To retrieve that data, you need to parse event.data.text() to a JSON object. I'm guessing something was updated since you tried to get this to work, but it works now. Unlucky!

However, since I made it to this post when searching for a solution myself, others would probably like a working answer. Here it is:

// Push message event handler

self.addEventListener('push', function(event) {



  // If true, the event holds data

  if(event.data){



    // Need to parse to JSON format

    // - Consider event.data.text() the stringify()

    //   version of the data

    var payload = JSON.parse(event.data.text());

    // For those of you who love logging

    console.log(payload); 



    var title = payload.data.title;

    var body  = payload.data.body;

    var icon  = './assets/icons/icon.ico'

    var tag   = 'notification-tag';



    // Wait until payload is fetched

    event.waitUntil(

      self.registration.showNotification(title, {

        body: body,

        icon: icon,

        tag: tag,

        data: {} // Keeping this here in case I need it later

      })

    );



  } else {

    console.log(Event does not have data...);

  }



}); // End push listener



// Notification Click event

self.addEventListener('notificationclick', function(event) {

  console.log(Notification Clicked);

}); // End click listener

Personally, I will be creating a generic notification in case my data is funky, and will also be using try/catch. I suggest doing the same.