Tampermonkey script to scroll through Google results with J/K

script.js

// ==UserScript==
// @name         J/K through Google results
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       Stretchkennedy
// @match        https://www.google.com/search?*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=google.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    let index = null;
    function setIndex(newIndex) {
        index = index === null ? 0 : newIndex; // if nothing's selected, always select first
        const searchLinks = [...document.getElementById('search').getElementsByTagName('a')];
        searchLinks.forEach(link => link.removeAttribute('style'));
        const visibleLinks = searchLinks.filter(link => link.offsetWidth !== 0 || link.offsetHeight !== 0);
        index = index % visibleLinks.length; // be overly paranoid; prevent integer overflow
        const selectedLink = visibleLinks[index];
        selectedLink.setAttribute('style', 'background: yellow;');
        selectedLink.focus({ focusVisible: true });
    }
    document.addEventListener('keydown', evt => {
        if (evt.key === 'j') {
            setIndex(index - 1);
        }
        else if (evt.key === 'k') {
            setIndex(index + 1);
        }
    });
})();