Validação Instantânea de Cartão de Crédito

function isValidCardNumber(number) {
  const digits = number.replace(/\s/g, '').split('').reverse();
  let sum = 0;

  for (let i = 0; i < digits.length; i++) {
    let digit = parseInt(digits[i], 10);

    // Double every second digit (odd index in reversed array)
    if (i % 2 === 1) {
      digit *= 2;
      if (digit > 9) digit -= 9;
    }

    sum += digit;
  }

  return sum % 10 === 0;
}

// Identify card network from first digits
function getCardNetwork(number) {
  const cleaned = number.replace(/\s/g, '');
  if (/^4/.test(cleaned)) return 'Visa';
  if (/^5[1-5]/.test(cleaned)) return 'Mastercard';
  if (/^3[47]/.test(cleaned)) return 'Amex';
  if (/^6011/.test(cleaned)) return 'Discover';
  return 'Unknown';
}

console.log(isValidCardNumber('4539 1488 0343 6467')); // true
console.log(getCardNetwork('4539 1488 0343 6467'));     // Visa

def luhn_check(card_number: str) -> bool:
    digits = [int(d) for d in card_number.replace(' ', '')][::-1]
    total = 0
    for i, digit in enumerate(digits):
        if i % 2 == 1:
            digit *= 2
            if digit > 9:
                digit -= 9
        total += digit
    return total % 10 == 0

# Valid test number
print(luhn_check('4539 1488 0343 6467'))  # True
# One digit off
print(luhn_check('4539 1488 0343 6468'))  # False