This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The ServiceWorkerGlobalScope interface of the ServiceWorker 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 ServiceWorkerGlobalScope.onfetch or ServiceWorkerGlobalScope.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.

This interface inherits from the WorkerGlobalScope interface, and its parent EventTarget, and therefore implements properties from WindowTimers, WindowBase64, and WindowEventHandlers.


ServiceWorkerGlobalScope.clients Read only
Contains the Clients object associated with the service worker.
ServiceWorkerGlobalScope.registration Read only
Contains the ServiceWorkerRegistration object that represents the service worker's registration.
ServiceWorkerGlobalScope.caches Read only
Contains the CacheStorage object associated with the service worker.

Event handlers

An event handler fired whenever an activate event occurs — when a ServiceWorkerRegistration acquires a new worker.
An event handler fired whenever a fetch event occurs — when a fetch() is called.
An event handler fired whenever an install event occurs — when a ServiceWorkerRegistration acquires a new ServiceWorkerRegistration.installing worker.
An event handler fired whenever a message event 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, corresponding to the controlled page.
An event handler fired whenever a notificationclick event occurs — when a user clicks on a displayed notification.
An event handler fired whenever a notificationclose event occurs — when a user closes a displayed notification.
An event handler fired whenever a push event occurs — when a server push notification is received.
An event handler fired whenever a pushsubscriptionchange event occurs — when a push subscription has been invalidated, or is about to be invalidated (e.g. when a push service sets an expiration time.)
An event handler fired whenever a SyncEvent event occurs. This is 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. 


Allows the current service worker registration to progress from waiting to active state while service worker clients are using it.

ServiceWorkerGlobalScope implements WorkerGlobalScope — which implements GlobalFetch. Therefore it also has the following property available to it:

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.


This code snippet is from the service worker prefetch sample (see prefetch example live.) The ServiceWorkerGlobalScope.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);

    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...');

      return fetch(event.request).then(function(response) {
        console.log('Response from network is:', response);

        return response;
      }).catch(function(error) {
        console.error('Fetching failed:', error);

        throw error;


Specification Status Comment
Service Workers
The definition of 'ServiceWorkerGlobalScope' in that specification.
Working Draft Initial definition
The definition of 'Fetch' in that specification.
Living Standard Adds the fetch method.
Push API
The definition of 'onpush' in that specification.
Working Draft Adds the onpush and onpushsubscriptionchange event handlers.
Notifications API
The definition of 'onnotificationclick' in that specification.
Recommendation Adds the onnotificationclick event handler.
Web Background Synchronization
The definition of 'onsync' in that specification.
Living Standard Adds the onsync event.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 40.0 44.0 (44.0)[1] No support 24 No support
onnotificationclick (Yes) 42.0 (42.0)[1] No support (Yes) No support
onsync 49.0 ? ? ? ?
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support No support 44.0 (44.0) (Yes) No support ? No support 40.0
onnotificationclick No support No support 42.0 (42.0) (Yes) No support ? No support (Yes)
onsync No support No support ? ? ? ? ? 49.0

[1] Service workers (and Push) have been disabled in the Firefox 45 Extended Support Release (ESR.)

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Draft Interface Offline offline Reference Service Workers ServiceWorkerGlobalScope Workers