Ambil Data AJAX berdasar NIS

// tampil.php
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script>
$(function){
$('#nis').change(function(){
$.ajax({
    url: 'ambilData.php',
    data:'nis='+$(this).val(),
    dataType; 'json',
    success: function(data){
        $('#nama').val(data.nama);
        $('#kelamin').val(data.kelamin);
        $('#kelas').val(data.kelas);
    }
})
})
})
</script>
<form>
<table>
<tr>
    <td>NIS</td>
    <td><select id="nis">
    <?php
    include "koneksi.php";
    $sql = mysql_query("SELECT NIS from tbl_siswa order by NIS");
    while($nis=mysql_fetch_array($sql))
        echo "<option value=\"$nis[NIS]\">$nis[NIS]</option>\n";
    ?>
    </select></td>
</tr>
<tr>
    <td>Nama</td>
    <td input type="text" name="nama" id="nama" /></td>
</tr>
<tr>
    <td>Jenis Kelamin</td>
    <td input type="text" name="kelamin" id="kelamin" /></td>
</tr>
<tr>
    <td>Kelas</td>
    <td input type="text" name="kelas" id="kelas" /></td>
</tr>
</table>
</form>

// file ambilData.php
<?php
include "koneksi.php";
$sql = mysql_query("SELECT * from tbl_siswa where NIS='$_GET[nis]'");
$data = mysql_fetch_array($sql);
$output = array('nama'=>$data['nama'], 'kelamin'=>$data['jenis_kelamin'], 'kelas'=>$data['kelas']);
echo json_encode($output);
?>