Itunes userscript to lower volume

itunes_lower_volume.js

// ==UserScript==
// @name         Itunes lower volume
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://itunes.apple.com/*/album/*/*$
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    var audioObserver = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            if (mutation.addedNodes) {
                mutation.addedNodes.forEach(function(node) {
                    if (node.tagName === 'AUDIO') {
                        audioObserver.disconnect();
                        var target = document.getElementsByTagName('audio')[0];
                        var observer = new MutationObserver(function(mutations) {
                            mutations.forEach(function(mutation) {
                                if (mutation.attributeName === 'src') {
                                    target.volume = 0.2;
                                }
                            });
                        });
                        observer.observe(target, { attributes: true });
                    }
                });
            }
        });
    });
    audioObserver.observe(document.body, { childList: true });
})();