Credit Card Validation Script

JavaScript Credit Card Validation Function

This JavaScript function checks the validity of a credit card specified by the supplied parameters containing the card number and card type. Note that this routine does not supply credit card verification functionality, which can only be provided from within the server. It is, however, useful for intercepting user errors, and hence help provide a friendlier user-interface.

The specifications for valid credit cards have been taken from various sources on the web. The commonest credit cards are are supported in this implementation, but more may be added as required. One of the advantages of this routine is the ease with which additional cards may be added, as it is totally data dependent.

Try the routine. Although no attempt is made to capture the input, it is suggested that you don't provide the number of your own credit card. The following are credit card numbers in a valid format:

American Express	3400 0000 0000 009
Carte Blanche	3000 0000 0000 04
Discover	6011 0000 0000 0004
Diner's Club	3000 0000 0000 04
enRoute	2014 0000 0000 009
JCB	2131 0000 0000 0008
MasterCard	5500 0000 0000 0004
Solo	6334 0000 0000 0004
Switch	4903 0100 0000 0009
Visa	4111 1111 1111 1111

The function returns true or false, depending on whether the credit card name / number combination is found to be valid. If it is not valid, a numeric code is loaded into a global variable, which may be used to index into a global array of error messages. In this example, the input fields have ids of CardType and CardNumber. The submit button has an onclick="testCreditCard();" associated with it. This latter function calls the main checkCreditCard function as follows:

function testCreditCard () {
  myCardNo = document.getElementById('CardNumber').value;
  myCardType = document.getElementById('CardType').value;
  if (checkCreditCard (myCardNo,myCardType)) {
    alert ("Credit card has a valid format")
  } 
  else {alert (ccErrors[ccErrorNo])};
}

The credit card details are held in an array within the function, and additional cards may be readily added. The format of the arrray is as follows:

cards [0] = {name: "Visa", 
             length: "13,16", 
             prefixes: "4",
             checkdigit: true};

name is the name of the credit card as supplied by the user.
length is a comma separated list of the number of valid digits in the associated card number. Thus in the above example, Visa cards may have either 13 or 16 digits.
prefixes is a comma separated list of the valid prefixes in the associated card number. In the above example, Visa cards must start with the digit "4".
checkdigit is a boolean value of true or false that indicates whether the last character of the credit card number is a modulus 10 check digit.

Download compressed JavaScript file (2.43 KB)

Note: This routine was updated on the 18th January 2008 to add support for 18 digit Maestro cards. Thanks to David Groom of Vectis Webdesign for pointing out the error.