Credit Card number validation in Coffee Script

creditcard.coffee

# Ported from https://github.com/jzaefferer/jquery-validation/blob/master/jquery.validate.js

creditcard = (value)->
  # accept only spaces, digits and dashes
  return unless /[^0-9 \-]+/.test(value)

  nCheck = nDigit = 0
  bEven = false

  checkDigit = (n) ->
    cDigit = value.charAt(n)
    nDigit = parseInt(cDigit, 10)
    if bEven && ((nDigit *= 2) > 9)
      nDigit -= 9
    nCheck += nDigit
    bEven = !bEven

  value = value.replace(/\D/g, "")
  checkDigit num for num in [0...value.length].reverse

  (nCheck % 10) == 0