javascript - [PHP-JQuery]: check if a form entry alreay exists in database without clicking on submit button -

i developing form in web page user supposed write tax code of person , system automatically checks database if person inserted tax code exists before clicking on submit button. here's jquery code of php page:

jquery("#form1").validate({     rules: {         name: "required",         surname: "required",         ...          <?php             echo '              tax_code:{                 remote: {                     url: "check_cf.php",                     type: "post",                     data: {                         tax_code: function() {                                     return jquery( "#tax_code" ).val();                                 }                         }                 }             },              ';         ?>     },      messages: {         name: "insert client's name!",         ... ,         <?php          echo '              tax_code: {                 remote: "you have inserted person tax code",             }          ';          ?>      } }); 

and here check_cf.php

<?php   $deep="";   include($deep."include/head.php");   $cfpost=$_post['tax_code'];   $cliente_cf=$sistema->clienti->allclienti(" codice_fiscale='".$cfpost."'  ");   //echo $usernamepost;     if(isset($cliente_cf[0]["id"])) echo json_encode(false);   else echo json_encode(true);  ?> 

and nothing works...i don't know making mistake. all