CUIT - CUIL

cuit-validation.js

function validCUIT(number) {
  number = String(number || '').split('');

  if (number.length !== 11) { return false; }

  var numbers = '5432765432'.split(''),
      result  = 0;

  for (var i = 0; i <= 9; i++) {
    result += Number(number[i]) * Number(numbers[i]);
  }

  result = result % 11;
  result = 11 - result;

  if (result === 11) { result = 0; }
  if (result === 10) { result = 9; }

  return result === Number(number[10]);
}
  
validCUIT(20311251407) // => true
validCUIT("20-31125140-7") // => true
validCUIT(20311251405) // => false

cuit_validation.rb

class Object
  def valid_cuit?
    number = self.to_s.gsub(/\D/, '').split('')

    return if number.size != 11

    numbers = %w(5 4 3 2 7 6 5 4 3 2)
    result  = 0

    10.times.each { |i| result += number[i].to_i * numbers[i].to_i }

    result = result % 11
    result = 11 - result

    result = 0 if result == 11
    result = 9 if result == 10

    result == number[10].to_i
  end
end

20311251407.valid_cuit? # => true
"20-31125140-7".valid_cuit? # => true
20311251405.valid_cuit? # => false