IsQuestCompleted

// ==UserScript==
// @name         IsQuestCompleted
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Simple macro that check you completed that quest before.
// @author       Przemekb88 / Yalahari
// @match        http://www.wowhead.com/quest=*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var url = window.location.href;
    var page = url.substring(url.lastIndexOf('quest=') + 6);
    var result = page.split('/');
    $("#infobox-contents0 ul").append('<li><div>/script print(IsQuestFlaggedCompleted('+result[0]+'))</div></li>');
})();