web-push-notif.js

const registerServiceWorker = async () => {
  const swRegistration = await navigator.serviceWorker.register(
    '/service-worker.js'
  )
  return swRegistration
}

const requestNotificationPermission = async () => {
  const permission = await window.Notification.requestPermission()
  // value of permission can be 'granted', 'default', 'denied'
  // granted: user has accepted the request
  // default: user has dismissed the notification permission popup by clicking on x
  // denied: user has denied the request.
  if (permission !== 'granted') {
    throw new Error('Permission not granted for Notification')
  }
}

registerServiceWorker().then(() => {
  requestNotificationPermission()
})

if (Notification.permission == 'granted') {
  navigator.serviceWorker.getRegistration().then(function(reg) {
    reg.showNotification('Hello world!')
  })
}