Ajax | Javascript And

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

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

$exists = in_array(strtolower($username), $takenUsernames); ) .catch(error =&gt

// AJAX request using Fetch API (modern replacement for XMLHttpRequest) fetch('check_username.php?username=' + encodeURIComponent(username)) .then(response => response.json()) .then(data => if (data.exists) statusSpan.innerHTML = '❌ Username already taken'; statusSpan.style.color = 'red'; else statusSpan.innerHTML = '✅ Available!'; statusSpan.style.color = 'green'; statusSpan.innerHTML = '⚠️ Error checking availability'