function askForNPerm()
{
  Notification.requestPermission(function(result)
  {
    if(result !== "granted")
    {
    }
    else
    {
      if(Notification.permission !== 'denied')
      {
        Notification.requestPermission().then(function(result)
        {
        });
      }
    }
  });
}
askForNPerm();

if('serviceWorker' in navigator)
{
  window.addEventListener('load', function()
  {
    navigator.serviceWorker.register('/sw.js', {scope: '/'}).then(function(registration)
    {
      registration.update();
      
      navigator.serviceWorker.addEventListener('message', event => {
        swMessage(event.data.action);
      });
      
      navigator.serviceWorker.addEventListener('periodicsync', event => {
        if (event.tag === 'notification')
        {
          event.waitUntil( () => {
            swMessage(event.data.action);
          });
        }
      });
      
      
      if( 'SyncManager' in window)
      {
        navigator.serviceWorker.ready.then(registration => {
          if (registration.sync)
          {
            try
            {
            
              async function registerSubSync()
              {
                const registration = await navigator.serviceWorker.ready;
                try
                {
                  await registration.sync.register("sub-sync");
                  
                }
                catch
                {
                }
              } 
              registerSubSync();            
            
            }
            catch
            {
            }
          }
          else
          {
          }
        });
        navigator.permissions.query({name: 'periodic-background-sync'}).then( (state) => {
          if( state.state === 'granted' )
          {
            async function registerPeriodicSubSync()
            {
              const registration = await navigator.serviceWorker.ready;
              try
              {
                await registration.periodicSync.register("content-sync", {
                  minInterval: 3000,
                });
              }
              catch
              {
              }
            } 
            registerPeriodicSubSync();
          }
        });
      }
    },function(err)
    {
    });
  });
}
else
{
  // serviceworker/sync not supported
}