jQuery/ajax won't send post data - php

Question

Trying to get jQuery to send the content of a textarea to update a record but it won't. When I change the value of the textarea so that it begins with a number then it sends fine. I can verify that the content is handed to the JS function successfully by using alert(), but it won't get to the PHP file. All other JS functions work fine.
Edited to add more code which may be relevant.
Javascript:
<script>
function add_vid(t) {
if ($('#vref').val().length <5) return;
var vref = $('#vref').val();
$.ajax({
type: 'POST',
url: 'inc/ajax.php',
data: { 'a':'add_vid', 't':'<?=$_SESSION['t']?>', 'vref':vref},
beforeSend:function(){
$('#add_vid_status').html('Adding...');
},
success:function(data){
if (data == 'added') {
$('#add_vid_status').html('Added');
$('#vid_list').prepend('<div align="center" class="vid">'+vref+'</div>');
$('#vref').val('');
}
else $('#add_vid_status').html('Error');
},
error:function(){
$('#add_vid_status').html('Error');
}
});
}
function del_vid(id) {
var confirmdel = confirm('Delete ?');
if (confirmdel) {
$.ajax({
type: 'POST',
url: 'inc/ajax.php',
data: { 'a':'del_vid', 't':'<?=$_SESSION['t']?>', 'id':id},
success:function(data){
if (data == 'deleted') {
$("#v"+id).hide(900);
}
},
error:function(){
//$("#"+msg_id+'_a').html('error');
}
});
}
return false;
}
function update_vid(id) {
vref = $("#update"+id).val();
alert(vref);
$.ajax({
type: 'POST',
url: 'inc/ajax.php',
data: { 'a':'update_vid', 't':'<?=$_SESSION['t']?>', 'id':id, 'vref':vref},
success:function(data){
alert(data);
if (data == 'updated') {
$("#if"+id).html(vref);
}
},
error:function(){
//$("#"+msg_id+'_a').html('error');
}
});
return false;
}
function move_vid(id,dir) {
$.ajax({
type: 'POST',
url: 'inc/ajax.php',
data: { 'a':'move_vid', 't':'<?=$_SESSION['t']?>', 'id':id,'dir':dir},
success:function(data){
pos = data.split('_');
pos_from = pos[0];
pos_to = pos[1];
//$("#if"+id).hide();
if ($("#pos"+pos_to).length) {//if the id2 is on page (and not on a different paginated page) - swap them on-screen
temp_html = $("#pos"+pos_from).html();
$("#pos"+pos_from).html($("#pos"+pos_to).html());
$("#pos"+pos_to).html(temp_html);
temp_html = null;
}
else $("#pos"+pos_from).html('<div>Video moved off page.<br> Reload to see the result.</div>');
//$("#if"+id).fadeIn(400);
},
error:function(){
//$("#"+msg_id+'_a').html('error');
}
});
return false;
}
</script>
HTML:
<textarea name="vref" cols="55" rows="3" id="vref" placeholder="Video embed code"></textarea>
<input type="button" value="Add" onclick="add_vid('<?=$_SESSION['t']?>')"> <span id="add_vid_status"></span>
<input type="button" value="update" onClick="update_vid(27)">
<textarea cols="65" rows="3" id="update27"><iframe src="http://player.vimeo.com/video/123456789?byline=0&portrait=0" width="500" height="281" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe></textarea>
PHP code:
<?
session_start();
if ($_SESSION['auth'] != 1 || $_POST['t'] != $_SESSION['t']) exit();
elseif (isset($_POST['a'])) {
require_once('cfg.php');
db_connect();
if ($_POST['a'] == 'add_vid' && strlen($_POST['vref'])>4) {
//ADDS VIDEO TO DB AND ECHOES "added"
}
elseif ($_POST['a'] == 'del_vid' && is_numeric($_POST['id'])) {
//DELETES VIDEO AND ECHOES "deleted"
}
elseif ($_POST['a'] == 'update_vid' && is_numeric($_POST['id']) && strlen($_POST['vref']>4)) {
$id = (int)$_POST['id'];
//echo 'PHP: '.$_POST['vref']; (here i can test if the argument reaches.)
$vref = mysql_real_escape_string($_POST['vref']);
$q = mysql_query("UPDATE `videos` SET `vref`='{$vref}' WHERE `id`={$id}") or die ('update error: '.mysql_error());
if ($q) echo 'updated';
}
// CODE GOES ON...
}
?>

Answer 1

You've got a typo in your Ajax data object:
't':'<?=$_SESSION['t']?>'
You use the same type of quotes twice, so Javascript thinks that t is a variable, and doesn't recognise it. Changing your quotes like this fixes the error that your code was throwing:
't':'<?=$_SESSION["t"]?>'
Otherwhise, if you did mean for this to be a variable, you need to use it as following:
't':'<?=$_SESSION["'+ t +'"]?>'

Answer 2

After abandoning the update feature, yesterday when I wanted to copy the code for a similar project I noticed the glaring mistake in the PHP code where I am checking the string length: I had written strlen($_POST['vref']>4) instead of strlen($_POST['vref'])>4. After
correcting this it works perfectly.