self.addEventListener('message', function(event) { self.clients.claim() .then(function(result) { if (result !== undefined) { event.data.port.postMessage( 'FAIL: claim() should be resolved with undefined'); return; } event.data.port.postMessage('PASS'); }) .catch(function(error) { event.data.port.postMessage('FAIL: exception: ' + error.name); }); }); self.addEventListener('fetch', function(event) { if (!/404/.test(event.request.url)) event.respondWith(new Response('Intercepted!')); });