如何在Javascript中检测网络丢失？

function checkNetworkStatus() {
  const connection = navigator.connection;
  if (connection.effectiveType === Connection.EFFECTIVE_TYPE.CELL_2G ||
      connection.effectiveType === Connection.EFFECTIVE_TYPE.CELL_3G ||
      connection.effectiveType === Connection.EFFECTIVE_TYPE.CELL_4G) {
    console.log("网络连接正常");
  } else {
    console.log("网络连接丢失");
  }
}

if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('sw.js')
    .then(registration => {
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        installingWorker.onstatechange = () => {
          if (installingWorker.state === 'installed' && navigator.connection.type !== 'none') {
            console.log('网络已连接');
          } else {
            console.log('网络连接丢失');
          }
        };
      };
    })
    .catch(error => {
      console.log('Error registering service worker:', error);
    });
}

fetch('https://example.com')
  .then(response => {
    if (response.ok) {
      return response.text();
    } else {
      throw new Error('Network response was not ok');
    }
  })
  .then(text => {
    console.log('Text:', text);
  })
  .catch(error => {
    console.error('Error:', error);
  });