Keybindings for Hacker news for tampermonkey

hackernews-keybindings.js

// ==UserScript==
// @name         HackerNews Keyboard Shortcuts
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Adds j,k,o,c keybindings to navigate hackernews.
// @author       Attila Kerekes
// @match        https://news.ycombinator.com/news
// @grant        none
// ==/UserScript==

(function () {
    'use strict';

    var CLASS_NAME_ARTICLE = 'athing';
    var CLASS_NAME_SELECTED = 'selected';
    var SELECTOR_SELECTED_ARTICLE_LINK = '.athing.selected .storylink';

    createSelectedStyle();
    addKeyBindings();

    function createSelectedStyle() {
        var node = document.createElement('style');
        node.innerHTML = '.athing.selected { background-color: rgba(0,0,0,0.1) }';
        document.body.appendChild(node);
    }

    function addKeyBindings() {
        var actions = {
            j: selectNextArticle,
            k: selectPrevArticle,
            o: openSelectedArticle,
            c: openSelectedArticleComments
        };

        document.addEventListener('keydown', function (event) {
            try {
                actions[event.key]();
            } catch (e) {

            }
        });
    }

    function selectNextArticle() {
        var allArticles = getAllArticles();
        var selectedArticle = getSelectedArticle();

        deselectArticle(allArticles, selectedArticle);

        addSelectedClassToNextArticle(allArticles, selectedArticle);
    }

    function getAllArticles() {
        return getNodeArrayBySelector('.' + CLASS_NAME_ARTICLE);
    }

    function getNodeArrayBySelector(selector) {
        return [].slice.call(document.querySelectorAll(selector))
    }

    function getSelectedArticle() {
        return document.querySelectorAll('.' + CLASS_NAME_ARTICLE + '.' + CLASS_NAME_SELECTED)[0];
    }

    function deselectArticle(allArticles, selectedArticle) {
        if (!selectedArticle) {
            return;
        }

        selectedArticle.classList.remove(CLASS_NAME_SELECTED);
    }

    function addSelectedClassToNextArticle(allArticles, selectedArticle) {
        if (isLastArticle(allArticles, selectedArticle)) {
            selectFirstArticle(allArticles);
            return;
        }

        allArticles[allArticles.indexOf(selectedArticle) + 1].classList.add(CLASS_NAME_SELECTED);
    }

    function isLastArticle(allArticles, selectedArticle) {
        return allArticles.indexOf(selectedArticle) >= allArticles.length - 1;
    }

    function selectFirstArticle(allArticles) {
        allArticles[0].classList.add(CLASS_NAME_SELECTED);
    }

    function selectPrevArticle() {
        var allArticles = getAllArticles();
        var selectedArticle = getSelectedArticle();

        deselectArticle(allArticles, selectedArticle);

        addSelectedClassToPrevArticle(allArticles, selectedArticle);
    }

    function addSelectedClassToPrevArticle(allArticles, selectedArticle) {
        if (isFirstArticle(allArticles, selectedArticle)
            || isUnselected(allArticles, selectedArticle)) {
            selectLastArticle(allArticles);
            return;
        }

        allArticles[allArticles.indexOf(selectedArticle) - 1].classList.add(CLASS_NAME_SELECTED);
    }

    function isFirstArticle(allArticles, selectedArticle) {
        return allArticles.indexOf(selectedArticle) === 0;
    }

    function isUnselected(allArticles, selectedArticle) {
        return allArticles.indexOf(selectedArticle) === -1;
    }

    function selectLastArticle(allArticles) {
        allArticles[allArticles.length - 1].classList.add(CLASS_NAME_SELECTED);
    }

    function openSelectedArticle() {
        window.open(getSelectedArticleAnchor().href, "_self");
    }

    function getSelectedArticleAnchor() {
        return document.querySelectorAll(SELECTOR_SELECTED_ARTICLE_LINK)[0];
    }

    function openSelectedArticleComments() {
        var selectedArticle = getSelectedArticle();
        var commentAnchor = getCommentAnchorForArticle(selectedArticle);
        window.open(commentAnchor.href, "_self");
    }

    function getCommentAnchorForArticle(selectedArticle) {
        return selectedArticle.nextSibling.querySelectorAll('a')[3];
    }
})();