CreditCard Number Verification Routines in JavaScript

Credit Card Number Verification Routines in JavaScript

What is it?
These are a bunch of JavaScript routines to verify the validity of a credit card number.

What does it not do?
Please note that these routines only determine whether a credit card is valid. A valid calid credit card number does not imply that it is a credit card that has actually been issued or (if it has been issued) is in good standing.

To actually see if a valid credit card number has been issued and is in good standing you would have to use a Credit Card Merchant Service. Credit card merchant services are beyond the scope of this document.

Copyright
These routines are licensed for usage and redistribution under The GNU General Public License

How do I use it?
You could use these routines along with your FORMs to validate credit card numbers. By doing this number validation via JavaScript you can save unneccesary calls on your CGI scripts.

To use these routines you would have to download the routines. You would then have to plug in these routines between the <HEAD> and </HEAD> of your HTML file containing the form. The routines provide the following functions -

typeOfCard()
Argument: number (ie. the credit card number)
Returns: string ("VISA", "MASTERCARD", "AMEX" or "DISCOVER")
Description: It is a function that returns a string indicating the type of the card. The function is called with the number of the credit card as an argument.
Example:
```
if (typeOfCard(document.ccForm.ccard.value == "AMEX") {
	alert("You have entered the number of an American Express card.\nWe do not acept this card at the moment.\nPlease try again with a Matercard or Visa card.");
}
```
isValidCreditCard()
Argument: number (ie. the credit card number)
Returns: boolean (TRUE if valid credit card number and FALSE if invalid)
Description: A function that is called with the number of the credit card as an argument. Since it returns boolean, the function call could be used directly in conditional statements.
Example:
```
if (! isValidCreditCard(document.ccForm.ccard.value) {
	alert("You have entered an invalid credit card number.\nPlease try again after entering a valid credit card number");
}
```

Feedback
If you use this code, please email me your comments and suggestions. Since this is purely voluntary work, any encouragement I get goes a long way in motivating me to keep working on these.