[jQuery] Can't read field value in remote method (Validation).

[kibi]

form id='f1' name='f1' method='post' action='ticket_confirm'
....
input name='field0' type='text'
input name='field1' type='text'
....
form


$(document).ready(function() {

var validator = $("#f1").validate({

        rules: {

                         field0: {
                                                                required: true,
                                                                minlength: 9,
                                                                remote: {
                                                                                
        url: "checkdocument.php",
                                                                                
        type: "get",
                                                                                
        data: { doctype: function() { return $("#field1").val
();  }

                                                                                
 }
                                                                         }
                                                                },


I see in FireFox FireBug folowing url when debug Get method :
"checkdocument.php?field0=1234567890&doctype=undefined"
What's wrong with reading value if field1 in remote data?
Could you explain please?
Thank you.