lowbird.com Arrow Keys (Chrome user script)

// ==UserScript==
// @match http://www.lowbird.com/*
// ==/UserScript==

/*global window */
(function () {
    "use strict";
    var
        w = window,
        d = window.document,

        prevBar = d.getElementById('prevBar'),
        nextBar = d.getElementById('nextBar'),
        prevUrl = prevBar ? prevBar.getAttribute('href') : null,
        nextUrl = nextBar ? nextBar.getAttribute('href') : null,

        keyDownHandler = function (e) {
            if (e.target.nodeName !== 'BODY') {
                return true;
            }
            if (e.keyCode === 37 && prevUrl) {
                d.location.href = prevUrl;
            } else if (e.keyCode === 39 && nextUrl) {
                d.location.href = nextUrl;
            }
            return true;
        };

    w.onkeydown = keyDownHandler;
}());