Ajax : check email availability with PHP

You need to send back the data to the ajax using echo or print (I use die() in this case). I also tend to use json to respond. You should check that the email is valid at the very least but you should be binding the email value instead of injecting it into the sql string:

PHP:

<?php include 'libraries/config.php'; # Set a default response $def = ['alert' => true]; # Remove empty values $email = trim($_POST['email']); # First check this is an actual email if (!filter_var($email, FILTER_VALIDATE_EMAIL)) { die(json_encode($def)); } # You should bind/prepare $email, not insert variable into string $stmt = $conn->prepare("SELECT COUNT(*) as count FROM `user_csr` WHERE `email` = ?"); $stmt->bind_param('s', $email); $stmt->execute(); $result = $stmt->get_result(); # Fetch the results of the count $result = $result->fetch_assoc(); # Write json response die(json_encode([ # If succeeded, write the count 'counted' => $result ? $result['count'] : 0 ])); 

JavaScript:

<script type="text/javascript"> $(document).ready(function(){ $('#email').blur(function(){ var email = $(this).val(); $.ajax({ type: 'POST', url: 'check-email.php', data: 'email='+email, success: function(response){ // Parse response response = JSON.parse(response); // See if alert is set (email is not valid) if(typeof response.alert !== "undefined") { // Set an program alert alert('A program error occurred.'); // Stop return false; } var counted = response.counted; swal({ title: (counted == 1)? "Email Address Already in Use" : "Email Address can used", text: "", type: (counted == 1)? "warning" : "success" }); }, }); }); }); </script>