Firebase IID persistence

firebase_iid_persistence.js

// Request permission to receive notifications via dialog
messaging.requestPermission().then(function(result) {
  // Permission granted.
  messaging.getToken().then(function(currentToken) {
    // Got IID. Persist to server and track state in localStorage
    var persistedIID = localStorage.getItem('messaging.persistedIID');
    if (persistedIID != currentToken) {
      $.post('/iid', {'iid': currentToken}, function() {
        localStorage.setItem('messaging.persistedIID', currentToken);
      });
    }
  }).catch(function(err) {
    // some messaging error
  });
}).catch(function(err) {
  // Permission blocked. Remove persistedIID from localStorage
  localStorage.removeItem('messaging.persistedIID');
  $.post('/iid', {'iid': null});
});