Luhn's on Prototype

luhns.js

/**
 * Luhn's algorithm in javascript with prototype.
 *
 * This is used for credit card number validation.
 * 
 * You'll have to scrub the number before passing it in.  If any 
 * non-numeric characters are passed then this will fail.
 * 
 * @see http://en.wikipedia.org/wiki/Luhn_algorithm
 */
luhn = function(cc) {
  return $A(cc).reverse().map(Number).inject(0, function(s, d, i) {
    return s + (i % 2 == 1 ? (d == 9 ? 9 : (d * 2) % 9) : d);
  }) % 10 == 0;
};

Luhn's algorithm in javascript with prototype.

This is used for credit card number validation.

You'll have to scrub the number before passing it in. If any
non-numeric characters are passed then this will fail.

@see http://en.wikipedia.org/wiki/Luhn_algorithm