// JavaScript Document
  function isValidCard(cardNumber){
	var ccard = new Array(cardNumber.length);
	var i     = 0;
        var sum   = 0;

	// 6 digit is issuer identifier
	// 1 last digit is check digit
	// most card number > 11 digit
	if(cardNumber.length < 11){
		return false;
	}
	// Init Array with Credit Card Number
	for(i = 0; i < cardNumber.length; i++){
		ccard[i] = parseInt(cardNumber.charAt(i));
	}
	// Run step 1-5 above above
	for(i = 0; i < cardNumber.length; i = i+2){
		ccard[i] = ccard[i] * 2;
		if(ccard[i] > 9){
			ccard[i] = ccard[i] - 9;
		}
	}
	for(i = 0; i < cardNumber.length; i++){
		sum = sum + ccard[i];
	}
	return ((sum%10) == 0);
  }

  function isValidVISA_MasterCard(cardNumber){
	// if you want to accept Mastercard, Visa (Debit/Electron/Credit Card) ONLY!
	if(cardNumber.charAt(0) == '4' && (cardNumber.length == 13 || cardNumber.length == 16)){
		return isValidCard(cardNumber);
	}
	if(cardNumber.charAt(0) == '5' &&
	               (cardNumber.charAt(1) == '1' || cardNumber.charAt(1) == '5')
	   && cardNumber.length == 16){
		return isValidCard(cardNumber);
	}
	return false;
  }

  function checkValid(cardNumber){

	if(isValidVISA_MasterCard(cardNumber)){
		alert('Credit Card number is valid VISA/MasterCard');
	}else{
		alert('Credit Card number is NOT valid VISA/MasterCard');
	}
  }