Email already exists using jQuery

It is the common requirement for any web application either it is PHP, .net, JSP etc., which has users involved. When creating/adding user from admin or end user registration we should check whether username or email address already exists. It will help to have unique registrations to our application and avoid confusion between various users. 

I see many developers struggle with this by submitting the form to server side script and validate their from database, in case username/email address already exists they take the pain to go back to previous page or form and show the error message with other form data filled. 

Few use AJAX to send the information onblur or onkeyup or onkeydown but face difficulties to stop form submission. Here is the simple solution that would help in validating username or email address existence without much hassle. 

Solution comes from popular jQuery Validator plugin I'm using this from ages. 

HTML Code:

<html>
    <head>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.16.0/jquery.validate.js"></script>
        <script>
              $(function(){
                    $('#UserForm').validate({
                           rules:{
                                   Name: {required: true},
                                   EmailID: { required: true, email: true, 
                                     remote: {
                                        url: "http://localhost/user/check-email",
                                        type: "post",
                                        data: {
                                              EmailID: function() {
                                                  return $( "#EmailID" ).val();
                                              },
                                              UserID: $('#UserID').val()
                                        }
                                     }
                                 }
                           }   
                    });
              });
        </script>
    </head>
    <body>
        <form action="" id="UserForm" method="post" name="UserForm">
            Name: <input id="Name" name="Name" type="text" />
            Email ID: <input id="EmailID" name="EmailID" type="text" />
            <input id="UserID" name="UserID" type="hidden" value="0" />
            <input id="Submit" name="Submit" type="submit" value="Submit" />
        </form>
</body>
</html>

 The remote block will do the trick, it sends the current field value to server side URL "http://localhost/user/check-email". This URL can be any file URL where it sends EmailID value using POST method and there you've to write SQL query to search in DB and if exists print 'false' otherwise 'true'. (Note: don't write return true or return false, just print true or false in quotes)

We can pass UserID as zero for new insertion for update UserID can be unsigned integer so that you can check if EmailID is same for other than selected UserID.