how to write - php -jquery 3.2.1 mysql - ajax for room number requied field fetch from database on selecting tthe roomtype in t

Question

book.php
----------------------
<button type="button" id="ref" onclick = "" value="REFRESH ROOMS AVAILABLE" />

<td width="215" align ="right"><select id="SelRooms" name="SelRooms" style="width:200px;">
<option value="00">--Select--</option>
<?php
$s14="SELECT rooma_nos FROM registration.roomnos where rooma_type='NON-AC-ROOM'";
$s15=mysql_query($s14) or die ("Error in query: $s15. ".mysql_error());
?>
<?php while($roomrequ = mysql_fetch_array($s15)) { ?>
<option value="<?php echo $roomrequ['rooma_nos']; ?>"> <?php echo $roomrequ['rooma_nos']; ?></option>
<?php } ?>
</select>
</td>
<script>
$("#ref").click(function() {
var user_roomtype = $("#roomtype").val();
$.post("fetchroomcount.php",{aroomtype:user_roomtype}, function(data){
$("SelRooms").text(data);
});

});

</script>

fetchroomcount,php
--------------------------

$romm = mysql_query("select * from roomnos where rooma_type ='$aroomtype'");
while($romm3=mysql_fetch_array($romm))
{
echo "<option value= ".$romm3['rooma_nos'].">".$romm3['rooma_nos']."</option>";
}
exit;
}
?>

error: (roomtype values obtained in params in developer tools view
but in response payload the error displayed)

fetchroomcount.php:10: Warning: '' (UnsetValue) is an unknown callback name
fetchroomcount.php:10: Warning: Callable: 'Array' is not a valid callable argument

form -----display
-------------------
roomtype : -select- (option - type1, type2, type3)
button(room required) clicked
room number: -select- ( ype1 - 1,2,3,4 ; type2 - 1,2,3 ; type3; 1,2,3,4,5) - should be fetched from database without refresh on same page itself

Answer 1

First of all where is your input with id roomtype?
This is wrong: $("SelRooms").
Try to use mysqli or pdo instead of mysql.
http://php.net/manual/en/pdo.connections.php

Answer 2

<select id="SelRooms" name="SelRooms" style="width:200px;">
input data for the roomtype.

This is wrong: $("SelRooms").

error in xhr tab
fetchroomcount.php:10: Warning: '' (UnsetValue) is an unknown callback name fetchroomcount.php:10: Warning: Callable: 'Array' is not a valid callable argument

on selection the roomcount for different types of room to be fetched from the mysql database