script.js

// Code goes here

var isPushEnabled = false;

// Once the service worker is registered set the initial state  
function initialiseState() {  
  // Are Notifications supported in the service worker?  
  if (!('showNotification' in ServiceWorkerRegistration.prototype)) {  
    console.warn('Notifications aren\'t supported.');  
    return;  
  }

  // Check the current Notification permission.  
  // If its denied, it's a permanent block until the  
  // user changes the permission  
  if (Notification.permission === 'denied') {  
    console.warn('The user has blocked notifications.');  
    return;  
  }

  // Check if push messaging is supported  
  if (!('PushManager' in window)) {  
    console.warn('Push messaging isn\'t supported.');  
    return;  
  }

  // We need the service worker registration to check for a subscription  
  navigator.serviceWorker.ready.then(function(serviceWorkerRegistration) {  
    // Do we already have a push message subscription?  
    serviceWorkerRegistration.pushManager.getSubscription()  
      .then(function(subscription) {  
        // Enable any UI which subscribes / unsubscribes from  
        // push messages.  
        var pushButton = document.querySelector('.js-push-button');  
        pushButton.disabled = false;

        if (!subscription) {  
          // We aren't subscribed to push, so set UI  
          // to allow the user to enable push  
          return;  
        }
        
        // Keep your server in sync with the latest subscriptionId
        sendSubscriptionToServer(subscription);

        // Set your UI to show they have subscribed for  
        // push messages  
        pushButton.textContent = 'Disable Push Messages';  
        isPushEnabled = true;  
      })  
      .catch(function(err) {  
        console.warn('Error during getSubscription()', err);  
      });  
  });  
}

window.addEventListener('load', function() {  
  var pushButton = document.querySelector('.js-push-button');  
  pushButton.addEventListener('click', function() {  
    if (isPushEnabled) {  
      unsubscribe();  
    } else {  
      subscribe();  
    }  
  });

  // Check that service workers are supported, if so, progressively  
  // enhance and add push messaging support, otherwise continue without it.  
  if ('serviceWorker' in navigator) {  
    navigator.serviceWorker.register('https://run.plnkr.co/vXQCSZ0ygd0kfkev/service-worker.js')  
    .then(function(){});  
  } else {  
    console.warn('Service workers aren\'t supported in this browser.');  
  }  
});