es5timeline.user.js

// ==UserScript==
// @name         Show Timeline
// @namespace    https://github.com/Tunaki/stackoverflow-userscripts
// @version      0.4
// @description  Adds an anchor below posts that links to their timeline
// @author       Tunaki @TinyGiant
// @include      /^https?:\/\/(?!chat)\w*.?(stackexchange.com|stackoverflow.com|serverfault.com|superuser.com|askubuntu.com|stackapps.com|mathoverflow.net)\/.*/
// @run-at       document-start
// @grant        none
// ==/UserScript==
/* jshint -W097 */
/* jshint esnext:true */
'use strict';

var funcs = {};

funcs.addXHRListener = function(callback)
{
    var open = XMLHttpRequest.prototype.open;

    XMLHttpRequest.prototype.open = function()
    {
        this.addEventListener('load', callback.bind(null, this), false);
        open.apply(this, arguments);
    };
};

funcs.addTimelineLink = function(postid)
{
    var posts;

    if (!postid)
    {
        posts = Array.from(document.querySelectorAll('.post-menu'));
    }
    else
    {
        posts = [document.querySelector('[data-questionid="' + postid + '"] .post-menu,[data-answerid="' + postid + '"] .post-menu')];
    }

    for (var i in posts)
    {
        var post = posts[i];

        var timelinelink = post.querySelector('.timeline-link');

        if (timelinelink !== null)
        {
            continue;
        }

        var _postid = (/\d+/.exec(post.querySelector('a.short-link')) || [false])[0];

        if (!_postid)
        {
            continue;
        }

        var lsep = document.createElement('span');
        lsep.className = 'lsep';
        lsep.textContent = '|';
        post.appendChild(lsep);

        var link = document.createElement('a');
        link.className = 'timeline-link';
        link.textContent = 'timeline';
        link.href = '/posts/' + _postid + '/timeline';
        link.target = '_blank';
        post.appendChild(link);
    }
};

window.addEventListener('load', function(event)
{
    funcs.addTimelineLink();
}, false);

funcs.addXHRListener(function(xhr)
{
    if (/ajax-load-realtime/.test(xhr.responseURL))
    {
        var matches = /question" data-questionid="(\d+)/.exec(xhr.responseText);

        if (matches === null)
        {
            matches = /answer" data-answerid="(\d+)/.exec(xhr.responseText);

            if (matches === null)
            {
                return;
            }
        }

        funcs.addTimelineLink(matches[1]);
    }
});