PushManager: supportedContentEncodings static property

An array of strings. This usually contains just one value: "aes128gcm".

TypeError

This is thrown when attempting to set a value in the returned array.

Push messages are encrypted on the application server for sending to the push server, and decrypted by the browser before being passed to the application service worker. The public and private keys used are generated by the browser, and only the public key and an associated secret are shared with the web app, and hence the application server. This ensures that push messages remain private as they pass through the push server infrastructure.

The p256dh public key and auth secret used for encrypting the message are provided to the service worker via its push subscription, using the PushSubscription.getKey() method, along with the target endpoint for sending push messages in PushSubscription.endpoint. The coding that should be used for encryption is provided by supportedContentEncodings.

This information may be sent to the application server using any mechanism. One approach is to put the needed information from PushSubscription and supportedContentEncodings into a JSON object, serialize it using JSON.stringify() and post the result to the application server.

// Get a PushSubscription object
const pushSubscription = await serviceWorkerRegistration.pushManager.subscribe();

// Create an object containing the information needed by the app server
const subscriptionObject = {
  endpoint: pushSubscription.endpoint,
  keys: {
    p256dh: pushSubscription.getKeys('p256dh'),
    auth: pushSubscription.getKeys('auth'),
  },
  encoding: PushManager.supportedContentEncodings,
  /* other app-specific data, such as user identity */
};

// Stringify the object an post to the app server
fetch(`https://example.com/push/`, {
  method: "post",
  body: JSON.stringify(pushSubscription);
});