service-worker.js

self.addEventListener('push', function(event) {
  //console.log('Received a push message', event);

  var title = 'Message title';
  var body = 'We have received a push message.';

if (typeof(self.data) !== 'undefined') {
    if (typeof(self.data.message) !== 'undefined') {
        title = "My custom message!";
        body=self.data.message;

    }
}


  var icon = '/img/icon-192x192.png';
  var tag = 'simple-push-demo-notification-tag';

  event.waitUntil(
    self.registration.showNotification(title, {
      body: body,
      icon: icon,
      tag: tag
    })
  );
});