Luhn Algorithm Number Checker

creditcheck.js

// 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]

//Batch of Valid and Invalid Cards
const validCards = [];
const badCards = [];

//Luhn's Algorithm Start
const validateCred = (array) => {
  let evenOdd = array.length % 2;
  let luhnArray = [];
  for (i = array.length - 1; i > -1; i--){
    if (i % 2 === evenOdd) {
      if (array[i] * 2 > 9) {
        luhnArray.push(array[i]*2 - 9)
      } else {
        luhnArray.push(array[i]*2)
      }
    } else {
      luhnArray.push(array[i])
    }
  }
  if (luhnArray.reduce((a,b) => a+b,0) % 10 === 0) {
    return true;
  } else {
    return false;
  }
}

const findInvalidCards = (cardNo) => {
  for(j=0; j < cardNo.length; j++){
    if(validateCred(cardNo[j])) {
      validCards.push(cardNo[j]);
    } else {
      badCards.push(cardNo[j]);
    }
  }
}

const idInvalidCardCompanies = (invalidCards) => {
  let companiesToNotify = new Set();
  for(i = 0; i < invalidCards.length; i++){
    if(invalidCards[i][0] === 3) {
      companiesToNotify.add('Amex')
    } else if(invalidCards[i][0] === 4) {
      companiesToNotify.add('Visa')
    } else if(invalidCards[i][0] === 5) {
      companiesToNotify.add('Mastercard')
    } else if(invalidCards[i][0] === 6) {
      companiesToNotify.add('Discover')
    } else {
      companiesToNotify.add('Creditor not on file')
    }
  }
  return companiesToNotify = Array.from(companiesToNotify)
};

findInvalidCards(batch);
console.log('Good Cards:')
console.log(validCards);
console.log('Bad Cards');
console.log(badCards);
console.log(idInvalidCardCompanies(badCards))