Build with a class, lambda-functions, destructuring and default-parameters. And of cause progressively - all though it doesn't do much if your browser doesn's support serviceworker.
Open your console to see the endpoint info...
Run this curl command to send the push notification.
curl --header "Authorization: key=##APIKEY##" --header "Content-Type: application/json" https://android.googleapis.com/gcm/send -d "{\"registration_ids\":[\"##ID##\"]}"