Handling PHP Form Postbacks: Same-Page Validation
Assuming a form will have problems allows you to more easily build validation routines.
Assuming a form will have problems allows you to more easily build validation routines.
You want to count how many times an element on your page was clicked. There's two ways to do it: with a PHP postback and, of course, via JavaScript with an AJAX...
The most important step in using the authorize.net payment gateway is properly designing your ordering system / shopping cart first.
JavaScript is too insecure to compute shopping cart totals. You can't rely on it when submitting payment requests to authorize.net.