title: Send Push Notification to everyone with Service Worker
body: <pre><code>curl --header "Authorization: key=blahblahblah" --header Content-Type:"application/json" https://android.googleapis.com/gcm/send -d "{\"registration_ids\":[\"blahblahblah\"]}"
  </code></pre>
  
  <p>Currently i am able to send push notification though the command above. In order to send the notification to user, i need to get the registration id from user. What if I want to push notification to everyone (who subscribed to that notification)? And how I get their registration ID?</p>
  
  <p>*Note: what I want is: push a notification to everyone when my something in the website updated.</p>
  
  <p>Link to my project: <a href="http://github.com/limhenry/bulletinbeta" rel="nofollow">Github</a></p>
  
  <p>I learnt push notification + sw from here: <a href="https://developers.google.com/web/updates/2015/03/push-notificatons-on-the-open-web?hl=en" rel="nofollow">Google Developer</a></p>