z0r.de UserScript key shortcuts for navigation

z0r-hotkeys.js

// ==UserScript==
// @name            z0r key shortcuts
// @namespace       http://www.example.com/gmscripts
// @description     key shortcuts for z0r
// @include         http://z0r.de/*
// @include         https://z0r.de/*
// @version         0.3
// ==/UserScript==

function addJQuery(callback) {
    var script = document.createElement("script");
    script.setAttribute("src", "//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js");
    script.addEventListener('load', function() {
        var script = document.createElement("script");
        script.textContent = "window.jQ=jQuery.noConflict(true);(" + callback.toString() + ")();";
        document.body.appendChild(script);
    }, false);
    document.body.appendChild(script);
}

function main() {
    var $ = jQ;
    var prevLink;
    var randLink;
    var nextLink;

    $("#unten").find("a").each(function(){
        var link = $(this);
        link.click(function(){
            window.location = link.attr("href");
        });
        if(link.html() == "« Previous"){
            prevLink = link;
        }
        if(link.html() == "Random"){
            randLink = link;
        }
        if(link.html() == "Next »"){
            nextLink = link;
        }
    });

    $(document).keydown(function(e){
        if(e.which == 37){ // Left
            prevLink.click();
        }
        if(e.which == 38){ // Up
            history.back();
        }
        if(e.which == 39){ // Right
            nextLink.click();
        }
        if(e.which == 40){ // Down
            randLink.click();
        }
    });
}

addJQuery(main);