The ServiceWorkerContainer interface of the Service Worker API provides an object representing the service worker as an overall unit in the network ecosystem, including facilities to register, unregister and update service workers, and access the state of service workers and their registrations.

Most importantly, it exposes the ServiceWorkerContainer.register() method used to register service workers, and the ServiceWorkerContainer.controller property used to determine whether or not the current page is actively controlled.

ServiceWorkerContainer.controller Read only

Returns a ServiceWorker object if its state is activating or activated (the same object returned by ServiceWorkerRegistration.active). This property returns null during a force-refresh request (Shift + refresh) or if there is no active worker.

ServiceWorkerContainer.ready Read only

Provides a way of delaying code execution until a service worker is active. It returns a Promise that will never reject, and which waits indefinitely until the ServiceWorkerRegistration associated with the current page has an ServiceWorkerRegistration.active worker. Once that condition is met, it resolves with the ServiceWorkerRegistration.

controllerchange

Occurs when the document's associated ServiceWorkerRegistration acquires a new active worker.

error Deprecated Non-standard

Fired whenever an error occurs in the associated service workers.

message

Occurs when incoming messages are received by the ServiceWorkerContainer object (e.g. via a MessagePort.postMessage() call).

ServiceWorkerContainer.register()

Creates or updates a ServiceWorkerRegistration for the given scriptURL.

ServiceWorkerContainer.getRegistration()

Gets a ServiceWorkerRegistration object whose scope matches the provided document URL. The method returns a Promise that resolves to a ServiceWorkerRegistration or undefined.

ServiceWorkerContainer.getRegistrations()

Returns all ServiceWorkerRegistration objects associated with a ServiceWorkerContainer in an array. The method returns a Promise that resolves to an array of ServiceWorkerRegistration.

ServiceWorkerContainer.startMessages()

explicitly starts the flow of messages being dispatched from a service worker to pages under its control (e.g. sent via Client.postMessage()). This can be used to react to sent messages earlier, even before that page's content has finished loading.

The example below first checks to see if the browser supports service workers. If supported, the code registers the service worker and determines if the page is actively controlled by the service worker. If it isn't, it prompts the user to reload the page so the service worker can take control. The code also reports any registration failures.

if ("serviceWorker" in navigator) {
  // Register a service worker hosted at the root of the
  // site using the default scope.
  navigator.serviceWorker
    .register("/sw.js")
    .then((registration) => {
      console.log("Service worker registration succeeded:", registration);

      // At this point, you can optionally do something
      // with registration. See https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration
    })
    .catch((error) => {
      console.error(`Service worker registration failed: ${error}`);
    });

  // Independent of the registration, let's also display
  // information about whether the current page is controlled
  // by an existing service worker, and when that
  // controller changes.

  // First, do a one-off check if there's currently a
  // service worker in control.
  if (navigator.serviceWorker.controller) {
    console.log(
      "This page is currently controlled by:",
      navigator.serviceWorker.controller,
    );
  }

  // Then, register a handler to detect when a new or
  // updated service worker takes control.
  navigator.serviceWorker.oncontrollerchange = () => {
    console.log(
      "This page is now controlled by",
      navigator.serviceWorker.controller,
    );
  };
} else {
  console.log("Service workers are not supported.");
}

• Using Service Workers
• Service workers basic code example
• Is ServiceWorker ready?
• Promise
• Using web workers