Credit Card Checker

//유효한 카드, 미유효한 카드, 알수없는 카드의 카드넘버
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 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 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];

//batch of the card number
const batch = [valid1, valid2, valid3, invalid1, invalid2, invalid3, mystery1, mystery2, mystery3];

//Luhn algorithm를 기초로 카드 번호가 유효한지 확인한다.
const validateCard = array => {
  let cardNumber = [];
  let sum = 0;

  for (let i = array.length-1; i >= 0; i--){
  let digit = array[i];
  cardNumber.push(digit)
  }

  for (let i=0; i<cardNumber.length; i++){
    let digit = cardNumber[i];
    if(i%2 === 1 && (digit *= 2) > 9) digit -= 9;
    sum += digit
  }

  sum%10 === 0 ? true : false;

  return sum
};

//Luhn algorithm를 기초로 카드 번호가 유효한지 확인한다.
const findInvalidCards = array => {
  let cardNumber = [];
  if(validateCard(array) === false){
    cardNumber.push(array);
  };
  console.log(cardNumber);
};

//카드회사를 식별한다.
const idInvalidCardCompanies = array => {
  if(validateCard(array) === false){
    switch(array[0]){
      case 3 :
      console.log('Amex (American Express)')
      break;
    case 4 :
      console.log('Visa')
      break;
    case 5 :
      console.log('Mastercard')
      break;
    case 6 :
      console.log('Discover')
      break;
    default:
      console.log('Company not found');
    }
  };
};