Hi, the following is my code 
// 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:
//validateCred() checks a credit number valid or not.
const validateCred = (arr) => {
const newarr = [...arr];
newarr.reverse();
for (let i = 1; i < newarr.length; i += 2) {
newarr[i] = newarr[i] * 2;
if (newarr[i] > 9) {
newarr[i] -= 9;
}
}
let sum = 0;
for (let i = 0; i < newarr.length; i++) {
sum += newarr[i];
}
if (sum % 10 === 0) {
return true;
} else {
return false;
}
};
//findInvalidCards() outputs an array of invalid card numbers.
const findInvalidCards = (nestedarr) => {
let invalidList = [];
for (let i = 0; i < nestedarr.length; i++) {
if (validateCred(nestedarr[i]) === false) {
invalidList.push(nestedarr[i]);
}
}
return invalidList;
};
//idInvalidCardCompanies() outputs a list of companies that issue invalid card numbers in the above invalid list.
const idInvalidCardCompanies = (nestedarr) => {
let firstDigits = [];
for (let i = 0; i < nestedarr.length; i++) {
firstDigits.push(nestedarr[i][0]);
}
console.log(`There are ${firstDigits.length} invalid card numbers. `);
console.log("First digits of the found invalid card numbers: " + firstDigits);
let companyList = [];
if (firstDigits.some((digit) => digit === 3)) {
companyList.push("Amex (American Express)");
}
if (firstDigits.some((digit) => digit === 4)) {
companyList.push("Visa");
}
if (firstDigits.some((digit) => digit === 5)) {
companyList.push("Mastercard");
}
if (firstDigits.some((digit) => digit === 6)) {
companyList.push("Discover");
}
// the following if statement: .filter() attempts to find the numbers either greater than 6 or less than 3, if there is any, 'an unnamed company' will be added to the company list.
let notdigit3to6 = firstDigits.filter((digit) => digit < 3 || digit > 6);
if (notdigit3to6.length !== 0) {
companyList.push("an unnamed company");
}
console.log(
"List of Companies that issue invalid numbers: " + companyList.join(", ")
);
};
//test these functions!
findInvalidCards(batch);
idInvalidCardCompanies(findInvalidCards(batch));