Как проверить доступность сайта

fetch('https://example.com')
  .then(response => {
    if (!response.ok) throw new Error('Site unavailable');
    console.log('Site is available');
  })
  .catch(error => console.error('Error:', error));

const socket = new WebSocket('wss://example.com');
socket.onopen = () => console.log('Connection established');
socket.onerror = () => console.log('Connection failed');

if (navigator.onLine) {
  console.log('Online');
} else {
  console.log('Offline');
}