function validCreditCard(cardNumber) // returns true or false
  { 
	  var ar = new Array( cardNumber.length );
	  var i = 0,sum = 0;

    for( i = 0; i < cardNumber.length; ++i )
    {
      ar[i] = parseInt(cardNumber.charAt(i));
    };
    
    for( i = ar.length -2; i >= 0; i-=2 )
    {
      ar[i] *= 2;
   		if( ar[i] > 9 ) 
   		  ar[i]-=9;
   	};
    
    for( i = 0; i < ar.length; ++i ) 
    {
      sum += ar[i];
    };
    
    return (((sum%10)==0)?true:false);	 	
  };
  
  function typeOfCreditCard(cardNumber) // returns "INVALID", "MC", "VISA", "AMEX", or "DISCOVER"
  {
    if (cardNumber.length < 13 || cardNumber.length > 16)
      return "INVALID";
    
    if (cardNumber.length == 13)
    {
      if (cardNumber.substr(0,1) != "4")
        return "INVALID";
      else
        return "VISA";
    };
    
    if (cardNumber.length == 14)
      return "INVALID";
      
    if (cardNumber.length == 15)
    {
      if (cardNumber.substr(0,2) == "34" || cardNumber.substr(0,2) == "37")
        return "AMEX";
      else
        return "INVALID";
    };
    
    if (cardNumber.length == 16)
    {
      if (cardNumber.substr(0,4) == "6011")
        return "DISCOVER";
      if (cardNumber.substr(0,1) == "4")
        return "VISA";
      if (cardNumber.substr(0,2) == "51" || cardNumber.substr(0,2) == "52" || cardNumber.substr(0,2) == "53" || cardNumber.substr(0,2) == "54" || cardNumber.substr(0,2) == "55")
        return "MC";
        
      return "INVALID";
    };
    
    return "INVALID";    
  };
  
  // checks if the cvv is valid for the type of card provided
  function validCVV2(cvv, cardNumber)
  {
    var type = typeOfCreditCard(cardNumber);
    
    if (type == "INVALID")
      return false;
      
    if ((type == "VISA" || type == "MC" || type == "DISCOVER") && cvv.length != 3)
      return false;
    
    if (type == "AMEX" && cvv.length != 4)
      return false;
      
    return true;
  };
  
  // checks if the expiration is before today's date
  // year needs to be 4 digit - 2008
  // month needs to be 1 through 12
  function validExpiration(year, month)
  {
    year = parseInt(year);
    month = parseInt(month);
    
    if (month == 12)
    {
      month = 1;
      year += 1;
    }
    else
      month += 1;
    
    var today = new Date();
    var exp = new Date(year, month-1, 1, 0, 0, 0);
    
    if (today > exp)
      return false;
    
    return true;
  };