I'm working on a registration form and it validates some parts while the user is still typing. For example, the username is being checked after each character is entered to see if it is available or taken. A field beside the input is updated telling the user whether or not the name is available.
The e-mail address is going to be validated as well. I'm wondering if it should be validated after the
Submit button for the form is clicked or if it can be validated after each character is typed? One idea is to hold off auto-validation until 10 characters are typed (this could be done for the other inputs as well).
Is this constructive for users? Is there a better/more correct way to do validation of form input fields?