}
      })
        .done(function(data) {
          var $favorited,
              $favoritedCount;
          if (data.result === "created") {
            $favorited = $favorite.siblings(".favorited");
            $favoritedCount = $(".favorited-count", $favorited);
            $favoritedCount.css("display", "none");
            $favorite.fadeOut(1000, function() {
              $favorited.fadeIn(1000);

        // requireNonNull is safe because we checked that not *both* siblings were null.
        keyList.head = requireNonNull(node.nextSibling);
      } else {
        node.previousSibling.nextSibling = node.nextSibling;
      }

      if (node.nextSibling == null) {
        // requireNonNull is safe because we checked that not *both* siblings were null.
        keyList.tail = requireNonNull(node.previousSibling);