Push notifications in Web Apps via Service Workers

A push notification is a message that is “pushed” from backend server or application to user interface, e.g. (But not limited to) mobile applications and desktop applications.

Service workers are a great way to run some script in the background and not putting the load on your main business logic running on front-end.

 Your app does not have to be open in the browser, to get the notification. It mean that’s the real purpose of push notifications, notify the user about the content of your application.

                         Application server tells Google Cloud Messaging (GCM) server that there is something new content and GCM server then awakens the service worker which generates the push notification.

Register Service Worker

if ('serviceWorker' in navigator && 'PushManager' in window) {
  navigator.serviceWorker.register('software-worker.js')
  .then(function(reg) {
    registration = reg;
  })
  .catch(function(error) {
    return;
  });
} else {
  // Well Service Worker or Push Notifications 
  // aren't supported 
  // yet in your browser
}

Here is what  did in above snippet of code:
1. Checking if the browser supports service worker and push notifications.
2. Handle accordingly if the browser doesn’t support them.
3. If they do, register the service worker file and get the registration object.

Subscribe to Notifications from client

registration.pushManager.subscribe({
    userVisibleOnly: true,
    applicationServerKey: UInt8array Key
  })
  .then(function(subscription) {
    if (subscription) {
       // User is already subscribed
    }
  })
  .catch(function(err) {
    // User have declined request for Push notifications
  });

This is what doing above:
1. Using push manager service create the subscription.
2. You need to have application Server Key for this.
3. Once got the subscription object, send it to server.

Note: user Visible Only: true must be true, otherwise you will get an error in your browser console.

Push notifications handler

self.addEventListener('push', function(event) {
  event.waitUntil(
    self.registration.showNotification(Title, {
      body: Body,
      icon: Icon
    })
  );
});




It will trigger every time, your service worker will be awakened by GCM server.

And that’s it, you have an active service worker that will push notifications to the user every time GCM server will call it.

This post’s scope was only to cover the use of service workers in push notifications