if (cardNmbr[0] === 5) {
cardObject = [“MasterCard”, cardNmbr];
companiesNcards.push(cardObject);
} else if (cardNmbr[0] === 6) {
cardObject = [“Discover”, cardNmbr];
companiesNcards.push(cardObject);
};
});
return companiesNcards;
}
console.log(idInvalidCardCompanies(findInvalidCards(batch)));
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