Serve cakes and let's party

serve_cakes.js

// ==UserScript==
// @name        Serve Cakes
// @namespace   https://github.com/mosaicer
// @author      mosaicer
// @description Serve cakes and let's party
// @match       http://*.reddit.com/*
// @match       https://*.reddit.com/*
// @version     1.0
// @run-at      document-idle
// @grant       GM_addStyle
// ==/UserScript==
(function () {
  'use strict';

  var hrefArray = location.href.split('/'),
      commentsFlag = hrefArray[5] === 'comments',
      siteTable = commentsFlag ?
        document.getElementById('siteTable_t3_' + hrefArray[6]) :
        document.getElementById('siteTable'),
      serveCakes = function (targetNode) {
        [].forEach.call(targetNode.querySelectorAll('.tagline'),
          function (tagLine) {
            var spanTag = tagLine.querySelector('.userattrs');

            if (!!spanTag) {
              if (!!spanTag.childElementCount) {
                if (!!!spanTag.querySelector('.cakeday')) {
                  spanTag.innerHTML = spanTag.innerHTML.slice(0, -1) +
                    ',' + generateCakesHtml(tagLine);
                }
              } else {
                spanTag.innerHTML = '[' + generateCakesHtml(tagLine);
              }
            }
          }
        );
      },
      generateCakesHtml = function (tagLine) {
        var userName = commentsFlag ?
          tagLine.children[1].textContent : tagLine.children[0].textContent;

        return '<a class="cakeday" title="' + userName +
          ' は reddit の誕生日を祝いました！" href="/user/' + userName +
          '">🍰</a>]';
      };

  [].forEach.call(siteTable.children, serveCakes);

  new MutationObserver(function (mutations) {
    mutations.forEach(function (mutation) {
      [].forEach.call(mutation.addedNodes, function (theNode) {
        if (theNode.nodeName === 'DIV') {
          if (commentsFlag) {
            if (theNode.hasAttribute('data-fullname')) {
              serveCakes(theNode);
            }
          } else if (!theNode.hasAttribute('url')) {
            [].forEach.call(theNode.children, serveCakes);
          }
        }
      });
    });
  }).observe(siteTable, {childList: true, subtree: true});
}());