Firebase: `on`

firebase-on-method.js

(function () {

  var firebaseRoot = 'https://bookmark-app.firebaseio.com/',
      bookmarkRef = new Firebase(firebaseRoot + 'bookmarks');

  bookmarkRef.on('value', function (snapshot) {

    var snapshotResult = snapshot.val();

    keys = Object.keys(snapshotResult);

    $.each(keys, function (index) {
      var $listItem = $('<option>', {
        value: snapshotResult[keys[index]].tag
      });
      $listItem.append(snapshotResult[keys[index]].tag);
      $('#output').append($listItem);
    });
  });
  
})();