PHP script returns an unexpected value to the AJAX call

Question

My javascript:

nombre = window.prompt('Escribe el nombre del autor/artista/letrista:','');
    if(nombre != ''){
      $.ajax({
          url: "admin/nuevo_autor.php",
          type: "POST",
          data: {autor: nombre},
          success: function (res) {
              alert(res);
              if(res=='verdadero'){
                  var opt = document.createElement('option');
                  opt.text = nombre;
                  opt.selected = true;
                  sel.add(opt);
              }
              return true;
          }
      });
    }

Calls 'nuevo_autor.php':

<?php
$nuevo = $_POST["autor"];
require("../includes/database.php");

$select = <<<EOT
SELECT * FROM autor
WHERE 1
EOT;
$resultado = $mysqli->query($select);
$res = "verdadero";
for($i=0;$i<$resultado->num_rows; $i++){
    $fila = mysqli_fetch_array($resultado, MYSQLI_ASSOC);
    if(stristr($fila["autor"], $nuevo)) {
        $res = "falso";
        break;
    }
}
echo json_encode($res);
?>

The Javascript alert shows: FIN (in spanish: END ). Neither ' verdadero ' nor ' falso '. I also tested using the $.get jQuery function with the same bad result. Where is the error?

Answer 1

stristr($fila["autor"], $nuevo) will return "0" if $nuevo and $fila['author'] are equal, which in your code will be the equivalent of false .

Instead you need to explicitly check for the false value, as in:

if(stristr($fila["autor"], $nuevo) !== false) {
    $res = "falso";
    break;
}