How to validate the existence of email before submitting form

Is there a way that I can validate the email before submitting the form ?? We do not want people who has already been registered to complete their data again, even if it is a short form.

Here is an example:  https://form.jotform.co/61176814534861 

The form is to register atendees at an event.  
People at the event should start typing their email, If the email is already on the database, there should be a warning saying "No registration is necesary ... xxx...xx".  If the email is not on the database, they should continue to the registration form. 

So in the example, the validation should happen on the first "Continue" button after typing their email (Page 1)... Page 2 shows the registration form. 

Please note that jotform is only for collecting data, and as such it cannot check the database and automatically display a result while the user is still typing their email address.

However, you can still set event registration form limits and setup the email field as a unique question to achieve your requirement. By using form limits, the user will no longer be able to submit the form if their email is already in the submissions. Unfortunately, this will not automatically display while the user is typing their email in the email field. The user will need to submit the form before they can see the error page if their email is already saved.

Simply follow this guide to learn how to setup form limits: How to set Form Limits Based on a Unique Question

If you need further assistance, please let us know.