I have a site and I am using this plugin for validation in the registration process. I have seen sites where when you exit the email address field, it goes out and checks to see if the email address exists before you hits the submit button. I know this is ajax but I cannot figure it out.
How do you validate if an email address (or any field) already exists before the users submits the form?
Check out the Source Code here
http://jquery.bassistance.de/validate/demo/milk/
Your Rule to check for an e-mail address might look like this
you would need to write the script server side to query your database and return true or false depending on whether or not the e-mail address had been used already.