Dynamically update user selection using using ajax - php

Question

I need help on this code. I want to dynamically prohibit a user from adding to cart if the requested stock item (Database) is less than his request (qty). Will appreciate, if I can know where I am wrong and probably someone correct it for me.
HTML FORM
<form action="cart.php?adm_id=<?php echo urlencode($patient["adm_id"]);?>" method="post" name="CartForm" target="_self">
<p>Product Name:<select name="prod_name" size="1" id="prod_name">
<option value="Select">Select</option>
<?php
while ($line = mysqli_fetch_array($query, MYSQL_ASSOC)) {
?>
<option value="<?php echo $line['prod_name'];?>"> <?php echo $line['prod_name'];?> </option>
<?php } ?>
</select></p>
<p>Quantity:<input type="number" name="qty" id="qty" size="30" required="required"/></p>
<input name="submit" type="submit" value="Add to Cart" id="btn"/> | <input name="reset" type="reset" value="Cancel" />
Ajax Code:
<script src="javascript/jquery-2.0.3.js">
</script>
<script type="text/javascript">
$(document).ready(function(ex) {
//$('#stock').load('pharmacy_summary.php');
$('#qty').change(function(){
var prod_name = $('#prod_name').val();
var qty= $('#qty').val();
$.ajax({
url: 'confirmStock.php',
data:{prod_name: prod_name, qty: qty},
success: function(e){
if(e == 'true'){
/*if the quantity is greater than the stock*/
alert('stock Item is lower to your request, reduce it');
$('#btn').prop('disabled', true);
}else{
$('#btn').prop('disabled', false);
} }
})});
});
</script>
PHP/MYSQLI Code:(ConfirmStock.php)
<?php require_once("/includes/db_connection.php");?>
<?php require_once("/includes/functions.php");?>
<?php
if(isset($_GET['prod_name'])){
$getProd = $_GET['prod_name'];
$getQty = $_GET['units'];
global $connection;
$val = "SELECT * FROM pharmacy_stock_tab WHERE prod_name='".$getProd."'";
$conf = mysqli_query($connection,$val);
$fetchVal = mysqli_fetch_array($conf);
$stock = $fetchVal['units'];
if($getQty>$stock){
return $stock;
}else{
return $stock;
}
}
?>

Answer 1

You must change the way you send response and the way you handle the response. change the code in ConfirmStock.php
change the return statements in following way
$result = array();
if($getQty>$stock){
$result['success'] = 'true';
$result['stock'] = $stock;
}else{
$result['success'] = 'false';
}
header('Content-Type: application/json');
echo json_encode($result);
die();
In Ajax success method
success: function(response){
if(response.success == 'true'){
/*if the quantity is greater than the stock*/
alert('stock Item is lower to your request, reduce it');
$('#btn').prop('disabled', true);
}else{
$('#btn').prop('disabled', false);
} }