Basic efforts with JavaScript, incorporating function construction and conditionals with loops, courtesy of the Codecademy Credit Card Checker Project.

The aim of the challenge was to practice using loops.

The premise is to check a batch of cards that have been created for a bank by a distributor, ready to be issued to customers.

The goal was to code the core functions of a JavaScript program to initially take in an array of single digits that together represent a credit card number.

The code should provide functions to:

• Check if the sequence of digits is a valid credit card number, using Luhns Algorithm
• Check an array of unchecked number arrays, returning an array containing only the invalid number arrays.
• Given an array of invalid number arrays, return an array containing the unique names of card issuers that have an invalid number within the array.

NOTE: The function does not validate the length of the number provided, merely that it conforms to Luhns Algorithm.

As an additional challenge, the code should provide functions to:

• Take in a credit card number as a string and convert it to an array of single digits for use in the core functions
• Given an invalid card number, create a function to convert it to a valid number.
```// 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];
//adding some extra arrays for providers that are not checked
//Valid CC number but unknown issuer
const added1 = [2,7,2,0,9,9,0,5,5,5,5,7,7,1,5,1]
//Invalid CC and unknown issuer
const added2 = [7,5,3,1,4,7,6,2,0,2,8,5,5,0,2,3]

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5, added1, added2];

//Function to return true/false if array of numbers conforms to a Luhn algorithm (check digit included)
const validateCred = array => {
//create Toggle to track every other element from check digit
let doubleCounter = false;
let checkArray = [];
let checkSum = 0;
for (let i=(array.length-1); i>=0; i--){
if (doubleCounter){
array[i] * 2 > 9 ? checkArray.push(array[i]*2-9):checkArray.push(array[i]*2);
} else {
checkArray.push(array[i]);
}
doubleCounter = !doubleCounter;
}
for (let j=0; j < checkArray.length; j++){
checkSum += checkArray[j];
}
return checkSum % 10 === 0;
}

//given nested array of number arrays, validate all number arrays and return an array of the invalid numbers
const findInvalidCards = nestedArray => {
let invalidArray = [];
for (let k=0; k < nestedArray.length; k++){
//use validation function created earlier
if (!validateCred(nestedArray[k])) {
invalidArray.push(nestedArray[k]);
}
}
return invalidArray;
}

//identify issuing company from first digit and return array of companies that have issued invalid number arrays (no duplicates)
const idInvalidCardCompanies = invalidNestArray => {
let companyArray = [];
for (let m=0; m < invalidNestArray.length; m++){
switch (invalidNestArray[m][0]) {
case 3:
if (!companyArray.includes("Amex (American Express)")){
companyArray.push("Amex (American Express)");
}
break;
case 4:
if (!companyArray.includes("Visa")){
companyArray.push("Visa");
}
break;
case 5:
if (!companyArray.includes("Mastercard")){
companyArray.push("Mastercard");
}
break;
case 6:
if (!companyArray.includes("Discover")){
companyArray.push("Discover");
}
break;
default:
}
}
return companyArray;
}
//Basic project test case using supplied data and created functions
//console.log(idInvalidCardCompanies(findInvalidCards(batch)));

//Extra Credit
//function to convert string number to an array of individual digits
const arrayNumber = stringNumber => {
let numberArray = [];
for (n = 0; n < stringNumber.length; n++) {
numberArray.push(parseInt(stringNumber[n]));
}
return numberArray;
}
//test case for arrayNumber
//console.log(arrayNumber("343988425164318"));

//function to correct the card number
const correctNumber = invalidNumArray => {
let correctedArray = invalidNumArray;
correctedArray.pop();
correctedArray.push(0);
while (!validateCred(correctedArray)) {
correctedArray.push(correctedArray.pop() + 1);
}
return correctedArray;
}
//tests for correctNumber
//console.log(correctNumber(invalid5));
//console.log(validateCred(correctNumber(invalid5)));
```