Form Submitted callback:

Function: mpfg_form_submitted
This function is called after the form is validated as valid & before the request is sent to the form-generator server for saving the data in the database.

Example:
function mpfg_form_submitted(form_id, form_data){

console.log(form_id);
console.log(form_data);
        //write you code here

}
This function will log the form id & form data.

You can define this function inside them Additional JS tab in forms.