Can I get some help with this AJAX question?

Form validation can be done using simple JavaScript. Using the <form>'s onsubmit handler, one can do basic checks using plain JavaScript.

Another way to check it is to send the form no matter what, then let the server-side scripting provide user feedback if the validation fails.

AJAX can be used to validate the form in the background even if that requires server-side operations like database access.

Say the user is filling out a form that requires a model number. AJAX can be used to check if the model number is in the database without sending the form.

Form validation should be started BEFORE sending the form, using javascript, ie to check if an email has a valid form, or data entered in some fields correspond to requirements.

However, some checks can be made, also before sending the form, using an AJAX call, ie to check, during a registration, if the new user already exists or not in the database. and output an error message if it does.

Credit cards, however, should NEVER be entered by the user, unless your site uses SSL (and it is formally registered). Leave CC checks to the approved payment gateway (ie PayPal). NEVER store sensitive details such as CC on an unsecure server.

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