Help With Javascript/Prototype form validation

Hello, I need some help with a javascript/prototype form validation script. I have a form that the user needs to input numbers that are associated with ID in database (there could be anywhere from 1-10 input fields). These fields all have the same class (image_no) I want to be able to loop through the from inputs that has class="image_no", then using ajax I want to validate that the numbers correspond to the ID in the database (using php), if ajax return is invalid (the number they input does not match an ID in database) alert the user they have input a invalid number, if all numbers are valid, then I want the form to submit