oglaf-keyboard-nav.js

// ==UserScript==
// @name         OGLAF Keyboard Navigation
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Add left/right arrow keyboard navigation.
// @author       You
// @match        https://www.oglaf.com/*
// @icon         https://static.oglaf.com/favicon.png
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    const keyNav = function( e ) {
        let url = false;

        if ( e.code == 'ArrowLeft' ) { // Left arrow key code
			url = document.querySelector( '#nav .previous' ).href;
		} else if ( e.code == 'ArrowRight' ) { // Right arrow key code
			url = document.querySelector( '#nav .next' ).href;
		}

		if ( url ) {
			window.location = url;
		}
    }

    document.addEventListener( 'keydown', keyNav );

})();