Thomas Fuchs
Hi, I'm Thomas Fuchs. I'm the author of Zepto.js, of script.aculo.us, and I'm a Ruby on Rails core alumnus. With Amy Hoy I'm building cheerful software, like Freckle Time Tracking and Every Time Zone and write books like Retinafy.me.
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Credit card validation

December 22nd, 2008

We all know that payment processing can be very painful. At least, everyone who’s ever tried to do it knows. To help ease the pain, Amy came up with a Jump Start Credit Card Processing cheat sheet for Ruby Advent 2008, based on our experiences when implementing freckle time tracking.

The cheat sheet does explaining-in-layman-terms of how this whole barely understandable mess works (need I say “merchant account”?), and an overview of how to use ActiveMerchant (and if you use Ruby on the backend, you should use ActiveMerchant!).

My contribution is an extraction from the freckle billing forms, a JavaScript library for doing client-side checking of credit card numbers, that does a couple of tricks:

  • Checks the number with the luhn algorithm (prevents typos)
  • Determines the type of the credit card from the number (you can use this to check the “type” checkboxes that you might have on your billing form automatically, as a convenience for your users)
  • Checks if the number is one of several test numbers (this prevents users from abusing/gaming your billing form)

This is valuable to both your users and you—Your users will have are more comfortable and responsive data input form, while you’re saving on transaction costs (most credit cards gateways also charge fees for false/bogus numbers!).

The credit card library can of course be used independent of what you use to acccess your gateway, so it’s not bound to Ruby or ActiveMerchant.

Download the Jump Start Credit Card Processing cheat sheet now for the details and download instructions for the JavaScript library!