SyntaxError: Unexpected end of JSON input

Question

I can record data in my db but ajax loading doesn't inter in success method. What's the problem?

error: "SyntaxError: Unexpected end of JSON input
    at Object.parse (native)
    at n.parseJSON "

record_data.php

<?php
$type=getPar_empty("type",$_GET,"");
$new_nome=$_GET['new_nome'];
$new_cognome=$_GET['new_cognome'];
$new_email=$_GET['new_email'];
$new_lingua=$_GET['new_lingua'];
if ($type=="add_user"){
  $stmt=null;
  $stmt=$db->prepare("INSERT INTO newsletter_utenti(email,abilitato,nome,cognome,lingua,lista,data_creazione,unsubscribe) VALUES('$new_email',1,'$new_nome','$new_cognome','$new_lingua','manual',now(),0)");
  if (!$stmt) {
    log_msg($db->error);
    die();
  }
  $stmt->execute();
  $stmt->close();
  $db->close();
}
?>

script

   $("#salvaBtn").click(function(){
  var nome = $('#nome').val();
  var cognome = $('#cognome').val();
  var email = $('#email').val();
  var lingua = $('#lingua').val();
  var dataString = 'nome='+nome+'&cognome='+cognome+'&email='+email+'&lingua='+lingua+'&type=add_user';
  $.ajax({
    type:'GET',
    data:dataString,
    url:"record_data.php",
    success:function(result) {
              $("#status_text").html(result);
              $('#nome').val('');
              $('#cognome').val('');
              $('#email').val('');
    },
    error:function(xhr,status,error) {
      console.log(error);
    }
  });
});

$('#adduser').submit(function (){
  return false;
});

form

<form name="adduser" id="adduser" method="GET" action="#">
            <div class="col-md-3">
              <div class="form-group m-b-30">
                <p>E-mail</p>
                <input class="form-control" type="email" id="email" name="email" placeholder="indirizzo e-mail" email required>
              </div>
            </div>
            <div class="col-md-3">
              <div class="form-group m-b-30">
                <p>Nome</p>
                <input class="form-control" type="text" id="nome" name="nome" placeholder="nome">
              </div>
            </div>
            <div class="col-md-3">
              <div class="form-group m-b-30">
                <p>Cognome</p>
                <input class="form-control" type="text" id="cognome" name="cognome" placeholder="cognome">
              </div>
            </div>
            <div class="col-md-3">
              <div class="form-group m-b-30">
                <p>Lingua</p>
                <select class="form-control" id="lingua" name="lingua">
                  <option value="it">IT</option>
                  <option value="en">EN</option>
                </select>
              </div>
              <input type="submit" class="btn btn-embossed btn-primary m-r-20" id="salvaBtn" value="Aggiungi utente"></input>
              <div id="status_text" /></div>
            </div>
          </form>

Answer 1

your jquery ajax call should include

dataType: 'html',

to explicitly state that the data coming back from the server is html

in fact you're taking result and putting it straight into the DOM node with id statusText

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Then you have to fix a major issue: your PHP script is not returning (echoing) any data !

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Bottom note: you really should use mysqli for your db queries http://php.net/manual/en/book.mysqli.php and also use prepared statements to build up the query (instead building up the SQL query by concatenating strings).