The ServiceWorkerGlobalScope interface of the Service Worker API represents the global execution context of a service worker.
Developers should keep in mind that the ServiceWorker state is not persisted across the termination/restart cycle, so each event handler should assume it's being invoked with a bare, default global state.
Once successfully registered, a service worker can and will be terminated when idle to conserve memory and processor power. An active service worker is automatically restarted to respond to events, such as onfetch or onmessage.
Additionally, synchronous requests are not allowed from within a service worker — only asynchronous requests, like those initiated via the fetch() method, can be used.
Occurs when incoming messages are received. Controlled pages can use the MessagePort.postMessage() method to send messages to service workers. The service worker can optionally send a response back via the MessagePort exposed in event.data.port, corresponding to the controlled page.
Triggered when a call to SyncManager.register is made from a service worker client page. The attempt to sync is made either immediately if the network is available or as soon as the network becomes available.
Starts the process of fetching a resource. This returns a promise that resolves to the Response object representing the response to your request. This algorithm is the entry point for the fetch handling handed to the service worker context.
Examples
This code snippet is from the service worker prefetch sample (see prefetch example live.) The onfetch event handler listens for the fetch event. When fired, the code returns a promise that resolves to the first matching request in the Cache object. If no match is found, the code fetches a response from the network.
The code also handles exceptions thrown from the fetch() operation. Note that an HTTP error response (e.g., 404) will not trigger an exception. It will return a normal response object that has the appropriate error code set.
self.addEventListener('fetch',function(event){
console.log('Handling fetch event for', event.request.url);
event.respondWith(
caches.match(event.request).then(function(response){if(response){
console.log('Found response in cache:', response);return response;}
console.log('No response found in cache. About to fetch from network...');returnfetch(event.request).then(function(response){
console.log('Response from network is:', response);return response;},function(error){
console.error('Fetching failed:', error);throw error;});}));});