Javascript And Ajax -

$exists = in_array(strtolower($username), $takenUsernames);

// In a real app, query your database $takenUsernames = ['admin', 'john', 'alice']; Javascript and AJAX

) .catch(error => console.error('AJAX error:', error); statusSpan.innerHTML = '⚠️ Error checking availability'; ); ); <?php header('Content-Type: application/json'); $username = $_GET['username'] ?? ''; $exists = in_array(strtolower($username)