Generic fallback depending on server response

cache-offline.js

self.addEventListener('fetch', function(event) {
  event.respondWith(
    fetch(event.request).then(function(response) {
        if (response.status === 404) {
          return caches.match('routes/404.html');
        }
        else if(response.status === 404){
          return caches.match('routes/no-mans-land.html')
        }
        return response
      });
    }).catch(function() {
      //network request failed, device is offline
      return caches.match('routes/offline.html');
    })
  );
});